Hurricanes

A hurricane is defined as a tropical revolving storm with violent winds. They are classed as force 12 on the Beaufort scale which means the wind speeds are greater than 75 mph (120 km/h). Winds of these speeds can uproot trees and destroy buildings so hurricanes endanger both the natural and built environments.

In general and for a variety of reasons, there are more deaths caused by the effects of hurricanes in LEDCs than MEDCs.

In MEDCs, the population has access to storm warnings via traditional media such as the radio and TV plus the internet and cell phones. This enables them to evacuate the area or take shelter in places that can withstand the battering from the hurricane. In LEDCs, the population are usually a lot poorer and the country's communications infrastructure is less well-developed so storm warnings may not reach large numbers of people. For many, the first they know is when they see it on the horizon. They don't have as much time to evacuate to safer areas and nor do they have much access to storm-proof shelters.

Hurricanes are huge intense low pressure systems - they can be up to about 800 km across. The intense storm at the center of the system is usually 300 km (the distance from Leeds to London) or less. Outside of the central storm, the winds and rain are less intense. They form from low pressure areas at sea and gain their enormous energy from warm water. The water needs to be at 26°C or more at the surface and between about 5 and 20 degrees either north or south of the equator. Shallow seas like the Caribbean and the Bay of Bengal are therefore ideal places for hurricanes to develop.

Warm moist air rises from just above the surface of the sea. As it does, it condenses to form large clouds that precipitate heavy rainfall. As the air rises, the coriolis force causes it to spin (clockwise in the northern hemisphere and counterclockwise in the southern hemisphere) so images from space show its spiral structure. The airflow high in the hurricane is diverging and cold air is thrown back in at the very center, forming the eye of the storm. Since cold air sinks, no clouds are formed in the eye. The eye can be up to 30 miles (45 km) across. Once a hurricane makes landfall, it starts to lose its strength as its energy comes from rising warm moist air from the sea.