Tropical cyclone

Part of a series on
Tropical cyclones
Structure Central dense overcast Development Eye
Effects By Region Warnings and watches Storm surge Preparedness Response
Climatology and tracking Basins Climate change effects RSMCs Scales Observation Forecasting Rainfall forecasting Rainfall climatology
Tropical cyclone naming History List of historical names Lists of retired names: Atlantic, Pacific hurricane, Pacific typhoon, Philippine, Australian, South Pacific
Outline of tropical cyclones  Tropical cyclones portal
v t e

A tropical cyclone is a rapidly rotating

The primary energy source for these storms is warm ocean waters. These storms are therefore typically strongest when over or near water, and they weaken quite rapidly over land. This causes inland regions to be much less vulnerable to cyclones than coastal regions, with residents of tropical islands facing the greatest threat of all, although tidal flooding is often worse on continental coasts than on islands. 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.

Tropical cyclones draw in air from a large area and concentrate the water content of that air (from atmospheric moisture and moisture evaporated from water) into

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.^[2]

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.^[3][4] The systems generally have a well-defined center which is surrounded by deep atmospheric convection and a closed wind circulation at the surface.^[3] 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.^[1] 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.^[1]

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

Formation

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.^[5] 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.^[5] These showers dissipate quite quickly; however, they can group together into large clusters of thunderstorms.^[5] This creates a flow of warm, moist, rapidly rising air, which starts to rotate cyclonically as it interacts with the rotation of the earth.^[5]

Several factors are required for these thunderstorms to develop further, including

Climate oscillations such as El Niño–Southern Oscillation (ENSO) and the Madden–Julian oscillation modulate the timing and frequency of tropical cyclone development.^{[10][11][12][13]} Rossby waves can aid in the formation of a new tropical cyclone by disseminating the energy of an existing, mature storm.^[14][15] Kelvin waves can contribute to tropical cyclone formation by regulating the development of the westerlies.^[16] Cyclone formation is usually reduced 3 days prior to the wave's crest and increased during the 3 days after.^[17]

Formation regions and warning centers

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 centres.

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.[24] 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.^[25][26] 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).^[27] 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.^[28]

Factors that influence intensity

Warm sea surface temperatures are required in order 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).^[29][30] Higher sea surface temperatures result in faster intensification rates and sometimes even rapid intensification.^[31] High ocean heat content, also known as Tropical Cyclone Heat Potential, allows storms to achieve a higher intensity.^[32] Most tropical cyclones that experience rapid intensification are traversing regions of high ocean heat content rather than lower values.^[33] 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.^[34] 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.^[33]

The passage of a tropical cyclone over the ocean causes the upper layers of the ocean to cool substantially, a process known as upwelling,^[35] 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.^[36] Conversely, the mixing of the sea can result in heat being inserted in deeper waters, with potential effects on global climate.^[37]

Vertical wind shear decreases tropical cyclone predicability, with storms exhibiting wide range of responses in the presence of shear.^[38] Wind shear often negatively affects tropical cyclone intensification by displacing moisture and heat from a system's center.^[39] Low levels of vertical wind shear are most optimal for strengthening, while stronger wind shear induces weakening.^[40][41] 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.^[42][43][44] Symmetric, strong outflow leads to a faster rate of intensification than observed in other systems by mitigating local wind shear.^[45][46][47] Weakening outflow is associated with the weakening of rainbands within a tropical cyclone.^[48] 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.^[49][50]

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.^[51] 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.^[52] Tropical cyclones typically weaken while situated over a landmass because conditions are often unfavorable as a result of the lack of oceanic forcing.^[53] 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.^[54] Orographic lift can cause an 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.^[55] Jet streams can both enhance and inhibit tropical cyclone intensity by influencing the storm's outflow as well as vertical wind shear.^[56][57]

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.^[58] 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.^[59] 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.^[60] However, some cyclones such as Hurricane Epsilon have rapidly intensified despite relatively unfavorable conditions.^[61][62]

Dissipation

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.[63]^[64]

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

Should a tropical cyclone make landfall or pass over an island, its circulation could start to break down, especially if it encounters mountainous terrain.[67] 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.^[67] This, combined with the increased friction over land areas, leads to the weakening and dissipation of the tropical cyclone.^[67] Over a mountainous terrain, a system can quickly weaken; however, over flat areas, it may endure for two to three days before circulation breaks down and dissipates.^[67]

Over the years, there have been a number of techniques considered to try to artificially modify tropical cyclones.^[68] 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.^[68] These techniques, however, fail to appreciate the duration, intensity, power or size of tropical cyclones.^[68]

Methods for assessing intensity

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.^[1] 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.^[69] 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.^[1] 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.^[70][71] Tropical cyclones agencies each use their own, fixed WPR, which can result in inaccuracies between agencies that are issuing estimates on the same system.^[71] The ASCAT is a scatterometer used by the MetOp satellites to map the wind field vectors of tropical cyclones.^[1] 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.^[72]

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, in order to determine the T-number and thus assess the intensity of the storm.^[73] 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.^[74] 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.^[75][76]

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.^[77] The calculation of the PDI is similar in nature to ACE, with the major difference being that wind speeds are cubed rather than squared.^[78] 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:

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

where v is the storm's wind speed and r is the radius of hurricane-force winds.^[79] 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.^[80] The IKE model measures the destructive capability of a tropical cyclone via winds, waves, and surge. It is calculated as:

${\displaystyle \int _{Vol}{\frac {1}{2}}pu^{2}d_{v}\,}$

where p is the density of air, u is a sustained surface wind speed value, and d_v is the volume element.^[80][81]

Classification and naming

Classification

The practice of using

In addition to tropical cyclones, there are two other classes of

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.^[90]

Structure

Eye and center

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 "

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".^[93] 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.^[91]

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.^[94]

The eyewall may vary over time in the form of

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.^[99] 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)).^[98] 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.^[97][99] 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.^[100]

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".^[101] 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.^{[102][103][104]}

Environmental steering

Environmental steering is the primary influence on the motion of tropical cyclones.^[105] It represents the movement of the storm due to prevailing winds and other wider environmental conditions, similar to "leaves carried along by a stream".^[106]

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.^[105] Tropical cyclones can be treated as local maxima of vorticity suspended within the large-scale background flow of the environment.^[107] In this way, tropical cyclone motion may be represented to first-order as advection of the storm by the local environmental flow.^[108] This environmental flow is termed the "steering flow" and is the dominant influence on tropical cyclone motion.^[105] 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".^[107] 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.^[109] When wind shear and latent heat release is present, tropical cyclones tend to move towards regions where potential vorticity is increasing most quickly.^[110]

Climatologically, tropical cyclones are steered primarily westward by the east-to-west

In addition to environmental steering, a tropical cyclone will tend to drift poleward and westward, a motion known as "beta drift".[115] 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.^[116] 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.^[117][115]

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.^[118][119] 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.^[120][121]

Multiple storm interaction

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.^[122]

Interaction with the mid-latitude westerlies

Natural phenomena caused or worsened by tropical cyclones

Tropical cyclones out at sea cause large waves,

Tropical cyclones regularly affect the coastlines of most of

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.^[207] 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.^[208] Sediment records in Western Australia suggest an intense tropical cyclone in the 4th millennium BC.^[207] 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.^[209][210] In the year 957, a powerful typhoon struck southern China, killing around 10,000 people due to flooding.^[211] The Spanish colonization of Mexico described "tempestades" in 1730,^[212] although the official record for Pacific hurricanes only dates to 1949.^[213] In the south-west Indian Ocean, the tropical cyclone record goes back to 1848.^[214] 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.^[215]

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.

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.[1] 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.^[218] In the Northern Atlantic Ocean, a distinct cyclone season occurs from June 1 to November 30, sharply peaking from late August through September.^[218] 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.^[219] The Northwest Pacific sees tropical cyclones year-round, with a minimum in February and March and a peak in early September.^[218] In the North Indian basin, storms are most common from April to December, with peaks in May and November.^[218] 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.^[218][22]

Of various

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.^[2] Tropical cyclones use warm, moist air as their fuel. As climate change is warming ocean temperatures, there is potentially more of this fuel available.^[231] 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.^[232] With 2 °C (3.6 °F) warming, a greater percentage (+13%) of tropical cyclones are expected to reach Category 4 and 5 strength.^[2] 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.^[233]

Warmer air can hold more water vapor: the theoretical maximum water vapor content is given by the

There is currently no consensus on how climate change will affect the overall frequency of tropical cyclones.[2] A majority of climate models show a decreased frequency in future projections.^[238] 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.^[239] Observations have shown little change in the overall frequency of tropical cyclones worldwide,^[240] with increased frequency in the North Atlantic and central Pacific, and significant decreases in the southern Indian Ocean and western North Pacific.^[241] 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.^[242] In the North Pacific, there may also have been an eastward expansion.^[236] 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.^[238]

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

Historically, tropical cyclones have occurred around the world for thousands of years, with one of the earliest tropical cyclones on record estimated to have occurred in Western Australia in around 4000 BC.^[207] However, before satellite imagery became available during the 20th century, there was no way to detect a tropical cyclone unless it impacted land or a ship encountered it by chance.^[1]

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.^[244]

Tropical cyclones are tracked by

Forecasting

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.^[256] 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.^[257] 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.^[258] 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 in order to establish where precipitation is likely to materialize.^[259] The next level occurs at 300 hPa (8.859 inHg) or a height of 8,200–9,800 m (27,000–32,000 ft).^[260] 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.^[261]

Society and culture

Preparations

Ahead of the formal season starting, people are urged to

An important decision in individual preparedness is determining if and when to evacuate an area that will be affected by a tropical cyclone.[269] 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.^[270]

Response

This section needs expansion. You can help by adding to it. (October 2022)

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.^[271] Hurricane response requires coordination between federal, tribal, state, local, and private entities.^[272] 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.^[273]

Hurricane responders face many hazards. Hurricane responders may be exposed to chemical and biological contaminants including stored chemicals,

• Cyclone
• Tropical cyclones by year
• Tropical cyclones in 2024
• 2024 Atlantic hurricane season
• 2024 Pacific hurricane season
• 2024 Pacific typhoon season
• 2024 North Indian Ocean cyclone season
• 2023–24 South-West Indian Ocean cyclone season
• 2023–24 Australian region cyclone season
• 2023–24 South Pacific cyclone season

References

External links

Look up tropical cyclone in Wiktionary, the free dictionary.

Wikimedia Commons has media related to Tropical cyclones.

Wikisource has original text related to this article:

The Hurricane

Wikivoyage has a travel guide for Cyclones.

• United States National Hurricane Center – North Atlantic, Eastern Pacific
• United States Central Pacific Hurricane Center – Central Pacific
• Japan Meteorological Agency – Western Pacific
• India Meteorological Department – Indian Ocean
• Météo-France – La Reunion – South Indian Ocean from 30°E to 90°E
• Indonesian Meteorological Department – South Indian Ocean from 90°E to 125°E, north of 10°S
• Australian Bureau of Meteorology – South Indian Ocean and South Pacific Ocean from 90°E to 160°E
• Papua New Guinea National Weather Service – South Pacific east of 160°E, north of 10°S
• Fiji Meteorological Service – South Pacific west of 160°E, north of 25° S
• MetService New Zealand – South Pacific west of 160°E, south of 25°S