Tropical Storm Debby drenched Florida on Monday, killing at least four people and threatening southeastern US states with heavy rainfall and catastrophic flooding. VIDEOGRAPHIC
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00:00Hurricanes form in areas of intense low pressure, and throughout their cycle can build up energy
00:13levels equivalent to 10,000 nuclear bombs.
00:17Usually occurring in each hemisphere's summer months, hurricanes are also known as cyclones
00:21or typhoons.
00:24They form over warm ocean waters, when sea temperature is 26.6 degrees Celsius or higher
00:30at a depth of some 50 metres, when there's enough humidity, and when surface winds meet.
00:37When warm air comes into contact with the ocean's surface, it heats up and starts
00:41to rise, creating an area of low pressure underneath.
00:44New, cooler air swirls in to take its place.
00:47As the heated, moist air rises and then cools off, the resulting water vapour forms clouds.
00:52Fed by the ocean's heat and surface evaporation, the swirls of air gather pace, whipping up
00:57a storm.
00:58Moving at about 30 kilometres an hour, generally from east to west, the storm's diameter ranges
01:02from 300 metres to 1,000 kilometres.
01:04In just over a week, it can travel thousands of kilometres.
01:09The Suffer-Simpson scale rates hurricanes from 1 to 5, depending on wind speed.
01:14A Category 1 hurricane could bring down trees and cause temporary power cuts, while a Category
01:185 would destroy homes and cause catastrophic damage.
01:22Meanwhile, in the eye of the storm, conditions can be calm enough for birds to fly.
01:30Once they move inland or over cool waters, hurricanes finally die out.
01:34Some scientists believe a recent increase in number and intensity could be due to global
01:39warming.
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