Source: Glossary of Meteorology. Reprinted with permission. As less moisture is evaporated into the atmosphere to supply cloud formation, the storm weakens. Sometimes, even in the tropical oceans, colder water churned up from beneath the sea surface by the hurricane can cause the hurricane to weaken see Interaction between a Hurricane and the Ocean. Even when the ocean conditions are favorable for the hurricane to be maintained, a hurricane may encounter an area of particularly dry and dusty air, such as the Saharan Air Layer SAL , causing the hurricane to weaken, though the role of the SAL is being debated.
Hurricane decay can also be caused by strong vertical wind shear , a change in wind direction or speed with height. As heat and moisture at upper levels are advected away from the low-level circulation of the hurricane, its development is inhibited. Without a strong secondary circulation, a hurricane cannot be sustained see Hurricane Development: From Birth to Maturity.
The response to vertical shear partially depends on the storm circulation, so the response to similar values of vertical shear can vary from storm to storm. Vertical wind shear is common in the mid-latitudes, although it can also occur over the tropical oceans where it cannot only weaken a hurricane but also help to prevent one from forming in the first place see Hurricane Genesis: Birth of a Hurricane.
Extratropical cyclones are responsible for much of the sensible weather such as rain and snow that people who live in the mid-latitudes experience, especially during the winter months. Unlike hurricanes, extratropical cyclones require areas of sharp horizontal temperature contrasts, called fronts, to form. Through trade Mayan religious beliefs spread throughout the Caribbean. Spanish sailors began to refer to these tropical storms by the name of the Taino storm god.
Throughout history there have been many alternative spellings in different languages: foracan, foracane, furacana, furacane, furicane, furicano, haracana, harauncana, haraucane, haroucana, harrycain, hauracane, haurachana, herican, hericane, hericano, herocane, herricao, herycano, heuricane, hiracano, hirecano, hurac[s]n, huracano, hurican, hurleblast, hurlecan, hurlecano, hurlicano, hurrican, hurricano, hyrracano, urycan, hyrricano, jimmycane, oraucan, uracan, uracano.
In order for a tropical cyclone to form, several atmospheric and marine conditions must be met. They also need an atmosphere which cools fast enough with increasing height so that the difference between the top and bottom of the atmosphere can create thunderstorm conditions. A moist mid-troposphere 3 miles high is also needed because dry air ingested into thunderstorms at mid-level can kill the circulation.
The force is greatest at the poles and zero at the equator, so the storm must be at least miles from the equator in order for the Coriolis force to create the spin. This force causes hurricanes in the Northern hemisphere to rotate counter-clockwise, and in the southern hemisphere to rotate clockwise.
This spin may play some role in helping tropical cyclones to organize. As a side note: the Coriolis force is not strong enough to affect small containers such as in sinks and toilets. The notion that the water flushes the other way in the opposite hemisphere is a myth. Wind: Low vertical wind shear the change of wind speed and direction with height between the surface and the upper troposphere favors the thunderstorm formation, which provides the energy for tropical cyclones. Too much wind shear will disrupt or weaken the convection.
Having these conditions met is necessary but not sufficient, as many disturbances that appear to have favorable conditions do not develop. Past work Velasco and Fritsch , Chen and Frank , Emanuel has identified that large thunderstorm systems called mesoscale convective complexes often produce an inertially stable, warm core vortex in the trailing altostratus decks of the MCC.
These mesovortices have a horizontal scale of approximately to km [75 to mi], are strongest in the mid-troposphere 5 km [3 mi] and have no appreciable signature at the surface. Zehr hypothesizes that genesis of the tropical cyclones occurs in two stages:.
Stage 2 occurs when a second blow up of convection at the mesoscale vortex initiates the intensification process of lowering central pressure and increasing swirling winds. References: Graham, N. Barnett, Sea surface temperature, surface wind divergence, and convection over tropical oceans. Science , No. Gray, W. Shaw Ed. Chen, S. Emanuel, K. Tropical Cyclone Disasters J. Lighthill, Z. Zhemin, G. Holland, K. Emanuel Eds.
Palmen, E. Geophysica , Univ. Velasco, I. Zehr, R. Department of Commerce, Washington, DC , pp. In addition to hurricane-favorable conditions such as temperature and humidity, many repeating atmospheric phenomenon contribute to causing and intensifying tropical cyclones.
For example, African Easterly Waves AEW are winds in the lower troposphere ocean surface to 3 miles above that originate and travel from Africa at speeds of about 3-mph westward as a result of the African Easterly Jet. These winds are seen from April until November. It is a mass of dry, mineral-rich, dusty air that forms over the Sahara from late spring to early fall and moves over the tropical North Atlantic every days at speeds of mph meters per second.
These air masses are miles deep and exist in the lower troposphere. They can be as wide as the continental US and have significant moderating impacts on tropical cyclone intensity and formation because the dry, intense air can deprive the storm of moisture and wind shear can interfere with its convection. However, disturbances on the periphery of the Saharan Air Layer can receive a boost in their convection and spin.
An upper atmospheric perturbation known as the Madden-Julian Oscillation MJO can travel around the globe on a time-scale of weeks. As its positive phase passes over an area it can bring favorable conditions for convection, while its negative phase can suppress it. This can affect forming tropical cyclones either giving them a boost or hindering them. The numbers range from none to around five per year — with an average of 2 per year.
References: Dunn, G. Riehl, H. Burpee, R. Landsea, C. Avila, L. When a tropical disturbance organizes into a tropical depression, the thunderstorms will begin to line up in spiral bands along the inflowing wind. The winds will begin to increase, and eventually the inner bands will close off into an eyewall, surrounding a central calm area known as the eye. This usually happens around the time wind speeds reach hurricane force. When the hurricane reaches its mature stage, eyewall replacement cycles may begin.
Each cycle will be accompanied by fluctuations in the strength of the storm. Peak winds may diminish when a new eyewall replaces the old, but then re-strengthen as the new eyewall becomes established.
If the storm passes through an area of high vertical wind shear or dry air the storm could be weakened. However, if it continues to pick up moisture from a warm environment, then it could become a major hurricane. Hurricanes are driven by larger scale circulation patterns. In the Atlantic this ridge is often called the Bermuda High due to its location. South of the ridge the circulation drives tropical cyclones westward with a slight poleward component.
But when the cyclone reaches the westward edge of the ridge it will tend to move around the high first poleward then easterly. This is known as recurvature. This motion means that many Atlantic hurricanes may recurve back out to sea without ever making landfall.
If a hurricane reaches the mid-latitudes, it can interact with fronts. Often the energy and moisture of tropical cyclones will be absorbed into such fronts, transitioning into extratropical low pressure storms. Studies have shown that this process can increase the unpredictability of mid-latitude weather downstream for days following.
However, some hurricanes will make landfall. Striking an island, especially a mountainous one, could cause its circulation to break down. If it hits a continent, a hurricane will be cut off from its supply of warm, moist maritime air. It will also begin to draw in dry continental air, which combined with increased friction over land leads to the weakening and eventual death of the hurricane. Over mountainous terrain this will be a quick end. But over flat areas, it may take two to three days to break down the circulation.
Even then you are still left with a large pocket of tropical moisture which can cause substantial inland flooding. There have been studies on the rate of storm decay once they make landfall Demaria Kaplan Decay Model.
References: Willoughby, H. Willoughby, H. Clos, and M. Powell, M. Forecasting , 11, pp. Tuleya, R. Tropical cyclones — to a first approximation — can be thought of as being steered by the surrounding environmental flow throughout the depth of the troposphere from the surface to about 12 km or 8 mi.
Neil Frank, former director of the U. National Hurricane Center, used the analogy that the movement of hurricanes is like a leaf being steered by the currents in the stream, except that for with a hurricane the stream has no set boundaries. This is because there exists an axis of high pressure called the subtropical ridge that extends east-west poleward of the storm. On the equatorward side of the subtropical ridge, general easterly winds prevail. However, if the subtropical ridge is weak — often times due to a trough in the jet stream — the tropical cyclone may turn poleward and then recurve back toward the east.
On the poleward side of the subtropical ridge, westerly winds prevail thus steering the tropical cyclone back to the east. These westerly winds are the same ones that typically bring extratropical cyclones with their cold and warm fronts from west to east. Many times it is difficult to tell whether a trough will allow the tropical cyclone to recurve back out to sea for those folks on the eastern edges of continents or whether the tropical cyclone will continue straight ahead and make landfall.
Storm tide is the combination of the storm surge and astronomical tide as a result of a storm. Storm surge is caused by the force of high wind speeds acting on the ocean surface combined with the forward speed of the storm. The height of a storms surge is determined by the approaching angle of the storm as well as the coastline characteristics, such as the shape of the continental shelf and local geographic features, such as inlets.
The degree of vulnerability of any stretch of coast is dependent on a number of factors which includes the central pressure, intensity, forward speed, storm size, angle of approach, width and slope of the off-shore continental shelf, and local bays and inlets. Sometimes these updates include higher grid size resolution to improve surge representation, increasing areas covered by hypothetical tracks for improved accuracy, conversion to updated vertical reference datums, and including the latest topography or bathymetric data for better representation of barrier, gaps, passes, and other local features.
Deterministic runs This is an operational product based on the official NHC track and intensity forecast of a tropical cyclone. Operational SLOSH runs are generated whenever a hurricane warning is issued, approximately 36 hours prior to arrival of tropical storm winds.
It is run every 6 hours coinciding with the full advisory package. This product is intended to provide valuable surge information in support of rescue and recovery efforts. P-Surge is available whenever a hurricane watch or warning is in effect. It is posted on the NHC webpage within approximately 30 minutes after the advisory release time. Maximum Envelope of Water MEOW runs This is an ensemble product representing the maximum height of storm surge water in a given basin grid cell using hypothetical storms run with the same:.
Internally a number of parallel SLOSH runs with same intensity, forward speed, storm trajectory, and initial tide level are performed for the basin. The only difference in runs is that each is conducted at some distance to the left or to the right of the main track typically at the center of the grid. Each component run computes a storm surge value for each grid cell.
For example, five parallel runs may yield storm surge values of 4. In this case, the MEOW for the cell is 7. It is unknown to the user which track generated the MEOW for a particular cell, so it is entirely possible that the MEOW values for adjacent cells may have come from different runs.
MEOWs are used to incorporate the uncertainties associated with a given forecast and help eliminate the possibility that a critical storm track will be missed in which extreme storm surge values are generated.
MEOWs provide a worst case scenario for a particular category, forward speed, storm trajectory, and initial tide level incorporating uncertainty in forecast landfall location.
Over 80 MEOWs have been generated for some basins. This product provides useful information aiding in hurricane evacuation planning. Maximum of MEOW MOM runs This is an ensemble product of maximum storm surge heights for all hurricanes of a given category regardless of forward speed, storm trajectory, landfall location, etc.
This procedure is done for each category of storm. It is able to resolve flow through barriers, gaps, and passes and model deep passes between bodies of water. It also resolves inland inundation and the overtopping of barrier systems, levees, and roads. It can even resolve coastal reflections of surges such as coastally trapped Kelvin waves.
However it does not model the impacts of waves on top of the surge, account for normal river flow or rain flooding, nor does it explicitly model the astronomical tide although operational runs can be run with different water level anomalies to model conditions at the onset of operational runs. Surprisingly, not much lightning occurs in the inner core within about km or 60 mi of the tropical cyclone center. Only around a dozen or less cloud-to-ground strikes per hour occur around the eyewall of the storm, in strong contrast to an overland mid-latitude mesoscale convective complex which may be observed to have lightning flash rates of greater than per hour maintained for several hours.
However, lightning can be more common in the outer cores of the storms beyond around km or 60 mi with flash rates on the order of s per hour.
This lack of inner core lightning is due to the relative weak nature of the eyewall thunderstorms. Weaker updrafts lack the super-cooled water e. The more common outer core lightning occurs in conjunction with the presence of convectively-active rainbands Samsury and Orville One of the exciting possibilities that recent lightning studies have suggested is that changes in the inner core strikes — though the number of strikes is usually quite low — may provide a useful forecast tool for intensification of tropical cyclones.
Black suggested that bursts of inner core convection which are accompanied by increases in electrical activity may indicate that the tropical cyclone will soon commence a deepening in intensity.
Analyses of Hurricanes Diana , Florence and Andrew , as well as an unnamed tropical storm in indicate that this is often true Lyons and Keen and Molinari et al. References: Molinari, J. Moore, V. Idone, R. Henderson, and A. Black, R. Samsury, C. Black, P. Lyons, W. How does this occur?
When the strong winds of a hurricane move over the ocean they churn-up much cooler water from below. The magnitude and distribution of the cooling pattern shown in this illustration is fairly typical for a post-storm SST analysis.
The amount of ocean cooling that occurs directly beneath the hurricane within the high wind region of the storm is a much more important question scientists would like to have answered. Hurricanes get their energy from the warm ocean water beneath them.
However, in order to get a more accurate estimate of just how much energy is being transferred from the sea to the storm, scientists need to know ocean temperature conditions directly beneath the hurricane. In most cases, the ocean temperature under a hurricane will range somewhere between 0. Exactly how much depends on many factors including ocean structure beneath the storm i.
While the estimates in Figure 2 represent a dramatic improvement when it comes to more accurately representing actual SST cooling patterns experienced under a hurricane, even small errors in inner core SST can result in significant miscalculations when it comes to accurately assessing how much energy is transferred from the warm ocean environment directly to the hurricane.
These efforts include statistical studies, modeling efforts and enhanced observational capabilities designed to help scientists better assess upper ocean thermal conditions under the storm. It is believed that future forecasts of tropical cyclone intensity change will be significantly improved. Reference: Cione, J. Monthly Weather Review , , The Eye is a roughly circular area of fair weather found at the center of a severe tropical storm.
The eye is the region of the lowest pressure at the surface and the warmest temperatures at the top. Eye size ranges from miles across, but most are miles in diameter.
Understanding exactly how the eye forms has been controversial. Some scientists believe the radial spreading of the wind creates a warm dry down flow from the upper atmosphere, and this forms the cloud-free eye.
Others have think the latent heat release in the eyewall forces the subsidence in the storm center creating the eye. The Eyewall is a ring of deep convection bordering the eye of the storm. This area has the highest surface winds in the tropical cyclone. Because air in the eye is slowly sinking, it creates an updraft in the eyewall. Eyewall replacement happens when a storm reaches its intensity threshold and the eye contracts to a smaller size miles.
Strong rain bands in the outer storm move inward towards the eye, robbing the inner eyewall of its moisture and momentum and weakening the storm. Spiral Bands are long, narrow bands of rain and thunderstorms that are oriented in the same direction as the wind movement. They are caused by convection the vertical movement of air masses and they spiral into the center of the tropical cyclone.
In contrast, the Moat of a storm usually refers to the region between the eyewall and an outer spiral band where rainfall is relatively lighter. Not all hurricanes have moats. References: Hawkins, H. Weatherford, C. Smith, R. Shapiro, L. Global Perspectives on Tropical Cyclones , R. Elsberry ed. World Meteorological Organization, Report No. TCP; Geneva, Switzerland, 62 pp. Tropical cyclones tend to be symmetrical. This means the winds should be the same in all quadrants at a given distance from the center.
If a hurricane is moving to the west, the right side would be to the north of the storm, if it is heading north, then the right side would be to the east of the storm. For example, a hurricane with 90mph winds moving at 10mph would have a mph wind speed on the forward-moving side and 80 mph on the side with the backward motion. The energy released from a hurricane can be explained in two ways: the total amount of energy released by the condensation of water droplets latent heat , or the amount of kinetic energy generated to maintain the strong, swirling winds of a hurricane.
The vast majority of the latent heat released is used to drive the convection of a storm, but the total energy released from condensation is times the world-wide electrical generating capacity, or 6. If you measure the total kinetic energy instead, it comes out to about 1. Reference: Emanuel, K. There are no other planets known to have warm water oceans from which true water cloud hurricanes can form. However, many astronomers and planetary meteorologists believe gas giant planets such as Jupiter and Saturn exhibit similar storms.
The principal candidate is the famous Great Red Spot GRS on Jupiter, and the numerous whorls that surround it, where ammonia takes the place of water.
The GRS exhibits an anticyclonic circulation at its top, just as tropical cyclones do at the top of the troposphere. On Saturn, a polar storm has been spotted by the Cassini spacecraft measuring up to 1, miles in diameter, about 20 time larger than an Earthly hurricane with winds four times stronger.
On Mars, a large, cyclonic cloud feature forms every year in the northern hemisphere. It forms in the morning and dissipates by the afternoon.
Over 3, extrasolar planets have been found to date, but no others are confirmed to have convectively driven storms. However, there is reason to believe such storms exist on extrasolar planets as well. When the Weather Bureau organized its new hurricane warning network in it scheduled a special telegraph line to connect the various centers to run from June 15th through November 15th.
These changes made the Atlantic hurricane season six months long and easier for people to remember. Maximum activity occurs in early to mid September. The Northwest Pacific basin has tropical cyclones occurring all year round regularly. There is no official definition of typhoon season for this reason.
The North Indian basin has a double peak of activity in May and November though tropical cyclones are seen from April to December. References: Neumann, C. Jarvinen, C. McAdie, and J. The best time to prepare is before hurricane season begins.
Make a plan for you and your family about what to do if a hurricane threatens. Put together a hurricane kit. Ensure your house is up to code, and check for problems, such as overhanging branches or missing roof tiles. Check your shutters and other window and door coverings. Once the season begins, stay informed. Check the outlook every day, and if anything is threatening keep updated on the latest advisories. The mean annual damage from hurricanes in the US is 9.
Hurricane damage varies greatly from year to year, depending on the number and strength of hurricanes making landfall, but there does not seem to be a long-term trend in adjusted damage over the last century.
There is very little association between the physical size of a hurricane and its intensity. A big hurricane does not have to be an intense one and vice versa. The damage a hurricane can cause is a function of both its maximum sustained wind and the extent of the hurricane force winds. A broad, weak storm may cause as much damage as a small, strong one. It is false to think that damage is linear with wind speed, that a mph winds will cause twice the damage as a mph winds.
The relationship is exponential, and not linear. A category 5 storm could cause up to times the damage of a category 1 hurricane of the same size. References: Weatherford, C. Pielke, Jr.
Forecasting, 13, pp. Just as every person is an individual, every hurricane is different. So every experience with such a storm will be unique. The summary below is of a general sequence of events one might expect from a Category 2 hurricane approaching a coastal area.
What you might experience could be vastly different. Hurricane forecasters estimate tropical cyclone strength from satellite using a method called the Dvorak technique. Vern Dvorak developed the scheme in the early s using a pattern recognition decision tree Dvorak , If infrared satellite imagery is available for Eye Patterns generally the pattern seen for hurricanes, severe tropical cyclones and typhoons , then the scheme utilizes the difference between the temperature of the warm eye and the surrounding cold cloud tops.
The larger the difference, the more intense the tropical cyclone is estimated to be. CI numbers have been calibrated against aircraft measurements of tropical cyclones in the Northwest Pacific and Atlantic basins.
On average, the CI numbers correspond to the following intensities:. Note that this estimation of both maximum winds and central pressure assumes that the winds and pressures are always consistent. The reason that lower pressures are given to the Northwest Pacific tropical cyclones in comparison to the higher pressures of the Atlantic basin tropical cyclones is because of the difference in the background climatology.
The Northwest Pacific basin has a lower background sea level pressure field. Thus to sustain a given pressure gradient and thus the winds, the central pressure must accordingly be smaller in this basin. The errors for using the above Dvorak technique in comparison to aircraft measurements taken in the Northwest Pacific average 10 mb with a standard deviation of 9 mb Martin and Gray Atlantic tropical cyclone estimates likely have similar errors.
Thus an Atlantic hurricane that is given a CI number of 4. These would be typical ranges to be expected; errors could be worse. However, in the absence of other observations, the Dvorak technique does at least provide a consistent estimate of what the true intensity is. While the Dvorak technique was calibrated for the Atlantic and Northwest Pacific basin because of the aircraft reconnaissance data ground truth, the technique has also been quite useful in other basins that have limited observational platforms.
However, at some point it would be preferable to re-derive the Dvorak technique to calibrate tropical cyclones with available data in the other basins. Lastly, while the Dvorak technique is primarily designed to provide estimates of the current intensity of the storm, a 24 h forecast of the intensity can be obtained also by extrapolating the trend of the CI number.
Whether this methodology provides skillful forecasts is unknown. References: Dvorak, V. Dvorak, V. Fitzpatrick, P. Knaff, C. Landsea, and S. Forecasting , 10, pp. Martin, J. Forecasting , 8, pp. Each method has advantages and draw backs. Post-storm analysis of storm surge requires resolving differences in what each measures in order to find the best approximation of the surge heights. Such massive cloud formation produces heavy rains with large-sized raindrops.
At the top of the storm system, the rising warm air is transported outward and form an anvil-shaped cloud called "cumulonimbus". Further away from the center, at the tip the air becomes colder and dry and starts "sinking" downward. In this area, which is outside the storm system, the weather is abnormally good. This is the basis for the saying "lull before the storm" which many perceptive people notice before the arrival of the storm.
Tropical cyclone constitutes one of the most destructive natural disasters that affects many countries around the globe and exacts tremendous annual losses in lives and property. Its impact is greatest over the coastal areas, which bear the brunt of the strong surface winds, squalls, induced tornadoes, and flooding from heavy rains, rather than strong winds, that cause the greatest loss in lives and destruction to property in coastal areas.
A squall is defined as an event in which the surface wind increases in magnitude above the mean by factors of 1. The spatial scales would be roughly 2 to 10 km. The increase in wind may occur suddenly or gradually. These development near landfall lead to unexpectedly large damage. Tornadoes are tropical cyclone spawned which are to expected for about half of the storms of tropical storm intensity.
These are heavily concentrated in the right front quadrant of the storm relative to the track in regions where the air has had a relatively short trajectory over land. These form in conjunction with strong convection. Rainfall associated with tropical cyclones is both beneficial and harmful. Although the rains contribute to the water needs of the areas traversed by the cyclones, the rains are harmful when the amount is so large as to cause flooding. The storm surge is an abnormal rise of water due to a tropical cyclone and it is an oceanic event responding to meteorological driving forces.
Potentially disastrous surges occur along coasts with low-lying terrain that allows inland inundation, or across inland water bodies such as bays, estuaries, lakes and rivers. For riverine situations, the surge is sea water moving up the river.
A fresh water flooding moving down a river due to rain generally occurs days after a storm event and is not considered a storm surge. For a typical storm, the surge affects about km of coastline for a period of several hours. Tropical cyclones owe their existence to the release of latent heat in intense convection. This convection depends on eddy transfers of heat, moisture and momentum at the sea surface and radiative effects, as well as on the tropical-cyclone-scale circulation itself.
The relationship between the ocean and the atmosphere during tropical cyclone conditions is not a one-way interaction. The stress exerted by strong winds on the surface water and the negative pressure anomaly leads to a rise of mean sea level under the storm of about 1 cm per mb of pressure drop. This mound of water follows the storm and contributes to the storm surge when the hurricane makes landfall.
The strong winds generate surface waves with amplitudes of 20 m or more. The curl of the stress generates divergence in the upper layer of the ocean, producing regions of upwelling and downwelling. Turbulence is also generated in the ocean by the wind stress and this turbulence mixes warm surface waters with deeper cooler water. As we know, the ocean is divided into an upper layer of constant in the vertical temperature and a lower layer in which the temperature decreases with depth.
The upper layer is termed the mixed layer because the constant temperature in the vertical is maintained by vertical mixing. Temperature across the interface thermocline between the mixed layer and the lower layer is depicted as discontinuous.
The response of the ocean to the approaching storm. As the storm approaches, the increasing winds produce stronger turbulence and a deepening and slight cooling of the mixed layer. Outside the radius of maximum wind, the anticyclonic relative vorticity is associated with a stress field with negative curl. Convergence is induced in the mixed layer and downwelling occurs, which also acts to deepen the mixed layer. As the radius of maximum winds passes, the vorticity becomes strongly positive, and a positive stress curl induces horizontal divergence of mixed-layer water and a strong upwelling.
Behind the storm, the reverse sequence of events occurs. In addition, imbalances between the current velocities and pressure field in the ocean lead to eddies which between the current velocities and pressure field in the ocean lead to eddies which persists far behind the storm.
Since the eddy circulations in the ocean which are induced by tropical cyclones and the sea-surface temperature decreases may persist for many days after a storm's passage, the behavior of subsequent storms which cross the modified ocean surface may be affected, although the small area of significant sea surface temperature decreases makes a large influence unlikely.
In addition to the cooling of the ocean by upwelling and mixing, there are four other processes that may also affect the oceanic temperature. These include the following:. In appearance, a tropical cyclone is like a huge whirlpool - a gigantic mass of revolving moist air. Tropical cyclones or storms are between kilometres wide and km high. The Coriolis force caused by the rotation of the Earth causes the tropical cyclone to spin.
The central part of the tropical cyclone is known as the eye. The eye is usually km across.
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