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{{Short description|Type of rapidly rotating storm system}}
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], a rare ] viewed from the ] on March 26, 2004.]]
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] in 2018 as viewed from ]: The ], eyewall, and surrounding ]s are characteristics of tropical cyclones.]]
{{Tropicalcyclone}}


A '''tropical cyclone''' is a rapidly rotating ] with a ], a closed low-level ], strong winds, and a spiral arrangement of ]s that produce heavy rain and ]s. Depending on its location and strength, a tropical cyclone is called a '''hurricane''' ({{IPAc-en|ˈ|h|ʌr|ᵻ|k|ən|,_|-|k|eɪ|n}}), '''typhoon''' ({{IPAc-en|t|aɪ|'|f|uː|n}}), '''tropical storm''', '''cyclonic storm''', '''tropical depression''', or simply '''cyclone'''. A ] is a strong tropical cyclone that occurs in the ] or northeastern ]. A ] occurs in the northwestern Pacific Ocean. In the ] and South Pacific, comparable storms are referred to as "tropical cyclones". In modern times, on average around 80 to 90 named tropical cyclones form each year around the world, over half of which develop ] of {{convert|65|kn|km/h mph|lk=in|abbr=on|round=5}} or more.<ref name="Global Guide 2017">{{cite report |url=https://cyclone.wmo.int/pdf/Global-Guide-to-Tropical-Cyclone-Forecasting.pdf |title=Global Guide to Tropical Cyclone Forecasting: 2017 |date=April 17, 2018 |publisher=] |access-date=September 6, 2020 |archive-url=https://web.archive.org/web/20190714014847/https://cyclone.wmo.int/pdf/Global-Guide-to-Tropical-Cyclone-Forecasting.pdf |archive-date=July 14, 2019 |url-status=live}}</ref>
In ], a ''']''' is a storm system with a closed circulation around a centre of ], fueled by the heat released when moist air rises and condenses. The name underscores their origin in the ] and their ] nature. They are distinguished from other cyclonic storms such as ]s and ]s by the heat mechanism that fuels them, which makes them "warm core" storm systems.


Tropical cyclones ] over large bodies of relatively warm water. They derive their energy through the evaporation of ] from the ] surface, which ultimately ] into ]s and rain when moist air rises and cools to ]. This ] differs from that of ], such as ]s and ]s, which are powered primarily by ]. Tropical cyclones are typically between {{convert|100|and|2000|km|mi|abbr=on}} in diameter. The strong rotating winds of a tropical cyclone are a result of the ] imparted by the ] as air flows inwards toward the axis of rotation. As a result, cyclones rarely form within 5° of the ]. Tropical cyclones are very rare in the South Atlantic (although ]) due to consistently strong ] and a weak ]. In contrast, the ] and areas of ] give rise to cyclones in the Atlantic Ocean and ].
Depending on their strength and location, there are various terms by which tropical cyclones can be described, such as '''tropical depression''', '''tropical storm''', '''hurricane''' and '''typhoon'''.


Heat energy from the ocean acts as the accelerator for tropical cyclones. This causes inland regions to suffer far less damage from cyclones than coastal regions, although the impacts of flooding are felt across the board. Coastal damage may be caused by strong winds and rain, high waves (due to winds), ]s (due to wind and severe pressure changes), and ] of spawning ]es. ] in several ways. Scientists found that climate change can exacerbate the impact of tropical cyclones by increasing their duration, occurrence, and intensity due to the ] and ].<ref name=":5">{{Cite journal |last1=Knutson |first1=Thomas |last2=Camargo |first2=Suzana J. |last3=Chan |first3=Johnny C. L. |last4=Emanuel |first4=Kerry |last5=Ho |first5=Chang-Hoi |last6=Kossin |first6=James |last7=Mohapatra |first7=Mrutyunjay |last8=Satoh |first8=Masaki |last9=Sugi |first9=Masato |last10=Walsh |first10=Kevin |last11=Wu |first11=Liguang |date=August 6, 2019 |title=Tropical Cyclones and Climate Change Assessment: Part II. Projected Response to Anthropogenic Warming |journal=Bulletin of the American Meteorological Society |language=en |volume=101 |issue=3 |pages=BAMS–D–18–0194.1 |bibcode=2020BAMS..101E.303K |doi=10.1175/BAMS-D-18-0194.1 |issn=0003-0007 |doi-access=free|hdl=1721.1/124705 |hdl-access=free }}</ref><ref>{{Cite web |date=May 18, 2020 |title=Major tropical cyclones have become '15% more likely' over past 40 years |url=https://www.carbonbrief.org/major-tropical-cyclones-have-become-15-more-likely-over-past-40-years |url-status=live |archive-url=https://web.archive.org/web/20200808212654/https://www.carbonbrief.org/major-tropical-cyclones-have-become-15-more-likely-over-past-40-years |archive-date=August 8, 2020 |access-date=August 31, 2020 |website=Carbon Brief |language=en}}</ref> Tropical cyclones draw in air from a large area and concentrate the water content of that air into ] over a much smaller area. This replenishing of moisture-bearing air after rain may cause multi-hour or multi-day extremely heavy rain up to {{convert|40|km|mi|abbr=on}} from the coastline, far beyond the amount of water that the local atmosphere holds at any one time. This in turn can lead to river ], overland flooding, and a general overwhelming of local water control structures across a large area. {{TOC limit|3}}
Tropical cyclones can produce extremely high winds, ]es, torrential ] (leading to mudslides and flash floods), and drive ] onto coastal areas. Though the effects on populations and ships can be catastrophic, tropical cyclones have been known to relieve drought conditions. They carry heat away from the tropics, an important mechanism of the global ] that maintains equilibrium in the environment.


==Definition and terminology==
==Mechanics of tropical cyclones==
A tropical cyclone is the generic term for a warm-cored, non-frontal ] ] over ] or ] waters around the world.<ref name="Gloss">{{cite web |title=Glossary of NHC Terms |url=https://www.nhc.noaa.gov/aboutgloss.shtml |url-status=live |archive-url=https://web.archive.org/web/20210216200241/https://www.nhc.noaa.gov/aboutgloss.shtml |archive-date=February 16, 2021 |access-date=February 18, 2021 |publisher=]}}</ref><ref name="What">{{cite web |title=Tropical cyclone facts: What is a tropical cyclone? |url=https://www.metoffice.gov.uk/research/weather/tropical-cyclones/facts#What%20is%20a%20TC |url-status=live |archive-url=https://web.archive.org/web/20210202123840/https://www.metoffice.gov.uk/research/weather/tropical-cyclones/facts |archive-date=February 2, 2021 |access-date=February 25, 2021 |publisher=]}}</ref> The systems generally have a well-defined center which is surrounded by deep ] and a closed wind circulation at the surface.<ref name="Gloss"/> A tropical cyclone is generally deemed to have formed once mean surface winds in excess of {{convert|35|kn|km/h mph|round=5|abbr=on}} are observed.<ref name="Global Guide 2017" /> It is assumed at this stage that a tropical cyclone has become self-sustaining and can continue to intensify without any help from its environment.<ref name="Global Guide 2017" />
]. The air heats up, rising further, which leads to more condensation. The air flowing out of the top of this "chimney" drops towards the ground, forming powerful winds.]]


Depending on its location and strength, a tropical cyclone is referred to by ], including ''hurricane'', ''typhoon'', ''tropical storm'', ''cyclonic storm'', ''tropical depression'', or simply ''cyclone''. A ] is a strong tropical cyclone that occurs in the ] or northeastern ], and a ] occurs in the northwestern Pacific Ocean. In the ] and South Pacific, comparable storms are referred to as "tropical cyclones", and such storms in the Indian Ocean can also be called "severe cyclonic storms".
Structurally, a tropical cyclone is a large, rotating system of ]s, ], and ]s. Its primary ] source is the release of the ] from water vapor ] at high altitudes, the heat ultimately derived from the ]. Therefore, a tropical cyclone can be thought of as a giant vertical ] supported by mechanics driven by physical forces such as the ] and ] of the ]. Condensation leads to higher wind speeds, as a tiny fraction of the released energy is converted into mechanical energy;<ref name="NHCC5C"> accessed March 31, 2006</ref> the faster winds and lower pressure associated with them in turn cause increased surface evaporation. Much of the released energy drives updrafts that increase the height of the storm clouds, speeding up condensation.<ref name="NOAA Question of the Month"> accessed March 31, 2006</ref> This gives rise to factors that provide the system with enough energy to be self-sufficient and cause a ] where it can draw more energy as long as the source of heat, warm water, remains. Factors such as a continued lack of ] in air mass distribution would also give supporting energy to the cyclone. The rotation of the Earth causes the system to spin, an effect known as the ], giving it a cyclonic characteristic and affecting the trajectory of the storm.


''Tropical'' refers to the geographical origin of these systems, which form almost exclusively over ] seas. '']'' refers to their winds moving in a circle, whirling round their central clear ], with their surface winds blowing ] in the ] and ] in the ]. The opposite direction of circulation is due to the ].
The factors to form a tropical cyclone include a pre-existing weather disturbance, warm tropical oceans, moisture, and relatively light winds aloft. If the right conditions persist and allow it to create a feedback loop by maximizing the energy intake possible, for example, such as high winds to increase the rate of evaporation, they can combine to produce the violent winds, incredible waves, torrential rains, and ] associated with this phenomenon.


== Formation ==
] as a driving force is what primarily distinguishes tropical cyclones from other meteorological phenomena.<ref name="BOM Question 6"> accessed March 31, 2006</ref> Because this is strongest in a ], this defines the initial domain of the tropical cyclone. By contrast, ]s draw their energy mostly from pre-existing horizontal temperature ]s in the atmosphere.<ref name="BOM Question 6"/> In order to continue to drive its ], a tropical cyclone must remain over warm water, which provides the atmospheric moisture needed. The evaporation of this moisture is accelerated by the high winds and reduced atmospheric pressure in the storm, resulting in a ]. As a result, when a tropical cyclone passes over land, its strength diminishes rapidly.<ref name="NHCC2"> accessed March 31, 2006</ref>
{{Main|Tropical cyclogenesis}}
]|alt=A schematic diagram of a tropical cyclone]]


Tropical cyclones tend to develop during the summer, but have been noted in nearly every month in most ]. Tropical cyclones on either side of the Equator generally have their origins in the ], where winds blow from either the northeast or southeast.<ref name="Form">{{cite web |title=Tropical cyclone facts: How do tropical cyclones form? |url=https://www.metoffice.gov.uk/research/weather/tropical-cyclones/facts#How%20do%20TCs%20form |url-status=live |archive-url=https://web.archive.org/web/20210202123840/https://www.metoffice.gov.uk/research/weather/tropical-cyclones/facts |archive-date=February 2, 2021 |access-date=March 1, 2021 |publisher=United Kingdom Met Office}}</ref> Within this broad area of low-pressure, air is heated over the warm tropical ocean and rises in discrete parcels, which causes thundery showers to form.<ref name="Form" /> These showers dissipate quite quickly; however, they can group together into large clusters of thunderstorms.<ref name="Form" /> This creates a flow of warm, moist, rapidly rising air, which starts to ] as it interacts with the rotation of the earth.<ref name="Form" />
] on September 12, 2001. Erin's eye is marked with a red hurricane symbol. In the eye, ozone concentrations are elevated (yellow and green). The core is surrounded by an area of much lower ozone concentrations (purple and blue).]]
] levels give a clue that a storm will develop before other methods. The early spin of a tropical cyclone is weak and sometimes covered by clouds, and not easily detected by satellites that provide pictures of clouds. However, instruments such as the ] can identify ozone amounts that are closely related to the formation, intensification, and movement of a cyclone. As a result, ozone levels turn out to be very helpful in determining the location of the ]. Concentrations of naturally-occurring ozone are highest in the ]. Air nearer to the ocean surface is less rich in ozone. Surrounding the eye is a ring of powerful thunderstorms that are sucking up warm, moist air from the ocean surface and hurling it miles into the atmosphere—sometimes all the way to the lower stratosphere. This ozone-poor air replaces the ozone-rich air, causing ozone concentrations to drop. The process reverses in the eye itself: high-altitude air sinks down to the surface, infusing the entire column of atmosphere with ozone. Dropping ozone levels around the eye may turn out to be a strong sign that a storm is strengthening.<ref>, NASA press release, accessed May 9, 2006</ref>


Several factors are required for these thunderstorms to develop further, including ] of around {{convert|27|°C|°F|abbr=on}} and low vertical ] surrounding the system,{{r|Form|A15}} atmospheric instability, high ] in the lower to middle levels of the ], enough ] to develop a ], and a pre-existing low-level focus or disturbance.<ref name="A15">{{cite web |last=Landsea |first=Chris |author-link=Chris Landsea |title=How do tropical cyclones form? |url=http://www.aoml.noaa.gov/hrd/tcfaq/A15.html |url-status=live |archive-url=https://web.archive.org/web/20090827030639/http://www.aoml.noaa.gov/hrd/tcfaq/A15.html |archive-date=August 27, 2009 |access-date=October 9, 2017 |work=Frequently Asked Questions |publisher=], Hurricane Research Division}}</ref>
] as Hurricanes ] and ] passed over. Sea surface temperatures decreased by more than 4°C in places along their paths and 1°C over the entire gulf.]]
There is a limit on tropical cyclone intensity which is strongly related to the water temperatures along its path.<ref name="RSMAS">{{cite web |last=Berg |first=Robbie |title=Tropical cyclone intensity in relation to SST and moisture variability |url=http://ams.confex.com/ams/pdfpapers/37899.pdf |url-status=live |archive-url=https://web.archive.org/web/20110610113232/http://ams.confex.com/ams/pdfpapers/37899.pdf |archive-date=June 10, 2011 |access-date=September 23, 2010 |publisher=] (])}}</ref> and upper-level divergence.<ref>{{cite journal |last1=Zhang |first1=Da-Lin |last2=Zhu |first2=Lin |date=September 12, 2012 |title=Roles of upper-level processes in tropical cyclogenesis |url=https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2012GL053140 |journal=Geophysical Research Letters |publisher=AGU |volume=39 |issue=17 |bibcode=2012GeoRL..3917804Z |doi=10.1029/2012GL053140 |s2cid=53341455 |access-date=October 4, 2022 |issn=0094-8276}}</ref>
The passage of a tropical cyclone over the ocean can cause the upper ocean to cool substantially, which can influence subsequent cyclone development. Tropical cyclones cool the ocean by acting like "heat engines" that transfer heat from the ocean surface to the atmosphere through ]. Cooling is also caused by upwelling of cold water from below. Additional cooling may come from cold water from raindrops that remain on the ocean surface for a time. Cloud cover may also play a role in cooling the ocean by shielding the ocean surface from direct sunlight before and slightly after the storm passage. All these effects can combine to produce a dramatic drop in sea surface temperature over a large area in just a few days.<ref name="NASA Cooling"> accessed April 26, 2006</ref>
An average of 86 tropical cyclones of tropical storm intensity form annually worldwide. Of those, 47 reach strength higher than {{convert|74|mph|km/h|abbr=on|order=flip}}, and 20 become intense tropical cyclones, of at least Category&nbsp;3 intensity on the ].<ref>{{cite web |author=Chris Landsea |author-link=Chris Landsea |date=January 4, 2000 |title=Climate Variability table&nbsp;— Tropical Cyclones |url=http://www.aoml.noaa.gov/hrd/Landsea/climvari/table.html |url-status=live |archive-url=https://web.archive.org/web/20121002045230/http://www.aoml.noaa.gov/hrd/Landsea/climvari/table.html |archive-date=October 2, 2012 |access-date=October 19, 2006 |publisher=], ]}}</ref>


Climate oscillations such as ] (ENSO) and the ] modulate the timing and frequency of tropical cyclone development.<ref name="AOML climt var">{{cite web |last=Landsea |first=Christopher |title=AOML Climate Variability of Tropical Cyclones paper |url=http://www.aoml.noaa.gov/hrd/Landsea/climvari/index.html |url-status=live |archive-url=https://web.archive.org/web/20211026211517/https://www.aoml.noaa.gov/hrd/Landsea/climvari/index.html |archive-date=October 26, 2021 |access-date=September 23, 2010 |publisher=Atlantic Oceanographic and Meteorological Laboratory}}</ref><ref>{{cite journal |last1=Aiyyer |first1=Anantha |last2=Molinari |first2=John |date=August 1, 2008 |title=MJO and Tropical Cyclogenesis in the Gulf of Mexico and Eastern Pacific: Case Study and Idealized Numerical Modeling |journal=Journal of the Atmospheric Sciences |publisher=American Meteorological Society |volume=65 |issue=8 |pages=2691–2704 |bibcode=2008JAtS...65.2691A |doi=10.1175/2007JAS2348.1 |s2cid=17409876 |doi-access=free}}</ref><ref>{{cite journal |last1=Zhao |first1=Chen |last2=Li |first2=Tim |date=October 20, 2018 |title=Basin dependence of the MJO modulating tropical cyclone genesis |url=https://link.springer.com/article/10.1007/s00382-018-4502-y |url-status=live |journal=Climate Dynamics |publisher=Springer |volume=52 |issue=9–10 |pages=6081–6096 |doi=10.1007/s00382-018-4502-y |s2cid=134747858 |archive-url=https://web.archive.org/web/20221002213931/https://link.springer.com/article/10.1007/s00382-018-4502-y |archive-date=October 2, 2022 |access-date=October 5, 2022}}</ref><ref>{{cite journal |last1=Camargo |first1=Suzana J. |last2=Emanuel |first2=Kerry A. |last3=Sobel |first3=Adam H. |date=October 1, 2007 |title=Use of a Genesis Potential Index to Diagnose ENSO Effects on Tropical Cyclone Genesis |journal=Journal of Climate |publisher=American Meteorological Society |volume=20 |issue=19 |pages=4819–4834 |bibcode=2007JCli...20.4819C |doi=10.1175/JCLI4282.1 |s2cid=17340459 |doi-access=free}}</ref> ]s can aid in the formation of a new tropical cyclone by disseminating the energy of an existing, mature storm.<ref>{{cite journal |last1=Molinari |first1=John |last2=Lombardo |first2=Kelly |last3=Vollaro |first3=David |date=April 1, 2007 |title=Tropical Cyclogenesis within an Equatorial Rossby Wave Packet |journal=Journal of the Atmospheric Sciences |publisher=American Meteorological Society |volume=64 |issue=4 |pages=1301–1317 |bibcode=2007JAtS...64.1301M |doi=10.1175/JAS3902.1 |s2cid=12920242 |doi-access=free}}</ref><ref>{{cite journal |last1=Li |first1=Tim |last2=Fu |first2=Bing |date=May 1, 2006 |title=Tropical Cyclogenesis Associated with Rossby Wave Energy Dispersion of a Preexisting Typhoon. Part I: Satellite Data Analyses |journal=Journal of the Atmospheric Sciences |publisher=American Meteorological Society |volume=63 |issue=5 |pages=1377–1389 |bibcode=2006JAtS...63.1377L |doi=10.1175/JAS3692.1 |s2cid=15372289 |doi-access=free}}</ref> ]s can contribute to tropical cyclone formation by regulating the development of the ].<ref>{{cite journal |last1=Schreck III |first1=Carl J. |last2=Molinari |first2=John |date=September 1, 2011 |title=Tropical Cyclogenesis Associated with Kelvin Waves and the Madden–Julian Oscillation |journal=Monthly Weather Review |publisher=American Meteorological Society |volume=139 |issue=9 |pages=2723–2734 |bibcode=2011MWRv..139.2723S |doi=10.1175/MWR-D-10-05060.1 |s2cid=16983131 |doi-access=free}}</ref> Cyclone formation is usually reduced 3 days prior to the wave's crest and increased during the 3 days after.<ref>{{cite journal |last1=Schreck III |first1=Carl J. |date=October 1, 2015 |title=Kelvin Waves and Tropical Cyclogenesis: A Global Survey |journal=Monthly Weather Review |publisher=American Meteorological Society |volume=143 |issue=10 |pages=3996–4011 |bibcode=2015MWRv..143.3996S |doi=10.1175/MWR-D-15-0111.1 |s2cid=118859063 |doi-access=free}}</ref>
Scientists at the ] estimate that a hurricane releases heat energy at the rate of 50 to 200 ] ]s per day.<ref name="NOAA Question of the Month"/> For comparison, this rate of energy release is equivalent to exploding a 10-megaton ] every 20 minutes<ref name="UCAR">] accessed March 31, 2006</ref> or 200 times the world-wide electrical generating capacity.<ref name="NOAA Question of the Month"/>


=== Formation regions and warning centers ===
While the most obvious motion of clouds is toward the center, tropical cyclones also develop an upper-level (high-altitude) outward flow of clouds. These originate from air that has released its moisture and is expelled at high altitude through the "chimney" of the storm engine.{{fact}} This outflow produces high, thin cirrus clouds that spiral away from the center. The high cirrus clouds may be the first signs of an approaching hurricane.<ref name="NHC FAQ H5">http://www.aoml.noaa.gov/hrd/tcfaq/H5.html</ref>
{{Main|Tropical cyclone basins|Regional Specialized Meteorological Centre}}
{| class="wikitable"
|+Tropical cyclone basins and official warning centers
|-
! scope="col" | Basin
! scope="col" | Warning center
! scope="col" | Area of responsibility
! scope="col" | Notes
|-
| colspan="4" style="text-align: center;" |'''Northern Hemisphere'''
|-
! scope="row" | ]
| United States ] (Miami)
| Equator northward, African Coast&nbsp;– 140°W
|<ref name="RA IV HOP" />
|-
! scope="row" | ]
| United States ] (Honolulu)
| Equator northward, 140–180°W
|<ref name="RA IV HOP" />
|-
! scope="row" | ]
| ]
| Equator –&nbsp;60°N, 180–100°E
| {{Typhoon committee operational plan}}
|-
! scope="row" | ]
| ]
| Equator northwards, 100–40°E
|<ref name="NIO TCOP" />
|-
| colspan="4" style="text-align: center;" |'''Southern Hemisphere'''
|-
! scope="row" | ]
| ] Reunion
| Equator – 40°S, African Coast –&nbsp;90°E
|<ref name="SWIO TCOP" />
|-
! rowspan="3" scope="row" | ]
| Indonesian ] (BMKG)
| Equator – 10°S, 90–141°E
| {{RA V Tropical cyclone operational plan}}<!-- defines<ref name="SPAC TCOP"/> -->
|-
| Papua New Guinea National Weather Service
| Equator – 10°S, 141–160°E
|<ref name="SPAC TCOP" />
|-
| Australian ]
| 10–40°S, 90–160°E
|<ref name="SPAC TCOP" />
|-
! rowspan="2" scope="row" | ]
| ]
| Equator&nbsp;– 25°S, 160°E&nbsp;– 120°W
|<ref name="SPAC TCOP" />
|-
| ]
| 25–40°S, 160°E – 120°W
|<ref name="SPAC TCOP" />
|}


The majority of tropical cyclones each year form in one of seven tropical cyclone basins, which are monitored by a variety of meteorological services and warning centers.<ref name="Global Guide 2017" /> Ten of these warning centers worldwide are designated as either a ] or a ] by the ]'s (WMO) tropical cyclone programme.<ref name="Global Guide 2017" /> These warning centers issue advisories which provide basic information and cover a systems present, forecast position, movement and intensity, in their designated areas of responsibility.<ref name="Global Guide 2017" />
===Physical structure===
]
A strong tropical cyclone consists of the following components.


Meteorological services around the world are generally responsible for issuing warnings for their own country. There are exceptions, as the United States National Hurricane Center and Fiji Meteorological Service issue alerts, watches and warnings for various island nations in their areas of responsibility.<ref name="Global Guide 2017" /><ref name="SPAC TCOP" /> The United States ] and Fleet Weather Center also publicly issue warnings about tropical cyclones on behalf of the ].<ref name="Global Guide 2017" /> The ] Hydrographic Center names ]s, however the South Atlantic is not a major basin, and not an official basin according to the WMO.<ref name="names_2011">{{cite web |year=2011 |title=Normas Da Autoridade Marítima Para As Atividades De Meteorologia Marítima |url=https://www.marinha.mil.br/dhn/sites/www.marinha.mil.br.dhn/files/normam/normam_19.pdf |url-status=dead |archive-url=https://web.archive.org/web/20150206213534/http://www.mar.mil.br/dhn/dhn/downloads/normam/normam_19.pdf |archive-date=February 6, 2015 |access-date=October 5, 2018 |publisher=Brazilian Navy |language=pt}}</ref>
* ''']:''' All tropical cyclones rotate around an area of low ] near the ]'s surface. The pressures recorded at the centers of tropical cyclones are among the lowest that occur on Earth's surface at ].
* '''Warm core:''' Tropical cyclones are characterized and driven by the release of large amounts of latent ] as moist air is carried upwards and its water vapor condenses. This heat is distributed vertically, around the center of the storm. Thus, at any given altitude (except close to the surface where water temperature dictates air temperature) the environment inside the cyclone is warmer than its outer surroundings.
* '''Central Dense Overcast (CDO):''' The Central Dense Overcast is a dense shield of very intense ] activity that make up the inner portion of the hurricane. This contains the eye wall, and the eye itself. The classic hurricane contains a symmetrical CDO, which means that it is perfectly circular and round on all sides.
* ''']:''' A strong tropical cyclone will harbor an area of sinking air at the center of circulation. Weather in the eye is normally calm and free of clouds (however, the sea may be extremely violent). Eyes are home to the coldest temperatures of the storm at the surface, and the warmest temperatures at the upper levels. The eye is normally circular in shape, and may range in size from 3 km to 320 km (2 miles to 200 miles) in diameter. In weaker cyclones, the CDO covers the circulation center, resulting in no visible eye.
* '''Eyewall:''' A band around the eye of greatest wind speed, where clouds reach highest and precipitation is heaviest. The heaviest wind damage occurs where a hurricane's eyewall passes over land.
* '''Rainbands:''' Bands of showers and thunderstorms which spiral cyclonically toward the storm center. High wind gusts and heavy downpours often occur in individual rainbands, with relatively calm weather between bands. Tornadoes often form in the rainbands of landfalling tropical cyclones. ] are distinctive for their lack of rainbands.
* '''Outflow:''' The upper levels of a tropical cyclone feature winds headed away from the center of the storm with an ] rotation. ] at the surface are strongly cyclonic, weaken with height, and eventually reverse themselves. Tropical cyclones owe this unique characteristic to the warm core at the center of the storm.


== Interactions with climate ==
==Formation==
{{main|Tropical cyclones by year}}
] image shows the height of rain columns within ]. The highest towers, the tallest of which reaches about 17 kilometers into the atmosphere, produce the heaviest rain, shown in red. The higher water vapor rises before cooling, the more intense the storm tends to be. Since these towers are like pistons that convert energy from water vapor into a powerful wind-and-rain-producing engine, high towers can be a sign of future strengthening.]]
]


Each year on average, around 80 to 90 named tropical cyclones form around the world, of which over half develop hurricane-force winds of {{convert|65|kn|km/h mph|abbr=on|round=5}} or more.<ref name="Global Guide 2017" /> Worldwide, tropical cyclone activity peaks in late summer, when the difference between temperatures aloft and ]s is the greatest. However, each particular basin has its own seasonal patterns. On a worldwide scale, May is the least active month, while September is the most active month. November is the only month in which all the ] are in season.<ref name="AOML FAQ G1">{{cite web |author=], Hurricane Research Division |title=Frequently Asked Questions: When is hurricane season? |url=http://www.aoml.noaa.gov/hrd/tcfaq/G1.html |url-status=dead |archive-url=https://web.archive.org/web/20090506152735/http://www.aoml.noaa.gov/hrd/tcfaq/G1.html |archive-date=May 6, 2009 |access-date=July 25, 2006 |publisher=]}}</ref>
The formation of tropical cyclones is the topic of extensive ongoing research, and is still not fully understood. Six general factors are necessary to make tropical cyclone formation possible, although tropical cyclones may occasionally form despite not meeting these conditions:


In the Northern ], a distinct ] occurs from June 1 to November 30, sharply peaking from late August through September.<ref name="AOML FAQ G1" /> The statistical peak of the Atlantic hurricane season is September 10.<ref name="NHC Atl climatology"/>
# ] of at least 26.5&nbsp;&deg;C (80&deg;F)<ref name="NHCA15"> accessed March 30, 2006</ref> down to a depth of at least 50&nbsp;m (150&nbsp;feet). Waters of this temperature cause the overlying atmosphere to be unstable enough to sustain convection and thunderstorms.<ref name="NHCA16"> accessed March 30, 2006</ref>
# Rapid cooling with height. This allows the release of ], which is the source of energy in a tropical cyclone.<ref name="NHCA15"/>
# High humidity, especially in the lower-to-mid ]. When there is lots of moisture in the atmosphere, conditions are more favourable for disturbances to develop.<ref name="NHCA15"/>
# Low ]. When wind shear is high, the convection in a cyclone or disturbance will be disrupted, blowing the system apart.<ref name="NHCA15"/>
# Distance from the ]. This allows the ] to deflect winds blowing towards the low pressure center, causing a circulation. The ''approximate'' distance is 500&nbsp;km (310&nbsp;miles) or about 5 degrees from the equator.<ref name="NHCA15"/>
# A pre-existing system of disturbed weather. The system must have some sort of circulation as well as a low pressure center.<ref name="NHCA15"/>


The Northeast Pacific Ocean has a broader period of activity, but in a similar time frame to the Atlantic.<ref name="NHC Atl climatology">{{cite web |author=McAdie, Colin |date=May 10, 2007 |title=Tropical Cyclone Climatology |url=http://www.nhc.noaa.gov/climo/ |url-status=live |archive-url=https://web.archive.org/web/20150321161433/http://www.nhc.noaa.gov/climo/ |archive-date=March 21, 2015 |access-date=June 9, 2007 |publisher=National Hurricane Center}}</ref> The Northwest Pacific sees tropical cyclones year-round, with a minimum in February and March and a peak in early September.<ref name="AOML FAQ G1" /> In the North Indian basin, storms are most common from April to December, with peaks in May and November.<ref name="AOML FAQ G1" /> In the Southern Hemisphere, the tropical cyclone year begins on July 1 and runs all year-round encompassing the tropical cyclone seasons, which run from November 1 until the end of April, with peaks in mid-February to early March.<ref name="AOML FAQ G1" /><ref name="SPAC TCOP" />
Only specific weather disturbances can result in tropical cyclones. These include:


Of various ] in the climate system, ] has the largest effect on tropical cyclone activity.<ref name=":3">{{Cite web |last=Ramsay |first=Hamish |year=2017 |title=The Global Climatology of Tropical Cyclones |url=https://oxfordre.com/view/10.1093/acrefore/9780199389407.001.0001/acrefore-9780199389407-e-79 |url-status=live |archive-url=https://web.archive.org/web/20210815230620/https://oxfordre.com/view/10.1093/acrefore/9780199389407.001.0001/acrefore-9780199389407-e-79 |archive-date=August 15, 2021 |access-date= |website=Oxford Research Encyclopedia of Natural Hazard Science |publisher=Oxford University Press |language=en |doi=10.1093/acrefore/9780199389407.013.79 |isbn=9780199389407}}</ref> Most tropical cyclones form on the side of the subtropical ridge closer to the equator, then move poleward past the ridge axis before recurving into the main belt of the ].<ref>{{cite web |author=Joint Typhoon Warning Center |year=2006 |title=3.3 JTWC Forecasting Philosophies |url=http://www.nrlmry.navy.mil/forecaster_handbooks/Philippines2/Forecasters%20Handbook%20for%20the%20Philippine%20Islands%20and%20Surrounding%20Waters%20Typhoon%20Forecasting.3.pdf |url-status=live |archive-url=https://web.archive.org/web/20071129132730/http://www.nrlmry.navy.mil/forecaster_handbooks/Philippines2/Forecasters%20Handbook%20for%20the%20Philippine%20Islands%20and%20Surrounding%20Waters%20Typhoon%20Forecasting.3.pdf |archive-date=November 29, 2007 |access-date=February 11, 2007 |publisher=]}}</ref> When the ] position shifts due to El Niño, so will the preferred tropical cyclone tracks. Areas west of Japan and ] tend to experience much fewer September–November tropical cyclone impacts during ] and neutral years.<ref name="China">{{Cite journal |last1=Wu |first1=M.C. |last2=Chang |first2=W.L. |last3=Leung |first3=W.M. |year=2004 |title=Impacts of El Niño–Southern Oscillation Events on Tropical Cyclone Landfalling Activity in the Western North Pacific |journal=Journal of Climate |volume=17 |issue=6 |pages=1419–1428 |bibcode=2004JCli...17.1419W |citeseerx=10.1.1.461.2391 |doi=10.1175/1520-0442(2004)017<1419:IOENOE>2.0.CO;2}}</ref>
# ], or easterly waves, which, as mentioned above, are westward moving areas of convergent winds. This often assists in the development of thunderstorms, which can develop into tropical cyclones. Most tropical cyclones form from these. A similar phenomenon to tropical waves are West African disturbance lines, which are squally lines of convection that form over ] and move into the Atlantic.
# Tropical upper ] troughs, which are cold-core upper level lows. A warm-core tropical cyclone may result when one of these (on occasion) works down to the lower levels and produces deep ].
# Decaying frontal boundaries may occasionally stall over warm waters and produce lines of active convection. If a low level circulation forms under this convection, it may develop into a tropical cyclone.


During ] years, the formation of tropical cyclones, along with the subtropical ridge position, shifts westward across the western Pacific Ocean, which increases the landfall threat to China and much greater intensity in the ].<ref name="China" /> The Atlantic Ocean experiences depressed activity due to increased vertical ] across the region during El Niño years.<ref>{{Cite journal |last=Klotzbach |first=Philip J. |year=2011 |title=El Niño–Southern Oscillation's Impact on Atlantic Basin Hurricanes and U.S. Landfalls |journal=Journal of Climate |language=en |volume=24 |issue=4 |pages=1252–1263 |bibcode=2011JCli...24.1252K |doi=10.1175/2010JCLI3799.1 |issn=0894-8755 |doi-access=free}}</ref> Tropical cyclones are further influenced by the ], the ] and the ].<ref name=":3" /><ref>{{Citation |last1=Camargo |first1=Suzana J. |title=The Influence of Natural Climate Variability on Tropical Cyclones, and Seasonal Forecasts of Tropical Cyclone Activity |work=Global Perspectives on Tropical Cyclones |volume=4 |pages=325–360 |year=2010 |url=https://www.worldscientific.com/doi/abs/10.1142/9789814293488_0011 |access-date= |archive-url=https://web.archive.org/web/20210815051723/https://www.worldscientific.com/doi/abs/10.1142/9789814293488_0011 |archive-date=August 15, 2021 |url-status=live |series=World Scientific Series on Asia-Pacific Weather and Climate |publisher=WORLD SCIENTIFIC |doi=10.1142/9789814293488_0011 |isbn=978-981-4293-47-1 |last2=Sobel |first2=Adam H. |last3=Barnston |first3=Anthony G. |last4=Klotzbach |first4=Philip J.}}</ref>
===Locations of formation===
Most tropical cyclones form in a worldwide band of thunderstorm activity called the Intertropical Discontinuity (ITD), also called the ] (ITCZ).


{{TC Season Stats}}
Nearly all of these systems form between 10 and 30 degrees of the ] and 87% form within 20 degrees of it. Because the ] initiates and maintains tropical cyclone rotation, such cyclones almost never form or move within about 10 degrees of the equator <ref name=BOMmap>] </ref>, where the Coriolis effect is weakest. However, it is possible for tropical cyclones to form within this boundary if there is another source of initial rotation. These conditions are extremely rare, and such storms are believed to form at most once per century. A combination of a pre-existing disturbance, upper level divergence and a ]-related cold spell led to ] at only 1.5 degrees north of the equator in ]. It is estimated that such conditions occur only once every 400 years.<ref name="USAToday Vamei">{{cite news | title= Scientists dissect rare typhoon near Equator | publisher = Associated Press | url = http://www.usatoday.com/weather/news/2003-04-05-typhoon-vamei_x.htm | accessdate=2006-03-31}}</ref>


===Influence of climate change===
{{Main|Tropical cyclones and climate change}}
<!-- The effects of climate change and global warming caused by the burning of fossil fuels on tropical cyclones, is the subject of ongoing debate and research. Evidence has been presented that indicates that tropical cyclone activity has increased as a result of climate change, while others argue that natural variations in tropical cyclone activity on either a regional, annual or inter-decadal scale mask any such increase.
There is no clear consensus on whether global warming is currently having any measurable effect on tropical cyclones, climate models indicate that there may be an increase in tropical cyclone intensity in the future, under continued global warming. However, the models also indicate that tropical cyclone frequency will either remain unchanged or decrease. -->


])</ref>]]
====Major basins====
]
There are seven main basins of tropical cyclone formation. They are the north ], the eastern and western parts of the ], the southwestern Pacific, and the southwestern and southeastern ]s, and the northern Indian Ocean. Worldwide, an average of 80 tropical cyclones form each year.<ref name=NHCE10> accessed March 31, 2006</ref>
] differ along political lines, on whether climate change was a "major factor" contributing to various extreme weather events experienced by respondents in 2023.<ref name="WashPost_20230823">{{cite news |last1=Ajasa |first1=Amudalat |last2=Clement |first2=Scott |last3=Guskin |first3=Emily |date=August 23, 2023 |title=Partisans remain split on climate change contributing to more disasters, and on their weather becoming more extreme |url=https://www.washingtonpost.com/climate-environment/2023/08/23/extreme-weather-climate-change-poll/ |url-status=live |archive-url=https://archive.today/20230823125945/https://www.washingtonpost.com/climate-environment/2023/08/23/extreme-weather-climate-change-poll/ |archive-date=August 23, 2023 |newspaper=The Washington Post}}</ref> "Severe storms" includes hurricanes.]]


The ] summarize the latest scientific findings about the impact of climate change on tropical cyclones. According to the report, we have now better understanding about the impact of climate change on tropical storm than before. Major tropical storms ''likely'' became more frequent in the last 40 years. We can say with ''high confidence'' that climate change increase rainfall during tropical cyclones. We can say with ''high confidence'' that a 1.5 degree warming lead to "increased proportion of and peak wind speeds of intense tropical cyclones". We can say with ''medium confidence'' that regional impacts of further warming include more intense tropical cyclones and/or extratropical storms.<ref>{{cite book |title=Climate Change 2023: Synthesis Report. Contribution of Working Groups I, II and III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change |date=2023 |publisher=IPCC |location=Geneva, Switzerland |pages=46, 51, 69, 98 |url=https://www.ipcc.ch/report/ar6/syr/downloads/report/IPCC_AR6_SYR_FullVolume.pdf |access-date=28 October 2024}}</ref>
{|class="wikitable"
! colspan=2 style="background: #ccf;" | Zones and Forecasters<ref name=NHCF1> accessed March 31, 2006</ref>
|-
! Basin !! WMO Regional Specialised Meteorological Center(s)
|-
| North Atlantic || ]
|-
| North Eastern Pacific || ] & ]
|-
| North Western Pacific || ]
|-
| North Indian || ]
|-
| South Western Pacific || ] & ] & ] & ]
|-
| South Eastern Indian || ]
|-
| South Western Indian || ]
|}


] can affect tropical cyclones in a variety of ways: an intensification of rainfall and wind speed, a decrease in overall frequency, an increase in the frequency of very intense storms and a poleward extension of where the cyclones reach maximum intensity are among the possible consequences of human-induced climate change.<ref name=":5" /> Tropical cyclones use warm, moist air as their fuel. As climate change is ], there is potentially more of this fuel available.<ref>{{Cite web |date=May 18, 2020 |title=Major tropical cyclones have become '15% more likely' over past 40 years |url=https://www.carbonbrief.org/major-tropical-cyclones-have-become-15-more-likely-over-past-40-years |url-status=live |archive-url=https://web.archive.org/web/20200808212654/https://www.carbonbrief.org/major-tropical-cyclones-have-become-15-more-likely-over-past-40-years |archive-date=August 8, 2020 |access-date=August 31, 2020 |website=Carbon Brief |language=en}}</ref>
* '''North Atlantic Ocean:''' The most-studied of all tropical basins, it includes the ], the ], and the ]. Tropical cyclone formation here varies widely from year to year, ranging from over twenty to one per year with an average of around ten.<ref name=NHCE10/> The ] Atlantic coast, ], ], the ] and ] are frequently affected by storms in this basin. Venezuela, the south-east of Canada and Atlantic ] are also occasionally affected. Many of the more intense Atlantic storms are ]s, which form off the west coast of ] near the ] islands.
* '''North Eastern Pacific Ocean:''' This is the second most active basin in the world, and the most dense (a large number of storms for a small area of ocean). Storms that form here can affect western ], ], northern ], and on extremely rare occasions, ] and ].
* '''North Western Pacific Ocean:''' Tropical storm activity in this region frequently affects ], ], ], the ], and ], but also many other countries in South-East Asia, such as ], ] and ], plus numerous ] islands. This is by far the most active basin, accounting for one-third of all tropical cyclone activity in the world. The coast of ] sees the most landfalling tropical cyclones worldwide.<ref name="Weyman and Anderson-Berry">Weyman, C & L Anderson-Berry accessed April 26, 2006</ref>
* '''Northern Indian Ocean:''' This basin is divided into two areas, the ] and the ], with the Bay of Bengal dominating (5 to 6 times more activity). This basin's season has an interesting double peak; one in April and May before the onset of the ], and another in October and November just after.{{citation needed}} Hurricanes which form in this basin have historically cost the most lives &mdash; most notably, the ] killed 200,000. Nations affected by this basin include ], ], ], ], ], and ]. Rarely, a tropical cyclone formed in this basin will affect the ].
* '''South Western Pacific Ocean:''' Tropical activity in this region largely affects ] and ].{{citation needed}}
* '''South Eastern Indian Ocean:''' Tropical activity in this region affects ] and ].{{citation needed}}
* '''South Western Indian Ocean:''' This basin is the least understood, due to a lack of historical data.{{citation needed}} Cyclones forming here impact ], ], ], and ].{{citation needed}}


Between 1979 and 2017, there was a global increase in the proportion of tropical cyclones of Category 3 and higher on the ]. The trend was most clear in the North Atlantic and in the Southern Indian Ocean. In the North Pacific, tropical cyclones have been moving poleward into colder waters and there was no increase in intensity over this period.<ref>{{Cite journal |last1=Kossin |first1=James P. |last2=Knapp |first2=Kenneth R. |last3=Olander |first3=Timothy L. |last4=Velden |first4=Christopher S. |date=May 18, 2020 |title=Global increase in major tropical cyclone exceedance probability over the past four decades |url=https://www.pnas.org/content/pnas/117/22/11975.full.pdf |url-status=live |journal=Proceedings of the National Academy of Sciences |language=en |volume=117 |issue=22 |pages=11975–11980 |bibcode=2020PNAS..11711975K |doi=10.1073/pnas.1920849117 |issn=0027-8424 |pmc=7275711 |pmid=32424081 |archive-url=https://web.archive.org/web/20201119095015/https://www.pnas.org/content/pnas/117/22/11975.full.pdf |archive-date=November 19, 2020 |access-date=October 6, 2020 |doi-access=free}}</ref> With {{Convert|2|C-change|F-change}} warming, a greater percentage (+13%) of tropical cyclones are expected to reach Category 4 and 5 strength.<ref name=":5" /> A 2019 study indicates that climate change has been driving the observed trend of ] of tropical cyclones in the Atlantic basin. Rapidly intensifying cyclones are hard to forecast and therefore pose additional risk to coastal communities.<ref>{{Cite book |last1=Collins |first1=M. |title=IPCC Special Report on the Ocean and Cryosphere in a Changing Climate |last2=Sutherland |first2=M. |last3=Bouwer |first3=L. |last4=Cheong |first4=S.-M. |last5=Frölicher |first5=T. |last6=Jacot Des Combes |first6=H. |last7=Koll Roxy |first7=M. |last8=Losada |first8=I. J. |last9=McInnes |first9=K. |year=2019 |pages=602 |chapter=Chapter 6: Extremes, Abrupt Changes and Managing Risks <!-- ipcc:20200202 --> |display-authors=4 |access-date=October 6, 2020 |chapter-url=https://www.ipcc.ch/site/assets/uploads/sites/3/2019/11/10_SROCC_Ch06_FINAL.pdf |archive-url=https://web.archive.org/web/20191220151131/https://www.ipcc.ch/site/assets/uploads/sites/3/2019/11/10_SROCC_Ch06_FINAL.pdf |archive-date=December 20, 2019 |url-status=live |last12=Susanto |last10=Ratter |last11=Rivera-Arriaga |first12=R. D. |last14=Tibig |first11=E. |last13=Swingedouw |first14=L. |first13=D. |first10=B.}}</ref>
====Unusual formation areas====
] on October 9, 2005 at 2300 UTC near the ].]]
The following areas spawn tropical cyclones only very rarely.
* '''''South Atlantic Ocean:''''' A combination of cooler waters and ] makes it very difficult for the ] to support tropical activity. However, three tropical cyclones have been observed here &mdash; a weak tropical storm in 1991 off the coast of ], ] (sometimes also referred to as Aldonça), which made landfall in ] in 2004 at Category 1 strength, and a smaller storm in ], east of ]. The January storm is thought to have reached tropical storm intensity based on ] winds.
* '''Central North Pacific:''' Shear in this area of the ] severely limits tropical development, with no storms having formed here since 2002. However, this region is commonly frequented by tropical cyclones that form in the much more favorable Eastern North Pacific Basin.<ref name=CPHC> accessed March 31, 2006</ref>
*'''South Eastern Pacific:''' Tropical cyclone formation is rare in this region; when they do form, it is frequently linked to El Niño episodes. Most of the storms that enter this region formed farther west in the Southwest Pacific. They affect the islands of ] in exceptional instances. During the 1982/83 El Niño event, French Polynesia was affected by six tropical cyclones in five months.<ref>http://www.hko.gov.hk/./publica/reprint/r170.pdf</ref>
* '''Mediterranean Sea:''' Storms which appear similar to tropical cyclones in structure sometimes occur in the Mediterranean basin. Examples of these "]" formed in September ], September ], January ], September ], and January ]. However, there is debate on whether these storms were tropical in nature.<ref name=NHCF1/>
* '''Temperate subtropics''': areas further than thirty degrees from the equator are not normally conducive to tropical cyclone formation or strengthening, and areas more than forty degrees from the equator are very hostile to such development. The primary limiting factor is water temperatures, although higher shear at increasing latitudes is also a factor. These areas are sometimes frequented by cyclones moving poleward from tropical latitudes. On rare occasions, such as in ]<ref name=UnisysAlberto> accessed March 31, 2006</ref> and ]<ref name=Unisys12> accessed March 31, 2006</ref> storms may form or strengthen in this region.
* '''Low latitudes'''. Areas within approximately ten degrees latitude of the equator do not experience a significant ], a vital ingredient in tropical cyclone formation. However, in December 2001, ] formed in the Southern South China Sea and made landfall in ]. It formed from a thunderstorm formation in ] that moved into the South China Sea.<ref name="UnisysVamei"> accessed March 30, 2006</ref>
* '''The ]:''' A storm system that appeared similar to a hurricane formed in ] on ]. It formed an eye-like structure in its center, and it may have briefly been a tropical cyclone.<ref name="Huron"> accessed May 3, 2006</ref>


Warmer air can hold more water vapor: the theoretical maximum water vapor content is given by the ], which yields ≈7% increase in water vapor in the atmosphere per {{Convert|1|C-change|F-change}} warming.<ref>{{cite journal |author1=Thomas R. Knutson |author2=Joseph J. Sirutis |author3=Ming Zhao |year=2015 |title=Global Projections of Intense Tropical Cyclone Activity for the Late Twenty-First Century from Dynamical Downscaling of CMIP5/RCP4.5 Scenarios |url=https://digitalcommons.odu.edu/cgi/viewcontent.cgi?article=1323&context=ccpo_pubs |url-status=live |journal=Journal of Climate |volume=28 |issue=18 |pages=7203–7224 |bibcode=2015JCli...28.7203K |doi=10.1175/JCLI-D-15-0129.1 |s2cid=129209836 |archive-url=https://web.archive.org/web/20200105210405/https://digitalcommons.odu.edu/cgi/viewcontent.cgi?article=1323&context=ccpo_pubs |archive-date=January 5, 2020 |access-date=October 6, 2020 |doi-access=free}}</ref><ref name="knutson 2013">{{cite journal |author=Knutson |display-authors=et al |year=2013 |title=Dynamical Downscaling Projections of Late 21st Century Atlantic Hurricane Activity: CMIP3 and CMIP5 Model-based Scenarios |url=https://www.gfdl.noaa.gov/research_highlight/dynamical-downscaling-projections-of-late-21st-century-atlantic-hurricane-activity-cmip3-and-cmip5-model-based-scenarios/ |url-status=live |journal=Journal of Climate |volume=26 |issue=17 |pages=6591–6617 |bibcode=2013JCli...26.6591K |doi=10.1175/JCLI-D-12-00539.1 |s2cid=129571840 |archive-url=https://web.archive.org/web/20201005005313/https://www.gfdl.noaa.gov/research_highlight/dynamical-downscaling-projections-of-late-21st-century-atlantic-hurricane-activity-cmip3-and-cmip5-model-based-scenarios/ |archive-date=October 5, 2020 |access-date=October 6, 2020 |doi-access=free}}</ref> All models that were assessed in a 2019 review paper show a future increase of rainfall rates.<ref name=":5" /> Additional ] will increase storm surge levels.<ref name=":6">{{Cite book |last1=Collins |first1=M. |title=IPCC Special Report on the Ocean and Cryosphere in a Changing Climate |last2=Sutherland |first2=M. |last3=Bouwer |first3=L. |last4=Cheong |first4=S.-M. |last5=Frölicher |first5=T. |last6=Jacot Des Combes |first6=H. |last7=Koll Roxy |first7=M. |last8=Losada |first8=I. J. |last9=McInnes |first9=K. |year=2019 |pages=603 |chapter=Chapter 6: Extremes, Abrupt Changes and Managing Risks |ref={{harvid|IPCC SROCC Ch6|2019}} <!-- ipcc:20200202 --> |display-authors=4 |access-date=October 6, 2020 |chapter-url=https://www.ipcc.ch/site/assets/uploads/sites/3/2019/11/10_SROCC_Ch06_FINAL.pdf |archive-url=https://web.archive.org/web/20191220151131/https://www.ipcc.ch/site/assets/uploads/sites/3/2019/11/10_SROCC_Ch06_FINAL.pdf |archive-date=December 20, 2019 |url-status=live |last12=Susanto |last10=Ratter |last11=Rivera-Arriaga |first12=R. D. |last14=Tibig |first11=E. |last13=Swingedouw |first14=L. |first13=D. |first10=B.}}</ref><ref name=":4">{{cite news |date=August 29, 2017 |title=Hurricane Harvey shows how we underestimate flooding risks in coastal cities, scientists say |url=https://www.washingtonpost.com/news/energy-environment/wp/2017/08/29/hurricane-harvey-shows-how-we-underestimate-flooding-risks-in-coastal-cities-scientists-say |url-status=live |archive-url=https://web.archive.org/web/20170830031541/https://www.washingtonpost.com/news/energy-environment/wp/2017/08/29/hurricane-harvey-shows-how-we-underestimate-flooding-risks-in-coastal-cities-scientists-say/ |archive-date=August 30, 2017 |access-date=August 30, 2017 |newspaper=The Washington Post}}</ref> It is plausible that extreme ]s see an increase as a consequence of changes in tropical cyclones, further exacerbating storm surge dangers to coastal communities.<ref name=":7">{{Cite journal |last1=Walsh |first1=K. J. E. |last2=Camargo |first2=S. J. |last3=Knutson |first3=T. R. |last4=Kossin |first4=J. |last5=Lee |first5=T. -C. |last6=Murakami |first6=H. |last7=Patricola |first7=C. |date=December 1, 2019 |title=Tropical cyclones and climate change |journal=Tropical Cyclone Research and Review |language=en |volume=8 |issue=4 |pages=240–250 |bibcode=2019TCRR....8..240W |doi=10.1016/j.tcrr.2020.01.004 |issn=2225-6032 |doi-access=free |hdl-access=free |hdl=11343/192963}}</ref> The compounding effects from floods, storm surge, and terrestrial flooding (rivers) are projected to increase ].<ref name=":4" />
===Times of formation===
Worldwide, tropical cyclone activity peaks in late ] when water temperatures are the warmest. However, each particular basin has its own seasonal patterns. On a worldwide scale, ] is the least active month, while ] is the most active.<ref name=NHCG1> accessed March 31, 2006</ref>


There is currently no consensus on how climate change will affect the overall frequency of tropical cyclones.<ref name=":5" /> A majority of ]s show a decreased frequency in future projections.<ref name=":7" /> For instance, a 2020 paper comparing nine high-resolution climate models found robust decreases in frequency in the Southern Indian Ocean and the Southern Hemisphere more generally, while finding mixed signals for Northern Hemisphere tropical cyclones.<ref>{{Cite journal |last1=Roberts |first1=Malcolm John |last2=Camp |first2=Joanne |last3=Seddon |first3=Jon |last4=Vidale |first4=Pier Luigi |last5=Hodges |first5=Kevin |last6=Vannière |first6=Benoît |last7=Mecking |first7=Jenny |last8=Haarsma |first8=Rein |last9=Bellucci |first9=Alessio |last10=Scoccimarro |first10=Enrico |last11=Caron |first11=Louis-Philippe |year=2020 |title=Projected Future Changes in Tropical Cyclones Using the CMIP6 HighResMIP Multimodel Ensemble |journal=Geophysical Research Letters |language=en |volume=47 |issue=14 |pages=e2020GL088662 |bibcode=2020GeoRL..4788662R |doi=10.1029/2020GL088662 |issn=1944-8007 |pmc=7507130 |pmid=32999514 |s2cid=221972087}}</ref> Observations have shown little change in the overall frequency of tropical cyclones worldwide,<ref>{{Cite web |title=Hurricanes and Climate Change |url=https://www.ucsusa.org/global-warming/science-and-impacts/impacts/hurricanes-and-climate-change.html |url-status=live |archive-url=https://web.archive.org/web/20190924043720/https://www.ucsusa.org/global-warming/science-and-impacts/impacts/hurricanes-and-climate-change.html |archive-date=September 24, 2019 |access-date=September 29, 2019 |website=Union of Concerned Scientists |language=en}}</ref> with increased frequency in the North Atlantic and central Pacific, and significant decreases in the southern Indian Ocean and western North Pacific.<ref>{{Cite journal |last1=Murakami |first1=Hiroyuki |last2=Delworth |first2=Thomas L. |last3=Cooke |first3=William F. |last4=Zhao |first4=Ming |last5=Xiang |first5=Baoqiang |last6=Hsu |first6=Pang-Chi |year=2020 |title=Detected climatic change in global distribution of tropical cyclones |journal=Proceedings of the National Academy of Sciences |language=en |volume=117 |issue=20 |pages=10706–10714 |bibcode=2020PNAS..11710706M |doi=10.1073/pnas.1922500117 |issn=0027-8424 |pmc=7245084 |pmid=32366651 |doi-access=free}}</ref>
In the North ], a distinct hurricane season occurs from ] to ], sharply peaking from late August through September. The statistical peak of the North Atlantic hurricane season is ]. The Northeast Pacific has a broader period of activity, but in a similar timeframe to the Atlantic. The Northwest Pacific sees tropical cyclones year-round, with a minimum in February and a peak in early September. In the North Indian basin, storms are most common from April to December, with peaks in May and November.<ref name=NHCG1/>


There has been a poleward expansion of the latitude at which the maximum intensity of tropical cyclones occurs, which may be associated with climate change.<ref>{{cite journal |author1=James P. Kossin |author2=Kerry A. Emanuel |author3=Gabriel A. Vecchi |year=2014 |title=The poleward migration of the location of tropical cyclone maximum intensity |journal=Nature |volume=509 |issue=7500 |pages=349–352 |bibcode=2014Natur.509..349K |doi=10.1038/nature13278 |pmid=24828193 |s2cid=4463311 |hdl-access=free |hdl=1721.1/91576}}</ref> In the North Pacific, there may also have been an eastward expansion.<ref name=":6" /> Between 1949 and 2016, there was a slowdown in tropical cyclone translation speeds. It is unclear still to what extent this can be attributed to climate change: climate models do not all show this feature.<ref name=":7" />
In the ], tropical cyclone activity begins in late October and ends in May. Southern Hemisphere activity peaks in mid-February to early March.<ref name=NHCG1/>


A 2021 study review article concluded that the geographic range of tropical cyclones will probably expand poleward in response to climate warming of the ].<ref>{{cite journal |last1=Studholme |first1=Joshua |last2=Fedorov |first2=Alexey V. |last3=Gulev |first3=Sergey K. |last4=Emanuel |first4=Kerry |last5=Hodges |first5=Kevin |date=December 29, 2021 |title=Poleward expansion of tropical cyclone latitudes in warming climates |url=https://www.nature.com/articles/s41561-021-00859-1 |url-status=live |journal=] |volume=15 |pages=14–28 |doi=10.1038/s41561-021-00859-1 |s2cid=245540084 |archive-url=https://web.archive.org/web/20220104110552/https://www.nature.com/articles/s41561-021-00859-1 |archive-date=January 4, 2022 |access-date=January 4, 2022}}</ref>
{| border="1" cellspacing="0" cellpadding="3" class=wikitable

!colspan=6| Seasons and Numbers of storms<ref name=NHCE10/><ref name=NHCG1/>
When hurricane winds speed rise by 5%, its destructive power rise by about 50%. Therefore, as climate change increased the wind speed of ] by 11%, it increased the destruction from it by more than twice.<ref>{{cite web |last1=Nuccitelli |first1=Dana |title=Climate change made Hurricane Helene and other 2024 disasters more damaging, scientists find |url=https://yaleclimateconnections.org/2024/10/climate-change-made-hurricane-helene-and-other-2024-disasters-more-damaging-scientists-find/ |website=Yale Climate Connections |date=October 9, 2024 |publisher=The Yale Center for Climate Communication, Yale School of the Environment |access-date=28 October 2024}}</ref> According to ] the influence of climate change on the rainfall of some latest hurricanes can be described as follows:<ref>{{cite web |title=Yet another hurricane wetter, windier and more destructive because of climate change |url=https://www.worldweatherattribution.org/yet-another-hurricane-wetter-windier-and-more-destructive-because-of-climate-change/ |website=World Weather Attribution |access-date=28 October 2024}}</ref>

{| class="wikitable"
|+ Impact of climate change on the rainfall during some recent hurricanes according to ].
|-
! The name of the hurricane !! How much climate change increased rainfall
|-
| ] || 4%
|- |-
| ] || 6%
! Basin !! Season Start !! Season End !! Tropical Storms (>34 knots) !! Tropical Cyclones (>63 knots)!! Category 3+ Tropical Cyclones (>95 knots)
|- |-
| ] || 9%
| Northwest Pacific || Year Round || Year Round || 26.7 || 16.9 || 8.5
|- |-
| ] || 5%
| South Indian || October || May || 20.6 || 10.3 || 4.3
|- |-
| ] || 5-18%
| Northeast Pacific || May || November || 16.3 || 9.0 || 4.1
|- |-
| ] || 18%
| North Atlantic || June || November || 10.6 || 5.9 || 2.0
|- |-
| ] || 7-38%
| Australia Southwest Pacific || October || May || 10.6 || 4.8 || 1.9
|- |-
| ] || 10%
| North Indian || April || December || 5.4 || 2.2 || 0.4
|} |}


==Intensity==
==Movement and track==
Tropical cyclone intensity is based on wind speeds and pressure. Relationships between winds and pressure are often used in determining the intensity of a storm.<ref>{{cite journal |last1=Knapp |first1=Kenneth R. |last2=Knaff |first2=John A. |last3=Sampson |first3=Charles R. |last4=Riggio |first4=Gustavo M. |last5=Schnapp |first5=Adam D. |title=A Pressure-Based Analysis of the Historical Western North Pacific Tropical Cyclone Intensity Record |journal=Monthly Weather Review |date=August 1, 2013 |volume=141 |issue=8 |pages=2611–2631 |doi=10.1175/MWR-D-12-00323.1 |publisher=American Meteorological Society |bibcode=2013MWRv..141.2611K |s2cid=19031120 |doi-access=free}}</ref> ], such as the ] and Australia's scale (Bureau of Meteorology), only use wind speed for determining the category of a storm.<ref>{{cite web |title=What is a Tropical Cyclone? |url=http://www.bom.gov.au/cyclone/tropical-cyclone-knowledge-centre/understanding/tc-info/ |publisher=Bureau of Meteorology |access-date=October 7, 2022 |archive-date=October 3, 2022 |archive-url=https://web.archive.org/web/20221003062556/http://www.bom.gov.au/cyclone/tropical-cyclone-knowledge-centre/understanding/tc-info/ |url-status=live}}</ref><ref>{{cite web |title=Saffir-Simpson Hurricane Wind Scale |url=https://www.nhc.noaa.gov/aboutsshws.php |publisher=National Hurricane Center |access-date=October 7, 2022 |archive-date=June 20, 2020 |archive-url=https://web.archive.org/web/20200620093804/https://www.nhc.noaa.gov/aboutsshws.php |url-status=live}}</ref> The most intense storm on record is ] in the northwestern Pacific Ocean in 1979, which reached a minimum pressure of {{convert|870|hPa|inHg|lk=on|abbr=on}} and maximum sustained wind speeds of {{convert|165|kn|m/s km/h mph|abbr=on|round=5}}.<ref name="jtwc">{{Cite journal |last1=Dunnavan |first1=G.M. |last2=Diercks |first2=J.W. |year=1980 |title=An Analysis of Super Typhoon Tip (October 1979) |journal=] |volume=108 |issue=11 |pages=1915–1923 |bibcode=1980MWRv..108.1915D |doi=10.1175/1520-0493(1980)108<1915:AAOSTT>2.0.CO;2 |doi-access=free}}</ref> The highest maximum sustained wind speed ever recorded was {{convert|185|kn|m/s km/h mph|abbr=on|round=5}} in ] in 2015—the most intense cyclone ever recorded in the ].<ref>{{cite web|last1=Pasch|first1=Richard|title=Hurricane Patricia Discussion Number 14|url=http://www.nhc.noaa.gov/text/refresh/MIATCDEP5+shtml/230834.shtml?|publisher=National Hurricane Center|date=October 23, 2015|quote=Data from three center fixes by the Hurricane Hunters indicate that the intensity, based on a blend of 700 mb-flight level and SFMR-observed surface winds, is near 175 kt. This makes Patricia the strongest hurricane on record in the National Hurricane Center's area of responsibility (AOR) which includes the Atlantic and the eastern North Pacific basins.|access-date=October 23, 2015|archive-url=https://web.archive.org/web/20151025142113/http://www.nhc.noaa.gov/text/refresh/MIATCDEP5+shtml/230834.shtml|archive-date=October 25, 2015|url-status=live}}</ref>
===Large-scale winds===
Although tropical cyclones are large systems generating enormous energy, their movements over the earth's surface are often compared to that of leaves carried along by a stream. That is, large-scale winds&mdash;the streams in the earth's atmosphere&mdash;are responsible for moving and steering tropical cyclones. The path of motion is referred to as a tropical cyclone's ''track.''


===Factors that influence intensity===
The major force affecting the track of tropical systems in all areas are winds circulating around high-pressure areas. Over the North Atlantic Ocean, tropical systems are steered generally westward by the east-to-west winds on the south side of the Bermuda High, a persistent high-pressure area over the North Atlantic. Also, in the area of the North Atlantic where hurricanes form, ], which are prevailing westward-moving wind currents, steer ''tropical waves'' (precursors to tropical depressions and cyclones) westward from off the African coast toward the Caribbean and North America.
Warm ]s are required for tropical cyclones to form and strengthen. The commonly-accepted minimum temperature range for this to occur is {{convert|26–27|C|F|abbr=on}}, however, multiple studies have proposed a lower minimum of {{convert|25.5|C|F|abbr=on}}.<ref>{{cite journal |last1=Tory |first1=K. J. |last2=Dare |first2=R. A. |date=October 15, 2015 |title=Sea Surface Temperature Thresholds for Tropical Cyclone Formation |url=https://journals.ametsoc.org/view/journals/clim/28/20/jcli-d-14-00637.1.xml?tab_body=pdf |url-status=live |journal=] |publisher=] |volume=28 |issue=20 |page=8171 |bibcode=2015JCli...28.8171T |doi=10.1175/JCLI-D-14-00637.1 |archive-url=https://web.archive.org/web/20210428230055/https://journals.ametsoc.org/view/journals/clim/28/20/jcli-d-14-00637.1.xml?tab_body=pdf |archive-date=April 28, 2021 |access-date=April 28, 2021 |doi-access=free}}</ref><ref>{{cite journal |last1=Lavender |first1=Sally |last2=Hoeke |first2=Ron |last3=Abbs |first3=Deborah |date=March 9, 2018 |title=The influence of sea surface temperature on the intensity and associated storm surge of tropical cyclone Yasi: a sensitivity study |url=https://nhess.copernicus.org/articles/18/795/2018/ |url-status=live |journal=Natural Hazards and Earth System Sciences |publisher=] |volume=18 |issue=3 |pages=795–805 |bibcode=2018NHESS..18..795L |doi=10.5194/nhess-18-795-2018 |archive-url=https://web.archive.org/web/20210428224550/https://nhess.copernicus.org/articles/18/795/2018/ |archive-date=April 28, 2021 |access-date=April 28, 2021 |doi-access=free}}</ref> Higher sea surface temperatures result in faster intensification rates and sometimes even ].<ref>{{cite journal |last1=Xu |first1=Jing |last2=Wang |first2=Yuqing |date=April 1, 2018 |title=Dependence of Tropical Cyclone Intensification Rate on Sea SurfaceTemperature, Storm Intensity, and Size in the Western North Pacific |url=https://journals.ametsoc.org/view/journals/wefo/33/2/waf-d-17-0095_1.xml?tab_body=pdf |url-status=live |journal=] |publisher=American Meteorological Society |volume=33 |issue=2 |pages=523–527 |bibcode=2018WtFor..33..523X |doi=10.1175/WAF-D-17-0095.1 |archive-url=https://web.archive.org/web/20210428230055/https://journals.ametsoc.org/view/journals/wefo/33/2/waf-d-17-0095_1.xml?tab_body=pdf |archive-date=April 28, 2021 |access-date=April 28, 2021 |doi-access=free}}</ref> High ], also known as ], allows storms to achieve a higher intensity.<ref name="NHC Intensity Forecasting">{{cite web |last1=Brown |first1=Daniel |title=Tropical Cyclone Intensity Forecasting: Still a Challenging Proposition |url=https://www.nhc.noaa.gov/outreach/presentations/NHC2017_IntensityChallenges.pdf |publisher=National Hurricane Center |access-date=April 27, 2021 |page=7 |date=April 20, 2017 |archive-date=April 27, 2021 |archive-url=https://web.archive.org/web/20210427013208/https://www.nhc.noaa.gov/outreach/presentations/NHC2017_IntensityChallenges.pdf |url-status=live}}</ref> Most tropical cyclones that experience rapid intensification are traversing regions of high ocean heat content rather than lower values.<ref name="OHC" /> High ocean heat content values can help to offset the oceanic cooling caused by the passage of a tropical cyclone, limiting the effect this cooling has on the storm.<ref>{{cite journal |last1=Lin |first1=I. |last2=Goni |first2=Gustavo |last3=Knaff |first3=John |last4=Forbes |first4=Cristina |last5=Ali |first5=M. |date=May 31, 2012 |title=Ocean heat content for tropical cyclone intensity forecasting and its impact on storm surge |url=https://www.aoml.noaa.gov/phod/docs/I-Ilin.pdf |url-status=live |journal=Journal of the International Society for the Prevention and Mitigation of Natural Hazards |publisher=] |volume=66 |issue=3 |pages=3–4 |doi=10.1007/s11069-012-0214-5 |issn=0921-030X |archive-url=https://web.archive.org/web/20210427013210/https://www.aoml.noaa.gov/phod/docs/I-Ilin.pdf |archive-date=April 27, 2021 |access-date=April 27, 2021 |s2cid=9130662}}</ref> Faster-moving systems are able to intensify to higher intensities with lower ocean heat content values. Slower-moving systems require higher values of ocean heat content to achieve the same intensity.<ref name="OHC">{{cite journal |last1=Chih |first1=Cheng-Hsiang |last2=Wu |first2=Chun-Chieh |title=Exploratory Analysis of Upper-Ocean Heat Content and Sea Surface Temperature Underlying Tropical Cyclone Rapid Intensification in the Western North Pacific |journal=Journal of Climate |date=February 1, 2020 |volume=33 |issue=3 |pages=1031–1033 |doi=10.1175/JCLI-D-19-0305.1 |bibcode=2020JCli...33.1031C |s2cid=210249119 |url=https://journals.ametsoc.org/view/journals/clim/33/3/jcli-d-19-0305.1.xml?tab_body=pdf |access-date=April 27, 2021 |archive-date=April 27, 2021 |archive-url=https://web.archive.org/web/20210427013208/https://journals.ametsoc.org/view/journals/clim/33/3/jcli-d-19-0305.1.xml?tab_body=pdf |url-status=live}}</ref>


The passage of a tropical cyclone over the ocean causes the upper layers of the ocean to cool substantially, a process known as ],<ref>{{cite journal |last1=Hu |first1=Jianyu |last2=Wang |first2=Xiao Hua |date=September 2016 |title=Progress on upwelling studies in the China seas |journal=] |publisher=AGU |volume=54 |issue=3 |pages=653–673 |bibcode=2016RvGeo..54..653H |doi=10.1002/2015RG000505 |s2cid=132158526 |doi-access=free}}</ref> which can negatively influence subsequent cyclone development. This cooling is primarily caused by wind-driven mixing of cold water from deeper in the ocean with the warm surface waters. This effect results in a negative feedback process that can inhibit further development or lead to weakening. Additional cooling may come in the form of cold water from falling raindrops (this is because the atmosphere is cooler at higher altitudes). Cloud cover may also play a role in cooling the ocean, by shielding the ocean surface from direct sunlight before and slightly after the storm passage. All these effects can combine to produce a dramatic drop in sea surface temperature over a large area in just a few days.<ref name="NASA Cooling">{{cite web|author1=D'Asaro, Eric A. |author2=Black, Peter G. |name-list-style=amp |url=https://ams.confex.com/ams/last2000/techprogram/paper_12726.htm |title=J8.4 Turbulence in the Ocean Boundary Layer Below Hurricane Dennis |year=2006 |access-date=February 22, 2008 |publisher=] |url-status=live |archive-url=https://web.archive.org/web/20120330131407/http://iop.apl.washington.edu/opd/user/dasaro/DENNIS/HurrConf.pdf |archive-date=March 30, 2012}}</ref> Conversely, the mixing of the sea can result in heat being inserted in deeper waters, with ] on global ].<ref>{{cite journal |last1=Fedorov |first1=Alexey V. |last2=Brierley |first2=Christopher M. |last3=Emanuel |first3=Kerry |date=February 2010 |title=Tropical cyclones and permanent El Niño in the early Pliocene epoch |journal=] |language=en |volume=463 |issue=7284 |pages=1066–1070 |bibcode=2010Natur.463.1066F |doi=10.1038/nature08831 |issn=0028-0836 |pmid=20182509 |hdl-access=free |hdl=1721.1/63099 |s2cid=4330367}}</ref>
===Coriolis effect===
] near peak intensity, showing ] rotation due to the ].]]
The earth's rotation also imparts an acceleration (termed the ''Coriolis Acceleration'' or '']''). This acceleration causes cyclonic systems to turn towards the poles in the absence of strong steering currents (i.e. in the north, the northern part of the cyclone has winds to the west, and the Coriolis force pulls them slightly north. The southern part is pulled south, but since it is closer to the equator, the Coriolis force is a bit weaker there). Thus, tropical cyclones in the Northern Hemisphere, which commonly move west in the beginning, normally turn north (and are then usually blown east), and cyclones in the Southern Hemisphere are deflected south, if no strong pressure systems are counteracting the Coriolis Acceleration. The Coriolis acceleration also initiates cyclonic rotation, but it is not the driving force that brings this rotation to high speeds. These speeds are due to the conservation of ] - air is drawn in from an area much larger than the cyclone such that the tiny rotational speed (originially imparted by the Coriolis acceleration) is magnified greatly as the air is drawn in to the low pressure center.


] decreases tropical cyclone predicability, with storms exhibiting wide range of responses in the presence of shear.<ref>{{cite journal |last1=Zhang |first1=Fuqing |last2=Tao |first2=Dandan |title=Effects of Vertical Wind Shear on the Predictability of Tropical Cyclones |journal=Journal of the Atmospheric Sciences |date=March 1, 2013 |volume=70 |issue=3 |pages=975–983 |doi=10.1175/JAS-D-12-0133.1 |doi-access=free|bibcode=2013JAtS...70..975Z}}</ref> Wind shear often negatively affects tropical cyclone intensification by displacing moisture and heat from a system's center.<ref>{{cite web |last1=Stovern |first1=Diana |last2=Ritchie |first2=Elizabeth |title=Modeling the Effect of Vertical Wind Shear on Tropical Cyclone Size and Structure |pages=1–2 |url=https://ams.confex.com/ams/pdfpapers/169136.pdf |access-date=April 28, 2021 |website=American Meteorological Society |archive-date=June 18, 2021 |archive-url=https://web.archive.org/web/20210618212223/https://ams.confex.com/ams/pdfpapers/169136.pdf |url-status=live}}</ref> Low levels of vertical wind shear are most optimal for strengthening, while stronger wind shear induces weakening.<ref>{{cite journal |last1=Wingo |first1=Matthew |last2=Cecil |first2=Daniel |title=Effects of Vertical Wind Shear on Tropical Cyclone Precipitation |journal=Monthly Weather Review |date=March 1, 2010 |volume=138 |issue=3 |pages=645–662 |doi=10.1175/2009MWR2921.1 |publisher=American Meteorological Society |bibcode=2010MWRv..138..645W |s2cid=73622535 |doi-access=free}}</ref><ref>{{cite journal |last1=Liang |first1=Xiuji |last2=Li |first2=Qingqing |date=March 1, 2021 |title=Revisiting the response of western North Pacific tropical cyclone intensity change to vertical wind shear in different directions |journal=Atmospheric and Oceanic Science Letters |volume=14 |issue=3 |page=100041 |doi=10.1016/j.aosl.2021.100041 |bibcode=2021AOSL...1400041L |doi-access=free}}</ref> Dry air entraining into a tropical cyclone's core has a negative effect on its development and intensity by diminishing atmospheric convection and introducing asymmetries in the storm's structure.<ref>{{cite journal |last1=Shi |first1=Donglei |last2=Ge |first2=Xuyang |last3=Peng |first3=Melinda |title=Latitudinal dependence of the dry air effect on tropical cyclone development |journal=Dynamics of Atmospheres and Oceans |date=September 2019 |volume=87 |page=101102 |doi=10.1016/j.dynatmoce.2019.101102 |url=https://www.sciencedirect.com/science/article/abs/pii/S0377026519300193 |access-date=May 14, 2022 |bibcode=2019DyAtO..8701102S |s2cid=202123299}}</ref><ref>{{cite journal |last1=Wang |first1=Shuai |last2=Toumi |first2=Ralf |date=June 1, 2019 |title=Impact of Dry Midlevel Air on the Tropical Cyclone Outer Circulation |journal=] |publisher=American Meteorological Society |volume=76 |issue=6 |pages=1809–1826 |bibcode=2019JAtS...76.1809W |doi=10.1175/JAS-D-18-0302.1 |hdl=10044/1/70065 |s2cid=145965553|doi-access=free |hdl-access=free}}</ref><ref>{{cite journal |last1=Alland |first1=Joshua J. |last2=Tang |first2=Brian H. |last3=Corbosiero |first3=Kristen L. |last4=Bryan |first4=George H. |title=Combined Effects of Midlevel Dry Air and Vertical Wind Shear on Tropical Cyclone Development. Part II: Radial Ventilation |journal=Journal of the Atmospheric Sciences |date=February 24, 2021 |volume=78 |issue=3 |pages=783–796 |doi=10.1175/JAS-D-20-0055.1 |url=https://journals.ametsoc.org/view/journals/atsc/78/3/JAS-D-20-0055.1.xml |access-date=May 14, 2022 |publisher=American Meteorological Society |bibcode=2021JAtS...78..783A |s2cid=230602004 |archive-date=May 14, 2022 |archive-url=https://web.archive.org/web/20220514132936/https://journals.ametsoc.org/view/journals/atsc/78/3/JAS-D-20-0055.1.xml |url-status=live}}</ref> Symmetric, strong ] leads to a faster rate of intensification than observed in other systems by mitigating local wind shear.<ref>{{cite journal |last1=Rappin |first1=Eric D. |last2=Morgan |first2=Michael C. |last3=Tripoli |first3=Gregory J. |title=The Impact of Outflow Environment on Tropical Cyclone Intensification and Structure |journal=Journal of the Atmospheric Sciences |date=February 1, 2011 |volume=68 |issue=2 |pages=177–194 |doi=10.1175/2009JAS2970.1 |publisher=American Meteorological Society |bibcode=2011JAtS...68..177R |s2cid=123508815 |doi-access=free}}</ref><ref>{{cite journal |last1=Shi |first1=Donglei |last2=Chen |first2=Guanghua |title=The Implication of Outflow Structure for the Rapid Intensification of Tropical Cyclones under Vertical Wind Shear |journal=Monthly Weather Review |date=December 10, 2021 |volume=149 |issue=12 |pages=4107–4127 |doi=10.1175/MWR-D-21-0141.1 |url=https://journals.ametsoc.org/view/journals/mwre/149/12/MWR-D-21-0141.1.xml |access-date=May 15, 2022 |publisher=American Meteorological Society |bibcode=2021MWRv..149.4107S |s2cid=244001444 |archive-date=May 14, 2022 |archive-url=https://web.archive.org/web/20220514131433/https://journals.ametsoc.org/view/journals/mwre/149/12/MWR-D-21-0141.1.xml |url-status=live}}</ref><ref>{{cite journal |last1=Ryglicki |first1=David R. |last2=Doyle |first2=James D. |last3=Hodyss |first3=Daniel |last4=Cossuth |first4=Joshua H. |last5=Jin |first5=Yi |last6=Viner |first6=Kevin C. |last7=Schmidt |first7=Jerome M. |title=The Unexpected Rapid Intensification of Tropical Cyclones in Moderate Vertical Wind Shear. Part III: Outflow–Environment Interaction |journal=Monthly Weather Review |date=August 1, 2019 |volume=147 |issue=8 |pages=2919–2940 |doi=10.1175/MWR-D-18-0370.1 |publisher=American Meteorological Society |bibcode=2019MWRv..147.2919R |s2cid=197485216 |doi-access=free}}</ref> Weakening outflow is associated with the weakening of ]s within a tropical cyclone.<ref>{{cite journal |last1=Dai |first1=Yi |last2=Majumdar |first2=Sharanya J. |last3=Nolan |first3=David S. |title=The Outflow–Rainband Relationship Induced by Environmental Flow around Tropical Cyclones |journal=Journal of the Atmospheric Sciences |date=July 1, 2019 |volume=76 |issue=7 |pages=1845–1863 |doi=10.1175/JAS-D-18-0208.1 |publisher=American Meteorological Society |bibcode=2019JAtS...76.1845D |s2cid=146062929 |doi-access=free}}</ref> Tropical cyclones may still intensify, even rapidly, in the presence of moderate or strong wind shear depending on the evolution and structure of the storm's convection.<ref>{{cite journal |last1=Ryglicki |first1=David R. |last2=Cossuth |first2=Joshua H. |last3=Hodyss |first3=Daniel |last4=Doyle |first4=James D. |title=The Unexpected Rapid Intensification of Tropical Cyclones in Moderate Vertical Wind Shear. Part I: Overview and Observations |journal=Monthly Weather Review |date=November 1, 2018 |volume=146 |issue=11 |pages=3773–3800 |doi=10.1175/MWR-D-18-0020.1|doi-access=free|bibcode=2018MWRv..146.3773R}}</ref><ref>{{cite journal |last1=Rios-Berrios |first1=Rosimar |last2=Finocchio |first2=Peter M. |last3=Alland |first3=Joshua J. |last4=Chen |first4=Xiaomin |last5=Fischer |first5=Michael S. |last6=Stevenson |first6=Stephanie N. |last7=Tao |first7=Dandan |title=A Review of the Interactions between Tropical Cyclones and Environmental Vertical Wind Shear |journal=Journal of the Atmospheric Sciences |date=October 27, 2023 |volume=81 |issue=4 |pages=713–741 |doi=10.1175/JAS-D-23-0022.1|url=https://repository.library.noaa.gov/view/noaa/60689}}</ref>
===Interaction with high and low pressure systems===
Finally, when a tropical cyclone moves into higher latitude, its general track around a high-pressure area can be deflected significantly by winds moving toward a low-pressure area. Such a track direction change is termed ''recurve.'' A hurricane moving from the Atlantic toward the ], for example, will recurve to the north and then northeast if it encounters winds blowing northeastward toward a low-pressure system passing over North America. Many tropical cyclones along the East Coast and in the Gulf of Mexico are eventually forced toward the northeast by low-pressure areas which move from west to east over North America.


The size of tropical cyclones plays a role in how quickly they intensify. Smaller tropical cyclones are more prone to rapid intensification than larger ones.<ref>{{cite journal |last1=Carrasco |first1=Cristina |last2=Landsea |first2=Christopher |last3=Lin |first3=Yuh-Lang |title=The Influence of Tropical Cyclone Size on Its Intensification |journal=Weather and Forecasting |date=June 1, 2014 |volume=29 |issue=3 |pages=582–590 |doi=10.1175/WAF-D-13-00092.1 |publisher=American Meteorological Society |bibcode=2014WtFor..29..582C |s2cid=18429068 |doi-access=free}}</ref> The ], which involves interaction between two tropical cyclones, can weaken and ultimately result in the dissipation of the weaker of two tropical cyclones by reducing the organization of the system's convection and imparting horizontal wind shear.<ref>{{cite journal |last1=Lander |first1=Mark |last2=Holland |first2=Greg J. |date=October 1993 |title=On the interaction of tropical-cyclone-scale vortices. I: Observations |url=https://rmets.onlinelibrary.wiley.com/doi/abs/10.1002/qj.49711951406 |journal=] |publisher=] |volume=119 |issue=514 |pages=1347–1361 |bibcode=1993QJRMS.119.1347L |doi=10.1002/qj.49711951406}}</ref> Tropical cyclones typically weaken while situated over a landmass because conditions are often unfavorable as a result of the lack of oceanic forcing.<ref>{{cite journal |last1=Andersen |first1=Theresa K. |last2=Shepherd |first2=J. Marshall |title=A global spatiotemporal analysis of inland tropical cyclone maintenance or intensification |journal=International Journal of Climatology |date=March 21, 2013 |volume=34 |issue=2 |pages=391–402 |doi=10.1002/joc.3693 |url=https://rmets.onlinelibrary.wiley.com/doi/abs/10.1002/joc.3693 |access-date=October 7, 2022 |publisher=Royal Meteorological Society|s2cid=129080562}}</ref> The ] can allow a tropical cyclone to maintain or increase its intensity following ], in cases where there has been copious rainfall, through the release of latent heat from the saturated soil.<ref>{{cite book |last1=Andersen |first1=Theresa |chapter-url=https://link.springer.com/chapter/10.1007/978-3-319-47594-3_5 |title=Hurricanes and Climate Change |last2=Sheperd |first2=Marshall |date=February 17, 2017 |publisher=] |isbn=978-3-319-47592-9 |pages=117–134 |chapter=Inland Tropical Cyclones and the "Brown Ocean" Concept |doi=10.1007/978-3-319-47594-3_5 |access-date=May 20, 2022 |archive-url=https://web.archive.org/web/20220515125238/https://link.springer.com/chapter/10.1007/978-3-319-47594-3_5 |archive-date=May 15, 2022 |url-status=live}}</ref> ] can cause a significant increase in the intensity of the convection of a tropical cyclone when its eye moves over a mountain, breaking the capped boundary layer that had been restraining it.<ref>{{cite journal |last1=Houze |first1=Robert A. Jr. |title=Orographic effects on precipitating clouds |journal=Reviews of Geophysics |date=January 6, 2012 |volume=50 |issue=1 |doi=10.1029/2011RG000365 |publisher=AGU |bibcode=2012RvGeo..50.1001H |s2cid=46645620 |doi-access=free}}</ref> Jet streams can both enhance and inhibit tropical cyclone intensity by influencing the storm's outflow as well as vertical wind shear.<ref>{{cite journal |last1=Ito |first1=Kosuke |last2=Ichikawa |first2=Hana |title=Warm ocean accelerating tropical cyclone Hagibis (2019) through interaction with a mid-latitude westerly jet |journal=Scientific Online Letters on the Atmosphere |date=August 31, 2020 |volume=17A |pages=1–6 |doi=10.2151/sola.17A-001 |url=https://www.jstage.jst.go.jp/article/sola/advpub/0/advpub_17A-001/_pdf/-char/ja |access-date=October 7, 2022 |publisher=Meteorological Society of Japan |s2cid=224874804 |archive-date=October 7, 2022 |archive-url=https://web.archive.org/web/20221007004526/https://www.jstage.jst.go.jp/article/sola/advpub/0/advpub_17A-001/_pdf/-char/ja |url-status=live |doi-access=free}}</ref><ref>{{cite journal |last1=Do |first1=Gunwoo |last2=Kim |first2=Hyeong-Seog |title=Effect of Mid-Latitude Jet Stream on the Intensity of Tropical Cyclones Affecting Korea: Observational Analysis and Implication from the Numerical Model Experiments of Typhoon Chaba (2016) |journal=Atmosphere |date=August 18, 2021 |volume=12 |issue=8 |page=1061 |doi=10.3390/atmos12081061 |publisher=MDPI |bibcode=2021Atmos..12.1061D |doi-access=free}}</ref>
===Strengthening due to warm water currents===
] and Eddy Vortex.]]
Although it has not been shown to affect storm direction, crossing over currents of warmer water is known to rapidly increase storm intensity. The best known of these is the ], where extremely warm water enters the Gulf of Mexico through the ]-] gap and "bulges" towards ]. ] and ], among others, gained great strength as they tracked over the Loop Current.


===Landfall=== ===Rapid intensification===
{{main|Rapid intensification}}
Officially, "]" is when a storm's center (the center of the eye, not its edge) reaches land. Naturally, storm conditions may be experienced on the coast and inland well before landfall. In fact, for a storm moving inland, the landfall area experiences half the storm before the actual landfall. For emergency preparedness, actions should be timed from when a certain wind speed will reach land, not from when landfall will occur.


On occasion, tropical cyclones may undergo a process known as rapid intensification, a period in which the maximum sustained winds of a tropical cyclone increase by {{Convert|30|kn|km/h mph|lk=in|abbr=on}} or more within 24 hours.<ref name="NWS Glossary">{{cite web|title=Glossary of NHC Terms|url=https://www.nhc.noaa.gov/aboutgloss.shtml#r|publisher=United States National Oceanic and Atmospheric Administration's National Hurricane Center|access-date=June 2, 2019|archive-url=https://web.archive.org/web/20190912164011/https://www.nhc.noaa.gov/aboutgloss.shtml#r|archive-date=September 12, 2019|url-status=live}}</ref> Similarly, rapid deepening in tropical cyclones is defined as a minimum sea surface pressure decrease of {{convert|1.75|hPa|inHg|abbr=on}} per hour or {{convert|42|hPa|inHg|abbr=on}} within a 24-hour period; explosive deepening occurs when the surface pressure decreases by {{convert|2.5|hPa|inHg|abbr=on}} per hour for at least 12 hours or {{convert|5|hPa|inHg|abbr=on}} per hour for at least 6 hours.<ref>{{cite journal |last1=Oropeza |first1=Fernando |last2=Raga |first2=Graciela B. |title=Rapid deepening of tropical cyclones in the northeastern Tropical Pacific: The relationship with oceanic eddies |journal=Atmósfera |date=January 2015 |volume=28 |issue=1 |pages=27–42 |doi=10.1016/S0187-6236(15)72157-0 |bibcode=2015Atmo...28...27O |doi-access=free}}</ref>
For a list of notable and unusual landfalling hurricanes, see ].


For rapid intensification to occur, several conditions must be in place. Water temperatures must be extremely high, near or above {{Convert|30|C|F}}, and water of this temperature must be sufficiently deep such that waves do not upwell cooler waters to the surface. On the other hand, ] is one of such non-conventional subsurface ] parameters influencing the ] intensity.<ref name="Energetics"/>
===Dissipation===
A tropical cyclone can cease to have tropical characteristics in several ways:


] must be low. When wind shear is high, the ] and circulation in the cyclone will be disrupted. Usually, an ] in the upper layers of the ] above the storm must be present as well—for extremely low surface pressures to develop, air must be rising very rapidly in the eyewall of the storm, and an upper-level anticyclone helps channel this air away from the cyclone efficiently.<ref name="Energetics">{{cite web|author=Diana Engle|title=Hurricane Structure and Energetics|publisher=Data Discovery Hurricane Science Center|access-date=October 26, 2008|url=http://www.newmediastudio.org/DataDiscovery/Hurr_ED_Center/Hurr_Structure_Energetics/Hurr_Struct.html|archive-url=https://web.archive.org/web/20080527094650/http://www.newmediastudio.org/DataDiscovery/Hurr_ED_Center/Hurr_Structure_Energetics/Hurr_Struct.html|archive-date=May 27, 2008}}</ref> However, some cyclones such as ] have rapidly intensified despite relatively unfavorable conditions.<ref>{{cite web |author1=Brad Reinhart |author2=Daniel Brown |date=October 21, 2020 |title=Hurricane Epsilon Discussion Number 12 |url=https://www.nhc.noaa.gov/archive/2020/al27/al272020.discus.012.shtml |url-status=live |archive-url=https://web.archive.org/web/20210321030619/https://www.nhc.noaa.gov/archive/2020/al27/al272020.discus.012.shtml |archive-date=March 21, 2021 |access-date=February 4, 2021 |website=nhc.noaa.gov |publisher=National Hurricane Center |location=]}}</ref><ref>{{cite news |last=Cappucci |first=Matthew |date=October 21, 2020 |title=Epsilon shatters records as it rapidly intensifies into major hurricane near Bermuda |newspaper=] |url=https://www.washingtonpost.com/weather/2020/10/21/hurricane-epsilon-bermuda-record/ |url-status=live |access-date=February 4, 2021 |archive-url=https://web.archive.org/web/20201210231234/https://www.washingtonpost.com/weather/2020/10/21/hurricane-epsilon-bermuda-record/ |archive-date=December 10, 2020}}</ref>
*It moves over land, thus depriving it of the warm water it needs to power itself, and quickly loses strength. Most strong storms lose their strength very rapidly after landfall, and become disorganized areas of low pressure within a day or two. There is, however, a chance they could regenerate if they manage to get back over open warm water. If a storm is over mountains for even a short time, it can rapidly lose its structure. However, many storm fatalities occur in mountainous terrain, as the dying storm unleashes torrential rainfall which can lead to deadly ]s and ]s.
*It remains in the same area of ocean for too long, drawing heat off of the ocean surface until it becomes too cool to support the storm. Without warm surface water, the storm cannot survive.
*It experiences ], causing the convection to lose direction and the heat engine to break down.
*It can be weak enough to be consumed by another area of low pressure, disrupting it and joining to become a large area of non-cyclonic thunderstorms. (Such, however, can strengthen the non-tropical system as a whole.)
*It enters colder waters. This does not necessarily mean the death of the storm, but the storm will lose its tropical characteristics. These storms are ].
<!--*An outer eye wall forms (typically around 50 miles from the center of the storm), choking off the convection toward the inner eye wall. Such weakening is generally temporary unless it meets other conditions above.-->


=== Dissipation ===
Even after a tropical cyclone is said to be extratropical or dissipated, it can still have tropical storm force (or occasionally hurricane force) winds and drop several inches of rainfall. When a tropical cyclone reaches higher latitudes or passes over land, it may merge with ]s or develop into a ], also called ]. In the ], such tropical-derived cyclones of higher latitudes can be violent and may occasionally remain at hurricane-force wind speeds when they reach Europe as a ].
], in ], is an example of a ] tropical cyclone, with deep ] slightly removed from the center of the system.|alt=Satellite image of a cyclone where the thickest clouds are displaced from the central vortex]]
There are a number of ways a tropical cyclone can weaken, dissipate, or lose its tropical characteristics. These include making landfall, moving over cooler water, encountering dry air, or interacting with other weather systems; however, once a system has dissipated or lost its tropical characteristics, its remnants could regenerate a tropical cyclone if environmental conditions become favorable.<ref name="HurricaneGraveyard">{{cite web |last1=Lam |first1=Linda |date=September 4, 2019 |title=Why the Eastern Caribbean Sea Can Be a 'Hurricane Graveyard' |url=https://weather.com/safety/hurricane/news/2019-08-27-caribbean-sea-graveyard-tropical-storms-hurricanes-hostile |url-status=live |archive-url=https://web.archive.org/web/20210704114314/https://weather.com/safety/hurricane/news/2019-08-27-caribbean-sea-graveyard-tropical-storms-hurricanes-hostile |archive-date=July 4, 2021 |access-date=April 6, 2021 |website=] |publisher=TWC Product and Technology}}</ref><ref name="Sadler and Kilonsky 1977">{{cite report |url=https://apps.dtic.mil/sti/pdfs/ADA046589.pdf |title=The Regeneration of South China Sea Tropical Cyclones in the Bay of Bengal |last1=Sadler |first1=James C. |last2=Kilonsky |first2=Bernard J. |date=May 1977 |publisher=Naval Environmental Prediction Research Facility |location=] |access-date=April 6, 2021 |archive-url=https://web.archive.org/web/20210622094956/https://apps.dtic.mil/sti/pdfs/ADA046589.pdf |archive-date=June 22, 2021 |url-status=live |via=]}}</ref>


A tropical cyclone can dissipate when it moves over waters significantly cooler than {{convert|26.5|C|F}}. This will deprive the storm of such tropical characteristics as a warm core with thunderstorms near the center, so that it becomes a remnant ]. Remnant systems may persist for several days before losing their identity. This dissipation mechanism is most common in the eastern North Pacific. Weakening or dissipation can also occur if a storm experiences vertical wind shear which causes the convection and heat engine to move away from the center. This normally ceases the development of a tropical cyclone.<ref name="EAM">{{cite book |author=Chang, Chih-Pei |url=https://books.google.com/books?id=N8QYOdqGdgkC&pg=PA484 |title=East Asian Monsoon |publisher=] |year=2004 |isbn=978-981-238-769-1 |oclc=61353183 |access-date=November 22, 2020 |archive-url=https://web.archive.org/web/20210814124330/https://books.google.com/books?id=N8QYOdqGdgkC&pg=PA484 |archive-date=August 14, 2021 |url-status=live}}</ref> In addition, its interaction with the main belt of the ], by means of merging with a nearby frontal zone, can cause tropical cyclones to evolve into ]. This transition can take 1–3&nbsp;days.<ref name="JWTC intensity">{{cite web|url=http://www.nrlmry.navy.mil/~chu/chap6/se300.htm|author=United States Naval Research Laboratory|work=Tropical Cyclone Forecasters' Reference Guide|title=Tropical Cyclone Intensity Terminology|access-date=November 30, 2006|date=September 23, 1999|author-link=United States Naval Research Laboratory|archive-url=https://web.archive.org/web/20120712084743/http://www.nrlmry.navy.mil/~chu/chap6/se300.htm|archive-date=July 12, 2012|url-status=live}}</ref>
===Artificial dissipation===
In the 1960s and 1970s, the United States government attempted to weaken hurricanes in its ] by ] selected storms with ]. It was thought that the seeding would cause supercooled water in the outer rainbands to freeze, causing the inner eyewall to collapse and thus reducing the winds. The winds of ] dropped as much as 30 percent, but then regained their strength after each of two seeding forays. In an earlier episode, disaster struck when a hurricane east of ], was seeded, promptly changed its course, and smashed into ].<ref name="Whipple ch. 5">Whipple, A. (1982, 1984)"Storm" p. 151 Time Life Books ISBN 0-8094-4312-0</ref> Because there was so much uncertainty about the behavior of these storms, the federal government would not approve seeding operations unless the hurricane had a less than 10 percent chance of making landfall within 48 hours. The project was dropped after it was discovered that ] occur naturally in strong hurricanes, casting doubt on the result of the earlier attempts. Today it is known that silver iodide seeding is not likely to have an effect because the amount of supercooled water in the rainbands of a tropical cyclone is too low.<ref name=NHCC5A> accessed April 2, 2006</ref>


Should a tropical cyclone make landfall or pass over an island, its circulation could start to break down, especially if it encounters mountainous terrain.<ref name="LifeCycle">{{cite web|url=http://www.aoml.noaa.gov/hrd/tcfaq/C2.html |title=Anatomy and Life Cycle of a Storm: What Is the Life Cycle of a Hurricane and How Do They Move?|year=2020|publisher=United States Hurricane Research Division|access-date=February 17, 2021|url-status=live|archive-url=https://web.archive.org/web/20210217090448/https://www.aoml.noaa.gov/hrd-faq/|archive-date=February 17, 2021}}</ref> When a system makes landfall on a large landmass, it is cut off from its supply of warm moist maritime air and starts to draw in dry continental air.<ref name="LifeCycle" /> This, combined with the increased friction over land areas, leads to the weakening and dissipation of the tropical cyclone.<ref name="LifeCycle" /> Over a mountainous terrain, a system can quickly weaken. Over flat areas, it may endure for two to three days before circulation breaks down and dissipates.<ref name="LifeCycle" />
Other approaches have been suggested over time, including cooling the water under a tropical cyclone by towing ]s into the tropical oceans; dropping large quantities of ice into the eye at very early stages so that latent heat is absorbed by ice at the entrance (storm cell perimeter bottom) instead of heat energy being converted to kinetic energy at high altitudes vertically above; covering the ocean in a substance that inhibits evaporation; or blasting the cyclone apart with nuclear weapons. These approaches all suffer from the same flaw: tropical cyclones are simply too large for any of them to be practical.<ref name=NHCC5F> accessed April 2, 2006</ref>


Over the years, there have been a number of techniques considered to try to artificially modify tropical cyclones.<ref name="Stop">{{cite web|url=http://www.aoml.noaa.gov/hrd/tcfaq/C2.html |title=Attempts to Stop a Hurricane in its Track: What Else has been Considered to Stop a Hurricane?|year=2020|publisher=United States Hurricane Research Division|access-date=February 17, 2021|url-status=live|archive-url=https://web.archive.org/web/20210217090448/https://www.aoml.noaa.gov/hrd-faq/|archive-date=February 17, 2021}}</ref> These techniques have included using ]s, cooling the ocean with icebergs, blowing the storm away from land with giant fans, and ] selected storms with dry ice or ].<ref name="Stop" /> These techniques, however, fail to appreciate the duration, intensity, power or size of tropical cyclones.<ref name="Stop" />
However, it has been suggested by some that we can change the course of a storm during its early stages of formation,<ref>http://web.mit.edu/hurricanelab/BostonGlobe.pdf</ref> <!-- We need an author for this article Controlling Hurricanes, Scientific American, 2005--> such as using satellites to alter the environmental conditions or, more realistically, spreading a degradable film of oil over the ocean, which prevent water vapor from fueling the storm.


===Methods for assessing intensity===
==Effects==
{{broader|Dvorak technique|Scatterometer}}
{{seealso|Tropical cyclone rainfall climatology}}
A variety of methods or techniques, including surface, satellite, and aerial, are used to assess the intensity of a tropical cyclone. Reconnaissance aircraft fly around and through tropical cyclones, outfitted with specialized instruments, to collect information that can be used to ascertain the winds and pressure of a system.<ref name="Global Guide 2017" /> Tropical cyclones possess winds of different speeds at different heights. Winds recorded at flight level can be converted to find the wind speeds at the surface.<ref>{{cite journal |last1=Knaff |first1=John |last2=Longmore |first2=Scott |last3=DeMaria |first3=Robert |last4=Molenar |first4=Debra |date=February 1, 2015 |title=Improved Tropical-Cyclone Flight-Level Wind Estimates Using RoutineInfrared Satellite Reconnaissance |url=https://journals.ametsoc.org/view/journals/apme/54/2/jamc-d-14-0112.1.xml?tab_body=pdf |url-status=live |journal=] |publisher=American Meteorological Society |volume=54 |issue=2 |page=464 |bibcode=2015JApMC..54..463K |doi=10.1175/JAMC-D-14-0112.1 |s2cid=17309033 |archive-url=https://web.archive.org/web/20210424010841/https://journals.ametsoc.org/view/journals/apme/54/2/jamc-d-14-0112.1.xml?tab_body=pdf |archive-date=April 24, 2021 |access-date=April 23, 2021|doi-access=free}}</ref> Surface observations, such as ship reports, land stations, ]s, coastal stations, and buoys, can provide information on a tropical cyclone's intensity or the direction it is traveling.<ref name="Global Guide 2017" />
]
A mature tropical cyclone can release heat at a rate upwards of 6x10<sup>14</sup> watts.<ref name="NOAA Question of the Month"/> Tropical cyclones on the open sea cause large waves, heavy rain, and high winds, disrupting international shipping and sometimes sinking ships. However, the most devastating effects of a tropical cyclone occur when they cross coastlines, making landfall. A tropical cyclone moving over land can do direct damage in four ways:


Wind-pressure relationships (WPRs) are used as a way to determine the pressure of a storm based on its wind speed. Several different methods and equations have been proposed to calculate WPRs.<ref>{{cite journal |last1=Knaff |first1=John |last2=Reed |first2=Kevin |last3=Chavas |first3=Daniel |date=November 8, 2017 |title=Physical understanding of the tropical cyclone wind-pressure relationship |journal=] |volume=8 |issue=1360 |page=1360 |bibcode=2017NatCo...8.1360C |doi=10.1038/s41467-017-01546-9 |pmc=5678138 |pmid=29118342}}</ref><ref name="WPRs">{{cite journal |last1=Kueh |first1=Mien-Tze |date=May 16, 2012 |title=Multiformity of the tropical cyclone wind–pressure relationship in the western North Pacific: discrepancies among four best-track archives |journal=] |publisher=] |volume=7 |issue=2 |pages=2–6 |bibcode=2012ERL.....7b4015K |doi=10.1088/1748-9326/7/2/024015 |doi-access=free}}</ref> Tropical cyclones agencies each use their own, fixed WPR, which can result in inaccuracies between agencies that are issuing estimates on the same system.<ref name="WPRs" /> The ASCAT is a ] used by the ] satellites to map the wind field vectors of tropical cyclones.<ref name="Global Guide 2017" /> The SMAP uses an L-band ] channel to determine the wind speeds of tropical cyclones at the ocean surface, and has been shown to be reliable at higher intensities and under heavy rainfall conditions, unlike scatterometer-based and other radiometer-based instruments.<ref>{{cite journal |last1=Meissner |first1=Thomas |last2=Ricciardulli |first2=L. |last3=Wentz |first3=F. |last4=Sampson |first4=C. |title=Intensity and Size of Strong Tropical Cyclones in 2017 from NASA's SMAP L-Band Radiometer |url=https://ams.confex.com/ams/33HURRICANE/webprogram/Paper339308.html |website=American Meteorological Society |access-date=April 21, 2021 |date=April 18, 2018 |archive-date=April 21, 2021 |archive-url=https://web.archive.org/web/20210421211403/https://ams.confex.com/ams/33HURRICANE/webprogram/Paper339308.html |url-status=live}}</ref>
* High ]s - Hurricane strength winds can damage or destroy vehicles, buildings, bridges, etc. High winds also turn loose debris into flying projectiles, making the outdoor environment even more dangerous.
* ] - Tropical cyclones cause an increase in sea level, which can flood coastal communities. This is the worst effect, as historically cyclones claimed 80% of their victims when they first strike shore.
* Heavy ] - The ] activity in a tropical cyclone causes intense rainfall. Rivers and streams flood, roads become impassable, and landslides can occur. Inland areas are particularly vulnerable to freshwater ], due to residents not preparing adequately.<ref name=NHCFlooding> accessed March 31, 2006</ref>
* ] activity - The broad rotation of a hurricane often spawns tornadoes. Also, tornadoes can be spawned as a result of ] which perisist until landfall. While these tornadoes are normally not as strong as their non-tropical counterparts, they can still cause tremendous damage.<ref name=AOMLTornado> accessed April 24, 2006</ref>
] in ]. Katrina was the costliest tropical cyclone in ] history.]]


The ] plays a large role in both the classification of a tropical cyclone and the determination of its intensity. Used in warning centers, the method was developed by ] in the 1970s, and uses both visible and infrared satellite imagery in the assessment of tropical cyclone intensity. The Dvorak technique uses a scale of "T-numbers", scaling in increments of 0.5 from T1.0 to T8.0. Each T-number has an intensity assigned to it, with larger T-numbers indicating a stronger system. Tropical cyclones are assessed by forecasters according to an array of patterns, including ], shear, central dense overcast, and eye, to determine the T-number and thus assess the intensity of the storm.<ref>{{cite book |last1=DeMaria |first1=Mark |last2=Knaff |first2=John |last3=Zehr |first3=Raymond |title=Satellite-based Applications on Climate Change |date=2013 |publisher=Springer |pages=152–154 |bibcode=2013saag.book.....J |url=https://rammb.cira.colostate.edu/resources/docs/DeMaria_Knaff_StarBook2013.pdf |access-date=April 21, 2021 |archive-date=April 22, 2021 |archive-url=https://web.archive.org/web/20210422013741/https://rammb.cira.colostate.edu/resources/docs/DeMaria_Knaff_StarBook2013.pdf |url-status=live}}</ref>
Often, the secondary effects of a tropical cyclone are equally damaging. These include:


The ] works to develop and improve automated satellite methods, such as the Advanced Dvorak Technique (ADT) and SATCON. The ADT, used by a large number of forecasting centers, uses infrared geostationary satellite imagery and an algorithm based upon the Dvorak technique to assess the intensity of tropical cyclones. The ADT has a number of differences from the conventional Dvorak technique, including changes to intensity constraint rules and the usage of microwave imagery to base a system's intensity upon its internal structure, which prevents the intensity from leveling off before an eye emerges in infrared imagery.<ref>{{cite journal |last1=Olander |first1=Timothy |last2=Veldan |first2=Christopher |title=The Advanced Dvorak Technique (ADT) for Estimating Tropical Cyclone Intensity: Update and New Capabilities |journal=American Meteorological Society |date=August 1, 2019 |volume=34 |issue=4 |pages=905–907 |doi=10.1175/WAF-D-19-0007.1 |bibcode=2019WtFor..34..905O |url=https://journals.ametsoc.org/view/journals/wefo/34/4/waf-d-19-0007_1.xml?tab_body=pdf |access-date=April 21, 2021 |doi-access=free |archive-date=April 21, 2021 |archive-url=https://web.archive.org/web/20210421201604/https://journals.ametsoc.org/view/journals/wefo/34/4/waf-d-19-0007_1.xml?tab_body=pdf |url-status=live}}</ref> The SATCON weights estimates from various satellite-based systems and ], accounting for the strengths and flaws in each individual estimate, to produce a consensus estimate of a tropical cyclone's intensity which can be more reliable than the Dvorak technique at times.<ref>{{cite journal |last1=Velden |first1=Christopher |last2=Herndon |first2=Derrick |title=A Consensus Approach for Estimating Tropical Cyclone Intensity from Meteorological Satellites: SATCON |journal=American Meteorological Society |date=July 21, 2020 |volume=35 |issue=4 |pages=1645–1650 |doi=10.1175/WAF-D-20-0015.1 |bibcode=2020WtFor..35.1645V |url=https://journals.ametsoc.org/view/journals/wefo/35/4/wafD200015.xml?tab_body=pdf |access-date=April 21, 2021 |doi-access=free |archive-date=April 21, 2021 |archive-url=https://web.archive.org/web/20210421204850/https://journals.ametsoc.org/view/journals/wefo/35/4/wafD200015.xml?tab_body=pdf |url-status=live}}</ref><ref>{{cite journal |last1=Chen |first1=Buo-Fu |last2=Chen |first2=Boyo |last3=Lin |first3=Hsuan-Tien |last4=Elsberry |first4=Russell |title=Estimating tropical cyclone intensity by satellite imagery utilizing convolutional neural networks |journal=American Meteorological Society |date=April 2019 |volume=34 |issue=2 |page=448 |doi=10.1175/WAF-D-18-0136.1 |bibcode=2019WtFor..34..447C |url=https://opensky.ucar.edu/islandora/object/articles%3A22481/datastream/PDF |access-date=April 21, 2021 |doi-access=free |archive-date=April 21, 2021 |archive-url=https://web.archive.org/web/20210421204900/https://opensky.ucar.edu/islandora/object/articles:22481/datastream/PDF |url-status=live|hdl=10945/62506 |hdl-access=free }}</ref>
* Disease - The wet environment in the aftermath of a tropical cyclone, combined with the destruction of sanitation facilities and a warm tropical climate, can induce epidemics of disease which claim lives long after the storm passes. One of the most common post-hurricane injuries is stepping on a ] in storm debris, leading to a risk of ] or other infection. Infections of cuts and bruises can be greatly amplified by wading in sewage-] water. Large areas of standing water caused by flooding also contribute to mosquito-borne illnesses.
* Power outages - Tropical cyclones often knock out power to tens or hundreds of thousands of people (or occasionally millions if a large urban area is affected), prohibiting vital communication and hampering rescue efforts.
* Transportation difficulties - Tropical cyclones often destroy key bridges, overpasses, and roads, complicating efforts to transport food, clean water, and medicine to the areas that need it.


===Intensity metrics===
===Beneficial effects of tropical cyclones===
Multiple intensity metrics are used, including ] (ACE), the ], the ], the ] (PDI), and ] (IKE). ACE is a metric of the total energy a system has exerted over its lifespan. ACE is calculated by summing the squares of a cyclone's sustained wind speed, every six hours as long as the system is at or above tropical storm intensity and either tropical or subtropical.<ref>{{cite journal|author1=Davis, Kyle |author2=Zeng, Xubin |title=Seasonal Prediction of North Atlantic Accumulated Cyclone Energy and Major Hurricane Activity |journal=Weather and Forecasting |date=February 1, 2019 |volume=34 |issue=1 |pages=221–232 |doi=10.1175/WAF-D-18-0125.1 |publisher=American Meteorological Society|bibcode=2019WtFor..34..221D |hdl=10150/632896 |s2cid=128293725 |doi-access=free |hdl-access=free}}</ref> The calculation of the PDI is similar in nature to ACE, with the major difference being that wind speeds are cubed rather than squared.<ref>{{cite journal|author1=Villarini, Gabriele |author2=Vecchi, Gabriel A |title=North Atlantic Power Dissipation Index (PDI) and Accumulated Cyclone Energy (ACE): Statistical Modeling and Sensitivity to Sea Surface Temperature Changes |journal=Journal of Climate |date=January 15, 2012 |volume=25 |issue=2 |pages=625–637 |doi=10.1175/JCLI-D-11-00146.1 |publisher=American Meteorological Society|bibcode=2012JCli...25..625V |s2cid=129106927}}</ref>
Although cyclones take an enormous toll in lives and personal property, they may be important factors in the ] regimes of places they impact, and bring much-needed precipitation to otherwise dry regions. Hurricanes in the eastern north Pacific often supply moisture to the ] and parts of Mexico.<ref name="2005 EPac outlook">] accessed May 2, 2006</ref> ] receives over half of its rainfall from typhoons.<ref name="Whipple p154">Whipple p 154</ref> ] averted drought conditions and ended ]s along much of its path.<ref name=Christopherson>Christopherson, R. (1992) "Geosystems An Introduction to Physical Geography" pp 222-224. Macmillan Publishing Company New York. ISBN 0-02-322443-6</ref>


The Hurricane Surge Index is a metric of the potential damage a storm may inflict via storm surge. It is calculated by squaring the dividend of the storm's wind speed and a climatological value ({{cvt|33|m/s|mph|disp=or}}), and then multiplying that quantity by the dividend of the radius of hurricane-force winds and its climatological value ({{cvt|96.6|km|mi|disp=or}}). This can be represented in equation form as:
In addition, the destruction caused by Camille on the Gulf coast spurred redevelopment as well, greatly increasing local property values.<ref name=Christopherson/> On the other hand, disaster response officials point out that redevelopment encourages more people to live in clearly dangerous areas subject to future deadly storms. ] is the most obvious example, as it devastated the region that had been revitalized after Hurricane Camille. Of course, many former residents and businesses do relocate to inland areas away from the threat of future hurricanes as well.
:<math>\left(\frac{v}{33\ \mathrm{m/s}}\right)^2\times\left(\frac{r}{96.6\ \mathrm{km}}\right)\,</math>
where <math display="inline">v</math> is the storm's wind speed and <math display="inline">r</math> is the radius of hurricane-force winds.<ref>{{cite journal |last1=Islam |first1=Md. Rezuanal |last2=Lee |first2=Chia-Ying |last3=Mandli |first3=Kyle T. |last4=Takagi |first4=Hiroshi |date=August 18, 2021 |title=A new tropical cyclone surge index incorporating the effects of coastal geometry, bathymetry and storm information |journal=] |volume=11 |issue=1 |page=16747 |bibcode=2021NatSR..1116747I |doi=10.1038/s41598-021-95825-7 |pmc=8373937 |pmid=34408207 |doi-access=free}}</ref> The Hurricane Severity Index is a scale that can assign up to 50 points to a system; up to 25 points come from intensity, while the other 25 come from the size of the storm's wind field.<ref name="IKE + HSI">{{cite journal |last1=Rezapour |first1=Mehdi |last2=Baldock |first2=Tom E. |title=Classification of Hurricane Hazards: The Importance of Rainfall |journal=Weather and Forecasting |date=December 1, 2014 |volume=29 |issue=6 |pages=1319–1331 |doi=10.1175/WAF-D-14-00014.1 |publisher=American Meteorological Society|bibcode=2014WtFor..29.1319R |s2cid=121762550 |doi-access=free}}</ref> The IKE model measures the destructive capability of a tropical cyclone via winds, waves, and surge. It is calculated as:
:<math>\int_{Vol} \frac{1}{2}pu^2d_{v}\,</math>
where <math display="inline">p</math> is the density of air, <math display="inline">u</math> is a sustained surface wind speed value, and <math display="inline">d_v</math> is the ].<ref name="IKE + HSI" /><ref>{{cite book |author1=Kozar, Michael E|author2=Misra, Vasubandhu |chapter=Integrated Kinetic Energy in North Atlantic Tropical Cyclones: Climatology, Analysis, and Seasonal Applications |title=Hurricane Risk |date=February 16, 2019 |volume=1 |publisher=Springer |isbn=978-3-030-02402-4 |pages=43–69 |doi=10.1007/978-3-030-02402-4_3|s2cid=133717045}}</ref>


== Classification and naming ==
Hurricanes also help to maintain global heat balance by moving warm, moist tropical air to the mid-latitudes and polar regions. ] has also hypothesised that by raising nutrients from the sea floor to surface layers of the ocean, hurricanes also increase ] in areas where life would be difficult through nutrient loss in the deeper reaches of the ].{{citation needed}}
=== Classification ===
{{Main|Tropical cyclone scales}}


] at different stages of development. ] (left) demonstrates only the most basic circular shape. ] (top right) demonstrates ] and increased centralization, while the ] (lower right) has developed an ].|alt=Satellite image of three simultaneous tropical cyclones]]
At sea, tropical cyclones can stir up water, leaving a cool wake behind them.<ref name="NASA Cooling"/> This can cause the region to be less favourable for a subsequent tropical cyclone. On rare occasions, tropical cyclones may actually do the opposite. 2005's ] blew warm water behind it, contributing to the unprecedented intensity of the close-following ].<ref name="Emily Discussion 8"> accessed May 2, 2006</ref>


Around the world, tropical cyclones are classified in different ways, based on the location (]), the structure of the system and its intensity. For example, within the Northern Atlantic and Eastern Pacific basins, a tropical cyclone with wind speeds of over {{convert|65|kn|km/h mph|lk=in|abbr=on}} is called a '''hurricane''', while it is called a '''typhoon''' or a severe cyclonic storm within the Western Pacific or North Indian oceans.{{RA IV Hurricane Operational Plan}}<ref name="WPAC TCOP" />{{North Indian Ocean tropical cyclone operational plan}} When a hurricane passes west across the ] in the Northern Hemisphere, it becomes known as a typhoon. This happened in 2014 for ], which became Typhoon Genevieve.<ref>, ], Inc., KGO-TV San Francisco, Channel 7 News. Retrieved May 25, 2023.</ref>
== Long term trends in cyclone activity ==
While the number of storms in the Atlantic has increased since 1995, there seems to be no signs of a global trend; the annual global number of tropical cyclones remains about 90&nbsp;&plusmn;&nbsp;10.<ref name=EmanuelHomepage> accessed March 30, 2006</ref>


Within the Southern Hemisphere, it is either called a hurricane, tropical cyclone or a severe tropical cyclone, depending on if it is located within the South Atlantic, South-West Indian Ocean, Australian region or the South Pacific Ocean.<ref name="SWIO TCOP" /><ref name="SPAC TCOP" /> The descriptors for tropical cyclones with wind speeds below {{cvt|65|kn|km/h mph|round=5}} vary by tropical cyclone basin and may be further subdivided into categories such as "tropical storm", "cyclonic storm", "tropical depression", or "deep depression".<ref name="WPAC TCOP" /><ref name="NIO TCOP" /><ref name="RA IV HOP" />
Atlantic storms are certainly becoming more destructive financially, since five of the ten most expensive storms in ] history have occurred since ]. This can, to a large extent, be attributed to the number of people living in susceptible coastal area, and massive development in the region since the last surge in Atlantic hurricane activity in the 1960s.


===Naming===
Often in part because of the threat of hurricanes, many coastal regions had sparse population between major ports until the advent of automobile tourism; therefore, the most severe portions of hurricanes striking the coast often went unmeasured. The combined effects of ship destruction and remote landfall severely limit the number of intense hurricanes in the official record before the era of hurricane reconnaissance aircraft and satellite meteorology. Although the record shows a distinct increase in the number and strength of intense hurricanes, therefore, experts regard the early data as suspect.
{{Main|Tropical cyclone naming|History of tropical cyclone naming}}


The practice of using ]s to identify tropical cyclones dates back to the late 1800s and early 1900s and gradually superseded the existing system—simply naming cyclones based on what they hit.<ref name="Whats in a name?">{{cite journal |author=Smith, Ray |year=1990 |title=What's in a Name? |url=http://www.metsoc.org.nz/system/files/journals/10/1/1990_101_24-26_rsmith.pdf |url-status=dead |journal=Weather and Climate |publisher=] |volume=10 |issue=1 |pages=24–26 |doi=10.2307/44279572 |jstor=44279572 |archive-url=https://web.archive.org/web/20141129194207/http://www.metsoc.org.nz/system/files/journals/10/1/1990_101_24-26_rsmith.pdf |archive-date=November 29, 2014 |access-date=August 25, 2014 |s2cid=201717866}}</ref><ref name="Mahina">{{cite web |author=Dorst, Neal M |date=October 23, 2012 |title=They Called the Wind Mahina: The History of Naming Cyclones |url=ftp://ftp.aoml.noaa.gov/hrd/pub/dorst/Mahina.pptx |work=], ] |publisher=] |page=Slides 8–72}}</ref> The system currently used provides positive identification of severe weather systems in a brief form, that is readily understood and recognized by the public.<ref name="Whats in a name?" /><ref name="Mahina" /> The credit for the first usage of personal names for weather systems is generally given to the ] Meteorologist ] who named systems between 1887 and 1907.<ref name="Whats in a name?" /><ref name="Mahina" /> This system of naming weather systems fell into disuse for several years after Wragge retired, until it was revived in the latter part of ] for the Western Pacific.<ref name="Whats in a name?" /><ref name="Mahina" /> Formal naming schemes have subsequently been introduced for the North and South Atlantic, Eastern, Central, Western and Southern Pacific basins as well as the Australian region and Indian Ocean.<ref name="Mahina" />
The number and strength of Atlantic hurricanes may undergo a 50-70-year cycle. Although more common since 1995, few above-normal hurricane seasons occurred during 1970-1994. Destructive hurricanes struck frequently from 1926-60, including many major New England hurricanes. A record 21 Atlantic tropical storms formed in 1933, only recently exceeded in 2005. Tropical hurricanes occurred infrequently during the seasons of 1900-1925; however, many intense storms formed 1870-1899. During the 1887 season, 19 tropical storms formed, of which a record 4 occurred after ] and 11 strengthened into hurricanes. Few hurricanes occurred in the 1840s to 1860s; however, many struck in the early 1800s, including an ] storm that made a direct hit on ] which some historical weather experts say may have been as high as Category 4 in strength.


At present, tropical cyclones are officially named by one of twelve ] and retain their names throughout their lifetimes to provide ease of communication between forecasters and the general public regarding forecasts, watches, and warnings.<ref name="Whats in a name?" /> Since the systems can last a week or longer, and more than one can be occurring in the same basin at the same time, the names are thought to reduce the confusion about what storm is being described.<ref name="Whats in a name?" /> Names are assigned in order from predetermined ] with one, three, or ten-minute sustained wind speeds of more than {{convert|65|km/h|mph|round=5|abbr=on}} depending on which basin it originates.<ref name="RA IV HOP" /><ref name="NIO TCOP" /><ref name="SWIO TCOP" />
These unusually active hurricane seasons predated satellite coverage of the Atlantic basin that now enables forecasters to see all tropical cyclones. Before the satellite era began in 1961, tropical storms or hurricanes went undetected unless a ship reported a voyage through the storm. The official record, therefore, probably misses many storms in which no ship experienced gale-force winds, recognized it as a tropical storm (as opposed to a high-latitude extra-tropical cyclone, a tropical wave, or a brief squall), returned to port, and reported the experience.


Standards vary from basin to basin. Some tropical depressions are named in the Western Pacific. Tropical cyclones have to have a significant amount of gale-force winds occurring around the center before they are named within the ].<ref name="SWIO TCOP" /><ref name="SPAC TCOP" /> The names of significant tropical cyclones in the North Atlantic Ocean, Pacific Ocean, and Australian region are retired from the naming lists and replaced with another name.<ref name="RA IV HOP" /><ref name="WPAC TCOP" /><ref name="SPAC TCOP" /> Tropical cyclones that develop around the world are assigned an identification code consisting of a two-digit number and suffix letter by the warning centers that monitor them.<ref name="SPAC TCOP" /><ref name="OFCM NHOP">{{cite report |url=http://www.ofcm.gov/publications/nhop/FCM-P12-2017.pdf |title=National Hurricane Operations Plan |author=Office of the Federal Coordinator for Meteorological Services and Supporting Research |date=May 2017 |publisher=] |pages=26–28 |access-date=October 14, 2018 |archive-url=https://web.archive.org/web/20181015042240/https://www.ofcm.gov/publications/nhop/FCM-P12-2017.pdf |archive-date=October 15, 2018 |url-status=live}}</ref>
===Global warming?===
A common question is whether ] can or will cause more frequent or more fierce tropical cyclones. So far, virtually all ]s seem to agree that a single storm, or even a single season, cannot clearly be attributed to a single cause such as global warming or natural variation.<ref name=realclimate> accessed March 20, 2006</ref> The question is thus whether a ] ] in frequency or strength of cyclones exists. The ] ] says in their Hurricane FAQ that "it is highly unlikely that global warming has (or will) contribute to a drastic change in the number or intensity of hurricanes."<ref name="NHCG4"> accessed March 30, 2006</ref>


=== Related cyclone types ===
Regarding strength, a similar conclusion was the prevailing consensus, until recently, when it was questioned by ]. In an article in '']'',<ref name=EmanuelNature> accessed March 20, 2006</ref> Emanuel states that the potential hurricane destructiveness, a measure which combines strength, duration, and frequency of hurricanes, "is highly correlated with tropical sea surface temperature, reflecting well-documented climate signals, including multidecadal oscillations in the North Atlantic and North Pacific, and global warming." K. Emanuel further predicts "a substantial increase in hurricane-related losses in the twenty-first century."<ref name=EmmanuelPreprint> accessed March 20, 2006</ref>
{{See also|Cyclone|Extratropical cyclone|Subtropical cyclone}}
In addition to tropical cyclones, there are two other classes of ]s within the spectrum of cyclone types. These kinds of cyclones, known as ]s and ]s, can be stages a tropical cyclone passes through during its ] or dissipation.<ref name="IWTC5">{{cite web |author=Lander, Mark A. |display-authors=etal |date=August 3, 2003 |title=Fifth International Workshop on Tropical Cyclones |url=http://www.aoml.noaa.gov/hrd/iwtc/Lander4-1.html |url-status=live |archive-url=https://web.archive.org/web/20090509043704/http://www.aoml.noaa.gov/hrd/iwtc/Lander4-1.html |archive-date=May 9, 2009 |access-date=May 6, 2009 |publisher=]}}</ref> An ''extratropical cyclone'' is a storm that derives energy from horizontal temperature differences, which are typical in higher latitudes. A tropical cyclone can become extratropical as it moves toward higher latitudes if its energy source changes from heat released by condensation to differences in temperature between air masses. Although not as frequently, an extratropical cyclone can transform into a subtropical storm, and from there into a tropical cyclone.<ref name="autogenerated2">{{cite web |author=Atlantic Oceanographic and Meteorological Laboratory, Hurricane Research Division |title=Frequently Asked Questions: What is an extra-tropical cyclone? |url=http://www.aoml.noaa.gov/hrd/tcfaq/A7.html |url-status=dead |archive-url=https://web.archive.org/web/20070209121005/http://www.aoml.noaa.gov/hrd/tcfaq/A7.html |archive-date=February 9, 2007 |access-date=July 25, 2006 |publisher=]}}</ref> From space, extratropical storms have a characteristic "]-shaped" cloud pattern.<ref name="L14">{{cite web |date=February 25, 2008 |title=Lesson 14: Background: Synoptic Scale |url=http://profhorn.meteor.wisc.edu/wxwise/satmet/lesson14/Satextracyclone.html |url-status=live |archive-url=https://web.archive.org/web/20090220150352/http://profhorn.meteor.wisc.edu/wxwise/satmet/lesson14/Satextracyclone.html |archive-date=February 20, 2009 |access-date=May 6, 2009 |publisher=]}}</ref> Extratropical cyclones can also be dangerous when their low-pressure centers cause powerful winds and high seas.<ref>{{cite web |year=2008 |title=An Overview of Coastal Land Loss: With Emphasis on the Southeastern United States. |url=http://pubs.usgs.gov/of/2003/of03-337/winter.html |url-status=live |archive-url=https://web.archive.org/web/20090212222023/http://pubs.usgs.gov/of/2003/of03-337/winter.html |archive-date=February 12, 2009 |access-date=May 6, 2009 |publisher=]}}</ref>


A ''subtropical cyclone'' is a ] system that has some characteristics of a tropical cyclone and some characteristics of an extratropical cyclone. They can form in a wide band of latitudes, from the equator to 50°. Although subtropical storms rarely have hurricane-force winds, they may become tropical in nature as their cores warm.<ref name="AOML FAQ A6">{{cite web |author=Atlantic Oceanographic and Meteorological Laboratory, Hurricane Research Division |title=Frequently Asked Questions: What is a sub-tropical cyclone? |url=http://www.aoml.noaa.gov/hrd/tcfaq/A6.html |url-status=dead |archive-url=https://web.archive.org/web/20111011042947/http://www.aoml.noaa.gov/hrd/tcfaq/A6.html |archive-date=October 11, 2011 |access-date=July 25, 2006 |publisher=]}}</ref>
Along similar lines, P.J. Webster and others published an article<ref name=zfacts1> accessed March 20, 2006</ref> in '']''<ref name="ScienceMag"></ref> examining "changes in tropical cyclone number, duration, and intensity" over the last 35 years, a period where satellite data is available. The main finding is that while the number of cyclones "decreased in all basins except the North Atlantic during the past decade" there is a "large increase in the number and proportion of hurricanes reaching categories 4 and 5." That is, while the number of cyclones decreased overall, the number of very strong cyclones increased.


==Structure==
Both Emanuel and Webster et al., consider the sea surface temperature as of key importance in the development of cyclones. The question then becomes: what caused the observed increase in sea surface temperatures? In the Atlantic, it could be due to the ] (AMO), a 50&ndash;70 year pattern of temperature variability. Emanuel, however, found the recent temperature increase was outside the range of previous oscillations. So, both a natural variation (such as the AMO) and global warming could have made contributions to the warming of the tropical Atlantic over the past decades, but an exact attribution is so far impossible to make.<ref name=realclimate/>
===Eye and center===
{{main|Eye (cyclone)}}


] as seen from the ]]]
While Emanuel analyzes total annual energy dissipation, Webster et al. analyze the slightly less relevant percentage of hurricanes in the combined categories 4 and 5, and find that this percentage has increased in each of six distinct hurricane basins: North Atlantic, North East and North West Pacific, South Pacific, and North and South Indian. Because each individual basin may be subject to intra-basin oscillations similar to the AMO, any single-basin statistic remains open to question. But if the local oscillations are not synchronized by some as-yet-unidentified global oscillation, the independence of the basins allows joint statistical tests that are more powerful than any set of individual basin tests. Unfortunately Webster et al. do not undertake any such test.
At the center of a mature tropical cyclone, air sinks rather than rises. For a sufficiently strong storm, air may sink over a layer deep enough to suppress cloud formation, thereby creating a clear "]". Weather in the eye is normally calm and free of ], although the sea may be extremely violent.<ref name="JetStream structure">{{cite web|url=http://www.srh.noaa.gov/jetstream/tropics/tc_structure.htm|author=National Weather Service|work=JetStream&nbsp;– An Online School for Weather|publisher=]|title=Tropical Cyclone Structure|access-date=May 7, 2009|date=October 19, 2005|author-link=National Weather Service|archive-url=https://web.archive.org/web/20131207193757/http://www.srh.noaa.gov/jetstream/tropics/tc_structure.htm|archive-date=December 7, 2013|url-status=live}}</ref> The eye is normally circular and is typically {{convert|30|–|65|km|mi|abbr=on}} in diameter, though eyes as small as {{convert|3|km|mi|abbr=on}} and as large as {{convert|370|km|mi|abbr=on}} have been observed.<ref name="WilmaTCR">{{cite web |last=Pasch |first=Richard J. |author2=Eric S. Blake |author3=Hugh D. Cobb III |author4=David P. Roberts |url=http://www.nhc.noaa.gov/data/tcr/AL252005_Wilma.pdf |title=Tropical Cyclone Report: Hurricane Wilma: 15–25 October 2005 |publisher=] |date=September 28, 2006 |access-date=December 14, 2006 |archive-date=March 4, 2016 |archive-url=https://web.archive.org/web/20160304000300/http://www.nhc.noaa.gov/data/tcr/AL252005_Wilma.pdf |url-status=live}}</ref><ref name="MWR 1996 AHS summary">{{Cite journal| doi = 10.1175/1520-0493(1999)127<1157:TMEAVO>2.0.CO;2| title = The Mean Evolution and Variability of the Asian Summer Monsoon: Comparison of ECMWF and NCEP–NCAR Reanalyses| journal = Monthly Weather Review| volume = 127| issue = 6| pages = 1157–1186| year = 1999| last1 = Annamalai| first1 = H.| last2 = Slingo| first2 = J.M.| last3 = Sperber| first3 = K.R.| last4 = Hodges| first4 = K.| bibcode = 1999MWRv..127.1157A| url = https://digital.library.unt.edu/ark:/67531/metadc793439/| access-date = December 12, 2019| archive-date = August 1, 2020| archive-url = https://web.archive.org/web/20200801195058/https://digital.library.unt.edu/ark:/67531/metadc793439/| url-status = live| doi-access = free}}</ref>


The cloudy outer edge of the eye is called the "eyewall". The eyewall typically expands outward with height, resembling an arena football stadium; this phenomenon is sometimes referred to as the "]".<ref name="MWR 1996 AHS summary" /> The eyewall is where the greatest wind speeds are found, air rises most rapidly, clouds reach their highest ], and precipitation is the heaviest. The heaviest wind damage occurs where a tropical cyclone's eyewall passes over land.<ref name="JetStream structure" />
Under the assumption that the six basins are statistically independent except for the effect of global warming,<ref name=zfacts2> accessed March 20, 2006</ref> has carried out the obvious paired ] and found that the null-hypothesis of no impact of global warming on the percentage of Category 4 and 5 hurricanes can be rejected at the 0.1% level. Thus, there is only a 1 in 1000 chance of simultaneously finding the observed six increases in the percentages of Category 4 or 5 hurricanes. This statistic needs refining because the variables being tested are not normally distributed with equal variances, but it may provide the best evidence yet that the impact of global warming on hurricane intensity has been detected.


In a weaker storm, the eye may be obscured by the ], which is the upper-level cirrus shield that is associated with a concentrated area of strong thunderstorm activity near the center of a tropical cyclone.<ref name="CDO AMS">{{cite web|author=American Meteorological Society|url=http://amsglossary.allenpress.com/glossary/browse?s=c&p=19|title=AMS Glossary: C|work=Glossary of Meteorology|access-date=December 14, 2006|publisher=]|author-link=American Meteorological Society|archive-url=https://web.archive.org/web/20110126121255/http://amsglossary.allenpress.com/glossary/browse?s=c&p=19|archive-date=January 26, 2011|url-status=live}}</ref>
==Observation and forecasting==
===Observation===
]'s rainbands photographed at 7,000 feet.]]
Intense tropical cyclones pose a particular observation challenge. As they are a dangerous oceanic phenomenon, ]s are rarely available on the site of the storm itself. Surface level observations are generally available only if the storm is passing over an island or a coastal area, or it has overtaken an unfortunate ship. Even in these cases, real-time measurement taking is generally possible only in the periphery of the cyclone, where conditions are less catastrophic.


The eyewall may vary over time in the form of ]s, particularly in intense tropical cyclones. ] can organize into an outer ring of thunderstorms that slowly moves inward, which is believed to rob the primary eyewall of moisture and ]. When the primary eyewall weakens, the tropical cyclone weakens temporarily. The outer eyewall eventually replaces the primary one at the end of the cycle, at which time the storm may return to its original intensity.<ref name="AOML FAQ D8">{{cite web|author=Atlantic Oceanographic and Hurricane Research Division |title=Frequently Asked Questions: What are "concentric eyewall cycles" (or "eyewall replacement cycles") and why do they cause a hurricane's maximum winds to weaken? |publisher=] |access-date=December 14, 2006 |url=http://www.aoml.noaa.gov/hrd/tcfaq/D8.html |url-status=dead |archive-url=https://web.archive.org/web/20061206051303/http://www.aoml.noaa.gov/hrd/tcfaq/D8.html |archive-date=December 6, 2006}}</ref>
It is however possible to take ] measurements, in real-time, by sending specially equipped reconnaissance flights into the cyclone. In the Atlantic basin, these flights are regularly flown by United States government ]. <ref name="Hurricane Hunters"> accessed March 30, 2006</ref> The aircraft used are ] Hercules and ] Orions, both four-engine ] cargo aircraft. These aircraft fly directly into the cyclone and take direct and remote-sensing measurements. The aircraft also launch ]s inside the cyclone. These sondes measure temperature, humidity, pressure, and especially winds between flight level and the ocean's surface.
{{clear}}


===Size===
A new era in hurricane observation began when a remotely piloted ], a small drone aircraft, was flown through Tropical Storm Ophelia as it passed Virginia's Eastern Shore during the 2005 hurricane season. This demonstrated a new way to probe the storms at low altitudes that human pilots seldom dare.<ref name="SunHerald">Bowman, L. "Drones defy heart of storm." accessed March 30, 2006</ref>
{| class="wikitable" style="float: right; font-size: 92%; margin: 1em 0 1em 1em;"
|+Size descriptions of tropical cyclones
|-
! scope="col" | ROCI (Diameter)
! scope="col" | Type
|-
! scope="row" | Less than 2&nbsp;degrees latitude
| Very small/minor
|-
! scope="row" | 2 to 3&nbsp;degrees of latitude
| Small
|-
! scope="row" | 3 to 6&nbsp;degrees of latitude
| Medium/average/normal
|-
! scope="row" | 6 to 8&nbsp;degrees of latitude
| Large
|-
! scope="row" | Over 8&nbsp;degrees of latitude
| Very large<ref name="JTWCsize">{{cite web|url=http://www.usno.navy.mil/JTWC/frequently-asked-questions-1#tcsize|title=Q: What is the average size of a tropical cyclone?|year=2009|publisher=]|access-date=May 7, 2009|archive-url=https://web.archive.org/web/20131004062635/http://www.usno.navy.mil/JTWC/frequently-asked-questions-1/#tcsize|archive-date=October 4, 2013|url-status=live}}</ref>
|}
]
There are a variety of metrics commonly used to measure storm size. The most common metrics include the radius of maximum wind, the radius of {{Convert|34|kn|m/s km/h mph|adj=on}} wind (i.e. ]), the radius of outermost closed ] (]), and the radius of vanishing wind.<ref name="Global">{{cite web|url=http://www.cawcr.gov.au/publications/BMRC_archive/tcguide/ch2/ch2_4.htm |title=Global Guide to Tropical Cyclone Forecasting: chapter 2: Tropical Cyclone Structure |date=May 7, 2009 |publisher=] |access-date=May 6, 2009 |url-status=dead |archive-url=https://web.archive.org/web/20110601213941/http://www.cawcr.gov.au/publications/BMRC_archive/tcguide/ch2/ch2_4.htm |archive-date=June 1, 2011}}</ref><ref name="Chavas Emanuel GRL">{{Cite journal | doi = 10.1029/2010GL044558| title = A QuikSCAT climatology of tropical cyclone size| journal = Geophysical Research Letters| volume = 37| issue = 18| year = 2010| last1 = Chavas | first1 = D.R.| last2 = Emanuel | first2 = K.A. | pages = n/a| bibcode=2010GeoRL..3718816C| hdl = 1721.1/64407| s2cid = 16166641| hdl-access = free}}</ref> An additional metric is the radius at which the cyclone's relative ] field decreases to 1×10<sup>−5</sup> s<sup>−1</sup>.<ref name="MWR 1996 AHS summary" />


On Earth, tropical cyclones span a large range of sizes, from {{convert|100–2000|km|mi|abbr=on}} as measured by the radius of vanishing wind. They are largest on average in the northwest Pacific Ocean basin and smallest in the northeastern ] basin.<ref name="Merrill" /> If the radius of outermost closed isobar is less than two ] ({{convert|222|km|mi|abbr=on}}), then the cyclone is "very small" or a "midget". A radius of 3–6 latitude degrees ({{convert|333|–|670|km|mi|abbr=on}}) is considered "average sized". "Very large" tropical cyclones have a radius of greater than 8&nbsp;degrees ({{convert|888|km|mi|abbr=on}}).<ref name="JTWCsize" /> Observations indicate that size is only weakly correlated to variables such as storm intensity (i.e. maximum wind speed), radius of maximum wind, latitude, and maximum potential intensity.<ref name="Chavas Emanuel GRL" /><ref name="Merrill">{{Cite journal |title=A comparison of Large and Small Tropical cyclones |journal=Monthly Weather Review |volume=112 |issue=7 |pages=1408–1418 |last=Merrill |first=Robert T |year=1984 |doi=10.1175/1520-0493(1984)112<1408:ACOLAS>2.0.CO;2 |bibcode=1984MWRv..112.1408M |hdl=10217/200 |s2cid=123276607 |hdl-access=free}}</ref> ] is the largest cyclone on record, with tropical storm-force winds {{convert|2170|km|mi|abbr=on}} in diameter. The smallest storm on record is ] of ], which generated tropical storm-force winds only {{convert|37|km|mi|abbr=on}} in diameter.<ref name="FAQ">{{cite web|author=Dorst, Neal |author2=Hurricane Research Division |title=Frequently Asked Questions: Subject: E5) Which are the largest and smallest tropical cyclones on record? |publisher=National Oceanic and Atmospheric Administration's Atlantic Oceanographic and Meteorological Laboratory |url=http://www.aoml.noaa.gov/hrd/tcfaq/E5.html |access-date=June 12, 2013 |date=May 29, 2009 |url-status=dead |archive-url=https://web.archive.org/web/20081222095921/http://www.aoml.noaa.gov/hrd/tcfaq/E5.html |archive-date=December 22, 2008}}</ref>
Tropical cyclones far from land are tracked by ]s capturing ] and ] images from space, usually at half-hour to quarter-hour intervals. As a storm approaches land, it can be observed by land-based ]. Radar plays a crucial role around landfall because it shows a storm's location and intensity minute by minute.


==Movement==
Recently, academic researchers have begun to deploy mobile weather stations fortified to withstand hurricane-force winds. The two largest programs are the Florida Coastal Monitoring Program <ref name=FCMP> accessed March 30, 2006</ref> and the Wind Engineering Mobile Instrumented Tower Experiment. <ref name=WEMITE> accessed March 30, 2006</ref> During landfall, the NOAA Hurricane Research Division compares and verifies data from reconnaissance aircraft, including wind speed data taken at flight level and from GPS dropwindsondes and stepped-frequency microwave radiometers, to wind speed data transmitted in real time from weather stations erected near or at the coast. The National Hurricane Center uses the data to evaluate conditions at landfall and to verify forecasts.
The movement of a tropical cyclone (i.e. its "track") is typically approximated as the sum of two terms: "steering" by the background environmental wind and "beta drift".<ref name="Holland JAS 1983">{{Cite journal| doi = 10.1175/1520-0469(1983)040<0328:TCMEIP>2.0.CO;2| title = Tropical Cyclone Motion: Environmental Interaction Plus a Beta Effect| journal = Journal of the Atmospheric Sciences| volume = 40| issue = 2| pages = 328–342| year = 1983| last1 = Holland| first1 = G.J.| bibcode = 1983JAtS...40..328H| s2cid = 124178238| doi-access = free}}</ref> Some tropical cyclones can move across large distances, such as ], the second longest-lasting tropical cyclone on record, which traveled {{convert|13280|km|mi|abbr=on}}, the longest track of any Northern Hemisphere tropical cyclone, over its 31-day lifespan in ].<ref name="john94">{{cite web|author=Dorst, Neal |author2=Hurricane Research Division |title=Subject: E6) Frequently Asked Questions: Which tropical cyclone lasted the longest? |access-date=June 12, 2013 |publisher=National Oceanic and Atmospheric Administration's Atlantic Oceanographic and Meteorological Laboratory |url=http://www.aoml.noaa.gov/hrd/tcfaq/E7.html |date=January 26, 2010 |url-status=dead |archive-url=https://web.archive.org/web/20090506175506/http://www.aoml.noaa.gov/hrd/tcfaq/E7.html |archive-date=May 6, 2009}}</ref><ref name="faqe7">{{cite web|author=Dorst, Neal |author2=Delgado, Sandy |author3=Hurricane Research Division |title=Frequently Asked Questions: Subject: E7) What is the farthest a tropical cyclone has travelled? |access-date=June 12, 2013 |publisher=National Oceanic and Atmospheric Administration's Atlantic Oceanographic and Meteorological Laboratory |url=http://www.aoml.noaa.gov/hrd/tcfaq/E7.html |date=May 20, 2011 |url-status=dead |archive-url=https://web.archive.org/web/20090506175506/http://www.aoml.noaa.gov/hrd/tcfaq/E7.html |archive-date=May 6, 2009}}</ref><ref>{{cite news|url=https://www.washingtonpost.com/weather/2023/03/07/cyclone-freddy-indian-ocean-hurricane/|newspaper=the Washington Post|title=Deadly cyclone Freddy has become Earth's longest-lived tropical storm|date=March 7, 2023|access-date=September 27, 2023}}</ref>


===Forecasting=== ===Environmental steering===
Environmental steering is the primary influence on the motion of tropical cyclones.<ref name="Galarneau and Davis 2013" /> It represents the movement of the storm due to prevailing winds and other wider environmental conditions, similar to "leaves carried along by a stream".<ref name="AOML FAQ G6">{{cite web|author=Atlantic Oceanographic and Meteorological Laboratory, Hurricane Research Division|title=Frequently Asked Questions: What determines the movement of tropical cyclones?|publisher=]|access-date=July 25, 2006|url=http://www.aoml.noaa.gov/hrd/tcfaq/G6.html|archive-url=https://web.archive.org/web/20120716182608/http://www.aoml.noaa.gov/hrd/tcfaq/G6.html|archive-date=July 16, 2012|url-status=live}}</ref>
] strengthened and organized in the Central North Atlantic Ocean despite highly unfavorable conditions. This unusual system defied most ] forecasts and demonstrated the difficulties of predicting tropical cyclones.]]
Because of the forces that affect tropical cyclone tracks, accurate track predictions depend on determining the position and strength of high- and low-pressure areas, and predicting how those areas will change during the life of a tropical system.


Physically, the winds, or ], in the vicinity of a tropical cyclone may be treated as having two parts: the flow associated with the storm itself, and the large-scale background flow of the environment.<ref name="Galarneau and Davis 2013">{{cite journal |last1=Galarneau |first1=Thomas J. |last2=Davis |first2=Christopher A. |title=Diagnosing Forecast Errors in Tropical Cyclone Motion |journal=Monthly Weather Review |date=February 1, 2013 |volume=141 |issue=2 |pages=405–430 |doi=10.1175/MWR-D-12-00071.1 |publisher=American Meteorological Society|bibcode=2013MWRv..141..405G |s2cid=58921153 |doi-access=free}}</ref> Tropical cyclones can be treated as local maxima of ] suspended within the large-scale background flow of the environment.<ref name="Wu and Emmanuel 1995" /> In this way, tropical cyclone motion may be represented to first-order as ] of the storm by the local ].<ref name="Carr and Elsberry 1990">{{cite journal |last1=Carr |first1=L. E. |last2=Elsberry |first2=Russell L. |title=Observational Evidence for Predictions of Tropical Cyclone Propagation Relative to Environmental Steering |journal=Journal of the Atmospheric Sciences |date=February 15, 1990 |volume=47 |issue=4 |pages=542–546 |doi=10.1175/1520-0469(1990)047<0542:OEFPOT>2.0.CO;2 |publisher=American Meteorological Society|bibcode=1990JAtS...47..542C |s2cid=121754290 |doi-access=free|hdl=10945/48910 |hdl-access=free }}</ref> This environmental flow is termed the "steering flow" and is the dominant influence on tropical cyclone motion.<ref name="Galarneau and Davis 2013" /> The strength and direction of the steering flow can be approximated as a vertical integration of the winds blowing horizontally in the cyclone's vicinity, weighted by the altitude at which those winds are occurring. Because winds can vary with height, determining the steering flow precisely can be difficult.
With their understanding of the forces that act on tropical cyclones, and a wealth of data from earth-orbiting satellites and other sensors, scientists have increased the accuracy of track forecasts over recent decades. High-speed computers and sophisticated simulation software allow forecasters to produce ] that forecast tropical cyclone tracks based on the future position and strength of high- and low-pressure systems. But while track forecasts have become more accurate than 20 years ago, scientists say they are less skillful at predicting the intensity of tropical cyclones. They attribute the lack of improvement in intensity forecasting to the complexity of tropical systems and an incomplete understanding of factors that affect their development.


The ] at which the background winds are most correlated with a tropical cyclone's motion is known as the "steering level".<ref name="Wu and Emmanuel 1995">{{cite journal |last1=Wu |first1=Chun-Chieh |last2=Emanuel |first2=Kerry A. |title=Potential vorticity Diagnostics of Hurricane Movement. Part 1: A Case Study of Hurricane Bob (1991) |journal=Monthly Weather Review |date=January 1, 1995 |volume=123 |issue=1 |pages=69–92 |doi=10.1175/1520-0493(1995)123<0069:PVDOHM>2.0.CO;2 |publisher=American Meteorological Society|bibcode=1995MWRv..123...69W |doi-access=free}}</ref> The motion of stronger tropical cyclones is more correlated with the background flow averaged across a thicker portion of ] compared to weaker tropical cyclones whose motion is more correlated with the background flow averaged across a narrower extent of the lower troposphere.<ref name="Velden and Leslie 1991">{{cite journal |last1=Velden |first1=Christopher S. |last2=Leslie |first2=Lance M. |title=The Basic Relationship between Tropical Cyclone Intensity and the Depth of the Environmental Steering Layer in the Australian Region |journal=Weather and Forecasting |date=June 1, 1991 |volume=6 |issue=2 |pages=244–253 |doi=10.1175/1520-0434(1991)006<0244:TBRBTC>2.0.CO;2 |publisher=American Meteorological Society|bibcode=1991WtFor...6..244V |doi-access=free}}</ref> When wind shear and ] release is present, tropical cyclones tend to move towards regions where ] is increasing most quickly.<ref>{{cite journal |last1=Chan |first1=Johnny C.L. |title=The Physics of Tropical Cyclone Motion |journal=Annual Review of Fluid Mechanics |date=January 2005 |volume=37 |issue=1 |pages=99–128 |doi=10.1146/annurev.fluid.37.061903.175702 |publisher=Annual Reviews|bibcode=2005AnRFM..37...99C}}</ref>
==Classifications, Terminology and Naming==
===Intensity classifications===
], showing the lack of organization in tropical depressions when compared to stronger cyclones.]]
Tropical cyclones are classified into three main groups, based on intensity: tropical depressions, tropical storms, and a third group of more intense storms, whose name depends on the region.


Climatologically, tropical cyclones are steered primarily westward by the east-to-west ] on the equatorial side of the ]—a persistent high-pressure area over the world's subtropical oceans.<ref name="AOML FAQ G6" /> In the tropical North Atlantic and Northeast Pacific oceans, the trade winds steer ] westward from the African coast toward the Caribbean Sea, North America, and ultimately into the central Pacific Ocean before the waves dampen out.<ref name="AOML FAQ A4">{{cite web|author=Atlantic Oceanographic and Meteorological Laboratory, Hurricane Research Division |title=Frequently Asked Questions: What is an easterly wave? |publisher=] |access-date=July 25, 2006 |url=http://www.aoml.noaa.gov/hrd/tcfaq/A4.html |url-status=dead |archive-url=https://web.archive.org/web/20060718105909/http://www.aoml.noaa.gov/hrd/tcfaq/A4.html |archive-date=July 18, 2006}}</ref> These waves are the precursors to many tropical cyclones within this region.<ref name="MWR Avila 1995">{{Cite journal | doi = 10.1175/1520-0493(1995)123<0887:ATSO>2.0.CO;2| title = Atlantic Tropical Systems of 1993| journal = Monthly Weather Review| volume = 123| issue = 3| pages = 887–896| year = 1995| last1 = Avila | first1 = L.A. | last2 = Pasch | first2 = R.J. |bibcode = 1995MWRv..123..887A | doi-access = free}}</ref> In contrast, in the ] and Western Pacific in both hemispheres, tropical ] is influenced less by tropical easterly waves and more by the seasonal movement of the Intertropical Convergence Zone and the ].<ref name="autogenerated1">{{cite web|author=DeCaria, Alex|work=ESCI 344&nbsp;– Tropical Meteorology|publisher=]|url=http://snowball.millersville.edu/~adecaria/ESCI344/esci344_lesson05_TC_climatology.html|title = Lesson 5&nbsp;– Tropical Cyclones: Climatology.|year=2005|access-date=February 22, 2008| archive-url = https://web.archive.org/web/20080507051727/http://snowball.millersville.edu/~adecaria/ESCI344/esci344_lesson05_TC_climatology.html| archive-date = May 7, 2008}}</ref> Other weather systems such as mid-latitude ]s and broad monsoon gyres can also influence tropical cyclone motion by modifying the steering flow.<ref name="Velden and Leslie 1991" /><ref name="Carr and Elsberry 1995">{{cite journal |last1=Carr |first1=Lester E. |last2=Elsberry |first2=Russell L. |title=Monsoonal Interactions Leading to Sudden Tropical Cyclone Track Changes |journal=Monthly Weather Review |date=February 1, 1995 |volume=123 |issue=2 |pages=265–290 |doi=10.1175/1520-0493(1995)123<0265:MILTST>2.0.CO;2 |publisher=American Meteorological Society|bibcode=1995MWRv..123..265C |doi-access=free}}</ref>
A '''tropical depression''' is an organized system of clouds and thunderstorms with a defined surface circulation and maximum sustained winds of less than 17&nbsp;] (33&nbsp;], 38&nbsp;], or 62&nbsp;]). It has no eye, and does not typically have the organization or the spiral shape of more powerful storms. It is already a low-pressure system, however, hence the name "depression."


===Beta drift===
A '''tropical storm''' is an organized system of strong thunderstorms with a defined surface circulation and maximum sustained winds between 17 and 32&nbsp;m/s (34&ndash;63&nbsp;kt, 39&ndash;73&nbsp;mph, or 62&ndash;117&nbsp;km/h). At this point, the distinctive cyclonic shape starts to develop, though an eye is usually not present. Government weather services assign first names to systems that reach this intensity (thus the term ''named storm'').
In addition to environmental steering, a tropical cyclone will tend to drift poleward and westward, a motion known as "beta drift".<ref name="Wang et al. 1998">{{cite journal |last1=Wang |first1=Bin |last2=Elsberry |first2=Russell L. |last3=Yuqing |first3=Wang |last4=Liguang |first4=Wu |title=Dynamics in Tropical Cyclone Motion: A Review |journal=Chinese Journal of the Atmospheric Sciences |year=1998 |volume=22 |issue=4 |pages=416–434 |url=http://www.soest.hawaii.edu/MET/Faculty/bwang/bw/paper/wang58.pdf |access-date=April 6, 2021 |publisher=Allerton Press |via=University of Hawaii |archive-date=June 17, 2021 |archive-url=https://web.archive.org/web/20210617170921/https://www.soest.hawaii.edu/MET/Faculty/bwang/bw/paper/wang58.pdf |url-status=live}}</ref> This motion is due to the superposition of a vortex, such as a tropical cyclone, onto an environment in which the ] varies with latitude, such as on a sphere or ].<ref name="Holland 1983">{{cite journal |last1=Holland |first1=Greg J. |title=Tropical Cyclone Motion: Environmental Interaction Plus a Beta Effect |journal=Journal of the Atmospheric Sciences |date=February 1, 1983 |volume=40 |issue=2 |pages=328–342 |doi=10.1175/1520-0469(1983)040<0328:TCMEIP>2.0.CO;2 |publisher=American Meteorological Society|bibcode=1983JAtS...40..328H |doi-access=free}}</ref> The magnitude of the component of tropical cyclone motion associated with the beta drift ranges between {{convert|1|–|3|m/s|km/h mph|abbr=on}} and tends to be larger for more intense tropical cyclones and at higher latitudes. It is induced indirectly by the storm itself as a result of feedback between the cyclonic flow of the storm and its environment.<ref name="Fiorino and Elsberry 1989">{{cite journal |last1=Fiorino |first1=Michael |last2=Elsberry |first2=Russell L. |title=Some Aspects of Vortex Structure Related to Tropical Cyclone Motion |journal=Journal of the Atmospheric Sciences |date=April 1, 1989 |volume=46 |issue=7 |pages=975–990 |doi=10.1175/1520-0469(1989)046<0975:SAOVSR>2.0.CO;2 |publisher=American Meteorological Society|bibcode=1989JAtS...46..975F |doi-access=free}}</ref><ref name="Wang et al. 1998" />


Physically, the cyclonic circulation of the storm advects environmental air poleward east of center and equatorial west of center. Because air must conserve its ], this flow configuration induces a cyclonic gyre equatorward and westward of the storm center and an anticyclonic gyre poleward and eastward of the storm center. The combined flow of these gyres acts to advect the storm slowly poleward and westward. This effect occurs even if there is zero environmental flow.<ref name="Li and Wang 1994">{{cite journal |last1=Li |first1=Xiaofan |last2=Wang |first2=Bin |title=Barotropic Dynamics of the Beta Gyres and Beta Drift |journal=Journal of the Atmospheric Sciences |date=March 1, 1994 |volume=51 |issue=5 |pages=746–756 |doi=10.1175/1520-0469(1994)051<0746:BDOTBG>2.0.CO;2 |publisher=American Meteorological Society|bibcode=1994JAtS...51..746L |doi-access=free}}</ref><ref name="Willoughby 1990">{{cite journal |last1=Willoughby |first1=H. E. |title=Linear Normal Modes of a Moving, Shallow-Water Barotropic Vortex |journal=Journal of the Atmospheric Sciences |date=September 1, 1990 |volume=47 |issue=17 |pages=2141–2148 |doi=10.1175/1520-0469(1990)047<2141:LNMOAM>2.0.CO;2 |publisher=American Meteorological Society|bibcode= 1990JAtS...47.2141W|doi-access=free}}</ref> Due to a direct dependence of the beta drift on angular momentum, the size of a tropical cyclone can affect the influence of beta drift on its motion; beta drift imparts a greater influence on the movement of larger tropical cyclones than that of smaller ones.<ref name="Hill and Lackmann 2009">{{cite journal |last1=Hill |first1=Kevin A. |last2=Lackmann |first2=Gary M. |title=Influence of Environmental Humidity on Tropical Cyclone Size |journal=Monthly Weather Review |date=October 1, 2009 |volume=137 |issue=10 |pages=3294–3315 |doi=10.1175/2009MWR2679.1 |publisher=American Meteorological Society|bibcode=2009MWRv..137.3294H |doi-access=free}}</ref><ref name="Sun et al. 2015">{{cite journal |last1=Sun |first1=Yuan |last2=Zhong |first2=Zhong |last3=Yi |first3=Lan |last4=Li |first4=Tim |last5=Chen |first5=Ming |last6=Wan |first6=Hongchao |last7=Wang |first7=Yuxing |last8=Zhong |first8=Kai |title=Dependence of the relationship between the tropical cyclone track and western Pacific subtropical high intensity on initial storm size: A numerical investigation: SENSITIVITY OF TC AND WPSH TO STORM SIZE |journal=Journal of Geophysical Research: Atmospheres |date=November 27, 2015 |volume=120 |issue=22 |pages=11,451–11,467 |doi=10.1002/2015JD023716 |publisher=John Wiley & Sons|doi-access=free}}</ref>
A '''tropical cyclone''' (or '''hurricane''' or '''typhoon''') is a system with sustained winds greater than 33&nbsp;m/s (64&nbsp;kt, 74&nbsp;mph, or 118&nbsp;km/h). A tropical cyclone tends to develop an '']'', an area of relative calm (and lowest atmospheric pressure) at the center of circulation. The eye is often visible in satellite images as a small, circular, cloud-free spot. Surrounding the eye is the eyewall, an area about 10&ndash;50&nbsp;mi (16&ndash;80&nbsp;km) wide in which the strongest thunderstorms and winds circulate around the storm's center.


===Multiple storm interaction===
The circulation of clouds around a cyclone's center imparts a distinct spiral shape to the system. Bands or arms may extend over great distances as clouds are drawn toward the cyclone. The direction of the cyclonic circulation depends on the hemisphere; it is counterclockwise in the ] and clockwise in the ]. Maximum sustained winds in the strongest tropical cyclones have been measured at more than 85&nbsp;m/s (165&nbsp;kt, 190&nbsp;mph, 305&nbsp;km/h). Intense, mature hurricanes can sometimes exhibit an inward curving of the eyewall top that resembles a football stadium: this phenomenon is thus sometimes referred to as the ].
{{Main|Fujiwhara effect}}


A third component of motion that occurs relatively infrequently involves the interaction of multiple tropical cyclones. When two cyclones approach one another, their centers will begin orbiting cyclonically about a point between the two systems. Depending on their separation distance and strength, the two vortices may simply orbit around one another, or else may spiral into the center point and merge. When the two vortices are of unequal size, the larger vortex will tend to dominate the interaction, and the smaller vortex will orbit around it. This phenomenon is called the Fujiwhara effect, after ].<ref>{{cite news|url=http://usatoday30.usatoday.com/weather/wfujiwha.htm|title=Fujiwhara effect describes a stormy waltz|access-date=February 21, 2008|work=]|date=November 9, 2007|archive-url=https://web.archive.org/web/20121105134542/http://usatoday30.usatoday.com/weather/wfujiwha.htm|archive-date=November 5, 2012|url-status=live}}</ref>
] naturally occur in intense tropical cyclones. When cyclones reach peak intensity they usually - but not always - have an eyewall and radius of maximum winds that contract to a very small size, around 5 to 15 miles. At this point, some of the outer rainbands may organize into an outer ring of thunderstorms that slowly moves inward and robs the inner eyewall of its needed moisture and momentum. During this phase, the tropical cyclone is weakening (i.e. the maximum winds die off a bit and the central pressure goes up). Eventually the outer eyewall replaces the inner one completely and the storm can be the same intensity as it was previously or, in some cases, even stronger.


===Interaction with the mid-latitude westerlies===
====Categories and ranking====
{{See also|Westerlies}}
{{Saffir-Simpson small}}{{main|Tropical cyclone scales}}
], showing ] off the ] in ]|alt=Path of a tropical cyclone]]
Though a tropical cyclone typically moves from east to west in the tropics, its track may shift poleward and eastward either as it moves west of the subtropical ridge axis or else if it interacts with the mid-latitude flow, such as the ] or an ]. This motion, termed "]", commonly occurs near the western edge of the major ocean basins, where the jet stream typically has a poleward component and extratropical cyclones are common.<ref>{{cite web|url=http://www.nrlmry.navy.mil/~chu/chap4/se200.htm|date=April 10, 2007|title=Section 2: Tropical Cyclone Motion Terminology|publisher=United States Naval Research Laboratory|access-date=May 7, 2009|archive-url=https://web.archive.org/web/20120212182753/http://www.nrlmry.navy.mil/~chu/chap4/se200.htm|archive-date=February 12, 2012|url-status=live}}</ref> An example of tropical cyclone recurvature was ] in 2006.<ref name="CPHC Ioke">{{cite web|url=http://www.prh.noaa.gov/cphc/summaries/2006.php#ioke|title=Hurricane Ioke: 20–27 August 2006|date=May 2007|access-date=June 9, 2007|author=Powell, Jeff|work=2006 Tropical Cyclones Central North Pacific|publisher=]|display-authors=etal|archive-url=https://web.archive.org/web/20160306135254/http://www.prh.noaa.gov/cphc/summaries/2006.php#ioke|archive-date=March 6, 2016|url-status=live}}</ref>


==Effects==
Hurricanes are ranked according to their maximum winds using the ]. A ''Category 1'' storm has the lowest maximum winds (74-95&nbsp;mph, 119-153&nbsp;km/h), a ''Category 5'' hurricane has the highest (>&nbsp;155&nbsp;mph, 249&nbsp;km/h). The ] ] classifies hurricanes of Category 3 and above as ''major hurricanes''.
{{Main|Effects of tropical cyclones|Tropical cyclone effects by region}}


===Natural phenomena caused or worsened by tropical cyclones===
The U.S. ] classifies West Pacific typhoons as tropical cyclones with winds greater than 73&nbsp;mph (118&nbsp;km/h). Typhoons with wind speeds of at least 150&nbsp;mph (67&nbsp;m/s or 241&nbsp;km/h, equivalent to a strong Category 4 hurricane) are dubbed ''Super Typhoons''.
Tropical cyclones out at sea cause large waves, ], ]s and high winds, disrupting international shipping and, at times, causing shipwrecks.<ref name="18cva">{{cite web|author1=Roth, David|author2=Cobb, Hugh|name-list-style=amp|year=2001|title=Eighteenth Century Virginia Hurricanes|publisher=NOAA|access-date=February 24, 2007|url=http://www.wpc.ncep.noaa.gov/research/roth/va18hur.htm|archive-url=https://web.archive.org/web/20130501032117/http://www.wpc.ncep.noaa.gov/research/roth/va18hur.htm|archive-date=May 1, 2013|url-status=live}}</ref> Tropical cyclones stir up water, leaving a cool wake behind them, which causes the region to be less favorable for subsequent tropical cyclones.<ref name="NASA Cooling" /> On land, strong ]s can damage or destroy vehicles, buildings, bridges, and other outside objects, turning loose debris into deadly flying projectiles. The ], or the increase in sea level due to the cyclone, is typically the worst effect from landfalling tropical cyclones, historically resulting in 90% of tropical cyclone deaths.<ref name="Shultz Epid Reviews 2005">{{Cite journal | doi = 10.1093/epirev/mxi011| title = Epidemiology of Tropical Cyclones: The Dynamics of Disaster, Disease, and Development| journal = Epidemiologic Reviews| volume = 27| pages = 21–35| year = 2005| last1 = Shultz | first1 = J.M.| last2 = Russell | first2 = J.| last3 = Espinel | first3 = Z. | pmid=15958424| doi-access = free}}</ref> ] produced the highest storm surge on record, {{convert|13|m|ft|abbr=on}}, at ], ], ], in March 1899.<ref>{{cite journal|title=The World Record Storm Surge and the Most Intense Southern Hemisphere Tropical Cyclone: New Evidence and Modeling|first1=Jonathan|last1= Nott|first2=Camilla |last2=Green|first3=Ian |last3=Townsend|first4=Jeffrey|last4= Callaghan|journal=Bulletin of the American Meteorological Society|date=July 9, 2014|issue=95|volume=5|page=757|doi=10.1175/BAMS-D-12-00233.1|bibcode=2014BAMS...95..757N|doi-access=free}}</ref>


Other ocean-based hazards that tropical cyclones produce are ]s and ]. These hazards can occur hundreds of kilometers (hundreds of miles) away from the center of a cyclone, even if other weather conditions are favorable.<ref>{{cite journal |last1=Carey |first1=Wendy |last2=Rogers |first2=Spencer |title=Rip Currents — Coordinating Coastal Research, Outreach and Forecast Methodologies to Improve Public Safety |journal=Solutions to Coastal Disasters Conference 2005 |date=April 26, 2012 |pages=285–296 |doi=10.1061/40774(176)29 |url=https://ascelibrary.org/doi/abs/10.1061/40774(176)29 |access-date=May 25, 2022 |publisher=American Society of Civil Engineers |isbn=9780784407745 |archive-date=May 26, 2022 |archive-url=https://web.archive.org/web/20220526171028/https://ascelibrary.org/doi/abs/10.1061/40774%28176%2929 |url-status=live}}</ref><ref>{{cite journal |last1=Rappaport |first1=Edward N. |title=Loss of Life in the United States Associated with Recent Atlantic Tropical Cyclones |journal=Bulletin of the American Meteorological Society |date=September 1, 2000 |volume=81 |issue=9 |pages=2065–2074 |doi=10.1175/1520-0477(2000)081<2065:LOLITU>2.3.CO;2 |url=https://journals.ametsoc.org/view/journals/bams/81/9/1520-0477_2000_081_2065_lolitu_2_3_co_2.xml?tab_body=pdf |access-date=May 25, 2022 |publisher=American Meteorological Society |bibcode=2000BAMS...81.2065R |s2cid=120065630 |archive-date=May 26, 2022 |archive-url=https://web.archive.org/web/20220526171031/https://journals.ametsoc.org/view/journals/bams/81/9/1520-0477_2000_081_2065_lolitu_2_3_co_2.xml?tab_body=pdf |url-status=live |doi-access=free}}</ref>
The Australian ] uses a 1-5 scale called tropical cyclone severity categories. Unlike the ], severity categories are based on estimated maximum wind ]s. A category 1 storm features gusts less than 126&nbsp;km/h (78&nbsp;mph), while gusts in a category 5 cyclone are at least 280&nbsp;km/h (174&nbsp;mph).
The broad rotation of a landfalling tropical cyclone, and vertical wind shear at its periphery, spawns ]. Tornadoes can also be spawned as a result of ], which persist until landfall.<ref name="AOML FAQ L6">{{cite web|author=Atlantic Oceanographic and Meteorological Laboratory, Hurricane Research Division |title=Frequently Asked Questions: Are TC tornadoes weaker than midlatitude tornadoes? |publisher=] |access-date=July 25, 2006 |url=http://www.aoml.noaa.gov/hrd/tcfaq/L6.html |url-status=dead |archive-url=https://web.archive.org/web/20090914103006/http://www.aoml.noaa.gov/hrd/tcfaq/L6.html |archive-date=September 14, 2009}}</ref> ] produced ], more than any other tropical cyclone.<ref>{{cite web |last1=Grazulis |first1=Thomas P. |last2=Grazulis |first2=Doris |title=Top 25 Tornado-Generating Hurricanes |url=http://www.tornadoproject.com/alltorns/tophurricanes.htm |website=The Tornado Project |publisher=Environmental Films |access-date=November 8, 2021 |location=] |date=February 27, 2018 |archive-date=December 12, 2013 |archive-url=https://web.archive.org/web/20131212032233/http://www.tornadoproject.com/alltorns/tophurricanes.htm |url-status=live}}</ref> Lightning activity is produced within tropical cyclones. This activity is more intense within stronger storms and closer to and within the storm's eyewall.<ref>{{cite journal |last1=Bovalo |first1=C. |last2=Barthe |first2=C. |last3=Yu |first3=N. |last4=Bègue |first4=N. |title=Lightning activity within tropical cyclones in the South West Indian Ocean |journal=Journal of Geophysical Research: Atmospheres |date=July 16, 2014 |volume=119 |issue=13 |pages=8231–8244 |doi=10.1002/2014JD021651 |publisher=AGU |bibcode=2014JGRD..119.8231B |s2cid=56304603 |doi-access=free}}</ref><ref>{{cite journal |last1=Samsury |first1=Christopher E. |last2=Orville |first2=Richard E. |title=Cloud-to-Ground Lightning in Tropical Cyclones: A Study of Hurricanes Hugo (1989) and Jerry (1989) |journal=Monthly Weather Review |date=August 1, 1994 |volume=122 |issue=8 |pages=1887–1896 |doi=10.1175/1520-0493(1994)122<1887:CTGLIT>2.0.CO;2 |publisher=American Meteorological Society |bibcode=1994MWRv..122.1887S |doi-access=free}}</ref> Tropical cyclones can increase the amount of snowfall a region experiences by delivering additional moisture.<ref>{{cite journal |last1=Collier |first1=E. |last2=Sauter |first2=T. |last3=Mölg |first3=T. |last4=Hardy |first4=D. |title=The Influence of Tropical Cyclones on Circulation, Moisture Transport, and Snow Accumulation at Kilimanjaro During the 2006–2007 Season |journal= Journal of Geophysical Research: Atmospheres|date=June 10, 2019 |volume=124 |issue=13 |pages=6919–6928 |doi=10.1029/2019JD030682 |url=https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019JD030682 |access-date=May 25, 2022 |publisher=AGU |bibcode=2019JGRD..124.6919C |s2cid=197581044}}</ref> Wildfires can be worsened when a nearby storm fans their flames with its strong winds.<ref>{{cite journal |last1=Osborne |first1=Martin |last2=Malavelle |first2=Florent F. |last3=Adam |first3=Mariana |last4=Buxmann |first4=Joelle |last5=Sugier |first5=Jaqueline |last6=Marenco |first6=Franco |title=Saharan dust and biomass burning aerosols during ex-hurricane Ophelia: observations from the new UK lidar and sun-photometer network |journal=Atmospheric Chemistry and Physics |date=March 20, 2019 |volume=19 |issue=6 |pages=3557–3578 |doi=10.5194/acp-19-3557-2019 |url=https://acp.copernicus.org/articles/19/3557/2019/ |access-date=May 25, 2022 |publisher=Copernicus Publications |bibcode=2019ACP....19.3557O |s2cid=208084167 |archive-date=January 24, 2022 |archive-url=https://web.archive.org/web/20220124090205/https://acp.copernicus.org/articles/19/3557/2019/ |url-status=live |doi-access=free |hdl=10871/36358 |hdl-access=free}}</ref><ref>{{cite journal |last1=Moore |first1=Paul |title=An analysis of storm Ophelia which struck Ireland on 16 October 2017 |journal=Weather |date=August 3, 2021 |volume=76 |issue=9 |pages=301–306 |doi=10.1002/wea.3978 |url=https://rmets.onlinelibrary.wiley.com/doi/abs/10.1002/wea.3978 |access-date=May 25, 2022 |publisher=Royal Meteorological Society |bibcode=2021Wthr...76..301M |s2cid=238835099}}</ref>


===Effect on property and human life===
Meteorologists in the United States use maximum 1-minute average sustained winds 10&nbsp;meters above the ground to determine tropical cyclone strength. Other countries use the maximum 10-minute average, as suggested by the World Meteorological Organization. Maximum wind speeds are typically about 12% lower with the 10-minute method than with the 1-minute method. <ref name="NWSM Defs">http://www.weather.gov/directives/sym/pd01006004curr.pdf</ref><ref name="FEMA glossary">{{cite web | author=] | title = Hurricane Glossary of Terms | year = 2004 | accessdate = 2006-03-24 | url = http://www.fema.gov/hazards/hurricanes/hurglos.shtm}}</ref>
] in ]]]
]


Tropical cyclones regularly affect the coastlines of most of ]'s major bodies of water along the ], ], and ] oceans. Tropical cyclones have caused significant destruction and loss of human life, resulting in about 2&nbsp;million deaths since the 19th century.<ref name="red">{{cite journal|url=https://www.who.int/bulletin/volumes/90/2/11-088302/en/|title=Reduced death rates from cyclones in Bangladesh: what more needs to be done?|first1=Ubydul|last1= Haque|first2=Masahiro|last2= Hashizume|first3=Korine N |last3=Kolivras|first4=Hans J |last4=Overgaard|first5=Bivash |last5=Das|first6=Taro |last6=Yamamoto|date=March 16, 2011|access-date=October 12, 2020|journal=Bulletin of the World Health Organization|archive-date=October 5, 2020|archive-url=https://web.archive.org/web/20201005083126/https://www.who.int/bulletin/volumes/90/2/11-088302/en/|url-status=dead}}</ref> Large areas of standing water caused by flooding lead to ], as well as contributing to ]. Crowded evacuees in ] increase the risk of disease propagation.<ref name="Shultz Epid Reviews 2005" /> Tropical cyclones significantly interrupt infrastructure, leading to ]s, bridge and road destruction, and the hampering of reconstruction efforts.<ref name="Shultz Epid Reviews 2005" /><ref name="Power failures">{{cite news|date=August 30, 2005 |title=Hurricane Katrina Situation Report #11|publisher=Office of Electricity Delivery and Energy Reliability (OE) ]|access-date=February 24, 2007|url=http://www.oe.netl.doe.gov/docs/katrina/katrina_083005_1600.pdf|archive-url=https://web.archive.org/web/20061108202531/http://www.oe.netl.doe.gov/docs/katrina/katrina_083005_1600.pdf|archive-date=November 8, 2006|url-status=dead}}</ref><ref>{{cite journal |last1=Adam |first1=Christopher |last2=Bevan |first2=David |title=Tropical cyclones and post-disaster reconstruction of public infrastructure in developing countries |journal=Economic Modelling |date=December 2020 |volume=93 |pages=82–99 |doi=10.1016/j.econmod.2020.07.003 |url=https://www.sciencedirect.com/science/article/abs/pii/S0264999319311824 |access-date=May 25, 2022 |s2cid=224926212}}</ref>
The rankings are not absolute in terms of damage and other effects. Lower-category storms can inflict greater damage than higher-category storms, depending on factors such as local terrain and total rainfall. For instance, a Category 2 hurricane that strikes a major urban area will likely do more damage than a large Category 5 hurricane that strikes a mostly rural region. In fact, tropical systems of minimal strength can produce significant damage and human casualties from flooding and landslides.


Winds and water from storms can damage or destroy homes, buildings, and other manmade structures.<ref>{{cite book |last1=Cuny |first1=Frederick C. |editor1-last=Abrams |editor1-first=Susan |title=Disasters and Development |date=1994 |url=https://oaktrust.library.tamu.edu/bitstream/handle/1969.1/159887/cuny_intertect_000001_49.pdf?sequence=1 |publisher=INTERTECT Press |isbn=0-19-503292-6 |page=45 |access-date=May 25, 2022 |archive-date=May 26, 2022 |archive-url=https://web.archive.org/web/20220526171026/https://oaktrust.library.tamu.edu/bitstream/handle/1969.1/159887/cuny_intertect_000001_49.pdf?sequence=1 |url-status=live}}</ref><ref>{{cite journal |last1=Le Dé |first1=Loïc |last2=Rey |first2=Tony |last3=Leone |first3=Frederic |last4=Gilbert |first4=David |title=Sustainable livelihoods and effectiveness of disaster responses: a case study of tropical cyclone Pam in Vanuatu |journal=Natural Hazards |date=January 16, 2018 |volume=91 |issue=3 |pages=1203–1221 |doi=10.1007/s11069-018-3174-6 |url=https://link.springer.com/article/10.1007/s11069-018-3174-6 |access-date=May 25, 2022 |publisher=Springer |bibcode=2018NatHa..91.1203L |s2cid=133651688 |archive-date=May 26, 2022 |archive-url=https://web.archive.org/web/20220526012645/https://link.springer.com/article/10.1007/s11069-018-3174-6 |url-status=live}}</ref> Tropical cyclones destroy agriculture, kill livestock, and prevent access to marketplaces for both buyers and sellers; both of these result in financial losses.<ref>{{cite journal |last1=Perez |first1=Eddie |last2=Thompson |first2=Paul |title=Natural Hazards: Causes and Effects: Lesson 5—Tropical Cyclones (Hurricanes, Typhoons, Baguios, Cordonazos, Tainos) |journal=Prehospital and Disaster Medicine |date=September 1995 |volume=10 |issue=3 |pages=202–217 |doi=10.1017/S1049023X00042023 |url=https://www.cambridge.org/core/journals/prehospital-and-disaster-medicine/article/abs/natural-hazards-causes-and-effects-lesson-5tropical-cyclones-hurricanes-typhoons-baguios-cordonazos-tainos/82B619E71E1132507E0A856CC713E7AF |publisher=Cambridge University Press |pmid=10155431 |s2cid=36983623 |access-date=May 25, 2022 |archive-date=May 26, 2022 |archive-url=https://web.archive.org/web/20220526171028/https://www.cambridge.org/core/journals/prehospital-and-disaster-medicine/article/abs/natural-hazards-causes-and-effects-lesson-5tropical-cyclones-hurricanes-typhoons-baguios-cordonazos-tainos/82B619E71E1132507E0A856CC713E7AF |url-status=live}}</ref><ref>{{cite journal |last1=Debnath |first1=Ajay |title=Condition of Agricultural Productivity of Gosaba C.D. Block, South24 Parganas, West Bengal, India after Severe Cyclone Aila |journal=International Journal of Scientific and Research Publications |date=July 2013 |volume=3 |issue=7 |pages=97–100 |url=http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.416.3757&rep=rep1&type=pdf#page=98 |citeseerx=10.1.1.416.3757 |access-date=May 25, 2022 |issn=2250-3153 |archive-date=May 26, 2022 |archive-url=https://web.archive.org/web/20220526171026/http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.416.3757&rep=rep1&type=pdf#page=98 |url-status=live}}</ref><ref>{{cite journal |last1=Needham |first1=Hal F. |last2=Keim |first2=Barry D. |last3=Sathiaraj |first3=David |title=A review of tropical cyclone-generated storm surges: Global data sources, observations, and impacts |journal=Reviews of Geophysics |date=May 19, 2015 |volume=53 |issue=2 |pages=545–591 |doi=10.1002/2014RG000477 |publisher=AGU |bibcode=2015RvGeo..53..545N |s2cid=129145744 |doi-access=free}}</ref> Powerful cyclones that make ] &ndash; moving from the ocean to over land &ndash; are some of the most powerful, although that is not always the case. An average of 86&nbsp;tropical cyclones of tropical storm intensity form annually worldwide, with 47 reaching hurricane or typhoon strength, and 20 becoming intense tropical cyclones, super typhoons, or major hurricanes (at least of ] intensity).<ref name="Landsea variability table">{{cite web | first1= Chris|last1= Landsea | url = http://www.aoml.noaa.gov/hrd/Landsea/climvari/table.html | title = Climate Variability table&nbsp;— Tropical Cyclones | publisher = ], ] | access-date = October 19, 2006 | author-link = Chris Landsea | archive-date = October 2, 2012 | archive-url = https://web.archive.org/web/20121002045230/http://www.aoml.noaa.gov/hrd/Landsea/climvari/table.html | url-status = live}}</ref>
===Regional terminology===
], Pacific Ocean, August ].]]


==== Africa ====
Terms used in weather reports for tropical cyclones that have surface winds over 64 ]s (73.6 ]) or 32 ] vary by region:
In ], tropical cyclones can originate from ]s generated over the ],<ref>{{cite web|first1=Jonathan|last1= Belles|title=Why Tropical Waves Are Important During Hurricane Season|date=August 28, 2018|publisher=Weather.com|access-date=October 2, 2020|url=https://weather.com/storms/hurricane/news/tropical-wave-explainer-tropics-hurricanes|archive-date=October 1, 2020|archive-url=https://web.archive.org/web/20201001221202/https://weather.com/storms/hurricane/news/tropical-wave-explainer-tropics-hurricanes|url-status=live}}</ref> or otherwise strike the ] and ].<ref>{{cite news|first1=Matthew |last1=Schwartz|date=November 22, 2020|title=Somalia's Strongest Tropical Cyclone Ever Recorded Could Drop 2 Years' Rain In 2 Days|publisher=NPR|url=https://www.npr.org/2020/11/22/937790467/somalias-strongest-tropical-cyclone-ever-recorded-could-drop-2-years-rain-in-2-d|access-date=November 23, 2020|archive-date=November 23, 2020|archive-url=https://web.archive.org/web/20201123000841/https://www.npr.org/2020/11/22/937790467/somalias-strongest-tropical-cyclone-ever-recorded-could-drop-2-years-rain-in-2-d|url-status=live}}</ref><ref>{{cite journal|title=Projected changes in tropical cyclones over the South West Indian Ocean under different extents of global warming|first1=M. S.|last1= Muthige|first2=J. |last2=Malherbe|first3=F. A. |last3=Englebrecht|first4=S. |last4=Grab|first5=A. |last5=Beraki|first6=T. R. |last6=Maisha|first7=J. |last7=Van der Merwe|journal=Environmental Research Letters|year=2018|volume=13|number=6|page=065019|doi=10.1088/1748-9326/aabc60|bibcode=2018ERL....13f5019M|s2cid=54879038 |doi-access=free}}</ref> ] in March 2019 hit central ], becoming the deadliest tropical cyclone on record in Africa, with 1,302&nbsp;fatalities, and damage estimated at US$2.2&nbsp;billion.<ref>{{cite web |last1=Masters |first1=Jeff |title=Africa's Hurricane Katrina: Tropical Cyclone Idai Causes an Extreme Catastrophe |url=https://www.wunderground.com/cat6/Africas-Hurricane-Katrina-Tropical-Cyclone-Idai-Causes-Extreme-Catastrophe |website=Weather Underground |access-date=March 23, 2019 |archive-url=https://web.archive.org/web/20190322214331/https://www.wunderground.com/cat6/Africas-Hurricane-Katrina-Tropical-Cyclone-Idai-Causes-Extreme-Catastrophe |archive-date=March 22, 2019 |url-status=live}}</ref><ref name="Global Catastrophe Recap">{{cite web |title=Global Catastrophe Recap: First Half of 2019 |url=http://thoughtleadership.aonbenfield.com//Documents/20190723-analytics-if-1h-global-report.pdf |publisher=Aon Benfield |access-date=August 12, 2019 |archive-url=https://web.archive.org/web/20190812000713/http://thoughtleadership.aonbenfield.com//Documents/20190723-analytics-if-1h-global-report.pdf |archive-date=August 12, 2019 |url-status=live}}</ref> ] island, located east of Southern Africa, experiences some of the wettest tropical cyclones on record. In January 1980, ] produced 6,083&nbsp;mm (239.5&nbsp;in) of rain over 15&nbsp;days, which was the largest rain total recorded from a tropical cyclone on record.<ref>{{cite web|author=Lyons, Steve|date=February 17, 2010|title=La Reunion Island's Rainfall Dynasty!|url=http://www.weather.com/blog/weather/8_21280.html|url-status=dead|archive-url=https://web.archive.org/web/20140210080403/http://www.weather.com/blog/weather/8_21280.html|archive-date=February 10, 2014|access-date=February 4, 2014|publisher=The Weather Channel}}</ref><ref>{{cite report|url=http://www.meteo.fr/temps/domtom/La_Reunion/meteoreunion2/climatologie/records/rec_RR1.html|title=Précipitations extrêmes|publisher=Meteo France|access-date=April 15, 2013|date=|archive-date=February 21, 2014|archive-url=https://web.archive.org/web/20140221182557/http://www.meteo.fr/temps/domtom/La_Reunion/meteoreunion2/climatologie/records/rec_RR1.html|url-status=live}}</ref><ref>{{cite journal|author=Randall S. Cerveny|display-authors=etal|date=June 2007|title=Extreme Weather Records|journal=Bulletin of the American Meteorological Society|volume=88|issue=6|pages=856, 858|bibcode=2007BAMS...88..853C|doi=10.1175/BAMS-88-6-853|doi-access=free}}</ref>


==== Asia ====
* ''Hurricane:'' ] and North ] east of the ]
In ], tropical cyclones from the Indian and Pacific oceans regularly affect some of the most populated countries on Earth. In 1970, ] struck ], then known as East Pakistan, producing a {{convert|20|ft|m|abbr=on|order=flip}} storm surge that killed at least 300,000&nbsp;people. This made it the deadliest tropical cyclone on record.<ref name="dead">{{cite journal|title=The Deadliest Tropical Cyclone in history?|first1=Neil L. |last1=Frank|first2=S. A. |last2=Husain|date=June 1971|journal=Bulletin of the American Meteorological Society|volume=52|number=6|page=438 |doi=10.1175/1520-0477(1971)052<0438:TDTCIH>2.0.CO;2 |bibcode=1971BAMS...52..438F |s2cid=123589011 |doi-access=free}}</ref> In October 2019, ] struck the ]ese island of ] and inflicted US$15&nbsp;billion in damage, making it the costliest storm on record in Japan.<ref>{{cite report|url=http://thoughtleadership.aon.com/Documents/20200122-if-natcat2020.pdf|title=Weather, Climate & Catastrophe Insight: 2019 Annual Report|date=January 22, 2020|publisher=AON Benfield|access-date=January 23, 2020|archive-date=January 22, 2020|archive-url=https://web.archive.org/web/20200122154950/http://thoughtleadership.aon.com/Documents/20200122-if-natcat2020.pdf|url-status=live}}</ref> The islands that comprise ], from ] to ], are routinely affected by tropical cyclones.<ref>{{cite report|year=2007|page=45|url=http://www.ga.gov.au/webtemp/image_cache/GA10821.pdf|title=Natural hazards in Australia: Identifying risk analysis requirements|first1=Alan |last1=Sharp|first2=Craig |last2=Arthur|author3=Bob Cechet|author4=Mark Edwards|publisher=Geoscience Australia|access-date=October 11, 2020|archive-date=October 31, 2020|archive-url=https://web.archive.org/web/20201031165443/http://www.ga.gov.au/webtemp/image_cache/GA10821.pdf|url-status=live}}</ref><ref>{{cite report |type=Information Sheet: 35 |title=The Climate of Fiji |url=https://www.met.gov.fj/ClimateofFiji.pdf |publisher=Fiji Meteorological Service |access-date=April 29, 2021 |date=April 28, 2006 |archive-date=March 20, 2021 |archive-url=https://web.archive.org/web/20210320081515/https://www.met.gov.fj/ClimateofFiji.pdf |url-status=live}}</ref><ref>{{cite report |title=Republic of Fiji: Third National Communication Report to the United Nations Framework Convention on Climate Change |url=https://unfccc.int/sites/default/files/resource/Fiji_TNC%20Report.pdf |publisher=United Nations Framework Convention on Climate Change |page=62 |date=April 27, 2020 |access-date=August 23, 2021 |archive-date=July 6, 2021 |archive-url=https://web.archive.org/web/20210706131843/https://unfccc.int/sites/default/files/resource/Fiji_TNC%20Report.pdf |url-status=live}}</ref> In ], ] struck the island of ] in April 1973, killing 1,653&nbsp;people, making it the deadliest tropical cyclone recorded in the ].<ref>{{cite news|title=Death toll|agency=Australian Associated Press|url=https://trove.nla.gov.au/newspaper/article/110715084?searchTerm=flores&searchLimits=exactPhrase|newspaper=The Canberra Times|date=June 18, 1973|access-date=April 22, 2020|archive-date=August 27, 2020|archive-url=https://web.archive.org/web/20200827205214/https://trove.nla.gov.au/newspaper/article/110715084?searchTerm=flores&searchLimits=exactPhrase|url-status=live}}</ref><ref>{{cite web |last1=Masters |first1=Jeff |title=Africa's Hurricane Katrina: Tropical Cyclone Idai Causes an Extreme Catastrophe |url=https://www.wunderground.com/cat6/Africas-Hurricane-Katrina-Tropical-Cyclone-Idai-Causes-Extreme-Catastrophe |website=Weather Underground |access-date=March 23, 2019 |archive-date=August 4, 2019 |archive-url=https://web.archive.org/web/20190804083147/https://www.wunderground.com/cat6/Africas-Hurricane-Katrina-Tropical-Cyclone-Idai-Causes-Extreme-Catastrophe |url-status=live}}</ref>
* ''Typhoon:'' Northwest Pacific west of the dateline
* ''Severe tropical cyclone:'' Southwest Pacific west of 160&deg;E and the southeast Indian Ocean east of 90&deg;E
* ''Very severe cyclonic storm:'' North ]
* ''Tropical cyclone:'' Southwest Indian Ocean and the South Pacific east of 160&deg;E.
* ''Cyclone'' (unofficially): South Atlantic Ocean


==== North and South America ====
There are many regional names for tropical cyclones, including ] in the ] and ''Taino'' in ].
] and ] regularly affect ]. In the ], hurricanes ] in 2005 and ] in 2017 are the country's costliest ever natural disasters, with monetary damage estimated at US$125&nbsp;billion. Katrina struck ] and largely destroyed the city of ],<ref>{{Cite web |url=https://www.ncdc.noaa.gov/billions/events/US/1980-2020 |title=Billion-Dollar Weather and Climate Disasters|publisher=National Centers for Environmental Information |access-date=August 23, 2021 |archive-date=August 11, 2021 |archive-url=https://web.archive.org/web/20210811152237/https://www.ncdc.noaa.gov/billions/events/US/1980-2020 |url-status=live}}</ref><ref name="Harvey TCR">{{Cite report |url=https://www.nhc.noaa.gov/data/tcr/AL092017_Harvey.pdf |first1=Eric S.|last1=Blake|first2=David A.|last2=Zelensky|title=Tropical Cyclone Report: Hurricane Harvey|access-date=August 23, 2021 |archive-date=January 26, 2018 |archive-url=https://web.archive.org/web/20180126083538/https://www.nhc.noaa.gov/data/tcr/AL092017_Harvey.pdf |publisher=National Hurricane Center|url-status=live}}</ref> while Harvey caused significant flooding in southeastern ] after it dropped {{convert|60.58|in|mm|abbr=on}} of rainfall; this was the highest rainfall total on record in the country.<ref name="Harvey TCR" />


The Caribbean islands are regularly hit by hurricanes, which have caused multiple humanitarian crises in ] since 2004 due in part to the lack of infrastructure and high population density in urban areas.<ref>{{cite web |title=Building a resilient Haiti |url=https://www.unops.org/news-and-stories/stories/building-a-resilient-haiti |website=UNOPS |access-date=8 October 2024}}</ref><ref>{{cite web |title=Disaster risk reduction in Haiti |url=https://unfccc.int/ttclear/misc_/StaticFiles/gnwoerk_static/TEC_NSI/7fe85d474c964de893e62da77926a738/d198abc4edb249128c1b15ad81e371f0.pdf#page=6 |website=UNFCCC |access-date=8 October 2024}}</ref> In 2004, hurricane ] caused severe flooding and mudslides, and a total estimated 3,006 deaths.<ref>{{cite web |title=Hurricane Relief |url=http://hurricane.info.usaid.gov/ |website=USAID |access-date=8 October 2024 |archive-url=https://web.archive.org/web/20041015085858/http://hurricane.info.usaid.gov/ |archive-date=15 October 2004}}</ref> More recently, in 2016, hurricane ] caused US$2.8 billion in damages, killing an estimated 674 people.<ref>{{cite web |title=After Hurricane Matthew, Many Victims in Haiti Feel Abandoned |url=http://www.govtech.com/em/disaster/After-Hurricane-Matthew-Many-Victims-in-Haiti-Feel-Abandoned.html |website=govtech.com |date=July 17, 2017 |publisher=Miami Herald |access-date=8 October 2024 |archive-url=https://web.archive.org/web/20170717190251/http://www.govtech.com/em/disaster/After-Hurricane-Matthew-Many-Victims-in-Haiti-Feel-Abandoned.html |archive-date=17 July 2017}}</ref><ref>{{cite web |title=Hurricane Matthew |url=http://www.nhc.noaa.gov/data/tcr/AL142016_Matthew.pdf |website=nhc.noaa.gov |access-date=8 October 2024 |archive-url=https://web.archive.org/web/20170405073622/http://www.nhc.noaa.gov/data/tcr/AL142016_Matthew.pdf |archive-date=5 April 2017}}</ref>
====Origin of storm terms====
The word ''typhoon'' has two possible origins:
* From the ] 大風 (daaih fūng (]); dà fēng (])) which means "great ]." (The Chinese term as 颱風 táifēng, and 台風 ''taifu'' in Japanese, has an independent origin traceable variously to 風颱, 風篩 or 風癡 ''hongthai'', going back to Song 宋 (960-1278) and Yuan 元(1260-1341) dynasties. The first record of the character 颱 appeared in 1685's edition of ''Summary of Taiwan'' 臺灣記略).{{citation needed}}
* From ], ] or ] ''ţūfān'' (&#1591;&#1608;&#1601;&#1575;&#1606;) < ] '']'' (Τυφών).{{citation needed}}


The northern portion of ] experiences occasional tropical cyclones, with 173&nbsp;fatalities from ] in August 1993.<ref>{{cite web |last1=Pielke |first1=R. A. Jr. |last2=Rubiera |first2=J |last3=Landsea |first3=C |last4=Fernández |first4=M. L. |last5=Klein |first5=R |year=2003 |title=Hurricane Vulnerability in Latin America & The Caribbean |url=http://sciencepolicy.colorado.edu/admin/publication_files/resource-1769-2003.21.pdf |url-status=live |archive-url=https://web.archive.org/web/20060810043441/http://sciencepolicy.colorado.edu/admin/publication_files/resource-1769-2003.21.pdf |archive-date=August 10, 2006 |access-date=July 20, 2006 |publisher=National Hazards Review}}</ref><ref>{{cite report |url=http://www.nhc.noaa.gov/archive/storm_wallets/atlantic/atl1993/bret/prenhc/prelim03.gif |title=Tropical Storm Bret Preliminary Report |last1=Rappaport |first1=Ed |date=December 9, 1993 |publisher=National Hurricane Center |page=3 |access-date=August 11, 2015 |archive-url=https://web.archive.org/web/20160303220621/http://www.nhc.noaa.gov/archive/storm_wallets/atlantic/atl1993/bret/prenhc/prelim03.gif |archive-date=March 3, 2016 |format=GIF |url-status=live}}</ref> The ] is generally inhospitable to the formation of a tropical storm.<ref>{{cite book |author=Landsea, Christopher W. |title=Tropical Cyclone Frequently Asked Question |date=July 13, 2005 |publisher=United States National Oceanic and Atmospheric Administration's Hurricane Research Division |chapter=Subject: Tropical Cyclone Names: G6) Why doesn't the South Atlantic Ocean experience tropical cyclones? |access-date=February 7, 2015 |chapter-url=http://www.aoml.noaa.gov/hrd/tcfaq/G6.html |archive-url=https://web.archive.org/web/20150327070050/http://www.aoml.noaa.gov/hrd/tcfaq/G6.html |archive-date=March 27, 2015 |url-status=live}}</ref> However, in March 2004, ] struck southeastern ] as the first hurricane on record in the South Atlantic Ocean.<ref>{{cite journal |last1=McTaggart-Cowan |first1=Ron |last2=Bosart |first2=Lance F. |last3=Davis |first3=Christopher A. |last4=Atallah |first4=Eyad H. |last5=Gyakum |first5=John R. |last6=Emanuel |first6=Kerry A. |date=November 2006 |title=Analysis of Hurricane Catarina (2004) |url=https://texmex.mit.edu/pub/emanuel/PAPERS/cowan_etal_2006.pdf |url-status=live |journal=Monthly Weather Review |publisher=American Meteorological Society |volume=134 |issue=11 |pages=3029–3053 |bibcode=2006MWRv..134.3029M |doi=10.1175/MWR3330.1 |archive-url=https://web.archive.org/web/20210830230858/http://texmex.mit.edu/pub/emanuel/PAPERS/cowan_etal_2006.pdf |archive-date=August 30, 2021 |access-date=May 23, 2022}}</ref>
] ''tufão'' is also related to typhoon. See ] for more information.


==== Europe ====
The word ''hurricane'' is derived from the name of a native ] ] storm ], ], via ] ''huracán''.<ref name=NHCB4> accessed April 15, 2006</ref>
] is rarely affected by tropical cyclones; however, the continent regularly encounters storms after they transitioned into ]s. Only one tropical depression &ndash; ] in 2005 &ndash; struck ],<ref>{{cite report|first=James L.|last=Franklin|title=Tropical Cyclone Report: Hurricane Vince|publisher=National Hurricane Center|date=February 22, 2006|access-date=August 14, 2011|url=http://www.nhc.noaa.gov/data/tcr/AL242005_Vince.pdf|archive-date=October 2, 2015|archive-url=https://web.archive.org/web/20151002011818/http://www.nhc.noaa.gov/data/tcr/AL242005_Vince.pdf|url-status=live}}</ref> and only one ] &ndash; ] in 2020 &ndash; struck ].<ref>{{cite report|title=Subtropical Storm Alpha Discussion Number 2|url=https://www.nhc.noaa.gov/archive/2020/al24/al242020.discus.002.shtml?|publisher=National Hurricane Center|access-date=September 18, 2020|date=September 18, 2020|first1=Eric|last1=Blake|archive-date=October 9, 2020|archive-url=https://web.archive.org/web/20201009024154/https://www.nhc.noaa.gov/archive/2020/al24/al242020.discus.002.shtml|url-status=live}}</ref> Occasionally, there are ] in the ].<ref>{{cite journal|author=Emanuel, K.|url=https://www.researchgate.net/publication/26438265|title=Genesis and maintenance of 'Mediterranean hurricanes'|journal=Advances in Geosciences|date=June 2005|volume=2|pages=217–220|doi=10.5194/adgeo-2-217-2005|bibcode=2005AdG.....2..217E|doi-access=free|access-date=May 23, 2022|archive-date=May 23, 2022|archive-url=https://web.archive.org/web/20220523221113/https://www.researchgate.net/publication/26438265_Genesis_and_maintenance_of_Mediterranean_hurricanes|url-status=live}}</ref>


===Environmental effects===
The word ''cyclone'' was coined by a Captain Henry Piddington, who used it to refer to the storm that blew a freighter in circles in Mauritius in February of 1845.<ref name=Whipplep53>Whipple, p. 53</ref> Tropical cyclones are then circular wind storms that form in the tropics.
Although cyclones take an enormous toll in lives and personal property, they may be important factors in the ] regimes of places they affect, as they may bring much-needed precipitation to otherwise dry regions.<ref name="2005 EPac outlook">]. {{Webarchive|url=https://web.archive.org/web/20150612041026/http://www.cpc.ncep.noaa.gov/products/Epac_hurr/Epac_hurricane.html |date=June 12, 2015}}. Retrieved May 2, 2006.</ref> Their precipitation may also alleviate drought conditions by restoring soil moisture, though one study focused on the ] suggested tropical cyclones did not offer significant drought recovery.<ref name="DontFix">{{cite news |title=Summer tropical storms don't fix drought conditions |url=https://www.sciencedaily.com/releases/2015/05/150527150948.htm |newspaper=ScienceDaily |access-date=April 10, 2021 |date=May 27, 2015 |archive-date=October 9, 2021 |archive-url=https://web.archive.org/web/20211009103634/https://www.sciencedaily.com/releases/2015/05/150527150948.htm |url-status=live}}</ref><ref name="Yoo et al. (2015)">{{cite journal |last1=Yoo |first1=Jiyoung |last2=Kwon |first2=Hyun-Han |last3=So |first3=Byung-Jin |last4=Rajagopalan |first4=Balaji |last5=Kim |first5=Tae-Woong |title=Identifying the role of typhoons as drought busters in South Korea based on hidden Markov chain models: ROLE OF TYPHOONS AS DROUGHT BUSTERS |journal=Geophysical Research Letters |date=April 28, 2015 |volume=42 |issue=8 |pages=2797–2804 |doi=10.1002/2015GL063753|doi-access=free}}</ref><ref name="Kam et al. (2013)">{{cite journal |last1=Kam |first1=Jonghun |last2=Sheffield |first2=Justin |last3=Yuan |first3=Xing|author4-link=Eric Franklin Wood |last4=Wood |first4=Eric F. |title=The Influence of Atlantic Tropical Cyclones on Drought over the Eastern United States (1980–2007) |journal=Journal of Climate |date=May 15, 2013 |volume=26 |issue=10 |pages=3067–3086 |doi=10.1175/JCLI-D-12-00244.1 |publisher=American Meteorological Society|bibcode=2013JCli...26.3067K |doi-access=free}}</ref> Tropical cyclones also help maintain the global heat balance by moving warm, moist tropical air to the ] and ],<ref name="JetStream introduction">{{cite web|url=http://www.srh.noaa.gov/jetstream/tropics/tc.htm|author=National Weather Service|work=JetStream&nbsp;– An Online School for Weather|publisher=]|title=Tropical Cyclone Introduction|access-date=September 7, 2010|date=October 19, 2005|author-link=National Weather Service|archive-url=https://web.archive.org/web/20120614093509/http://www.srh.noaa.gov/jetstream/tropics/tc.htm|archive-date=June 14, 2012|url-status=live}}</ref> and by regulating the ] through ].<ref>{{cite journal|last=Emanuel|first=Kerry|title=Contribution of tropical cyclones to meridional heat transport by the oceans|journal=]|date=July 2001|volume=106|issue=D14|pages=14771–14781|doi=10.1029/2000JD900641|bibcode = 2001JGR...10614771E |doi-access=free}}</ref> Research on Pacific cyclones has demonstrated that deeper layers of the ocean receive a ] from these powerful storms.<ref>Alex Fox. (June 20, 2023). "New Measurements Suggest Tropical Cyclones May Influence Global Climate". Retrieved June 30, 2023.</ref><ref>{{Cite journal |last1=Gutiérrez Brizuela |first1=Noel |last2=Alford |first2=Matthew H. |last3=Xie |first3=Shang-Ping |author-link3=Shang-Ping Xie |last4=Sprintall |first4=Janet |last5=Voet |first5=Gunnar |last6=Warner |first6=Sally J. |last7=Hughes |first7=Kenneth |last8=Moum |first8=James N. |title=Prolonged thermocline warming by near-inertial internal waves in the wakes of tropical cyclones |journal=Proceedings of the National Academy of Sciences of the United States of America |date=2023 |volume=120 |issue=26 |pages=e2301664120 |doi=10.1073/pnas.2301664120 |issn=0027-8424 |pmid=37339203|doi-access=free |pmc=10293854 |bibcode=2023PNAS..12001664G}}</ref>


The storm surge and winds of hurricanes may be destructive to human-made structures, but they also stir up the waters of coastal ], which are typically important ] locales.<ref name="Christopherson">{{cite book|author=Christopherson, Robert W.|year=1992|title=Geosystems: An Introduction to Physical Geography|pages=222–224|publisher=Macmillan Publishing Company|location=New York|isbn=978-0-02-322443-0}}</ref> Ecosystems, such as ]es and ]s, can be severely damaged or destroyed by tropical cyclones, which erode land and destroy vegetation.<ref>{{cite journal |last1=Khanna |first1=Shruti |last2=Santos |first2=Maria J. |last3=Koltunov |first3=Alexander |last4=Shapiro |first4=Kristen D. |last5=Lay |first5=Mui |last6=Ustin |first6=Susan L. |title=Marsh Loss Due to Cumulative Impacts of Hurricane Isaac and the Deepwater Horizon Oil Spill in Louisiana |journal=Remote Sensing |date=February 17, 2017 |volume=9 |issue=2 |page=169 |doi=10.3390/rs9020169 |publisher=MDPI|bibcode=2017RemS....9..169K |doi-access=free}}</ref><ref>{{cite journal |last1=Osland |first1=Michael J. |last2=Feher |first2=Laura C. |last3=Anderson |first3=Gordon H. |last4=Varvaeke |first4=William C. |last5=Krauss |first5=Ken W. |last6=Whelan |first6=Kevin R.T. |last7=Balentine |first7=Karen M. |last8=Tiling-Range |first8=Ginger |last9=Smith III |first9=Thomas J. |last10=Cahoon |first10=Donald R. |title=A Tropical Cyclone-Induced Ecological Regime Shift: Mangrove Forest Conversion to Mudflat in Everglades National Park (Florida, USA) |journal=Wetlands and Climate Change |date=May 26, 2020 |volume=40 |issue=5 |pages=1445–1458 |doi=10.1007/s13157-020-01291-8 |url=https://link.springer.com/article/10.1007/s13157-020-01291-8 |access-date=May 27, 2022 |publisher=Springer |bibcode=2020Wetl...40.1445O |s2cid=218897776 |archive-date=May 17, 2022 |archive-url=https://web.archive.org/web/20220517122435/https://link.springer.com/article/10.1007/s13157-020-01291-8 |url-status=live}}</ref> Tropical cyclones can cause harmful ]s to form in bodies of water by increasing the amount of nutrients available.<ref name="Oil+Algae" /><ref>{{cite journal |last1=Zang |first1=Zhengchen |last2=Xue |first2=Z. George |last3=Xu |first3=Kehui |last4=Bentley |first4=Samuel J. |last5=Chen |first5=Qin |last6=D'Sa |first6=Eurico J. |last7=Zhang |first7=Le |last8=Ou |first8=Yanda |title=The role of sediment-induced light attenuation on primary production during Hurricane Gustav (2008) |journal=Biogeosciences |date=October 20, 2020 |volume=17 |issue=20 |pages=5043–5055 |doi=10.5194/bg-17-5043-2020 |url=https://bg.copernicus.org/articles/17/5043/2020/ |access-date=May 19, 2022 |publisher=Copernicus Publications |bibcode=2020BGeo...17.5043Z |s2cid=238986315 |archive-date=January 19, 2022 |archive-url=https://web.archive.org/web/20220119222647/https://bg.copernicus.org/articles/17/5043/2020/ |url-status=live |doi-access=free |hdl=1912/26507 |hdl-access=free}}</ref><ref>{{cite journal |last1=Huang |first1=Wenrui |last2=Mukherjee |first2=Debraj |last3=Chen |first3=Shuisen |title=Assessment of Hurricane Ivan impact on chlorophyll-a in Pensacola Bay by MODIS 250 m remote sensing |journal=Marine Pollution Bulletin |date=March 2011 |volume=62 |issue=3 |pages=490–498 |doi=10.1016/j.marpolbul.2010.12.010 |url=https://www.sciencedirect.com/science/article/abs/pii/S0025326X10005333 |access-date=May 19, 2022 |pmid=21272900 |bibcode=2011MarPB..62..490H}}</ref> Insect populations can decrease in both quantity and diversity after the passage of storms.<ref>{{cite journal |last1=Chen |first1=Xuan |last2=Adams |first2=Benjamin J. |last3=Platt |first3=William J. |last4=Hooper-Bùi |first4=Linda M. |title=Effects of a tropical cyclone on salt marsh insect communities and post-cyclone reassembly processes |journal=Ecography |date=February 28, 2020 |volume=43 |issue=6 |pages=834–847 |doi=10.1111/ecog.04932 |publisher=Wiley Online Library |s2cid=212990211 |doi-access=free |bibcode=2020Ecogr..43..834C}}</ref> Strong winds associated with tropical cyclones and their remnants are capable of felling thousands of trees, causing damage to forests.<ref>{{cite news |title=Tempestade Leslie provoca grande destruição nas Matas Nacionais |trans-title=Storm Leslie wreaks havoc in the National Forests |url=https://www.noticiasdecoimbra.pt/tempestade-leslie-provoca-grande-destruicao-nas-matas-nacionais/ |access-date=May 27, 2022 |work=Notícias de Coimbra |date=October 17, 2018 |language=pt |archive-date=January 28, 2019 |archive-url=https://web.archive.org/web/20190128031143/https://www.noticiasdecoimbra.pt/tempestade-leslie-provoca-grande-destruicao-nas-matas-nacionais/ |url-status=live}}</ref>
===Naming of tropical cyclones===
{{hurricane main|Lists of tropical cyclone names}}
Storms reaching tropical storm strength are given names, to assist in recording insurance claims, to assist in warning people of the coming storm, and to further indicate that these are important storms that should not be ignored. These names are taken from lists which vary from region to region and are drafted a few years ahead of time. The lists are decided upon, depending on the regions, either by committees of the ] (called primarily to discuss many other issues), or by national weather offices involved in the forecasting of the storms.


When hurricanes surge upon shore from the ocean, salt is introduced to many freshwater areas and raises the ] levels too high for some habitats to withstand. Some are able to cope with the salt and recycle it back into the ocean, but others can not release the extra surface water quickly enough or do not have a large enough freshwater source to replace it. Because of this, some species of plants and vegetation die due to the excess salt.<ref>{{cite web|last=Doyle|first=Thomas|title=Wind damage and Salinity Effects of Hurricanes Katrina and Rita on Coastal Baldcypress Forests of Louisiana|url=http://pubs.usgs.gov/circ/1306/pdf/c1306_ch6_f.pdf|access-date=February 13, 2014|year=2005|archive-url=https://web.archive.org/web/20160304040402/http://pubs.usgs.gov/circ/1306/pdf/c1306_ch6_f.pdf|archive-date=March 4, 2016|url-status=live}}</ref> Hurricanes can carry ] and ] onshore when they make landfall. The floodwater can pick up the toxins from different spills and contaminate the land that it passes over. These toxins are harmful to the people and animals in the area, as well as the environment around them.<ref>{{cite web|last=Cappielo|first=Dina|title=Spills from hurricanes stain coast With gallery|url=http://www.chron.com/news/hurricanes/article/Spills-from-hurricanes-stain-coast-With-gallery-1915858.php|work=Houston Chronicle|access-date=February 12, 2014|year=2005|archive-url=https://web.archive.org/web/20140425055112/http://www.chron.com/news/hurricanes/article/Spills-from-hurricanes-stain-coast-With-gallery-1915858.php|archive-date=April 25, 2014|url-status=live}}</ref> Tropical cyclones can cause ]s by damaging or destroying pipelines and storage facilities.<ref>{{cite journal |last1=Pine |first1=John C. |title=Hurricane Katrina and Oil Spills: Impact on Coastal and Ocean Environments |journal=Oceanography |year=2006 |volume=19 |issue=2 |pages=37–39 |url=https://tos.org/oceanography/assets/docs/19-2_pine.pdf |access-date=May 19, 2022 |publisher=The Oceanography Society |doi=10.5670/oceanog.2006.61 |archive-date=January 20, 2022 |archive-url=https://web.archive.org/web/20220120022223/https://tos.org/oceanography/assets/docs/19-2_pine.pdf |url-status=live}}</ref><ref name="Oil+Algae">{{cite journal |last1=You |first1=Zai-Jin |title=Tropical Cyclone-Induced Hazards Caused by Storm Surges and Large Waves on the Coast of China |journal=Geosciences |date=March 18, 2019 |volume=9 |issue=3 |page=131 |doi=10.3390/geosciences9030131 |bibcode=2019Geosc...9..131Y |issn=2076-3263|doi-access=free}}</ref><ref name="Oil + Chemicals">{{cite journal |last1=Santella |first1=Nicholas |last2=Steinberg |first2=Laura J. |last3=Sengul |first3=Hatice |title=Petroleum and Hazardous Material Releases from Industrial Facilities Associated with Hurricane Katrina |journal=Risk Analysis |date=April 12, 2010 |volume=30 |issue=4 |pages=635–649 |doi=10.1111/j.1539-6924.2010.01390.x |pmid=20345576 |bibcode=2010RiskA..30..635S |s2cid=24147578 |url=https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1539-6924.2010.01390.x |access-date=May 21, 2022}}</ref> Similarly, chemical spills have been reported when chemical and processing facilities were damaged.<ref name="Oil + Chemicals" /><ref>{{cite journal |last1=Qin |first1=Rongshui |last2=Khakzad |first2=Nima |last3=Zhu |first3=Jiping |title=An overview of the impact of Hurricane Harvey on chemical and process facilities in Texas |journal=International Journal of Disaster Risk Reduction |date=May 2020 |volume=45 |page=101453 |doi=10.1016/j.ijdrr.2019.101453 |url=https://www.sciencedirect.com/science/article/abs/pii/S2212420919313949 |access-date=May 19, 2022 |bibcode=2020IJDRR..4501453Q |s2cid=214418578}}</ref><ref>{{cite journal |last1=Misuri |first1=Alessio |last2=Moreno |first2=Valeria Casson |last3=Quddus |first3=Noor |last4=Cozzani |first4=Valerio |title=Lessons learnt from the impact of hurricane Harvey on the chemical and process industry |journal=Reliability Engineering & System Safety |date=October 2019 |volume=190 |page=106521 |doi=10.1016/j.ress.2019.106521 |url=https://www.sciencedirect.com/science/article/abs/pii/S0951832019303990 |access-date=May 19, 2022 |s2cid=191214528}}</ref> Waterways have become contaminated with toxic levels of metals such as ], ], and ] during tropical cyclones.<ref>{{cite news |last1=Cañedo |first1=Sibely |title=Tras el Huracán Willa, suben niveles de metales en río Baluarte |trans-title=After Hurricane Willa, metal levels rise in the Baluarte River|url=https://www.noroeste.com.mx/publicaciones/view/huracan-willa-azoto-en-el-sur-y-niveles-de-cromo-niquel-y-mercurio-subieron-en-rio-baluarte-1159453 |access-date=May 19, 2022 |publisher=Noreste |date=March 29, 2019 |archive-url=https://web.archive.org/web/20200930145023/https://www.noroeste.com.mx/publicaciones/view/huracan-willa-azoto-en-el-sur-y-niveles-de-cromo-niquel-y-mercurio-subieron-en-rio-baluarte-1159453 |archive-date=September 30, 2020 |language=es}}</ref><ref name="Erosion + Mercury">{{cite journal |last1=Dellapenna |first1=Timothy M. |last2=Hoelscher |first2=Christena |last3=Hill |first3=Lisa |last4=Al Mukaimi |first4=Mohammad E. |last5=Knap |first5=Anthony |title=How tropical cyclone flooding caused erosion and dispersal of mercury-contaminated sediment in an urban estuary: The impact of Hurricane Harvey on Buffalo Bayou and the San Jacinto Estuary, Galveston Bay, USA |journal=Science of the Total Environment |date=December 15, 2020 |volume=748 |page=141226 |doi=10.1016/j.scitotenv.2020.141226 |pmid=32818899 |pmc=7606715 |bibcode=2020ScTEn.74841226D}}</ref>
Each year, the names of particularly destructive storms (if there are any) are "retired" and new names are chosen to take their place.


Tropical cyclones can have an extensive effect on geography, such as creating or destroying land.<ref name="Land created" /><ref name="Land Destroyed" /> ] increased the size of ] island, ], by nearly 20%.<ref name="Land created">{{cite journal |last1=Volto |first1=Natacha |last2=Duvat |first2=Virginie K.E. |title=Applying Directional Filters to Satellite Imagery for the Assessment of Tropical Cyclone Impacts on Atoll Islands |journal=Coastal Research |date=July 9, 2020 |volume=36 |issue=4 |pages=732–740 |doi=10.2112/JCOASTRES-D-19-00153.1 |url=https://meridian.allenpress.com/jcr/article-abstract/36/4/732/440511/Applying-Directional-Filters-to-Satellite-Imagery |access-date=May 21, 2022 |publisher=Meridian Allen Press |s2cid=220323810 |archive-date=January 25, 2021 |archive-url=https://web.archive.org/web/20210125103957/https://meridian.allenpress.com/jcr/article-abstract/36/4/732/440511/Applying-Directional-Filters-to-Satellite-Imagery |url-status=live}}</ref><ref>{{cite journal |last1=Onaka |first1=Susumu |last2=Ichikawa |first2=Shingo |last3=Izumi |first3=Masatoshi |last4=Uda |first4=Takaaki |last5=Hirano |first5=Junichi |last6=Sawada |first6=Hideki |title=Effectiveness of Gravel Beach Nourishment on Pacific Island |journal=Asian and Pacific Coasts |year=2017 |pages=651–662 |doi=10.1142/9789813233812_0059 |url=https://www.worldscientific.com/doi/abs/10.1142/9789813233812_0059 |access-date=May 21, 2022 |publisher=World Scientific |isbn=978-981-323-380-5 |archive-date=May 16, 2022 |archive-url=https://web.archive.org/web/20220516233836/https://www.worldscientific.com/doi/abs/10.1142/9789813233812_0059 |url-status=live}}</ref><ref>{{cite journal |last1=Kench |first1=P.S. |last2=McLean |first2=R.F. |last3=Owen |first3=S.D. |last4=Tuck |first4=M. |last5=Ford |first5=M.R. |title=Storm-deposited coral blocks: A mechanism of island genesis, Tutaga island, Funafuti atoll, Tuvalu |journal=Geology |date=October 1, 2018 |volume=46 |issue=10 |pages=915–918 |doi=10.1130/G45045.1 |url=https://pubs.geoscienceworld.org/gsa/geology/article-abstract/46/10/915/548204/Storm-deposited-coral-blocks-A-mechanism-of-island |access-date=May 21, 2022 |publisher=Geo Science World |bibcode=2018Geo....46..915K |s2cid=135443385}}</ref> ] destroyed the small ] in 2018,<ref name="Land Destroyed">{{cite book |last1=Bush |first1=Martin J. |title=Climate Change and Renewable Energy |date=October 9, 2019 |publisher=Springer |isbn=978-3-030-15423-3 |pages=421–475 |chapter-url=https://link.springer.com/chapter/10.1007/978-3-030-15424-0_9 |access-date=May 21, 2022 |chapter=How to End the Climate Crisis |doi=10.1007/978-3-030-15424-0_9 |s2cid=211444296 |archive-date=May 17, 2022 |archive-url=https://web.archive.org/web/20220517014331/https://link.springer.com/chapter/10.1007/978-3-030-15424-0_9 |url-status=live}}</ref><ref>{{cite journal |last1=Baker |first1=Jason D. |last2=Harting |first2=Albert L. |last3=Johanos |first3=Thea C. |last4=London |first4=Joshua M. |last5=Barbieri |first5=Michelle M. |last6=Littnan |first6=Charles L. |title=Terrestrial Habitat Loss and the Long-term Viability of the French Frigate Shoals Hawaiian Monk Seal Subpopulation |journal=NOAA Technical Memorandum NMFS-PIFSC |date=August 2020 |doi=10.25923/76vx-ve75 |url=https://repository.library.noaa.gov/view/noaa/26090 |access-date=May 20, 2022 |publisher=NOAA Fisheries |archive-date=May 12, 2022 |archive-url=https://web.archive.org/web/20220512003115/https://repository.library.noaa.gov/view/noaa/26090 |url-status=live}}</ref> which destroyed the habitat for the endangered ], as well as, threatened ]s and ]s.<ref>{{cite book |last1=Tokar |first1=Brian |last2=Gilbertson |first2=Tamra |title=Climate Justice and Community Renewal: Resistance and Grassroots Solutions |date=March 31, 2020 |page=70 |publisher=Routledge |isbn=9781000049213 |url=https://books.google.com/books?id=ORHaDwAAQBAJ&q=hurricane+walaka+east+island+monk+seal |access-date=May 27, 2022 |archive-date=May 17, 2022 |archive-url=https://web.archive.org/web/20220517122435/https://books.google.com/books?id=ORHaDwAAQBAJ&dq=hurricane+walaka+east+island+monk+seal&lr=&source=gbs_navlinks_s |url-status=live}}</ref> ]s frequently occur during tropical cyclones and can vastly alter landscapes. Some storms are capable of causing hundreds to tens of thousands of landslides.<ref>{{cite journal |last1=Samodra |first1=Guruh |last2=Ngadisih |first2=Ngadisih |last3=Malawani |first3=Mukhamad Ngainul |last4=Mardiatno |first4=Djati |last5=Cahyadi |first5=Ahmad |last6=Nugroho |first6=Ferman Setia |title=Frequency–magnitude of landslides affected by the 27–29 November 2017 Tropical Cyclone Cempaka in Pacitan, East Java |journal=Journal of Mountain Science |date=April 11, 2020 |volume=17 |issue=4 |pages=773–786 |url=https://link.springer.com/article/10.1007/s11629-019-5734-y |access-date=May 21, 2022 |publisher=Springer |doi=10.1007/s11629-019-5734-y |bibcode=2020JMouS..17..773S |s2cid=215725140 |archive-date=May 17, 2022 |archive-url=https://web.archive.org/web/20220517014552/https://link.springer.com/article/10.1007/s11629-019-5734-y |url-status=live}}</ref><ref>{{cite journal |last1=Zinke |first1=Laura |title=Hurricanes and landslides |journal= Nature Reviews Earth & Environment|date=April 28, 2021 |volume=2 |issue=5 |page=304 |doi=10.1038/s43017-021-00171-x |url=https://www.nature.com/articles/s43017-021-00171-x |access-date=May 21, 2022 |bibcode=2021NRvEE...2..304Z |s2cid=233435990 |archive-date=May 17, 2022 |archive-url=https://web.archive.org/web/20220517015939/https://www.nature.com/articles/s43017-021-00171-x |url-status=live}}</ref><ref>{{cite journal |last1=Tien |first1=Pham Van |last2=Luong |first2=Le Hong |last3=Duc |first3=Do Minh |last4=Trinh |first4=Phan Trong |last5=Quynh |first5=Dinh Thi |last6=Lan |first6=Nguyen Chau |last7=Thuy |first7=Dang Thi |last8=Phi |first8=Nguyen Quoc |last9=Cuong |first9=Tran Quoc |last10=Dang |first10=Khang |last11=Loi |first11=Doan Huy |title=Rainfall-induced catastrophic landslide in Quang Tri Province: the deadliest single landslide event in Vietnam in 2020 |journal=Landslides |date=April 9, 2021 |volume=18 |issue=6 |pages=2323–2327 |doi=10.1007/s10346-021-01664-y |url=https://link.springer.com/article/10.1007/s10346-021-01664-y |access-date=May 21, 2022 |publisher=Springer |bibcode=2021Lands..18.2323V |s2cid=233187785 |archive-date=May 17, 2022 |archive-url=https://web.archive.org/web/20220517014536/https://link.springer.com/article/10.1007/s10346-021-01664-y |url-status=live}}</ref><ref>{{cite journal |last1=Santos |first1=Gemma Dela Cruz |title=2020 tropical cyclones in the Philippines: A review |journal=Tropical Cyclone Research and Review |date=September 20, 2021 |volume=10 |issue=3 |pages=191–199 |doi=10.1016/j.tcrr.2021.09.003 |bibcode=2021TCRR...10..191S |s2cid=239244161 |doi-access=free}}</ref> Storms can erode coastlines over an extensive area and transport the sediment to other locations.<ref name="Erosion + Mercury" /><ref>{{cite journal |last1=Mishra |first1=Manoranjan |last2=Kar |first2=Dipika |last3=Debnath |first3=Manasi |last4=Sahu |first4=Netrananda |last5=Goswami |first5=Shreerup |title=Rapid eco-physical impact assessment of tropical cyclones using geospatial technology: a case from severe cyclonic storms Amphan |journal=Natural Hazards |date=August 30, 2021 |volume=110 |issue=3 |pages=2381–2395 |doi=10.1007/s11069-021-05008-w |url=https://link.springer.com/article/10.1007/s11069-021-05008-w |access-date=May 21, 2022 |publisher=Springer |s2cid=237358608 |archive-date=May 17, 2022 |archive-url=https://web.archive.org/web/20220517010258/https://link.springer.com/article/10.1007/s11069-021-05008-w |url-status=live}}</ref><ref>{{cite journal |last1=Tamura |first1=Toru |last2=Nicholas |first2=William A. |last3=Oliver |first3=Thomas S. N. |last4=Brooke |first4=Brendan P. |title=Coarse-sand beach ridges at Cowley Beach, north-eastern Australia: Their formative processes and potential as records of tropical cyclone history |journal=Sedimentology |date=July 14, 2017 |volume=65 |issue=3 |pages=721–744 |doi=10.1111/sed.12402 |publisher=Wiley Library |s2cid=53403886 |doi-access=free}}</ref>
====Naming schemes====
{{further|]}}
The WMO's Regional Association IV Hurricane Committee selects the names for Atlantic Basin and central and eastern Pacific storms.


== Observation and forecasting ==
In the Atlantic and Eastern North Pacific regions, feminine and masculine names are assigned alternately in alphabetic order during a given season. The "gender" of the season's first storm also alternates year to year: the first storm of an odd-numbered year gets feminine name, while the first storm of an even-numbered year gets a masculine name. Six lists of names are prepared in advance, and each list is used once every six years. Five letters &mdash; "Q," "U," "X," "Y" and "Z" &mdash; are omitted in the Atlantic; only "Q" and "U" are omitted in the Eastern Pacific, so the format accommodates 21 or 24 named storms in a hurricane season. Names of storms may be retired by request of affected countries if they have caused extensive damage. The affected countries then decide on a replacement name of the same gender, and if possible, the same ethnicity, as the name being retired.
===Observation===
{{Main|Tropical cyclone observation}}
]'s ]s photographed at {{convert|7000|ft|m|abbr=on|order=flip}}|alt=Aerial view of storm clouds]]
]" – ] is used to go into the ] for data collection and measurements purposes.|alt=Head-on view of an airplane]]


Tropical cyclones have occurred around the world for millennia. Reanalyses and research are being undertaken to extend the historical record, through the usage of ] such as overwash deposits, ]s and historical documents such as diaries.<ref name="6000 WA">{{cite journal |author=Nott, Jonathan |date=March 1, 2011 |title=A 6000 year tropical cyclone record from Western Australia |url=https://www.sciencedirect.com/science/article/abs/pii/S0277379110004324 |url-status=live |journal=] |volume=30 |issue=5 |pages=713–722 |bibcode=2011QSRv...30..713N |doi=10.1016/j.quascirev.2010.12.004 |issn=0277-3791 |archive-url=https://web.archive.org/web/20201221144531/https://www.sciencedirect.com/science/article/abs/pii/S0277379110004324 |archive-date=December 21, 2020 |access-date=March 13, 2021}}</ref> Major tropical cyclones leave traces in ] and shell layers in some coastal areas, which have been used to gain insight into hurricane activity over the past thousands of years.<ref name=":8">{{Citation |last1=Muller |first1=Joanne |title=Recent Advances in the Emerging Field of Paleotempestology |work=Hurricanes and Climate Change: Volume 3 |pages=1–33 |year=2017 |editor-last=Collins |editor-first=Jennifer M. |access-date= |place=Cham |publisher=Springer International Publishing |language=en |doi=10.1007/978-3-319-47594-3_1 |isbn=978-3-319-47594-3 |s2cid=133456333 |last2=Collins |first2=Jennifer M. |last3=Gibson |first3=Samantha |last4=Paxton |first4=Leilani |editor2-last=Walsh |editor2-first=Kevin}}</ref> Sediment records in Western Australia suggest an intense tropical cyclone in the ].<ref name="6000 WA" />
If there are more than 21 named storms in an Atlantic season or 24 named storms in an Eastern Pacific season, the rest are named as letters from the ]: the twenty-second storm is called "Alpha," the twenty-third "Beta," and so on. This was first necessary during the ] when the list was exhausted. There is no precedent for a storm named with a Greek Letter causing enough damage to justify retirement; how this situation would be handled is unknown.


Proxy records based on ] research have revealed that major hurricane activity along the ] coast varies on timescales of centuries to millennia.<ref name="Liu1999">{{cite conference |last=Liu |first=Kam-biu |year=1999 |title=Millennial-scale variability in catastrophic hurricane landfalls along the Gulf of Mexico coast |conference=23rd Conference on Hurricanes and Tropical Meteorology |location=Dallas, TX |publisher=American Meteorological Society |pages=374–377}}</ref><ref name="LiuFearn2000">{{cite journal |last=Liu |first=Kam-biu |author2=Fearn, Miriam L. |year=2000 |title=Reconstruction of Prehistoric Landfall Frequencies of Catastrophic Hurricanes in Northwestern Florida from Lake Sediment Records |journal=Quaternary Research |volume=54 |issue=2 |pages=238–245 |bibcode=2000QuRes..54..238L |doi=10.1006/qres.2000.2166 |s2cid=140723229}}</ref> In the year 957, a powerful typhoon struck ], killing around 10,000&nbsp;people due to flooding.<ref>{{cite web |author=G. Huang |author2=W.W. S. Yim |date=January 2001 |title=Reconstruction of an 8,000-year record of typhoons in the Pearl River estuary, China |url=https://hub.hku.hk/bitstream/10722/188774/2/Content.pdf?accept=1 |url-status=live |archive-url=https://web.archive.org/web/20210720175126/https://hub.hku.hk/bitstream/10722/188774/2/Content.pdf?accept=1 |archive-date=July 20, 2021 |access-date=April 2, 2021 |website=University of Hong Kong}}</ref> The ] described "tempestades" in 1730,<ref name="calif">{{cite book |author=Arnold Court |url=http://babel.hathitrust.org/cgi/pt?id=uc1.31822009671892;seq=10;size=125;view=image |title=Tropical Cyclone Effects on California |publisher=California State University |year=1980 |series=NOAA technical memorandum NWS WR; 159 |location=Northridge, California |pages=2, 4, 6, 8, 34 |access-date=February 2, 2012 |archive-url=https://web.archive.org/web/20181001115852/https://babel.hathitrust.org/cgi/pt?id=uc1.31822009671892;seq=10;size=125;view=image |archive-date=October 1, 2018 |url-status=live}}</ref> although the official record for Pacific hurricanes only dates to 1949.{{hurdat}} In the south-west Indian Ocean, the tropical cyclone record goes back to 1848.<ref>{{cite report |url=https://library.wmo.int/doc_num.php?explnum_id=6291 |title=Operational procedures of TC satellite analysis at RSMC La Reunion |author=Philippe Caroff |date=June 2011 |publisher=World Meteorological Organization |access-date=April 22, 2013 |archive-url=https://web.archive.org/web/20210427174202/https://library.wmo.int/doc_num.php?explnum_id=6291 |archive-date=April 27, 2021 |url-status=live |display-authors=etal}}</ref> In 2003, the ] examined and analyzed the historical record of tropical cyclones in the Atlantic back to 1851, extending the existing database from 1886.<ref>{{cite web |author=Christopher W. Landsea |display-authors=etal |title=Documentation for 1851–1910 Alterations and Additions to the HURDAT Database |url=https://www.aoml.noaa.gov/hrd/hurdat/august01/rpibook-jan03.htm |url-status=live |archive-url=https://web.archive.org/web/20210615030803/https://www.aoml.noaa.gov/hrd/hurdat/august01/rpibook-jan03.htm |archive-date=June 15, 2021 |access-date=April 27, 2021 |series=The Atlantic Hurricane Database Re-analysis Project |publisher=Hurricane Research Division}}</ref>
In the Central North Pacific region, the name lists are maintained by the ] in ]. Four lists of ] names are selected and used in sequential order without regard to year.


Before satellite imagery became available during the 20th century, many of these systems went undetected unless it impacted land or a ship encountered it by chance.<ref name="Global Guide 2017" /> Often in part because of the threat of hurricanes, many coastal regions had sparse population between major ports until the advent of automobile tourism; therefore, the most severe portions of hurricanes striking the coast may have gone unmeasured in some instances. The combined effects of ship destruction and remote landfall severely limit the number of intense hurricanes in the official record before the era of hurricane reconnaissance aircraft and satellite meteorology. Although the record shows a distinct increase in the number and strength of intense hurricanes, therefore, experts regard the early data as suspect.<ref name="BOM TC Guide 1.3">{{cite web |author=Neumann, Charles J |title=1.3: A Global Climatology |url=http://www.cawcr.gov.au/publications/BMRC_archive/tcguide/ch1/ch1_3.htm |url-status=dead |archive-url=https://web.archive.org/web/20110601213525/http://www.cawcr.gov.au/publications/BMRC_archive/tcguide/ch1/ch1_3.htm |archive-date=June 1, 2011 |access-date=November 30, 2006 |work=Global Guide to Tropical Cyclone Forecasting |publisher=]}}</ref> The ability of climatologists to make a long-term analysis of tropical cyclones is limited by the amount of reliable historical data.<ref>{{cite journal |last1=Knutson |first1=Thomas |last2=Camargo |first2=Suzana |last3=Chan |first3=Johnny |last4=Emanuel |first4=Kerry |last5=Ho |first5=Chang-Hoi |last6=Kossin |first6=James |last7=Mohapatra |first7=Mrutyunjay |last8=Satoh |first8=Masaki |last9=Sugi |first9=Masato |last10=Walsh |first10=Kevin |last11=Wu |first11=Liguang |date=October 1, 2019 |title=TROPICAL CYCLONES AND CLIMATE CHANGE ASSESSMENT Part I: Detection and Attribution |url=https://journals.ametsoc.org/view/journals/bams/100/10/bams-d-18-0189.1.xml?tab_body=pdf |url-status=live |journal=American Meteorological Society |volume=100 |issue=10 |page=1988 |bibcode=2019BAMS..100.1987K |doi=10.1175/BAMS-D-18-0189.1 |s2cid=191139413 |archive-url=https://web.archive.org/web/20210813210000/https://journals.ametsoc.org/view/journals/bams/100/10/bams-d-18-0189.1.xml?tab_body=pdf |archive-date=August 13, 2021 |access-date=April 17, 2021 |hdl-access=free |hdl=1721.1/125577}}</ref>
In the Western North Pacific, name lists are maintained by the WMO Typhoon Committee. Five lists of names are used, with each of the 14 nations on the Typhoon Committee submitting two names to each list. Names are used in the order of the countries' English names, sequentially without regard to year. Since 1981, the numbering system had been the primary system to identify tropical cyclone among Typhoon Committee members and it is still in use. International numbers are assigned by ] on the order that a tropical storm forms while different internal numbers may be assigned by different NMCs. The Typhoon "Songda" in September 2004 was internally called the typhoon number 18 in Japan but typhoon number 19 in China. Internationally, it is recorded as the TY Sonda (0418) with "04" taken from the year.


In the 1940s, routine aircraft reconnaissance started in both the Atlantic and Western Pacific basin in the mid-1940s, which provided ground truth data. Early flights were only made once or twice a day.<ref name="Global Guide 2017" /> In 1960, Polar-orbiting weather satellites were first launched by the United States ], but were not declared operational until 1965.<ref name="Global Guide 2017" /> It took several years for some of the warning centers to take advantage of this new viewing platform and develop the expertise to associate satellite signatures with storm position and intensity.<ref name="Global Guide 2017" />
The Australian ] maintains three lists of names, one for each of the Western, Northern and Eastern Australian regions. There are also ] region and ] region names<!-- (''maintained by whom?'')-->.


Intense tropical cyclones pose a particular observation challenge, as they are a dangerous oceanic phenomenon, and ]s, being relatively sparse, are rarely available on the site of the storm itself. In general, surface observations are available only if the storm is passing over an island or a coastal area, or if there is a nearby ship. Real-time measurements are usually taken in the periphery of the cyclone, where conditions are less catastrophic and its true strength cannot be evaluated. For this reason, there are teams of meteorologists that move into the path of tropical cyclones to help evaluate their strength at the point of landfall.<ref name="FCMP">{{cite web|url=http://users.ce.ufl.edu/~fcmp/overview/overview.htm|author=Florida Coastal Monitoring Program|title=Project Overview|access-date=March 30, 2006|publisher=]|archive-url = https://web.archive.org/web/20060503084406/http://users.ce.ufl.edu/~fcmp/overview/overview.htm |archive-date = May 3, 2006|url-status=dead}}</ref>
The ] Meteorological Service maintains a list for the Southwest Indian Ocean. There, a new list is used each year.


Tropical cyclones are tracked by ]s capturing ] and ] images from space, usually at half-hour to quarter-hour intervals. As a storm approaches land, it can be observed by land-based ] ]. Radar plays a crucial role around landfall by showing a storm's location and intensity every several minutes.<ref name="CPHC">{{cite web|date=December 9, 2006|title=Observations|url=http://www.prh.noaa.gov/cphc/HAW/observations.php|url-status=dead|archive-url=https://web.archive.org/web/20120212231044/http://www.prh.noaa.gov/cphc/HAW/observations.php|archive-date=February 12, 2012|access-date=May 7, 2009|publisher=Central Pacific Hurricane Center}}</ref> Other satellites provide information from the perturbations of ] signals, providing thousands of snapshots per day and capturing atmospheric temperature, pressure, and moisture content.<ref>{{Cite web|date=June 1, 2020|title=NOAA harnessing the power of new satellite data this hurricane season|url=https://www.noaa.gov/media-release/noaa-harnessing-power-of-new-satellite-data-hurricane-season|access-date=March 25, 2021|website=National Oceanic and Atmospheric Administration|archive-date=March 18, 2021|archive-url=https://web.archive.org/web/20210318001639/https://www.noaa.gov/media-release/noaa-harnessing-power-of-new-satellite-data-hurricane-season|url-status=live}}</ref>
====Renaming of tropical cyclones====
In most cases, a tropical cyclone retains its name throughout its life. However, a tropical cyclone may be renamed in several occasions.


] measurements, in real-time, can be taken by sending specially equipped reconnaissance flights into the cyclone. In the Atlantic basin, these flights are regularly flown by United States government ].<ref name="Hurricane Hunters">{{cite web |title=Hurricane Hunters (homepage) |url=http://www.hurricanehunters.com |publisher=Hurricane Hunter Association |archive-url=https://web.archive.org/web/20120530232904/http://www.hurricanehunters.com/ |archive-date=May 30, 2012 |url-status=live |access-date=March 30, 2006}}</ref> These aircraft fly directly into the cyclone and take direct and remote-sensing measurements. The aircraft launch ]s inside the cyclone. These sondes measure temperature, humidity, pressure, and especially winds between flight level and the ocean's surface. A new era in hurricane observation began when a remotely piloted ], a small drone aircraft, was flown through ] as it passed ]'s eastern shore during the ]. A similar mission was also completed successfully in the western Pacific Ocean.<ref name="SunHerald">{{cite news|author=Lee, Christopher|title=Drone, Sensors May Open Path Into Eye of Storm|url=https://www.washingtonpost.com/wp-dyn/content/article/2007/10/07/AR2007100700971_pf.html|newspaper=The Washington Post|access-date=February 22, 2008|archive-url=https://web.archive.org/web/20121111093844/http://www.washingtonpost.com/wp-dyn/content/article/2007/10/07/AR2007100700971_pf.html|archive-date=November 11, 2012|url-status=live}}</ref>
#'''A tropical storm enters the southwestern Indian Ocean from the east'''
#:In the southwestern Indian Ocean, ] in ] names a tropical storm once it crosses 90&deg;E from the east, even though it has been named. In this case, the ] (JTWC) will put two names together with a hyphen. Examples include ] in early 2005 and ] in late 2005.
#'''A tropical storm crosses from the Atlantic into the Pacific, or vice versa, before 2001'''
#:It was the policy of ] (NHC) to rename a tropical storm which crossed from Atlantic into Pacific, or vice versa. Examples include ] in 1996 and ] in 1988.<ref name=NHCE15> accessed March 30, 2006</ref>
#:In 2001, when Iris moved across Central America, NHC mentioned that Iris would retain its name if it regenerated in the Pacific. However, the Pacific tropical depression developed from the remnants of Iris was called Fifteen-E instead. The depression later became tropical storm Manuel.
#:NHC explained that Iris had dissipated as a tropical cyclone prior to entering the eastern North Pacific basin; the new depression was properly named Fifteen-E, rather than Iris.<ref name=NHCManuel> accessed March 31, 2006</ref>
#:In 2003, when Larry was about to move across Mexico, NHC attempted to provide greater clarity:
#::"Should Larry remain a tropical cyclone during its passage over Mexico into the Pacific, it would retain its name. However, a new name would be given if the surface circulation dissipates and then regenerates in the Pacific."<ref name=NHCLarry> accessed March 31, 2006</ref>
#:Up to now, there has been no tropical cyclone retaining its name during the passage from Atlantic to Pacific, or vice versa.
#'''Uncertainties of the continuation'''
#:When the remnants of a tropical cyclone redevelop, the redeveloping system will be treated as a new tropical cyclone if there are uncertainties of the continuation, even though the original system may contribute to the forming of the new system. One example is ]-Tropical Depression 12 (which became ]) from 2005.
#'''Human errors'''
#:Sometimes, there may be human faults leading to the renaming of a tropical cyclone. This is especially true if the system is poorly organized or if it passes from the area of responsibility of one forecaster to another. Examples include ] in ]<ref name=JTWCKenLola> accessed March 30, 2006</ref> and ] in 2000<ref name=Padgett>Padgett, G. accessed March 30, 2000</ref>


===Forecasting===
====History of tropical cyclone naming====
{{See also|Tropical cyclone track forecasting|Tropical cyclone prediction model|Tropical cyclone rainfall forecasting}}
For several hundred years after Europeans arrived in the ], hurricanes there were named after the ] on which the storm struck.
]

The practice of giving storms people's names was introduced by ], an Anglo-Australian ] at the end of the 19th century. He used girls' names, the names of politicians who had offended him, and names from history and mythology.<ref name=NHCB1> accessed March 30, 2006</ref><ref name="BOM Question 13"> accessed March 31, 2006</ref>

During ], tropical cyclones were given feminine names, mainly for the convenience of the forecasters and in a somewhat ] manner. In addition, ]'s 1941 novel '']'' help to popularize the concept of giving names to tropical cyclones.<ref name=NHCJ4> accessed March 31, 2006</ref>

From ] to ], names from the ] were used. The modern naming convention came about in response to the need for unambiguous radio communications with ships and aircraft. As transportation traffic increased and meteorological observations improved in number and quality, several typhoons, hurricanes or cyclones might have to be tracked at any given time. To help in their identification, beginning in ] the practice of systematically naming tropical storms and hurricanes was initiated by the United States ]. Naming is now maintained by the ].

In keeping with the common ] practice of referring to named inanimate objects such as boats, trains, etc., using the female pronoun "she," names used were exclusively feminine. The first storm of the year was assigned a name beginning with the letter "A", the second with the letter "B", etc. However, since tropical storms and hurricanes are primarily destructive, some considered this practice ]. The ] responded to these concerns in ] with the introduction of masculine names to the nomenclature. It was also in 1979 that the practice of preparing a list of names before the season began. The names are usually of ], ] or ] origin in the Atlantic basin, since these are the three predominant languages of the region which the storms typically affect. In the southern hemisphere, male names were given to cyclones starting in 1975.<ref name="BOM Question 13"/>

==Notable cyclones==
{{hurricane main|List of notable tropical cyclones}}
Tropical cyclones that cause massive destruction are fortunately rare, but when they happen, they can cause damage in the range of billions of ] and disrupt or end thousands of lives.

The ] on record hit the densely populated ] region of ] (now ]) on ], ], likely as a ] tropical cyclone. It killed an estimated 500,000 people. The North Indian basin has historically been the deadliest, with several storms since 1900 killing over 100,000 people<!-- In addition to the 1970 and April 1991 storms, the Encarta reference claims a June 10 1991 storm did so, but the June storm may be in error as no other sources seem to support this. -->, each in Bangladesh.<ref name=Encarta1> accessed March 31, 2006</ref>


High-speed computers and sophisticated simulation software allow forecasters to produce ] that predict tropical cyclone tracks based on the future position and strength of high- and low-pressure systems. Combining forecast models with increased understanding of the forces that act on tropical cyclones, as well as with a wealth of data from Earth-orbiting ] and other sensors, scientists have increased the accuracy of track forecasts over recent decades.<ref name="NHC forecast verifications models">{{cite web|author=National Hurricane Center|url=http://www.nhc.noaa.gov/verification/verify6.shtml?#FIG1|work=National Hurricane Center Forecast Verification|title=Annual average model track errors for Atlantic basin tropical cyclones for the period 1994–2005, for a homogeneous selection of "early" models|access-date=November 30, 2006|publisher=]|date=May 22, 2006|author-link=National Hurricane Center|archive-url=https://web.archive.org/web/20120510225232/http://www.nhc.noaa.gov/verification/verify6.shtml#FIG1|archive-date=May 10, 2012|url-status=live}}</ref>
In the ], at least three storms have killed more than 10,000 people. ] during the ] caused severe flooding and mudslides in ], killing about 18,000 people and changing the landscape enough that entirely new maps of the country were needed.<ref name=NHCMitch> accessed March 31, 2006</ref> The ], which made landfall at ] as an estimated Category 4 storm, killed 8,000 to 12,000 people, and remains the deadliest natural disaster in the history of the ].<ref name=NHCPastDeadly>] accessed March 31, 2006</ref> The deadliest Atlantic storm on record was the ], which killed about 22,000 people in the ].<ref name=NHCPastDeadly/>


However, scientists are not as skillful at predicting the intensity of tropical cyclones.<ref name="NHC forecast verifications Atlantic">{{cite web|author=National Hurricane Center|work=National Hurricane Center Forecast Verification|url=http://www.nhc.noaa.gov/verification/verify5.shtml?|title=Annual average official track errors for Atlantic basin tropical cyclones for the period 1989–2005, with least-squares trend lines superimposed|access-date=November 30, 2006|publisher=]|date=May 22, 2006|author-link=National Hurricane Center|archive-url=https://web.archive.org/web/20120510225314/http://www.nhc.noaa.gov/verification/verify5.shtml|archive-date=May 10, 2012|url-status=live}}</ref> The lack of improvement in intensity forecasting is attributed to the complexity of tropical systems and an incomplete understanding of factors that affect their development. New tropical cyclone position and forecast information is available at least every six hours from the various warning centers.<ref name="WMO RSMC list">{{cite web|work=Tropical Cyclone Program (TCP)|publisher=]|title=Regional Specialized Meteorological Center|date=April 25, 2006|access-date=November 5, 2006|url=http://severe.worldweather.wmo.int/rsmcs.html|archive-url=https://web.archive.org/web/20100814135352/http://severe.worldweather.wmo.int/rsmcs.html|archive-date=August 14, 2010|url-status=live}}</ref><ref>{{cite web|url=http://www.met.gov.fj/services.php|title=Services|author=Fiji Meteorological Service|access-date=June 4, 2017|year=2017|archive-url=https://web.archive.org/web/20170618023828/http://www.met.gov.fj/services.php|archive-date=June 18, 2017|url-status=live}}</ref><ref>{{cite web|url=http://www.usno.navy.mil/JTWC/products-and-services-notice|title=Products and Service Notice|author=Joint Typhoon Warning Center|publisher=United States Navy|year=2017|access-date=June 4, 2017|archive-url=https://web.archive.org/web/20170609092158/http://www.usno.navy.mil/JTWC/products-and-services-notice|archive-date=June 9, 2017|url-status=live}}</ref><ref name="NHCprod">{{cite web|url=http://www.nhc.noaa.gov/pdf/NHC_Product_Description.pdf|title=National Hurricane Center Product Description Document: A User's Guide to Hurricane Products|author=National Hurricane Center|date=March 2016|access-date=June 3, 2017|publisher=National Oceanic and Atmospheric Administration|archive-url=https://web.archive.org/web/20170617023135/http://www.nhc.noaa.gov/pdf/NHC_Product_Description.pdf|archive-date=June 17, 2017|url-status=live}}</ref><ref>{{cite web|url=http://www.jma.go.jp/jma/jma-eng/jma-center/rsmc-hp-pub-eg/advisory.html|title=Notes on RSMC Tropical Cyclone Information|publisher=Japan Meteorological Agency|year=2017|access-date=June 4, 2017|archive-url=https://web.archive.org/web/20170319230044/http://www.jma.go.jp/jma/jma-eng/jma-center/rsmc-hp-pub-eg/advisory.html|archive-date=March 19, 2017|url-status=live}}</ref>
], ], and the United States.]]
The most intense storm on record was ] in the northwestern Pacific Ocean in ], which had a minimum pressure of only 870 ] and maximum sustained wind speeds of 190 mph (305 km/h). It weakened before striking ]. Tip does not hold the record for fastest sustained winds in a cyclone alone; ] in the Pacific, and ] and ] in the North Atlantic currently share this record as well,<ref name="Weatherwatchers Mitch">Weatherwatchers accessed March 30, 2006</ref> although recorded wind speeds that fast are suspect since most monitoring equipment is likely to be destroyed by such extreme conditions. Camille was the only storm to actually strike land while at that intensity, making it, with 190 mph (305 km/h) sustained winds and 210 mph (335 km/h) gusts, the strongest tropical cyclone on record at landfall. For comparison, these speeds are encountered at the center of a strong ], but Camille, like all tropical cyclones, was much larger and long-lived than any tornado.


===Geopotential height===
] in ] had recorded wind speeds of 215 mph (345 km/h), but recent research indicates that wind speeds from the 1940s to the 1960s were gauged too high, and this is no longer considered the fastest storm on record.<ref name=NHCE1> accessed March 30, 2006</ref> Similarly, a surface-level gust caused by ] on ] was recorded at 236 mph (380 km/h); had it been confirmed, this would be the strongest non-] wind ever recorded at the ]'s surface, but the reading had to be discarded since the ] was damaged by the storm.<ref name=NWSPaka>] accessed March 30, 2006</ref>
{{main|Geopotential height}}


In meteorology, geopotential heights are used when creating forecasts and analyzing pressure systems. Geopotential heights represent the estimate of the real height of a pressure system above the average sea level.<ref name="Geo Height">{{cite web |title=Geopotential Height |url=https://www.weather.gov/source/zhu/ZHU_Training_Page/Miscellaneous/Heights_Thicknesses/thickness_temperature.htm |publisher=National Weather Service |access-date=October 7, 2022 |archive-date=March 24, 2022 |archive-url=https://web.archive.org/web/20220324054919/https://www.weather.gov/source/zhu/ZHU_Training_Page/Miscellaneous/Heights_Thicknesses/thickness_temperature.htm |url-status=live}}</ref> Geopotential heights for weather are divided up into several levels. The lowest geopotential height level is {{convert|850|hPa|inHg|sigfig=4|abbr=on}}, which represents the lowest {{convert|5000|ft|m|abbr=on|disp=flip}} of the atmosphere. The moisture content, gained by using either the relative humidity or the precipitable water value, is used in creating forecasts for precipitation.<ref>{{cite web |title=Constant Pressure Charts: 850 mb |url=https://www.weather.gov/jetstream/850mb |publisher=National Weather Service |access-date=October 7, 2022 |archive-date=May 4, 2022 |archive-url=https://web.archive.org/web/20220504135947/https://www.weather.gov/jetstream/850mb |url-status=live}}</ref>
Tip was also the largest cyclone on record, with a circulation of tropical storm-force winds 1,350 miles (2,170 km) wide. The average tropical cyclone is only 300 miles (480 km) wide. The smallest storm on record, ]'s ], which devastated ], ], was roughly 60 miles (100 km) wide.<ref name=NHCE5> accessed March 30, 2006</ref>


The next level, {{convert|700|hPa|inHg|sigfig=4|abbr=on}}, is at a height of {{convert|7700–10500|ft|m|abbr=on|disp=flip}}. 700 hPa is regarded as the highest point in the lower atmosphere. At this layer, both vertical movement and moisture levels are used to locate and create forecasts for precipitation.<ref>{{cite web |title=Constant Pressure Charts: 700 mb |url=https://www.weather.gov/jetstream/300mb |publisher=National Weather Service |access-date=October 7, 2022 |archive-date=June 29, 2022 |archive-url=https://web.archive.org/web/20220629223346/https://www.weather.gov/jetstream/300mb |url-status=live}}</ref> The middle level of the atmosphere is at {{convert|500|hPa|inHg|sigfig=4|abbr=on}} or a height of {{convert|16000–20000|ft|m|abbr=on|disp=flip}}. The 500 hPa level is used for measuring atmospheric vorticity, commonly known as the spin of air. The relative humidity is also analyzed at this height to establish where precipitation is likely to materialize.<ref>{{cite web |title=Constant Pressure Charts: 500 mb |url=https://www.weather.gov/jetstream/500mb |publisher=National Weather Service |access-date=October 7, 2022 |archive-date=May 21, 2022 |archive-url=https://web.archive.org/web/20220521143701/https://www.weather.gov/jetstream/500mb |url-status=live}}</ref> The next level occurs at {{convert|300|hPa|inHg|sigfig=4|abbr=on}} or a height of {{convert|27000–32000|ft|m|abbr=on|disp=flip}}.<ref>{{cite web |title=Constant Pressure Charts: 300 mb |url=https://www.weather.gov/jetstream/300mb |publisher=National Weather Service |access-date=October 7, 2022 |archive-date=October 7, 2022 |archive-url=https://web.archive.org/web/20221007215843/https://www.weather.gov/jetstream/300mb |url-status=live}}</ref> The top-most level is located at {{convert|200|hPa|inHg|sigfig=4|abbr=on}}, which corresponds to a height of {{convert|35000–41000|ft|m|abbr=on|disp=flip}}. Both the 200 and 300 hPa levels are mainly used to locate the jet stream.<ref>{{cite web |title=Constant Pressure Charts: 200 mb |url=https://www.weather.gov/jetstream/200mb |publisher=National Weather Service |access-date=October 7, 2022 |archive-date=August 5, 2022 |archive-url=https://web.archive.org/web/20220805062247/https://www.weather.gov/jetstream/200mb |url-status=live}}</ref>
] in ] was the most powerful storm to strike ] in recorded history, hitting ] as a Category 4 hurricane, killing six and causing $3 billion in damage.<ref name=CPHCIniki> accessed March 31, 2006</ref> Other destructive Pacific hurricanes include ]<ref name=NHCPauline> accessed March 31, 2006</ref> and ].<ref name=NHCKenna> accessed March 31, 2006</ref>


== Society and culture ==
] from 2004.]]
On ], ], ] became the first recorded ]. Previous South Atlantic cyclones in ] and ] reached only tropical storm strength. Tropical cyclones may have formed there before ] but were not observed until ]s began monitoring the Earth's oceans in that year.


=== Preparations ===
A tropical cyclone need not be particularly strong to cause memorable damage; ], in November ] killed thousands in the Philippines even though it never became a typhoon; the damage from Thelma was mostly due to flooding, not winds or ].<ref name=JTWCThelma> accessed March 31, 2006</ref> In 1982, the unnamed tropical depression that eventually became ] caused the deaths of around 1,000 people in Central America due to the effects of its rainfall.<ref name=MWRPaul>] "Eastern North Pacific Tropical Cyclones of 1982" accessed March 31, 2006</ref>
{{main|Tropical cyclone preparedness|Tropical cyclone engineering}}
] shows lines from long standing floodwaters after ].]]


Ahead of the formal season starting, people are urged to ] by politicians and weather forecasters, among others. They prepare by determining their risk to the different types of weather, tropical cyclones cause, checking their insurance coverage and emergency supplies, as well as determining where to evacuate to if needed.<ref name="ReadyGov Preparedness">{{cite web |date=February 18, 2021 |title=Hurricane Seasonal Preparedness Digital Toolkit |url=https://www.ready.gov/ru/node/5121 |url-status=live |archive-url=https://web.archive.org/web/20210321121554/https://www.ready.gov/ru/node/5121 |archive-date=March 21, 2021 |access-date=April 6, 2021 |publisher=Ready.gov}}</ref><ref name="Gray et al. 2019">{{cite conference |last1=Gray |first1=Briony |last2=Weal |first2=Mark |last3=Martin |first3=David |year=2019 |title=Proceedings of the 52nd Hawaii International Conference on System Sciences |conference=52nd Hawaii International Conference on System Sciences |publisher=University of Hawaii |doi=10.24251/HICSS.2019.338 |isbn=978-0-9981331-2-6 |doi-access=free |hdl-access=free |chapter=The Role of Social Networking in Small Island Communities: Lessons from the 2017 Atlantic Hurricane Season |hdl=10125/59718}}</ref><ref name="Morrissey and Reser 2003">{{cite journal |last1=Morrissey |first1=Shirley A. |last2=Reser |first2=Joseph P. |date=May 1, 2003 |title=Evaluating the Effectiveness of Psychological Preparedness Advice in Community Cyclone Preparedness Materials |url=https://search.informit.org/doi/10.3316/informit.281780145360789 |url-status=live |journal=The Australian Journal of Emergency Management |volume=18 |issue=2 |pages=46–61 |archive-url=https://web.archive.org/web/20220523221113/https://search.informit.org/doi/10.3316/informit.281780145360789 |archive-date=May 23, 2022 |access-date=April 6, 2021}}</ref> When a tropical cyclone develops and is forecast to impact land, each member nation of the ] issues various ] to cover the expected effects.<ref name="WMO TC">{{cite web |date=April 8, 2020 |title=Tropical Cyclones |url=https://public-old.wmo.int/en/our-mandate/focus-areas/natural-hazards-and-disaster-risk-reduction/tropical-cyclones |url-status=dead |archive-url=https://web.archive.org/web/20231218180931/https://public-old.wmo.int/en/our-mandate/focus-areas/natural-hazards-and-disaster-risk-reduction/tropical-cyclones |archive-date=December 18, 2023 |access-date=April 6, 2021 |publisher=World Meteorological Organization}}</ref> However, there are some exceptions with the United States National Hurricane Center and Fiji Meteorological Service responsible for issuing or recommending warnings for other nations in their area of responsibility.<ref name="AboutFMS">{{cite web |title=Fiji Meteorological Services |url=http://www.moit.gov.fj/about-us/27-departments/fiji-meteorological-services |url-status=live |archive-url=https://web.archive.org/web/20210814123025/http://www.moit.gov.fj/about-us/27-departments/fiji-meteorological-services |archive-date=August 14, 2021 |access-date=April 6, 2021 |website=Ministry of Infrastructure & Meteorological Services |publisher=Ministry of Infrastructure & Transport}}</ref><ref name="About NHC">{{cite web |title=About the National Hurricane Center |url=https://www.nhc.noaa.gov/aboutintro.shtml |url-status=live |archive-url=https://web.archive.org/web/20201012163706/https://www.nhc.noaa.gov/aboutintro.shtml |archive-date=October 12, 2020 |access-date=April 6, 2021 |publisher=National Hurricane Center |location=Miami, Florida}}</ref><ref name="RAIV2017">{{cite book |url=https://library.wmo.int/doc_num.php?explnum_id=3781 |title=Regional Association IV – Hurricane Operational Plan for NOrth America, Central America and the Caribbean |date=2017 |publisher=World Meteorological Organization |isbn=9789263111630 |access-date=April 6, 2021 |archive-url=https://web.archive.org/web/20201114181542/https://library.wmo.int/doc_num.php?explnum_id=3781 |archive-date=November 14, 2020 |url-status=live}}</ref>{{rp|2–4}}
On ] ], ] made landfall in ] and ]. The U.S. National Hurricane Center, in its August review of the tropical storm season stated that Katrina was probably the worst natural disaster in U.S. history.<ref name="NHC Atlantic Monthly Report for August 2005"> accessed March 31, 2006</ref> Currently, its death toll is at least 1,604, mainly from flooding and the aftermath in ], ]. It is also estimated to have caused $75 billion in damages. Before Katrina, the costliest system in monetary terms had been ]'s ], which caused an estimated $39 billion (2005 ]) in damage in ].<ref name=NHCKatrina> accessed March 31, 2006</ref>


An important decision in individual preparedness is determining if and when to evacuate an area that will be affected by a tropical cyclone.<ref>{{Cite web |title=National Hurricane Center – "Be Prepared" |url=http://www.nhc.noaa.gov/HAW2/english/disaster_prevention.shtml |access-date=November 9, 2023}}</ref> ]s allow people to track ongoing systems to form their own opinions regarding where the storms are going and whether or not they need to prepare for the system being tracked, including possible evacuation. This continues to be encouraged by the ] and National Hurricane Center.<ref name="FTH">{{cite web |author=National Ocean Service |author-link=National Ocean Service |date=September 7, 2016 |title=Follow That Hurricane! |url=http://oceanservice.noaa.gov/education/for_fun/FollowthatHurricane.pdf |access-date=June 2, 2017 |publisher=]}}</ref>
==Other storm systems==
{{seealso|Cyclone}}
Many other forms of cyclone can form in nature. Several of these relate to the formation or dissipation of tropical cyclones.


===Extratropical cyclone=== === Response ===
{{hurricane main|Extratropical cyclone}} {{Main|Tropical cyclone response}}
{{Expand section|date=October 2022}}
An ''extratropical cyclone'' is a storm that derives energy from horizontal temperature differences, which are typical in higher latitudes. A tropical cyclone can become extratropical as it moves toward higher latitudes if its energy source changes from heat released by condensation to differences in temperature between air masses;<ref name=NHCA7> accessed March 31, 2006</ref> Infrequently, an extratropical cyclone can transform into a subtropical storm, and from there into a tropical cyclone. From space, extratropical storms have a characteristic "]-shaped" cloud pattern. Extratropical cyclones can also be dangerous because their low-pressure centers cause powerful winds.
] in ]|alt=View of tropical cyclone damage from a helicopter]]
Hurricane response is the ] after a hurricane. Activities performed by hurricane responders include assessment, restoration, and demolition of buildings; removal of ] and waste; repairs to land-based and maritime ]; and public health services including ] operations.<ref>{{Cite web |year=2005 |title=OSHA's Hazard Exposure and Risk Assessment Matrix for Hurricane Response and Recovery Work: List of Activity Sheets |url=https://www.osha.gov/SLTC/etools/hurricane/sheets.html |url-status=live |archive-url=https://web.archive.org/web/20180929041351/https://www.osha.gov/SLTC/etools/hurricane/sheets.html |archive-date=September 29, 2018 |access-date=September 25, 2018 |website=U.S. ] |language=en-US}}</ref> Hurricane response requires coordination between federal, tribal, state, local, and private entities.<ref>{{Cite web |title=Before You Begin – The Incident Command System (ICS) |url=https://www.aiha.org/publications-and-resources/HealthandSafetyIssuesinNaturalDisasters/Pages/Before-You-Begin.aspx |url-status=dead |archive-url=https://web.archive.org/web/20180929041449/https://www.aiha.org/publications-and-resources/HealthandSafetyIssuesinNaturalDisasters/Pages/Before-You-Begin.aspx |archive-date=September 29, 2018 |access-date=September 26, 2018 |website=American Industrial Hygiene Association |language=en-us}}</ref> According to the ], potential response volunteers should affiliate with established organizations and should not self-deploy, so that proper training and support can be provided to mitigate the danger and stress of response work.<ref>{{Cite web |title=Volunteer |url=https://www.nvoad.org/howtohelp/volunteer-3/ |url-status=live |archive-url=https://web.archive.org/web/20180929041523/https://www.nvoad.org/howtohelp/volunteer-3/ |archive-date=September 29, 2018 |access-date=September 25, 2018 |website=] |language=en-US}}</ref>


Hurricane responders face many hazards. Hurricane responders may be exposed to chemical and biological contaminants including stored chemicals, ], ], and ] growth encouraged by flooding,<ref name=":0">{{Cite journal |year=2017 |title=Hurricane Key Messages for Employers, Workers and Volunteers |url=https://www.hsdl.org/?abstract&did=815992 |url-status=live |archive-url=https://web.archive.org/web/20181124162356/https://www.hsdl.org/?abstract&did=815992 |archive-date=November 24, 2018 |access-date=September 24, 2018 |website=U.S. ]}}</ref><ref name=":2">{{Cite web |title=Hazardous Materials and Conditions |url=https://www.aiha.org/publications-and-resources/HealthandSafetyIssuesinNaturalDisasters/Pages/Hazardous-Materials.aspx |url-status=dead |archive-url=https://web.archive.org/web/20180929080011/https://www.aiha.org/publications-and-resources/HealthandSafetyIssuesinNaturalDisasters/Pages/Hazardous-Materials.aspx |archive-date=September 29, 2018 |access-date=September 26, 2018 |website=American Industrial Hygiene Association |language=en-us}}</ref><ref>{{Cite web |title=Mold and Other Microbial Growth |url=https://www.aiha.org/publications-and-resources/HealthandSafetyIssuesinNaturalDisasters/Pages/Mold-and-Other-Microbial-Growth.aspx |url-status=dead |archive-url=https://web.archive.org/web/20180929041433/https://www.aiha.org/publications-and-resources/HealthandSafetyIssuesinNaturalDisasters/Pages/Mold-and-Other-Microbial-Growth.aspx |archive-date=September 29, 2018 |access-date=September 26, 2018 |website=American Industrial Hygiene Association |language=en-us}}</ref> as well as ] and ] that may be present in older buildings.<ref name=":2" /><ref name=":1">{{Cite web |year=2005 |title=OSHA's Hazard Exposure and Risk Assessment Matrix for Hurricane Response and Recovery Work: Recommendations for General Hazards Commonly Encountered during Hurricane Response and Recovery Operations |url=https://www.osha.gov/SLTC/etools/hurricane/recommendations.html#encounter |url-status=live |archive-url=https://web.archive.org/web/20180929041128/https://www.osha.gov/SLTC/etools/hurricane/recommendations.html#encounter |archive-date=September 29, 2018 |access-date=September 25, 2018 |website=U.S. Occupational Safety and Health Administration |language=en-US}}</ref> Common injuries arise from ] from heights, such as from a ladder or from level surfaces; from ] in flooded areas, including from ] from ]s; or from ].<ref name=":0" /><ref name=":1" /><ref>{{Cite web |title=Electrical Hazards |url=https://www.aiha.org/publications-and-resources/HealthandSafetyIssuesinNaturalDisasters/Pages/Electrical-Hazards-Floods.aspx |url-status=dead |archive-url=https://web.archive.org/web/20180929041458/https://www.aiha.org/publications-and-resources/HealthandSafetyIssuesinNaturalDisasters/Pages/Electrical-Hazards-Floods.aspx |archive-date=September 29, 2018 |access-date=September 26, 2018 |website=American Industrial Hygiene Association |language=en-us}}</ref> ] may lead to ] and ], increasing the risk of injuries, and workers may experience ]. ] is a concern as workers are often exposed to hot and humid temperatures, wear protective clothing and equipment, and have physically difficult tasks.<ref name=":0" /><ref name=":1" />
===Subtropical storm===
{{hurricane main|Subtropical cyclone}}
A subtropical cyclone is a ] system that has some characteristics of a tropical cyclone and some characteristics of an extratropical cyclone. They can form in a wide band of ], from the ] to 50&deg;. Although subtropical storms rarely attain hurricane-force winds, they may become tropical in nature as their core warms.<ref name=NHCA6> accessed March 31, 2006</ref> From an operational standpoint, a tropical cyclone is usually not considered to become subtropical during its extratropical transition.<ref name=PadgetDecember2000>Padgett, G. accessed March 31, 2006</ref>


==See also== ==See also==
{{Portal|Tropical cyclones}}
===Current Seasons===
* {{annotated link|Cyclone}}
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===Meteorology=== ==References==
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==Notes==
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==External links== ==External links==
{{wiktionary}} {{Wiktionary}}
{{Commons category|Tropical cyclones}}
{{commons2}}
{{Wikisource|The Hurricane}}
{{Wikivoyage|Cyclones}}


* &nbsp;– North Atlantic, Eastern Pacific
===Learning resources===
* &nbsp;– Central Pacific
*
* &nbsp;– Western Pacific
*
* &nbsp;– Indian Ocean
* Interactive fun site from NOAA, allows to specify conditions and see how they impact storm formation
* &nbsp;– South Indian Ocean from 30°E to 90°E
* - Data, research, science & multimedia resources from NASA
* &nbsp;– South Indian Ocean from 90°E to 125°E, north of 10°S
*
* &nbsp;– South Indian Ocean and South Pacific Ocean from 90°E to 160°E
*
* &nbsp;– South Pacific east of 160°E, north of 10°S
* - Information on tropical cyclones, as well as information on hurricane naming, and all Atlantic storms 1950-2005
* &nbsp;– South Pacific west of 160°E, north of 25° S
*
* &nbsp;– South Pacific west of 160°E, south of 25°S
*, by Dr. Robert Hart


{{Cyclones}}
===Tracking and warning===
{{Seasons}}
* - Shows all current tropical systems worldwide and their tracks
{{Nature}}
* - Western Pacific
{{Authority control}}
* - Tasman Sea, South Pacific south of 25&deg S
* - Southern hemisphere from 90&deg; E to 160&deg; E
* - Northwest Atlantic (overlaps US NHC)

=== Regional specialised meteorological centers ===
* - North Atlantic, Eastern Pacific
* - Central Pacific
* - NW Pacific
* - ] and the ]
* - South Indian Ocean from Africa to 90&deg; E
* - South Pacific east of 160&deg;, north of 25&deg; S

=== Past storms ===
* - About 10 years of origins and tracks, in color, up to present. Broken up by year and region; for example "Atlantic, 2005"
* - Information on all past storms to 1950, along with images and individual storm summaries.
* e.g.
*.
* - Over 20 years of tropical cyclone histories with an emphasis on storm total rainfall, in color, up to present. Broken up by year, region, and by point of landfall
* and
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* Preserving the Stories and Digital Record of Hurricanes Katrina, Rita, and Wilma

=== Miscellaneous ===
* Big collection of hurricane webcams.
*- Lates news from the WN network.
* - Chapter from the online edition of ]'s ''American Practical Navigator''
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* - Review based on latest articles in ''Science'' and ''Nature''. Graph of trends in 6 hurricane basins.
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* Hurricane and Tropical Storms
* Great research site for kids.
* Preserving the Stories and Digital Record of Hurricanes Katrina, Rita, and Wilma


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Latest revision as of 18:50, 31 December 2024

Type of rapidly rotating storm system Several terms of bands and albums redirect here. For other uses, see Tropical Depression (band), The Mountain Goats discography#Split EPs, and Tropical Storm (album). For technical reasons, "Hurricane #1" redirects here. For the band, see Hurricane No. 1. "Hurricane" redirects here. For other uses, see Hurricane (disambiguation).

View of a tropical cyclone from space
Hurricane Florence in 2018 as viewed from International Space Station: The eye, eyewall, and surrounding rainbands are characteristics of tropical cyclones.
Part of a series on
Tropical cyclones
Structure
Effects
Climatology and tracking
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Tropical cyclones portal

A tropical cyclone is a rapidly rotating storm system with a low-pressure area, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain and squalls. Depending on its location and strength, a tropical cyclone is called a hurricane (/ˈhʌrɪkən, -keɪn/), typhoon (/taɪˈfuːn/), tropical storm, cyclonic storm, tropical depression, or simply cyclone. A hurricane is a strong tropical cyclone that occurs in the Atlantic Ocean or northeastern Pacific Ocean. A typhoon occurs in the northwestern Pacific Ocean. In the Indian Ocean and South Pacific, comparable storms are referred to as "tropical cyclones". In modern times, on average around 80 to 90 named tropical cyclones form each year around the world, over half of which develop hurricane-force winds of 65 kn (120 km/h; 75 mph) or more.

Tropical cyclones typically form over large bodies of relatively warm water. They derive their energy through the evaporation of water from the ocean surface, which ultimately condenses into clouds and rain when moist air rises and cools to saturation. This energy source differs from that of mid-latitude cyclonic storms, such as nor'easters and European windstorms, which are powered primarily by horizontal temperature contrasts. Tropical cyclones are typically between 100 and 2,000 km (62 and 1,243 mi) in diameter. The strong rotating winds of a tropical cyclone are a result of the conservation of angular momentum imparted by the Earth's rotation as air flows inwards toward the axis of rotation. As a result, cyclones rarely form within 5° of the equator. Tropical cyclones are very rare in the South Atlantic (although occasional examples do occur) due to consistently strong wind shear and a weak Intertropical Convergence Zone. In contrast, the African easterly jet and areas of atmospheric instability give rise to cyclones in the Atlantic Ocean and Caribbean Sea.

Heat energy from the ocean acts as the accelerator for tropical cyclones. This causes inland regions to suffer far less damage from cyclones than coastal regions, although the impacts of flooding are felt across the board. Coastal damage may be caused by strong winds and rain, high waves (due to winds), storm surges (due to wind and severe pressure changes), and the potential of spawning tornadoes. Climate change affects tropical cyclones in several ways. Scientists found that climate change can exacerbate the impact of tropical cyclones by increasing their duration, occurrence, and intensity due to the warming of ocean waters and intensification of the water cycle. Tropical cyclones draw in air from a large area and concentrate the water content of that air into precipitation over a much smaller area. This replenishing of moisture-bearing air after rain may cause multi-hour or multi-day extremely heavy rain up to 40 km (25 mi) from the coastline, far beyond the amount of water that the local atmosphere holds at any one time. This in turn can lead to river flooding, overland flooding, and a general overwhelming of local water control structures across a large area.

Definition and terminology

A tropical cyclone is the generic term for a warm-cored, non-frontal synoptic-scale low-pressure system over tropical or subtropical waters around the world. The systems generally have a well-defined center which is surrounded by deep atmospheric convection and a closed wind circulation at the surface. A tropical cyclone is generally deemed to have formed once mean surface winds in excess of 35 kn (65 km/h; 40 mph) are observed. It is assumed at this stage that a tropical cyclone has become self-sustaining and can continue to intensify without any help from its environment.

Depending on its location and strength, a tropical cyclone is referred to by different names, including hurricane, typhoon, tropical storm, cyclonic storm, tropical depression, or simply cyclone. A hurricane is a strong tropical cyclone that occurs in the Atlantic Ocean or northeastern Pacific Ocean, and a typhoon occurs in the northwestern Pacific Ocean. In the Indian Ocean and South Pacific, comparable storms are referred to as "tropical cyclones", and such storms in the Indian Ocean can also be called "severe cyclonic storms".

Tropical refers to the geographical origin of these systems, which form almost exclusively over tropical seas. Cyclone refers to their winds moving in a circle, whirling round their central clear eye, with their surface winds blowing counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. The opposite direction of circulation is due to the Coriolis effect.

Formation

Main article: Tropical cyclogenesis
A schematic diagram of a tropical cyclone
A diagram of a tropical cyclone in the Northern Hemisphere

Tropical cyclones tend to develop during the summer, but have been noted in nearly every month in most tropical cyclone basins. Tropical cyclones on either side of the Equator generally have their origins in the Intertropical Convergence Zone, where winds blow from either the northeast or southeast. Within this broad area of low-pressure, air is heated over the warm tropical ocean and rises in discrete parcels, which causes thundery showers to form. These showers dissipate quite quickly; however, they can group together into large clusters of thunderstorms. This creates a flow of warm, moist, rapidly rising air, which starts to rotate cyclonically as it interacts with the rotation of the earth.

Several factors are required for these thunderstorms to develop further, including sea surface temperatures of around 27 °C (81 °F) and low vertical wind shear surrounding the system, atmospheric instability, high humidity in the lower to middle levels of the troposphere, enough Coriolis force to develop a low-pressure center, and a pre-existing low-level focus or disturbance. There is a limit on tropical cyclone intensity which is strongly related to the water temperatures along its path. and upper-level divergence. An average of 86 tropical cyclones of tropical storm intensity form annually worldwide. Of those, 47 reach strength higher than 119 km/h (74 mph), and 20 become intense tropical cyclones, of at least Category 3 intensity on the Saffir–Simpson scale.

Climate oscillations such as El Niño–Southern Oscillation (ENSO) and the Madden–Julian oscillation modulate the timing and frequency of tropical cyclone development. Rossby waves can aid in the formation of a new tropical cyclone by disseminating the energy of an existing, mature storm. Kelvin waves can contribute to tropical cyclone formation by regulating the development of the westerlies. Cyclone formation is usually reduced 3 days prior to the wave's crest and increased during the 3 days after.

Formation regions and warning centers

Main articles: Tropical cyclone basins and Regional Specialized Meteorological Centre
Tropical cyclone basins and official warning centers
Basin Warning center Area of responsibility Notes
Northern Hemisphere
North Atlantic United States National Hurricane Center (Miami) Equator northward, African Coast – 140°W
Eastern Pacific United States Central Pacific Hurricane Center (Honolulu) Equator northward, 140–180°W
Western Pacific Japan Meteorological Agency Equator – 60°N, 180–100°E
North Indian Ocean India Meteorological Department Equator northwards, 100–40°E
Southern Hemisphere
South-West
Indian Ocean
Météo-France Reunion Equator – 40°S, African Coast – 90°E
Australian region Indonesian Meteorology, Climatology,
and Geophysical Agency
(BMKG)
Equator – 10°S, 90–141°E
Papua New Guinea National Weather Service Equator – 10°S, 141–160°E
Australian Bureau of Meteorology 10–40°S, 90–160°E
Southern Pacific Fiji Meteorological Service Equator – 25°S, 160°E – 120°W
Meteorological Service of New Zealand 25–40°S, 160°E – 120°W

The majority of tropical cyclones each year form in one of seven tropical cyclone basins, which are monitored by a variety of meteorological services and warning centers. Ten of these warning centers worldwide are designated as either a Regional Specialized Meteorological Centre or a Tropical Cyclone Warning Centre by the World Meteorological Organization's (WMO) tropical cyclone programme. These warning centers issue advisories which provide basic information and cover a systems present, forecast position, movement and intensity, in their designated areas of responsibility.

Meteorological services around the world are generally responsible for issuing warnings for their own country. There are exceptions, as the United States National Hurricane Center and Fiji Meteorological Service issue alerts, watches and warnings for various island nations in their areas of responsibility. The United States Joint Typhoon Warning Center and Fleet Weather Center also publicly issue warnings about tropical cyclones on behalf of the United States Government. The Brazilian Navy Hydrographic Center names South Atlantic tropical cyclones, however the South Atlantic is not a major basin, and not an official basin according to the WMO.

Interactions with climate

Main article: Tropical cyclones by year

Each year on average, around 80 to 90 named tropical cyclones form around the world, of which over half develop hurricane-force winds of 65 kn (120 km/h; 75 mph) or more. Worldwide, tropical cyclone activity peaks in late summer, when the difference between temperatures aloft and sea surface temperatures is the greatest. However, each particular basin has its own seasonal patterns. On a worldwide scale, May is the least active month, while September is the most active month. November is the only month in which all the tropical cyclone basins are in season.

In the Northern Atlantic Ocean, a distinct cyclone season occurs from June 1 to November 30, sharply peaking from late August through September. The statistical peak of the Atlantic hurricane season is September 10.

The Northeast Pacific Ocean has a broader period of activity, but in a similar time frame to the Atlantic. The Northwest Pacific sees tropical cyclones year-round, with a minimum in February and March and a peak in early September. In the North Indian basin, storms are most common from April to December, with peaks in May and November. In the Southern Hemisphere, the tropical cyclone year begins on July 1 and runs all year-round encompassing the tropical cyclone seasons, which run from November 1 until the end of April, with peaks in mid-February to early March.

Of various modes of variability in the climate system, El Niño–Southern Oscillation has the largest effect on tropical cyclone activity. Most tropical cyclones form on the side of the subtropical ridge closer to the equator, then move poleward past the ridge axis before recurving into the main belt of the Westerlies. When the subtropical ridge position shifts due to El Niño, so will the preferred tropical cyclone tracks. Areas west of Japan and Korea tend to experience much fewer September–November tropical cyclone impacts during El Niño and neutral years.

During La Niña years, the formation of tropical cyclones, along with the subtropical ridge position, shifts westward across the western Pacific Ocean, which increases the landfall threat to China and much greater intensity in the Philippines. The Atlantic Ocean experiences depressed activity due to increased vertical wind shear across the region during El Niño years. Tropical cyclones are further influenced by the Atlantic Meridional Mode, the Quasi-biennial oscillation and the Madden–Julian oscillation.

Season lengths and averages
Basin Season
start
Season
end
Tropical
cyclones
Refs
North Atlantic June 1 November 30 14.4
Eastern Pacific May 15 November 30 16.6
Western Pacific January 1 December 31 26.0
North Indian January 1 December 31 12
South-West Indian July 1 June 30 9.3
Australian region November 1 April 30 11.0
Southern Pacific November 1 April 30 7.1
Total: 96.4

Influence of climate change

Main article: Tropical cyclones and climate change
The 20-year average of the number of annual Category 4 and 5 hurricanes in the Atlantic region has approximately doubled since the year 2000.
Climate change's increase of water temperatures intensified peak wind speeds in all eleven 2024 Atlantic hurricanes.
Perceptions in the United States differ along political lines, on whether climate change was a "major factor" contributing to various extreme weather events experienced by respondents in 2023. "Severe storms" includes hurricanes.

The IPCC Sixth Assessment Report summarize the latest scientific findings about the impact of climate change on tropical cyclones. According to the report, we have now better understanding about the impact of climate change on tropical storm than before. Major tropical storms likely became more frequent in the last 40 years. We can say with high confidence that climate change increase rainfall during tropical cyclones. We can say with high confidence that a 1.5 degree warming lead to "increased proportion of and peak wind speeds of intense tropical cyclones". We can say with medium confidence that regional impacts of further warming include more intense tropical cyclones and/or extratropical storms.

Climate change can affect tropical cyclones in a variety of ways: an intensification of rainfall and wind speed, a decrease in overall frequency, an increase in the frequency of very intense storms and a poleward extension of where the cyclones reach maximum intensity are among the possible consequences of human-induced climate change. Tropical cyclones use warm, moist air as their fuel. As climate change is warming ocean temperatures, there is potentially more of this fuel available.

Between 1979 and 2017, there was a global increase in the proportion of tropical cyclones of Category 3 and higher on the Saffir–Simpson scale. The trend was most clear in the North Atlantic and in the Southern Indian Ocean. In the North Pacific, tropical cyclones have been moving poleward into colder waters and there was no increase in intensity over this period. With 2 °C (3.6 °F) warming, a greater percentage (+13%) of tropical cyclones are expected to reach Category 4 and 5 strength. A 2019 study indicates that climate change has been driving the observed trend of rapid intensification of tropical cyclones in the Atlantic basin. Rapidly intensifying cyclones are hard to forecast and therefore pose additional risk to coastal communities.

Warmer air can hold more water vapor: the theoretical maximum water vapor content is given by the Clausius–Clapeyron relation, which yields ≈7% increase in water vapor in the atmosphere per 1 °C (1.8 °F) warming. All models that were assessed in a 2019 review paper show a future increase of rainfall rates. Additional sea level rise will increase storm surge levels. It is plausible that extreme wind waves see an increase as a consequence of changes in tropical cyclones, further exacerbating storm surge dangers to coastal communities. The compounding effects from floods, storm surge, and terrestrial flooding (rivers) are projected to increase due to global warming.

There is currently no consensus on how climate change will affect the overall frequency of tropical cyclones. A majority of climate models show a decreased frequency in future projections. For instance, a 2020 paper comparing nine high-resolution climate models found robust decreases in frequency in the Southern Indian Ocean and the Southern Hemisphere more generally, while finding mixed signals for Northern Hemisphere tropical cyclones. Observations have shown little change in the overall frequency of tropical cyclones worldwide, with increased frequency in the North Atlantic and central Pacific, and significant decreases in the southern Indian Ocean and western North Pacific.

There has been a poleward expansion of the latitude at which the maximum intensity of tropical cyclones occurs, which may be associated with climate change. In the North Pacific, there may also have been an eastward expansion. Between 1949 and 2016, there was a slowdown in tropical cyclone translation speeds. It is unclear still to what extent this can be attributed to climate change: climate models do not all show this feature.

A 2021 study review article concluded that the geographic range of tropical cyclones will probably expand poleward in response to climate warming of the Hadley circulation.

When hurricane winds speed rise by 5%, its destructive power rise by about 50%. Therefore, as climate change increased the wind speed of Hurricane Helene by 11%, it increased the destruction from it by more than twice. According to World Weather Attribution the influence of climate change on the rainfall of some latest hurricanes can be described as follows:

Impact of climate change on the rainfall during some recent hurricanes according to World Weather Attribution.
The name of the hurricane How much climate change increased rainfall
Hurricane Katrina 4%
Hurricane Irma 6%
Hurricane Maria 9%
Hurricane Florence 5%
Hurricane Dorian 5-18%
Hurricane Ian 18%
Hurricane Harvey 7-38%
Hurricane Helene 10%

Intensity

Tropical cyclone intensity is based on wind speeds and pressure. Relationships between winds and pressure are often used in determining the intensity of a storm. Tropical cyclone scales, such as the Saffir-Simpson hurricane wind scale and Australia's scale (Bureau of Meteorology), only use wind speed for determining the category of a storm. The most intense storm on record is Typhoon Tip in the northwestern Pacific Ocean in 1979, which reached a minimum pressure of 870 hPa (26 inHg) and maximum sustained wind speeds of 165 kn (85 m/s; 305 km/h; 190 mph). The highest maximum sustained wind speed ever recorded was 185 kn (95 m/s; 345 km/h; 215 mph) in Hurricane Patricia in 2015—the most intense cyclone ever recorded in the Western Hemisphere.

Factors that influence intensity

Warm sea surface temperatures are required for tropical cyclones to form and strengthen. The commonly-accepted minimum temperature range for this to occur is 26–27 °C (79–81 °F), however, multiple studies have proposed a lower minimum of 25.5 °C (77.9 °F). Higher sea surface temperatures result in faster intensification rates and sometimes even rapid intensification. High ocean heat content, also known as Tropical Cyclone Heat Potential, allows storms to achieve a higher intensity. Most tropical cyclones that experience rapid intensification are traversing regions of high ocean heat content rather than lower values. High ocean heat content values can help to offset the oceanic cooling caused by the passage of a tropical cyclone, limiting the effect this cooling has on the storm. Faster-moving systems are able to intensify to higher intensities with lower ocean heat content values. Slower-moving systems require higher values of ocean heat content to achieve the same intensity.

The passage of a tropical cyclone over the ocean causes the upper layers of the ocean to cool substantially, a process known as upwelling, which can negatively influence subsequent cyclone development. This cooling is primarily caused by wind-driven mixing of cold water from deeper in the ocean with the warm surface waters. This effect results in a negative feedback process that can inhibit further development or lead to weakening. Additional cooling may come in the form of cold water from falling raindrops (this is because the atmosphere is cooler at higher altitudes). Cloud cover may also play a role in cooling the ocean, by shielding the ocean surface from direct sunlight before and slightly after the storm passage. All these effects can combine to produce a dramatic drop in sea surface temperature over a large area in just a few days. Conversely, the mixing of the sea can result in heat being inserted in deeper waters, with potential effects on global climate.

Vertical wind shear decreases tropical cyclone predicability, with storms exhibiting wide range of responses in the presence of shear. Wind shear often negatively affects tropical cyclone intensification by displacing moisture and heat from a system's center. Low levels of vertical wind shear are most optimal for strengthening, while stronger wind shear induces weakening. Dry air entraining into a tropical cyclone's core has a negative effect on its development and intensity by diminishing atmospheric convection and introducing asymmetries in the storm's structure. Symmetric, strong outflow leads to a faster rate of intensification than observed in other systems by mitigating local wind shear. Weakening outflow is associated with the weakening of rainbands within a tropical cyclone. Tropical cyclones may still intensify, even rapidly, in the presence of moderate or strong wind shear depending on the evolution and structure of the storm's convection.

The size of tropical cyclones plays a role in how quickly they intensify. Smaller tropical cyclones are more prone to rapid intensification than larger ones. The Fujiwhara effect, which involves interaction between two tropical cyclones, can weaken and ultimately result in the dissipation of the weaker of two tropical cyclones by reducing the organization of the system's convection and imparting horizontal wind shear. Tropical cyclones typically weaken while situated over a landmass because conditions are often unfavorable as a result of the lack of oceanic forcing. The Brown ocean effect can allow a tropical cyclone to maintain or increase its intensity following landfall, in cases where there has been copious rainfall, through the release of latent heat from the saturated soil. Orographic lift can cause a significant increase in the intensity of the convection of a tropical cyclone when its eye moves over a mountain, breaking the capped boundary layer that had been restraining it. Jet streams can both enhance and inhibit tropical cyclone intensity by influencing the storm's outflow as well as vertical wind shear.

Rapid intensification

Main article: Rapid intensification

On occasion, tropical cyclones may undergo a process known as rapid intensification, a period in which the maximum sustained winds of a tropical cyclone increase by 30 kn (56 km/h; 35 mph) or more within 24 hours. Similarly, rapid deepening in tropical cyclones is defined as a minimum sea surface pressure decrease of 1.75 hPa (0.052 inHg) per hour or 42 hPa (1.2 inHg) within a 24-hour period; explosive deepening occurs when the surface pressure decreases by 2.5 hPa (0.074 inHg) per hour for at least 12 hours or 5 hPa (0.15 inHg) per hour for at least 6 hours.

For rapid intensification to occur, several conditions must be in place. Water temperatures must be extremely high, near or above 30 °C (86 °F), and water of this temperature must be sufficiently deep such that waves do not upwell cooler waters to the surface. On the other hand, Tropical Cyclone Heat Potential is one of such non-conventional subsurface oceanographic parameters influencing the cyclone intensity.

Wind shear must be low. When wind shear is high, the convection and circulation in the cyclone will be disrupted. Usually, an anticyclone in the upper layers of the troposphere above the storm must be present as well—for extremely low surface pressures to develop, air must be rising very rapidly in the eyewall of the storm, and an upper-level anticyclone helps channel this air away from the cyclone efficiently. However, some cyclones such as Hurricane Epsilon have rapidly intensified despite relatively unfavorable conditions.

Dissipation

Satellite image of a cyclone where the thickest clouds are displaced from the central vortex
Hurricane Paulette, in 2020, is an example of a sheared tropical cyclone, with deep convection slightly removed from the center of the system.

There are a number of ways a tropical cyclone can weaken, dissipate, or lose its tropical characteristics. These include making landfall, moving over cooler water, encountering dry air, or interacting with other weather systems; however, once a system has dissipated or lost its tropical characteristics, its remnants could regenerate a tropical cyclone if environmental conditions become favorable.

A tropical cyclone can dissipate when it moves over waters significantly cooler than 26.5 °C (79.7 °F). This will deprive the storm of such tropical characteristics as a warm core with thunderstorms near the center, so that it becomes a remnant low-pressure area. Remnant systems may persist for several days before losing their identity. This dissipation mechanism is most common in the eastern North Pacific. Weakening or dissipation can also occur if a storm experiences vertical wind shear which causes the convection and heat engine to move away from the center. This normally ceases the development of a tropical cyclone. In addition, its interaction with the main belt of the Westerlies, by means of merging with a nearby frontal zone, can cause tropical cyclones to evolve into extratropical cyclones. This transition can take 1–3 days.

Should a tropical cyclone make landfall or pass over an island, its circulation could start to break down, especially if it encounters mountainous terrain. When a system makes landfall on a large landmass, it is cut off from its supply of warm moist maritime air and starts to draw in dry continental air. This, combined with the increased friction over land areas, leads to the weakening and dissipation of the tropical cyclone. Over a mountainous terrain, a system can quickly weaken. Over flat areas, it may endure for two to three days before circulation breaks down and dissipates.

Over the years, there have been a number of techniques considered to try to artificially modify tropical cyclones. These techniques have included using nuclear weapons, cooling the ocean with icebergs, blowing the storm away from land with giant fans, and seeding selected storms with dry ice or silver iodide. These techniques, however, fail to appreciate the duration, intensity, power or size of tropical cyclones.

Methods for assessing intensity

For broader coverage of this topic, see Dvorak technique and Scatterometer.

A variety of methods or techniques, including surface, satellite, and aerial, are used to assess the intensity of a tropical cyclone. Reconnaissance aircraft fly around and through tropical cyclones, outfitted with specialized instruments, to collect information that can be used to ascertain the winds and pressure of a system. Tropical cyclones possess winds of different speeds at different heights. Winds recorded at flight level can be converted to find the wind speeds at the surface. Surface observations, such as ship reports, land stations, mesonets, coastal stations, and buoys, can provide information on a tropical cyclone's intensity or the direction it is traveling.

Wind-pressure relationships (WPRs) are used as a way to determine the pressure of a storm based on its wind speed. Several different methods and equations have been proposed to calculate WPRs. Tropical cyclones agencies each use their own, fixed WPR, which can result in inaccuracies between agencies that are issuing estimates on the same system. The ASCAT is a scatterometer used by the MetOp satellites to map the wind field vectors of tropical cyclones. The SMAP uses an L-band radiometer channel to determine the wind speeds of tropical cyclones at the ocean surface, and has been shown to be reliable at higher intensities and under heavy rainfall conditions, unlike scatterometer-based and other radiometer-based instruments.

The Dvorak technique plays a large role in both the classification of a tropical cyclone and the determination of its intensity. Used in warning centers, the method was developed by Vernon Dvorak in the 1970s, and uses both visible and infrared satellite imagery in the assessment of tropical cyclone intensity. The Dvorak technique uses a scale of "T-numbers", scaling in increments of 0.5 from T1.0 to T8.0. Each T-number has an intensity assigned to it, with larger T-numbers indicating a stronger system. Tropical cyclones are assessed by forecasters according to an array of patterns, including curved banding features, shear, central dense overcast, and eye, to determine the T-number and thus assess the intensity of the storm.

The Cooperative Institute for Meteorological Satellite Studies works to develop and improve automated satellite methods, such as the Advanced Dvorak Technique (ADT) and SATCON. The ADT, used by a large number of forecasting centers, uses infrared geostationary satellite imagery and an algorithm based upon the Dvorak technique to assess the intensity of tropical cyclones. The ADT has a number of differences from the conventional Dvorak technique, including changes to intensity constraint rules and the usage of microwave imagery to base a system's intensity upon its internal structure, which prevents the intensity from leveling off before an eye emerges in infrared imagery. The SATCON weights estimates from various satellite-based systems and microwave sounders, accounting for the strengths and flaws in each individual estimate, to produce a consensus estimate of a tropical cyclone's intensity which can be more reliable than the Dvorak technique at times.

Intensity metrics

Multiple intensity metrics are used, including accumulated cyclone energy (ACE), the Hurricane Surge Index, the Hurricane Severity Index, the Power Dissipation Index (PDI), and integrated kinetic energy (IKE). ACE is a metric of the total energy a system has exerted over its lifespan. ACE is calculated by summing the squares of a cyclone's sustained wind speed, every six hours as long as the system is at or above tropical storm intensity and either tropical or subtropical. The calculation of the PDI is similar in nature to ACE, with the major difference being that wind speeds are cubed rather than squared.

The Hurricane Surge Index is a metric of the potential damage a storm may inflict via storm surge. It is calculated by squaring the dividend of the storm's wind speed and a climatological value (33 m/s or 74 mph), and then multiplying that quantity by the dividend of the radius of hurricane-force winds and its climatological value (96.6 km or 60.0 mi). This can be represented in equation form as:

( v 33   m / s ) 2 × ( r 96.6   k m ) {\displaystyle \left({\frac {v}{33\ \mathrm {m/s} }}\right)^{2}\times \left({\frac {r}{96.6\ \mathrm {km} }}\right)\,}

where v {\textstyle v} is the storm's wind speed and r {\textstyle r} is the radius of hurricane-force winds. The Hurricane Severity Index is a scale that can assign up to 50 points to a system; up to 25 points come from intensity, while the other 25 come from the size of the storm's wind field. The IKE model measures the destructive capability of a tropical cyclone via winds, waves, and surge. It is calculated as:

V o l 1 2 p u 2 d v {\displaystyle \int _{Vol}{\frac {1}{2}}pu^{2}d_{v}\,}

where p {\textstyle p} is the density of air, u {\textstyle u} is a sustained surface wind speed value, and d v {\textstyle d_{v}} is the volume element.

Classification and naming

Classification

Main article: Tropical cyclone scales
Satellite image of three simultaneous tropical cyclones
Three tropical cyclones of the 2006 Pacific typhoon season at different stages of development. The weakest (left) demonstrates only the most basic circular shape. A stronger storm (top right) demonstrates spiral banding and increased centralization, while the strongest (lower right) has developed an eye.

Around the world, tropical cyclones are classified in different ways, based on the location (tropical cyclone basins), the structure of the system and its intensity. For example, within the Northern Atlantic and Eastern Pacific basins, a tropical cyclone with wind speeds of over 65 kn (120 km/h; 75 mph) is called a hurricane, while it is called a typhoon or a severe cyclonic storm within the Western Pacific or North Indian oceans. When a hurricane passes west across the International Dateline in the Northern Hemisphere, it becomes known as a typhoon. This happened in 2014 for Hurricane Genevieve, which became Typhoon Genevieve.

Within the Southern Hemisphere, it is either called a hurricane, tropical cyclone or a severe tropical cyclone, depending on if it is located within the South Atlantic, South-West Indian Ocean, Australian region or the South Pacific Ocean. The descriptors for tropical cyclones with wind speeds below 65 kn (120 km/h; 75 mph) vary by tropical cyclone basin and may be further subdivided into categories such as "tropical storm", "cyclonic storm", "tropical depression", or "deep depression".

Naming

Main articles: Tropical cyclone naming and History of tropical cyclone naming

The practice of using given names to identify tropical cyclones dates back to the late 1800s and early 1900s and gradually superseded the existing system—simply naming cyclones based on what they hit. The system currently used provides positive identification of severe weather systems in a brief form, that is readily understood and recognized by the public. The credit for the first usage of personal names for weather systems is generally given to the Queensland Government Meteorologist Clement Wragge who named systems between 1887 and 1907. This system of naming weather systems fell into disuse for several years after Wragge retired, until it was revived in the latter part of World War II for the Western Pacific. Formal naming schemes have subsequently been introduced for the North and South Atlantic, Eastern, Central, Western and Southern Pacific basins as well as the Australian region and Indian Ocean.

At present, tropical cyclones are officially named by one of twelve meteorological services and retain their names throughout their lifetimes to provide ease of communication between forecasters and the general public regarding forecasts, watches, and warnings. Since the systems can last a week or longer, and more than one can be occurring in the same basin at the same time, the names are thought to reduce the confusion about what storm is being described. Names are assigned in order from predetermined lists with one, three, or ten-minute sustained wind speeds of more than 65 km/h (40 mph) depending on which basin it originates.

Standards vary from basin to basin. Some tropical depressions are named in the Western Pacific. Tropical cyclones have to have a significant amount of gale-force winds occurring around the center before they are named within the Southern Hemisphere. The names of significant tropical cyclones in the North Atlantic Ocean, Pacific Ocean, and Australian region are retired from the naming lists and replaced with another name. Tropical cyclones that develop around the world are assigned an identification code consisting of a two-digit number and suffix letter by the warning centers that monitor them.

Related cyclone types

See also: Cyclone, Extratropical cyclone, and Subtropical cyclone

In addition to tropical cyclones, there are two other classes of cyclones within the spectrum of cyclone types. These kinds of cyclones, known as extratropical cyclones and subtropical cyclones, can be stages a tropical cyclone passes through during its formation or dissipation. An extratropical cyclone is a storm that derives energy from horizontal temperature differences, which are typical in higher latitudes. A tropical cyclone can become extratropical as it moves toward higher latitudes if its energy source changes from heat released by condensation to differences in temperature between air masses. Although not as frequently, an extratropical cyclone can transform into a subtropical storm, and from there into a tropical cyclone. From space, extratropical storms have a characteristic "comma-shaped" cloud pattern. Extratropical cyclones can also be dangerous when their low-pressure centers cause powerful winds and high seas.

A subtropical cyclone is a weather system that has some characteristics of a tropical cyclone and some characteristics of an extratropical cyclone. They can form in a wide band of latitudes, from the equator to 50°. Although subtropical storms rarely have hurricane-force winds, they may become tropical in nature as their cores warm.

Structure

Eye and center

Main article: Eye (cyclone)
The eye and surrounding clouds of 2018 Hurricane Florence as seen from the International Space Station

At the center of a mature tropical cyclone, air sinks rather than rises. For a sufficiently strong storm, air may sink over a layer deep enough to suppress cloud formation, thereby creating a clear "eye". Weather in the eye is normally calm and free of convective clouds, although the sea may be extremely violent. The eye is normally circular and is typically 30–65 km (19–40 mi) in diameter, though eyes as small as 3 km (1.9 mi) and as large as 370 km (230 mi) have been observed.

The cloudy outer edge of the eye is called the "eyewall". The eyewall typically expands outward with height, resembling an arena football stadium; this phenomenon is sometimes referred to as the "stadium effect". The eyewall is where the greatest wind speeds are found, air rises most rapidly, clouds reach their highest altitude, and precipitation is the heaviest. The heaviest wind damage occurs where a tropical cyclone's eyewall passes over land.

In a weaker storm, the eye may be obscured by the central dense overcast, which is the upper-level cirrus shield that is associated with a concentrated area of strong thunderstorm activity near the center of a tropical cyclone.

The eyewall may vary over time in the form of eyewall replacement cycles, particularly in intense tropical cyclones. Outer rainbands can organize into an outer ring of thunderstorms that slowly moves inward, which is believed to rob the primary eyewall of moisture and angular momentum. When the primary eyewall weakens, the tropical cyclone weakens temporarily. The outer eyewall eventually replaces the primary one at the end of the cycle, at which time the storm may return to its original intensity.

Size

Size descriptions of tropical cyclones
ROCI (Diameter) Type
Less than 2 degrees latitude Very small/minor
2 to 3 degrees of latitude Small
3 to 6 degrees of latitude Medium/average/normal
6 to 8 degrees of latitude Large
Over 8 degrees of latitude Very large
Though large hurricane size does not imply strength—which is based on sustained wind measurements—it can mean that more people are exposed to its hazards.

There are a variety of metrics commonly used to measure storm size. The most common metrics include the radius of maximum wind, the radius of 34-knot (17 m/s; 63 km/h; 39 mph) wind (i.e. gale force), the radius of outermost closed isobar (ROCI), and the radius of vanishing wind. An additional metric is the radius at which the cyclone's relative vorticity field decreases to 1×10 s.

On Earth, tropical cyclones span a large range of sizes, from 100–2,000 km (62–1,243 mi) as measured by the radius of vanishing wind. They are largest on average in the northwest Pacific Ocean basin and smallest in the northeastern Pacific Ocean basin. If the radius of outermost closed isobar is less than two degrees of latitude (222 km (138 mi)), then the cyclone is "very small" or a "midget". A radius of 3–6 latitude degrees (333–670 km (207–416 mi)) is considered "average sized". "Very large" tropical cyclones have a radius of greater than 8 degrees (888 km (552 mi)). Observations indicate that size is only weakly correlated to variables such as storm intensity (i.e. maximum wind speed), radius of maximum wind, latitude, and maximum potential intensity. Typhoon Tip is the largest cyclone on record, with tropical storm-force winds 2,170 km (1,350 mi) in diameter. The smallest storm on record is Tropical Storm Marco of 2008, which generated tropical storm-force winds only 37 km (23 mi) in diameter.

Movement

The movement of a tropical cyclone (i.e. its "track") is typically approximated as the sum of two terms: "steering" by the background environmental wind and "beta drift". Some tropical cyclones can move across large distances, such as Hurricane John, the second longest-lasting tropical cyclone on record, which traveled 13,280 km (8,250 mi), the longest track of any Northern Hemisphere tropical cyclone, over its 31-day lifespan in 1994.

Environmental steering

Environmental steering is the primary influence on the motion of tropical cyclones. It represents the movement of the storm due to prevailing winds and other wider environmental conditions, similar to "leaves carried along by a stream".

Physically, the winds, or flow field, in the vicinity of a tropical cyclone may be treated as having two parts: the flow associated with the storm itself, and the large-scale background flow of the environment. Tropical cyclones can be treated as local maxima of vorticity suspended within the large-scale background flow of the environment. In this way, tropical cyclone motion may be represented to first-order as advection of the storm by the local environmental flow. This environmental flow is termed the "steering flow" and is the dominant influence on tropical cyclone motion. The strength and direction of the steering flow can be approximated as a vertical integration of the winds blowing horizontally in the cyclone's vicinity, weighted by the altitude at which those winds are occurring. Because winds can vary with height, determining the steering flow precisely can be difficult.

The pressure altitude at which the background winds are most correlated with a tropical cyclone's motion is known as the "steering level". The motion of stronger tropical cyclones is more correlated with the background flow averaged across a thicker portion of troposphere compared to weaker tropical cyclones whose motion is more correlated with the background flow averaged across a narrower extent of the lower troposphere. When wind shear and latent heat release is present, tropical cyclones tend to move towards regions where potential vorticity is increasing most quickly.

Climatologically, tropical cyclones are steered primarily westward by the east-to-west trade winds on the equatorial side of the subtropical ridge—a persistent high-pressure area over the world's subtropical oceans. In the tropical North Atlantic and Northeast Pacific oceans, the trade winds steer tropical easterly waves westward from the African coast toward the Caribbean Sea, North America, and ultimately into the central Pacific Ocean before the waves dampen out. These waves are the precursors to many tropical cyclones within this region. In contrast, in the Indian Ocean and Western Pacific in both hemispheres, tropical cyclogenesis is influenced less by tropical easterly waves and more by the seasonal movement of the Intertropical Convergence Zone and the monsoon trough. Other weather systems such as mid-latitude troughs and broad monsoon gyres can also influence tropical cyclone motion by modifying the steering flow.

Beta drift

In addition to environmental steering, a tropical cyclone will tend to drift poleward and westward, a motion known as "beta drift". This motion is due to the superposition of a vortex, such as a tropical cyclone, onto an environment in which the Coriolis force varies with latitude, such as on a sphere or beta plane. The magnitude of the component of tropical cyclone motion associated with the beta drift ranges between 1–3 m/s (3.6–10.8 km/h; 2.2–6.7 mph) and tends to be larger for more intense tropical cyclones and at higher latitudes. It is induced indirectly by the storm itself as a result of feedback between the cyclonic flow of the storm and its environment.

Physically, the cyclonic circulation of the storm advects environmental air poleward east of center and equatorial west of center. Because air must conserve its angular momentum, this flow configuration induces a cyclonic gyre equatorward and westward of the storm center and an anticyclonic gyre poleward and eastward of the storm center. The combined flow of these gyres acts to advect the storm slowly poleward and westward. This effect occurs even if there is zero environmental flow. Due to a direct dependence of the beta drift on angular momentum, the size of a tropical cyclone can affect the influence of beta drift on its motion; beta drift imparts a greater influence on the movement of larger tropical cyclones than that of smaller ones.

Multiple storm interaction

Main article: Fujiwhara effect

A third component of motion that occurs relatively infrequently involves the interaction of multiple tropical cyclones. When two cyclones approach one another, their centers will begin orbiting cyclonically about a point between the two systems. Depending on their separation distance and strength, the two vortices may simply orbit around one another, or else may spiral into the center point and merge. When the two vortices are of unequal size, the larger vortex will tend to dominate the interaction, and the smaller vortex will orbit around it. This phenomenon is called the Fujiwhara effect, after Sakuhei Fujiwhara.

Interaction with the mid-latitude westerlies

See also: Westerlies
Path of a tropical cyclone
Storm track of Typhoon Ioke, showing recurvature off the Japanese coast in 2006

Though a tropical cyclone typically moves from east to west in the tropics, its track may shift poleward and eastward either as it moves west of the subtropical ridge axis or else if it interacts with the mid-latitude flow, such as the jet stream or an extratropical cyclone. This motion, termed "recurvature", commonly occurs near the western edge of the major ocean basins, where the jet stream typically has a poleward component and extratropical cyclones are common. An example of tropical cyclone recurvature was Typhoon Ioke in 2006.

Effects

Main articles: Effects of tropical cyclones and Tropical cyclone effects by region

Natural phenomena caused or worsened by tropical cyclones

Tropical cyclones out at sea cause large waves, heavy rain, floods and high winds, disrupting international shipping and, at times, causing shipwrecks. Tropical cyclones stir up water, leaving a cool wake behind them, which causes the region to be less favorable for subsequent tropical cyclones. On land, strong winds can damage or destroy vehicles, buildings, bridges, and other outside objects, turning loose debris into deadly flying projectiles. The storm surge, or the increase in sea level due to the cyclone, is typically the worst effect from landfalling tropical cyclones, historically resulting in 90% of tropical cyclone deaths. Cyclone Mahina produced the highest storm surge on record, 13 m (43 ft), at Bathurst Bay, Queensland, Australia, in March 1899.

Other ocean-based hazards that tropical cyclones produce are rip currents and undertow. These hazards can occur hundreds of kilometers (hundreds of miles) away from the center of a cyclone, even if other weather conditions are favorable. The broad rotation of a landfalling tropical cyclone, and vertical wind shear at its periphery, spawns tornadoes. Tornadoes can also be spawned as a result of eyewall mesovortices, which persist until landfall. Hurricane Ivan produced 120 tornadoes, more than any other tropical cyclone. Lightning activity is produced within tropical cyclones. This activity is more intense within stronger storms and closer to and within the storm's eyewall. Tropical cyclones can increase the amount of snowfall a region experiences by delivering additional moisture. Wildfires can be worsened when a nearby storm fans their flames with its strong winds.

Effect on property and human life

total collapse of houses, cars and facilities
Aftermath of Hurricane Ike in Bolivar Peninsula, Texas
The number of $1 billion Atlantic hurricanes almost doubled from the 1980s to the 2010s, and inflation-adjusted costs have increased more than elevenfold. The increases have been attributed to climate change and to greater numbers of people moving to coastal areas.

Tropical cyclones regularly affect the coastlines of most of Earth's major bodies of water along the Atlantic, Pacific, and Indian oceans. Tropical cyclones have caused significant destruction and loss of human life, resulting in about 2 million deaths since the 19th century. Large areas of standing water caused by flooding lead to infection, as well as contributing to mosquito-borne illnesses. Crowded evacuees in shelters increase the risk of disease propagation. Tropical cyclones significantly interrupt infrastructure, leading to power outages, bridge and road destruction, and the hampering of reconstruction efforts.

Winds and water from storms can damage or destroy homes, buildings, and other manmade structures. Tropical cyclones destroy agriculture, kill livestock, and prevent access to marketplaces for both buyers and sellers; both of these result in financial losses. Powerful cyclones that make landfall – moving from the ocean to over land – are some of the most powerful, although that is not always the case. An average of 86 tropical cyclones of tropical storm intensity form annually worldwide, with 47 reaching hurricane or typhoon strength, and 20 becoming intense tropical cyclones, super typhoons, or major hurricanes (at least of Category 3 intensity).

Africa

In Africa, tropical cyclones can originate from tropical waves generated over the Sahara Desert, or otherwise strike the Horn of Africa and Southern Africa. Cyclone Idai in March 2019 hit central Mozambique, becoming the deadliest tropical cyclone on record in Africa, with 1,302 fatalities, and damage estimated at US$2.2 billion. Réunion island, located east of Southern Africa, experiences some of the wettest tropical cyclones on record. In January 1980, Cyclone Hyacinthe produced 6,083 mm (239.5 in) of rain over 15 days, which was the largest rain total recorded from a tropical cyclone on record.

Asia

In Asia, tropical cyclones from the Indian and Pacific oceans regularly affect some of the most populated countries on Earth. In 1970, a cyclone struck Bangladesh, then known as East Pakistan, producing a 6.1 m (20 ft) storm surge that killed at least 300,000 people. This made it the deadliest tropical cyclone on record. In October 2019, Typhoon Hagibis struck the Japanese island of Honshu and inflicted US$15 billion in damage, making it the costliest storm on record in Japan. The islands that comprise Oceania, from Australia to French Polynesia, are routinely affected by tropical cyclones. In Indonesia, a cyclone struck the island of Flores in April 1973, killing 1,653 people, making it the deadliest tropical cyclone recorded in the Southern Hemisphere.

North and South America

Atlantic and Pacific hurricanes regularly affect North America. In the United States, hurricanes Katrina in 2005 and Harvey in 2017 are the country's costliest ever natural disasters, with monetary damage estimated at US$125 billion. Katrina struck Louisiana and largely destroyed the city of New Orleans, while Harvey caused significant flooding in southeastern Texas after it dropped 60.58 in (1,539 mm) of rainfall; this was the highest rainfall total on record in the country.

The Caribbean islands are regularly hit by hurricanes, which have caused multiple humanitarian crises in Haiti since 2004 due in part to the lack of infrastructure and high population density in urban areas. In 2004, hurricane Jeanne caused severe flooding and mudslides, and a total estimated 3,006 deaths. More recently, in 2016, hurricane Matthew caused US$2.8 billion in damages, killing an estimated 674 people.

The northern portion of South America experiences occasional tropical cyclones, with 173 fatalities from Tropical Storm Bret in August 1993. The South Atlantic Ocean is generally inhospitable to the formation of a tropical storm. However, in March 2004, Hurricane Catarina struck southeastern Brazil as the first hurricane on record in the South Atlantic Ocean.

Europe

Europe is rarely affected by tropical cyclones; however, the continent regularly encounters storms after they transitioned into extratropical cyclones. Only one tropical depression – Vince in 2005 – struck Spain, and only one subtropical cycloneSubtropical Storm Alpha in 2020 – struck Portugal. Occasionally, there are tropical-like cyclones in the Mediterranean Sea.

Environmental effects

Although cyclones take an enormous toll in lives and personal property, they may be important factors in the precipitation regimes of places they affect, as they may bring much-needed precipitation to otherwise dry regions. Their precipitation may also alleviate drought conditions by restoring soil moisture, though one study focused on the Southeastern United States suggested tropical cyclones did not offer significant drought recovery. Tropical cyclones also help maintain the global heat balance by moving warm, moist tropical air to the middle latitudes and polar regions, and by regulating the thermohaline circulation through upwelling. Research on Pacific cyclones has demonstrated that deeper layers of the ocean receive a heat transfer from these powerful storms.

The storm surge and winds of hurricanes may be destructive to human-made structures, but they also stir up the waters of coastal estuaries, which are typically important fish breeding locales. Ecosystems, such as saltmarshes and Mangrove forests, can be severely damaged or destroyed by tropical cyclones, which erode land and destroy vegetation. Tropical cyclones can cause harmful algae blooms to form in bodies of water by increasing the amount of nutrients available. Insect populations can decrease in both quantity and diversity after the passage of storms. Strong winds associated with tropical cyclones and their remnants are capable of felling thousands of trees, causing damage to forests.

When hurricanes surge upon shore from the ocean, salt is introduced to many freshwater areas and raises the salinity levels too high for some habitats to withstand. Some are able to cope with the salt and recycle it back into the ocean, but others can not release the extra surface water quickly enough or do not have a large enough freshwater source to replace it. Because of this, some species of plants and vegetation die due to the excess salt. Hurricanes can carry toxins and acids onshore when they make landfall. The floodwater can pick up the toxins from different spills and contaminate the land that it passes over. These toxins are harmful to the people and animals in the area, as well as the environment around them. Tropical cyclones can cause oil spills by damaging or destroying pipelines and storage facilities. Similarly, chemical spills have been reported when chemical and processing facilities were damaged. Waterways have become contaminated with toxic levels of metals such as nickel, chromium, and mercury during tropical cyclones.

Tropical cyclones can have an extensive effect on geography, such as creating or destroying land. Cyclone Bebe increased the size of Tuvalu island, Funafuti Atoll, by nearly 20%. Hurricane Walaka destroyed the small East Island in 2018, which destroyed the habitat for the endangered Hawaiian monk seal, as well as, threatened sea turtles and seabirds. Landslides frequently occur during tropical cyclones and can vastly alter landscapes. Some storms are capable of causing hundreds to tens of thousands of landslides. Storms can erode coastlines over an extensive area and transport the sediment to other locations.

Observation and forecasting

Observation

Main article: Tropical cyclone observation
Aerial view of storm clouds
A sunset view of Hurricane Isidore's rainbands photographed at 2,100 m (7,000 ft)
Head-on view of an airplane
"Hurricane Hunter" – WP-3D Orion is used to go into the eye of a hurricane for data collection and measurements purposes.

Tropical cyclones have occurred around the world for millennia. Reanalyses and research are being undertaken to extend the historical record, through the usage of proxy data such as overwash deposits, beach ridges and historical documents such as diaries. Major tropical cyclones leave traces in overwash records and shell layers in some coastal areas, which have been used to gain insight into hurricane activity over the past thousands of years. Sediment records in Western Australia suggest an intense tropical cyclone in the 4th millennium BC.

Proxy records based on paleotempestological research have revealed that major hurricane activity along the Gulf of Mexico coast varies on timescales of centuries to millennia. In the year 957, a powerful typhoon struck southern China, killing around 10,000 people due to flooding. The Spanish colonization of Mexico described "tempestades" in 1730, although the official record for Pacific hurricanes only dates to 1949. In the south-west Indian Ocean, the tropical cyclone record goes back to 1848. In 2003, the Atlantic hurricane reanalysis project examined and analyzed the historical record of tropical cyclones in the Atlantic back to 1851, extending the existing database from 1886.

Before satellite imagery became available during the 20th century, many of these systems went undetected unless it impacted land or a ship encountered it by chance. Often in part because of the threat of hurricanes, many coastal regions had sparse population between major ports until the advent of automobile tourism; therefore, the most severe portions of hurricanes striking the coast may have gone unmeasured in some instances. The combined effects of ship destruction and remote landfall severely limit the number of intense hurricanes in the official record before the era of hurricane reconnaissance aircraft and satellite meteorology. Although the record shows a distinct increase in the number and strength of intense hurricanes, therefore, experts regard the early data as suspect. The ability of climatologists to make a long-term analysis of tropical cyclones is limited by the amount of reliable historical data.

In the 1940s, routine aircraft reconnaissance started in both the Atlantic and Western Pacific basin in the mid-1940s, which provided ground truth data. Early flights were only made once or twice a day. In 1960, Polar-orbiting weather satellites were first launched by the United States National Aeronautics and Space Administration, but were not declared operational until 1965. It took several years for some of the warning centers to take advantage of this new viewing platform and develop the expertise to associate satellite signatures with storm position and intensity.

Intense tropical cyclones pose a particular observation challenge, as they are a dangerous oceanic phenomenon, and weather stations, being relatively sparse, are rarely available on the site of the storm itself. In general, surface observations are available only if the storm is passing over an island or a coastal area, or if there is a nearby ship. Real-time measurements are usually taken in the periphery of the cyclone, where conditions are less catastrophic and its true strength cannot be evaluated. For this reason, there are teams of meteorologists that move into the path of tropical cyclones to help evaluate their strength at the point of landfall.

Tropical cyclones are tracked by weather satellites capturing visible and infrared images from space, usually at half-hour to quarter-hour intervals. As a storm approaches land, it can be observed by land-based Doppler weather radar. Radar plays a crucial role around landfall by showing a storm's location and intensity every several minutes. Other satellites provide information from the perturbations of GPS signals, providing thousands of snapshots per day and capturing atmospheric temperature, pressure, and moisture content.

In situ measurements, in real-time, can be taken by sending specially equipped reconnaissance flights into the cyclone. In the Atlantic basin, these flights are regularly flown by United States government hurricane hunters. These aircraft fly directly into the cyclone and take direct and remote-sensing measurements. The aircraft launch GPS dropsondes inside the cyclone. These sondes measure temperature, humidity, pressure, and especially winds between flight level and the ocean's surface. A new era in hurricane observation began when a remotely piloted Aerosonde, a small drone aircraft, was flown through Tropical Storm Ophelia as it passed Virginia's eastern shore during the 2005 hurricane season. A similar mission was also completed successfully in the western Pacific Ocean.

Forecasting

See also: Tropical cyclone track forecasting, Tropical cyclone prediction model, and Tropical cyclone rainfall forecasting
A graph shows five colored curves (actually, jagged point-to-point data sets) measuring average forecast errors in nautical miles (0 to 700, the y-axis on the left) for each year (from 1970 to 2022, the x-axis at the bottom). The red curve indicates forecast errors 24 hours in advance, and is the lowest of the five curves; its points and the resultant trend line are below that of the other curves. The 24-hour forecast trends from approximately 140 nm in 1970 to about 45 nm in 2022. The green line shows forecast errors 48 hours in advance, with a trend line from about 290 nm in 1970 to 45 nm in 2022. The yellow curve indicates errors from 72-hour forecasts, and jags dramatically up and down in the first 10 years shown. Its trend line runs from approx. 445 nm (1970) to about 50 nm (2022). The two remaining lines stretch only from 2001. The brown curve shows a 96-hour forecast (trending from about 240 nm in 2001 to 100 nm in 2022), and the blue line for forecasts 120 hours in advance trends from about 310 nm (2001) to 150 nm (2022). With remarkable consistency, the farther in advance the forecast is, the greater the error visible here, and the trend line for each set of plotted points is clearly downward, generally with increasing steepness for the wider-ranging forecasts.
A general decrease in error trends in tropical cyclone path prediction is evident since the 1970s.

High-speed computers and sophisticated simulation software allow forecasters to produce computer models that predict tropical cyclone tracks based on the future position and strength of high- and low-pressure systems. Combining forecast models with increased understanding of the forces that act on tropical cyclones, as well as with a wealth of data from Earth-orbiting satellites and other sensors, scientists have increased the accuracy of track forecasts over recent decades.

However, scientists are not as skillful at predicting the intensity of tropical cyclones. The lack of improvement in intensity forecasting is attributed to the complexity of tropical systems and an incomplete understanding of factors that affect their development. New tropical cyclone position and forecast information is available at least every six hours from the various warning centers.

Geopotential height

Main article: Geopotential height

In meteorology, geopotential heights are used when creating forecasts and analyzing pressure systems. Geopotential heights represent the estimate of the real height of a pressure system above the average sea level. Geopotential heights for weather are divided up into several levels. The lowest geopotential height level is 850 hPa (25.10 inHg), which represents the lowest 1,500 m (5,000 ft) of the atmosphere. The moisture content, gained by using either the relative humidity or the precipitable water value, is used in creating forecasts for precipitation.

The next level, 700 hPa (20.67 inHg), is at a height of 2,300–3,200 m (7,700–10,500 ft). 700 hPa is regarded as the highest point in the lower atmosphere. At this layer, both vertical movement and moisture levels are used to locate and create forecasts for precipitation. The middle level of the atmosphere is at 500 hPa (14.76 inHg) or a height of 4,900–6,100 m (16,000–20,000 ft). The 500 hPa level is used for measuring atmospheric vorticity, commonly known as the spin of air. The relative humidity is also analyzed at this height to establish where precipitation is likely to materialize. The next level occurs at 300 hPa (8.859 inHg) or a height of 8,200–9,800 m (27,000–32,000 ft). The top-most level is located at 200 hPa (5.906 inHg), which corresponds to a height of 11,000–12,000 m (35,000–41,000 ft). Both the 200 and 300 hPa levels are mainly used to locate the jet stream.

Society and culture

Preparations

Main articles: Tropical cyclone preparedness and Tropical cyclone engineering
Evacuation route sign on Tulane Avenue in New Orleans shows lines from long standing floodwaters after Hurricane Katrina.

Ahead of the formal season starting, people are urged to prepare for the effects of a tropical cyclone by politicians and weather forecasters, among others. They prepare by determining their risk to the different types of weather, tropical cyclones cause, checking their insurance coverage and emergency supplies, as well as determining where to evacuate to if needed. When a tropical cyclone develops and is forecast to impact land, each member nation of the World Meteorological Organization issues various watches and warnings to cover the expected effects. However, there are some exceptions with the United States National Hurricane Center and Fiji Meteorological Service responsible for issuing or recommending warnings for other nations in their area of responsibility.

An important decision in individual preparedness is determining if and when to evacuate an area that will be affected by a tropical cyclone. Tropical cyclone tracking charts allow people to track ongoing systems to form their own opinions regarding where the storms are going and whether or not they need to prepare for the system being tracked, including possible evacuation. This continues to be encouraged by the National Oceanic and Atmospheric Administration and National Hurricane Center.

Response

Main article: Tropical cyclone response
This section needs expansion. You can help by making an edit requestadding to it . (October 2022)
View of tropical cyclone damage from a helicopter
Relief efforts for Hurricane Dorian in the Bahamas

Hurricane response is the disaster response after a hurricane. Activities performed by hurricane responders include assessment, restoration, and demolition of buildings; removal of debris and waste; repairs to land-based and maritime infrastructure; and public health services including search and rescue operations. Hurricane response requires coordination between federal, tribal, state, local, and private entities. According to the National Voluntary Organizations Active in Disaster, potential response volunteers should affiliate with established organizations and should not self-deploy, so that proper training and support can be provided to mitigate the danger and stress of response work.

Hurricane responders face many hazards. Hurricane responders may be exposed to chemical and biological contaminants including stored chemicals, sewage, human remains, and mold growth encouraged by flooding, as well as asbestos and lead that may be present in older buildings. Common injuries arise from falls from heights, such as from a ladder or from level surfaces; from electrocution in flooded areas, including from backfeed from portable generators; or from motor vehicle accidents. Long and irregular shifts may lead to sleep deprivation and fatigue, increasing the risk of injuries, and workers may experience mental stress associated with a traumatic incident. Heat stress is a concern as workers are often exposed to hot and humid temperatures, wear protective clothing and equipment, and have physically difficult tasks.

See also

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