Hurricanes

The strongest tropical storms are called hurricanes, typhoons or tropical cyclones. The different names all mean the same thing, but are used in different parts of the world. If these huge stormsstart in the Atlantic, off the west coast of Africa, they are called hurricanes.
In an average year, over a dozen hurricanes form over the Atlantic Ocean and head westwards towards the Caribbean, theeast coast of Central America and the southern USA (Florida in particular). Hurricanes may last as long as a month and although they travel very slowly - usually at about 24 km/h (15 mph) - wind speedscan reach over 120 mk/h (75 mph).

How hurricanes form
* When this warm and wet air rises, it condenses to form towering clouds, heavy rainfall. It also creates a low pressure zone near thesurface of the water.
* Rising warm air causes the pressure to decrease at higher altitudes. Warm air is under a higher pressure than cold air, so moves towards the ‘space’ occupied by the colder,lower pressure, air. So the low pressure ‘sucks in’ air from the warm surroundings, which then also rises. A continuous upflow of warm and wet air continues to create clouds and rain.
* Air thatsurrounds the low pressure zone at the centre flows in a spiral at very high speeds - anti-clockwise in the northern hemisphere - at speeds of around 120 km/h (75 mph).
* Air is ejected at the top ofthe storm – which can be 15km high – and falls to the outside of the storm, out and over the top, away from the eye of the storm. As this happens, it reduces the mass of air over the ‘eye of thestorm’ - causing the wind speed to increase further. Some ejected air also cools and dries, and sinks through the eye of the storm, adding to the low pressure at the centre.
* The faster the winds blow,the lower the air pressure in the centre, and so the cycle continues. The hurricane grows stronger and stronger.
* Seen from above, hurricanes are huge circular bodies of thick cloud around...