Hurricanes, Cyclones and Typhoons

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Spinning, tropical storms receive different names depending on where they originate, but they all start the same way, and are capable of causing terrible destruction.

Autumn in the North Hemisphere is the peak season for hurricanes approaching the Caribbean and Southern US, in an average season 2 or 3 will hit US and The Caribbean.

Hurricanes originate in tropics, where temperature is warm (27ºC/81ºF, or more) and where the Coriolis effect is strong. They must start in the African coast and head west, growing as they go.

The Coriolis effect: As Earth spins, anything moving on its surface is deflected to the right in the northern hemisphere, and to the left in the southern hemisphere.

Moisture rising off warm sea starts to form clouds. If winds are slight, a mass of cloud can start to build up over one area. As vapour rises, pressure falls, and more air moves up to fill the gap. Under the influence of the Coriolis effect incoming air is deflected to right and the clouds start to spin anti-clockwise.

As moist air rises, it cools and water condenses out as rain. This releases latent heat (the heat released or absorbed by a substance as it changes its state). Latent heat warms and expands surrounding air so clouds grows and, as warm air is lighter than cold, pressure drops more, and more air is sucked inwards and upwards, in a continuous cycle. This is known as a tropical depression.

Cloud becomes wider and deeper, and the maximum air speed is around 35-64 Kt/39-73 mph. The storm itself becomes more organized and to be more circular in shape, resembling a hurricane. This stage is known as a tropical storm and is generally when meteorologists will give it a name and track it more closely.

If conditions stay stable, the process builds up on and on. When sustained wind speeds reach 64 Kt, it’s designated a hurricane. A Typical hurricane is about 500 km wide, but can vary substantially. Size isn’t necessarily an indication of destructive power. Hurricane Andrew, in 1992, was the most devastating in 100 years and even thus, relatively small.

A slice through a hurricane reveals spiral bends of deep storm clouds with thunder and lightning, plus heavy rain. At center, is the eye – the still center around which everything rotates. As rotating winds spin faster towards the center of the hurricane, Coriolis effect increases so air never get to the center, but curves around it. The convergence of air does towards increase pressure, and air actually falls down the eye where skies are clear and winds speed down.

Under influence of prevailing winds, hurricanes forming off the coast of west Africa move westwards and across to the Caribbean and across the southern US coast. They can run at speeds form 15 to 60 mph. Some follow straight course, others loop or wobble. Once over large land masses they quickly dissipate.

Hurricane-force wind can extend 40-200 km from the edge.

Strong, spinning storms that originate over tropical seas are called different names depending on where originated.

Hurricanes: Africa Typhoons: Oceania/Asia Severe Tropical Cyclones: Oceania Severe Cyclone storms: East Africa Coast, India, Indonesia Tropical Cyclones: South East Africa Coast