Hurricane Occurence, Movement

Hurricanes have their power from the warm tropical water and also from the latent warm released as water vapor condenses into clouds.

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Figure 3:In an typical year, 90 - 100 tropical storms develop.This figure shows wherein they form and the most typical paths theytake.
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Figure 4: Sea surface temperature map for the northern hemisphere summer. The yellow, orange, and also red colors display water temperatures warm sufficient to sustain hurricanes (> 26.5°C).
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Figure 3 shows where most hurricanes room born and also the general direction in which they move. Notice that they kind over tropic oceans, except in the south Atlantic and also in the eastern southern Pacific. The surface ar water temperatures in these locations are as well cold for their development (see number 4). The warmth waters that the west NorthPacific is theworld"s hot spot because that tropical storm development. The table belowgive statistics because that an "average" season in each s basin.

BasinSeason StartSeason EndTropical StormsHurricanesMajor Hurricanes
Northwest PacificYear RoundYear Round26.716.98.5
Northeast PacificMayNovember16.39.04.1
Southwest IndianOctoberMay13.36.72.7
North AtlanticJuneNovember10.65.92.0
Australia Southwest PacificOctoberMay10.64.81.9
Australia south east IndianOctoberMay7.33.61.6
North IndianMayNovember5.42.20.4

Movement and Seasonal time of Atlantic Hurricanes

It is shown above that the official Atlantic Hurricane season lasts native June first through the finish of November, and also that ~ above average, there space 10.6 tropic storms, 5.9 hurricanes, and 2.0 major hurricanes (category 3 and higher). Number 8 mirrors that Atlantic hurricane task peaks in early September and that storms occasionally kind outside the main hurricane season in May and also December. This sample of hurricane occurrence is closely correlated v the seasonal adjust in Atlantic sea surface temperature. The greatest sea surface ar temperatures in the Atlantic typically occur in early on September.

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Figure 8: Average variety of Atlantic Hurricanes every century together a function of calendar date.

The most important determinent that hurricane motion is the regional environmentalair circulation in the middle troposphere. In other words, hurricanes often tend to it is in "steered"around through the winds punch at about 500 mb push (5 to 6 km over sea level). In so late summer and earlyfall the "typical" wind patterns at 500 mb are usually easterly (or east towardwest) below or southern of 30° phibìc latitude and also westerly (west towards east) over ornorth the 30° phibìc latitude. The reason for this is the a broad and elongated areaof higher pressure is typically found near 30° latitude (See number N (top)). Hurricanes come the south30° latitude will usually be steered from east to west. However, as displayed in figure 3 above, it is not unusual for hurricanes revolve away indigenous the equator (toward thenorth in the north Hemisphere) in ~ some suggest along your track.If hurricanes movenorth the 30° latitude, they frequently make a turn toward the east.

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Figure 5: Burmuda high and also hurricane tracks.

The subtropical high push area end the Atlantic s is often found asa high pressure cell (See number N (bottom)). If the position and overall dimension of this attribute changes,its facility is frequently located close to the island that Burmuda, hence it is regularly calledthe Burmuda High. This is quite important to hurricane activity in the vicinity of the United says as presented in number 5. In the height panel, tropicalcylones moving across the Atlantic will turn northward before reaching Florida,while in the bottom panel, they room steered toward the east coast of Florida.In instances where the Burmuda high extend slightly further west, tropical solution canbe steered towards the west either across Florida or south of Florida prior to turningnorth come hit the gulf coast. If the Burmuda high extends even further west, tropicalstorms have the right to move west right across the Gulf that Mexico and hit Texas or Mexico. A figureshowing the number of Atlantic landfalling UShurricanes from 1900 - 2007 by county has been produced by the national HurricaneCenter.

Recall from the vault material around the southwest monsoon the the place of one more subtropicalhigh press cell (often called the monsoon high in this an ar of the country) is really importantin understanding the advance of summer thunderstorms in civicpride-kusatsu.net.

Once hurricanes move north that 30° latitude, they generally pick up speed (becausethe steering winds generally end up being stronger far from the topics) and will eventuallyturn toward the east (because prevailing 500 mb winds in the center latitudesare an ext likely to it is in from west to east). Once tropical storms move into the center latitudes, that is commonfor them to obtain "picked up" by the winds associated with a 500 mb longwave trough and move towards the north and east.The areas of the United claims at risk from hurricanesincludes the whole Gulf that Mexico coastline and the whole eastern seaboard, whichincludes the larger northeastern urban like brand-new York. While that is much less likely the a major hurricane would certainly hit new York City than areas further south(because the Burmuda high would need to be positioned simply right and also the oceanwater termperature to reduce on the way), it has happened in the past. history Reveals Hurricane risk to brand-new York City.The "Great Hurricane that 1938" slammed into Long Island and devistated much of southernNew England as a group 3 storm. The last direct hit on new York City was backin 1821.And muchof the brand-new York metro area is just over sea level, making the city rather vulnerableto a solid hit. To make matters worse, the only way a really strong hurricane isgoing come hit brand-new York City is if it turns north and moves an extremely quickly, so that itdoes not have time come weaken lot as it moves over cooler water, potentially leavinglittle time because that evacuations.

The effects of Pacific Hurricanes ~ above the Continental unified States

Although the west coast of the united States has never been hit by a hurricane, that is no all that uncommonfor the west coast and also desert southwest to gain heavy rain events from remnants that easternPacific tropic storms and also hurricanes (see California"s tropical Storms).As displayed in number 3 above, most eastern Pacifichurricanes relocate westward out right into the Pacific s away indigenous the north American continent.However, if a storm it s okay "picked up" by the winds associated with a middle latitude 500 mbtrough, it can be turned north and also east ago toward phibìc America. This is most most likely to happenlate in the hurricane season (mid-September and also later) since as the seasons change, there isenough cold air that troughs can begin to dig right into southern parts of the US. As these storms move northward, they encounter the chillier waters of the eastern Pacific and also weaken listed below hurricane strength before reaching the joined States. Farther south along Baja California and theMexican Pacific coast, the water have the right to be warm sufficient to support a hurricane, and these areasdo endure hurricanes native time to time. Current sea surface ar temperaturesin Tropical east Pacific region.

Predicting Hurricane Movement and also Intensity, offering Public Warnings

The text above summarizes the common paths take away by hurricanes.However, as many of you recognize the actual course taken through a hurricanecan it is in caotic and daunting to predict. One difficulty lies inthe fact that the upper level winds that have the right to steer hurricanes (pressure levels at 500 mb and higheraltitudes) are frequently quite weak in the tropics.
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Figure 6: main Track Errors because that Atlantic s Tropical Storms and Hurricanes by te (source NHC) (n mi = nautical miles, whereby 1 n mi = 1.15 mi)
When steeringwinds room weak, the actual course of a hurricane is established bythe framework of the storm and the storm"s interaction with the environment. Determinants that may contribute to a storms path include: a surrounding area of ever before so slightly warmer orcolder sea temperatures, interactions in between the storm and surrounding land areas,the family member location and also intensity the convection in ~ a storm, orweak and also unnoticed disturbances in the top air wind flow. Thus, that is notall that uncommon for hurricanes to take it erratic paths and make oddturns that capture weather forecasters by surprise. If you room interested, youcan look in ~ the monitor of every Atlantic Hurricanes from 1851-2010 (from Unisys)

The nationwide Hurrican facility in Miami, Florida uses innovative computermodels to predict hurricane movement. Back there space still numerous aspectsof hurricane advancement that we execute not understand, stable progress has been madein improving forecasts the hurricane activity (see number 6).

A more complicated problem is to predict the future intensity of hurricanes, the is will certainly they combine or weaken and how quick will these transforms occur. Theproblem below is brought about by both by our absence of understanding of hurricane evolutionwhich outcomes in bad computer modeling and the lack of observationsor measurements near the storm"s center, i m sorry are essential to understand exactlywhat is happening. The huge problem is discussed by Max Mayfield, manager of theNational Hurricane center -- "Most significant hurricanes become significant hurricanes by goingthrough some fast intensification cycle the we just don"t recognize ..."This sets increase the opportunity of what Mayfield phone call his "nightmare scenario" --where for example, a quite weak hurricane just off the shore rapidly intensifiesto a major hurricane overnight, and slams into a coastal region wherein the populationis unprepared. "We quiet haven"t had actually that nightmare script where human being go come bed prepared for a group 1 hurricane and wake approximately a classification 4," Mayfield says. "That"s walk to occur one of these days, and it"s going to be devastating."

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Figure 7: example showing area over which hurricane warnings are issued (source NHC)

With modern-day techniques of forecasting and also tracking hurricane paths, that is always possible to issue warnings around the "probable" places that will be affected by any given hurricane. Return hurricanes deserve to be easily tracked utilizing satellite data, predictions of their future movement and also intensity room by no way certain. Based upon the approximated uncertainty in future hurricanemovement, hurricane watches and also warnings space issued because that a broad swath as shownin figure 7. The nationwide Hurricane center defines hurricane watches and warnings together follows: Hurricane Watch: An notice of specific coastal areas that a hurricane or one incipient hurricane problem (sustained winds > 74 mph) poses a feasible threat, usually within 36 hours. Hurricane Warning: A warning that sustained winds the 74 mph or higher associated v a hurricane room expected in a specified seaside area in 24 hrs or less. A hurricane warning have the right to remain in impact when dangerously high water or a mix of dangerously high water and exceptionally high waves continue, even though winds may be less than hurricane force.

Destruction at Landfall

return we generally categorize hurricanes in regards to their windspeed(see Safir-Simpson table below), coastal flooding because of what is called the storm surge usually reasons the most damage. A stormsurge is an abnormally high climb in sea level along a coastline causedprimarily by high winds pushing and also piling up water. It have the right to be fairly misleading to think the the storm surge as large waves. The storm rise is a big dome of water that can more than 100 kilometres in width, which sweeps end the coastline. Storm surges have actually demolished marinas, piers, boardwalks, houses, and other coastline structures, if eroding beaches and also washing out seaside roads and railroads. The elevation of the dome of water counts on the windspeed as displayed in the Saffir-Simpson table below.With a hurricane (in the north Hemisphere),the many damaging storm surge and also strongest winds occur to the best of the storm"s center. Theright side of the storm is where the wind blows directly onshore and where the windspeedis highest possible for a relocating storm (See figure O). The damage potential linked with a storm surge depends upon (1) the stamin of the wind and also the areal extent of the solid winds,i.e., big storms develop stronger surges than little storms. The size of the storm is importantbecause the much longer the "fetch" or the path length of strong winds over the ocean, the more waterthat deserve to be piled up; (2) the shape of the coastline, i.e.,the slope of the Earth"s hard surface near the coastline. In other words, if you to be to go outinto the ocean, how rapidly walk the water depth increase.The more gradual the slope, the greater the damage potential because the same elevation storm surgewill move more inland; and (3)the timing of the surging with partnership to the normal high and low tides. The storm surge to add on peak of the typical tides. Thus, the worst case wouldbe because that the storm come hit in ~ high tide due to the fact that the water level is already high and also the storm surgeadds on peak of that. If the storm access time at low birds (normal high tide adds to the elevation ofthe storm surge).

Forecasting the storm surge that will occur as a hurricane makes landfall is complicated. Forecasters mustrely on computer models. The models need to accurately account for the shape and also slope the thecoastline in connection to the wind direction. That s right predicting the storm surge close to inlets, bays, and also river outlets is quite complicated as described in the link.

Assorted annimations showing locations in United claims that would certainly be innundated through storm surges rangingfrom one to seven meters above normal sea level are displayed in the web links below. Keep in mind the an actualhurricane would have a an ext local effect and also would no inundate the entire region shown in the annimations. Itmore highlights areas that are fragile to hurricane storm surges.High winds also cause substantial damage. Hurricane strength winds can damages or destroy vehicles, buildings, bridges, etc. High winds also turn loose debris into flying projectiles, making the outdoor civicpride-kusatsu.netsphere even an ext dangerous. Together hurricanes come in many sizes, the areacovered through hurricane pressure winds is a factor in the complete amount of damage done. For example,not only was Katrina a very powerful storm, it was also a very huge storm.

Flooding is also caused by the hefty rains linked with hurricanes, specifically whena slow moving or virtually stationary hurricane sits simply offshore bring about a an extensive period of heavy rainsover nearby seaside areas. This have the right to be particularly problematic if the adjacent coast has sharply risingmountains, enhancing the hefty rains by orographic lifting, with the runoff resulting in landslides.

Damage may also occur native hurricane-spawned tornadoes the may type as the hurricane interacts v land areas. Most hurricanes the strike the united States develop at least one tornado. Around one-quarter of castle producesignificant numbers of tornadoes.Tornadoes space most likely to construct in theright former quadrant that the storm (in relationship to the movement of the storm), and also are an ext likely to be associatedwith a spiral rain band rather than the storm"s center. They an outcome fromthe vertical wind shear that often creates in the lower levels the the hurricane"scirculation together the storm winds communicate with the land. Most hurricane-spawned tornadoes are of the weak range (compared come the monsters that can form overthe great plains that the unified States), yet can quiet produce far-reaching damage.

Hurricanes weaken quickly after make landfall because the storm is cutoff from its fuel supply(the warm ocean water). Return winds weaken, heavy and flooding rains might move much inlandwith the storm remnants.

In summary, the feasible dangers associated with a hurricane are: storm surge solid winds hefty rains (and flooding) connected tornadoes

In an effort to calculation the feasible damage the a hurricane"s sustained winds and also the storm surge can do come a coastal area, the Saffir-Simpson scale was developed (see table below). Hurricanes that reach group 3, 4, or 5 strength and also calledmajor hurricanes. One trouble with this group system is the it does not accoutfor the size of the storm (the areal extent of hurricane and also tropical force winds).As we have seen with Katrina in 2005 and also Ike in 2008, large storms canproduce a much larger storm rise than estimated in the tables below, whichis solely based on the windspeed of the storm.

Saffir-Simpson Hurricane Damage-Potential Scale scale Number (Category) main Pressure mb (in.) Winds mi/hr (knots) Storm surging ft (m) Damage
1 >980 (>28.94) 74-95 (64-82) 4-5 (~1.5) Damage mainly to trees, shrubbery and also unanchored mobile residences
2 965-979 (28.50-28.91) 96-110 (83-95) 6-8 (~2.0-2.5) Some trees blown down; significant damage come exposed mobile homes; some damage to roofs that buildings
3 945-964 (27.91-28.47) 111-130 (96-113) 9-12 (~2.5-4.0) Foliage eliminated from trees; large trees swollen down; mobile homes destroyed; some structural damages to tiny buildings
4 920-944 (27.17-27.88) 131-155 (114-135) 13-18 (~4.0-5.5) All indicators blown down; extensive damages to roofs, windows, and also doors; complete destruction of mobile homes; flooding inland as far as 10 kilometres (6 mi); significant damage to lower floors that structures near shore
5 155 (>135) >18 (>5.5) Severe damage to windows and doors; extensive damages to roofs the homes and industrial buildings; little buildings overturned and also blown away; significant damage to lower floors of all structures much less than 4.5 m (15 ft) above sea level within 500 m that shore

Hurricane Katrina Videos

Ever wonder what it would certainly be like to be close to the shore when a major hurricane strikes?Many amateur videos taken during and also after hurricane Katrina deserve to beviewed YouTube table of contents of Hurricane Katrina vidoes.

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Distribution of major Landfalling hurricanes in the unified States

Map describe the location and also strength that all significant landfallinghurricanes (category 3 and also higher) in the United claims from 1899 through 2008.The all at once average is slightly much less than one every year. 2005had a document of four major landfalling hurricanes: Dennis, Katrina,Rita, and also Wilma.