Meteorological hazards: Tropical storms, hurricanes, cyclones and typhoons

Definition and characteristics

Tropical storms, cyclones, hurricanes and typhoons, although named differently, describe the same disaster type.

Essentially, these disaster types refer to a large scale closed circulation system in the atmosphere which combines low pressure and strong winds that rotate counter clockwise in the northern hemisphere and clockwise in the southern hemisphere.

The system is referred to as a "cyclone" in the Indian Ocean and and South Pacific, "hurricane" in the Western Atlantic and Eastern Pacific and "typhoon" in the Western Pacific.

Hurricanes and typhoons are the same storm types as "tropical cyclones" (the local name for storms which originate in the Caribbean and China Sea region respectively).

A tropical cyclone is a non-frontal storm system that is characterised by a low pressure center, spiral rain bands and strong winds. Usually it originates over tropical or subtropical waters and rotates clockwise in the southern hemisphere and counter-clockwise in the northern hemisphere. The system is fueled by heat released when moist air rises and the water vapor it contains condenses ("warm core" storm system). Therefore the water temperature must be >27 °C.

Cyclones, hurricanes and typhoons can be predicted several days in advance. The onset is extensive and often very destructive. These disasters are usually more destructive than floods.

First, in a sudden, brief onslaught, high winds cause major damage to infrastructure and housing, in particular fragile constructions. They are generally followed by heavy rains and floods and, in flat coastal areas, by tidal waves.

In the case of cyclones, accurate landfall predictions can give only a few hours' notice to threatened populations. In addition, people generally opt to wait until the very last minute before abandoning their home and possessions. Deaths from drowning in the high tides and sudden flooding and material losses are therefore often very high.

 

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