2. Hurricanes blow themselves out as they reach the edge of the first of the three cells that move warm air towards the poles: at the boundary between the Hadley cell and the Ferrel cell.
3. The universal meteorological term for violent storms that start life over tropical waters is “tropical cyclone”, but they have different names around the world: “typhoon” in the northern Pacific and a “cyclone” in India and Australia are exactly the same phenomenon, and in the Atlantic it has the more familiar name of “hurricane”, which originates from the Central American Taino word huracan , meaning “god of evil”. Fran 1996
4. Donna Camille Elena Bob Andrew 1960 1969 1985 1991 1992
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8. Tropical cyclones affect a very large part of the Earth’s surface. They vary in scale from tropical disturbances to hurricanes and are classified according to windspeed. Hurricanes in the Caribbean and Atlantic Ocean Typhoons in the western Pacific Cyclones in the Indian Ocean
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10. In a mature hurricane, pressure may fall to as low as 880-970 millibars. This, and the strong contrast in pressure between the eye and the outer part of the hurricane leads to strong winds.
11. Since tropical cyclones require heat and moisture, they always form over oceans with warm sea surface temperatures (at least 26 0 C). As a consequences, they originate mainly over the western parts of the main ocean basins, where no cold ocean currents exist. Hurricanes occur only in tropical latitudes, but not in all tropical latitudes. They are absent from the east and south Atlantic and the eastern south Pacific. Why?
12. As well as requiring high sea temperatures, the low pressure area has to be far enough away from the equator so that the Coriolis force (the force caused by the rotation of the Earth) creates rotation in the rising air mass. If it is too close to the equator there will be insufficient rotation and a hurricane will not develop. Why do hurricanes not develop on the equator itself?
13. Because of the thermal requirements for formation, hurricanes are a hazard to specific locations at specific times of the year (eg from June to November in the west Atlantic).
14. A hurricane derives its energy from warm ocean water, but it loses power as it crosses land and quickly dries out. It may regenerate if it passes over the ocean again. Hurricanes may move in straight lines, curves and loops influenced by the large-scale air masses they encounter. Their path is erratic; hence it is not always possible to give more than 12 hours notice. Why do hurricanes die out over land?
15. This meant coastal areas in several Gulf states had to be evacuated. Then Elena slowed and was pushed eastward by local air masses towards the central Florida coast. It stopped for a while offshore, causing evacuation along the length of coastal Florida. Elena then turned westward and northward again, causing the evacuation again of coastal Gulf states. It finally made landfall near Biloxi in Mississippi and caused US$1.4 billion in damage (1989 dollars). The erratic nature of hurricanes is well illustrated by Hurricane Elena. This was a category 3 storm that caused considerable damage in the Gulf of Mexico in 1985. It headed west, rounded Florida then turned northward, towards an expected landfall in Mississippi.
