Hurricanes

AFP English

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.

01:48For more UN videos visit www.un.org

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