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Why do tropical cyclones require sea surface temperatures of 26oC to form?

   Written by: C.C. Chan

It is a well known observation that sea surface temperatures of at least 26oC would favour the formation of tropical cyclones. Studies showed that this warm water needs to be a relatively deep layer of around 50 metres.

The sea surface temperature requirement is related to how tropical cyclones derive their energy. A tropical cyclone can be thought of as an engine that requires warm, moist air as fuel. This warm, moist air cools as it rises in convective clouds in the rainbands and eyewall of the typhoon. The water vapour in the cloud condenses into water droplets and releases heat (known as latent heat). This heat provides the energy for the tropical cyclone. 

The 26oC value is tied to the thermal properties of the atmosphere in the tropical and subtropical areas. Above this temperature deep convection can occur, but below this value little or no convection can be found. 

Last revision date: <21 Dec 2012>