Higher than normal sea surface temperatures in the South China Sea set the scene for an active typhoon season. Nevertheless, the Hong Kong Observatory is conservatively predicting a normal level of storm activity this year, four to seven typhoons coming within 500km of the territory.
The observatory’s C C Chan writes that sea temperatures have to be above 26 degrees Celsius to favour typhoon development. The warm water needs to go down at least 50 metres. A typhoon can be thought of as an engine that needs warm moist air as fuel. This warm moist air rises in convective clouds in the rain bands and eyewall of a storm. The water vapour in the clouds condenses into water droplets and releases latent heat. This provides the energy for a tropical storm.
Rainfall this year will range from 2300 mm to 2900 mm, the observatory says, and could be higher than normal.
The US’s National Oceanic and Atmospheric Administration has said it is likely that storm activity in the Pacific will be near average or above average. This means there will be 15 to 22 storms, 8 to 13 typhoons and 4 to 8 major typhoons. The reason given is El Nino activity, which raises sea surface temperatures. Global computer models are predicting positive “Pacific decadal oscillation”. Cycles over decades can favour warmer than average sea surface temperatures at times. That is what is happening this summer.
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