Sunday, September 22, 2013

Super Typhoon Usagi drawing energy from record warm waters

Super Typhoon Usagi is the strongest tropical cyclone storm on a global level this year, bringing destruction to the Northern Philippines, Taiwan, Hong Kong and southern China.

Warmer surface waters contribute energy for much stronger, more intense storms. Parts of the Western Pacific have experienced record and much warmer than average sea surface temperatures in August, part of record global sea surface temperatures.

A NASA analysis of the storm remarked on it's super rapid intensification, identifying warm ocean waters as a contributor to the storm's rapid growth and strength.

Data was collected on Thursday, September 19, 2013, when Usagi was at category 3 on the Saffir-Simpson hurricane intensity scale. A few hours later, Usagi completed its lightning-fast intensification to category 5, the highest category in the scale. While the center of this tropical cyclone is forecast to past just south of Taiwan in a few days, some forecasts have it striking Hong Kong a few days after that.

A number of the features of the TRMM radar observations are consistent with a well-organized storm with an efficient "heat engine." A tropical cyclone's heat engine extracts heat from the ocean's surface through wind-enhanced evaporation and converts a portion of that energy into kinetic energy of the destructive winds that circle under the eyewall of the storm. The eyewall is an arc or ring of string storms just outside the mostly cloud-free eye at the center of rotation of the tropical cyclone.


Figure: Projected storm surge impact of Typhoon Usagi. Courtesy: GDACS

Super Typhoon Usagi, a Saffir-Simpson Category 5 tropical cyclone that formed mid-September was the strongest storm so far in 2013. Maximum sustained wind speed is estimated at 259 km/h. Maximum storm surge height is 2.3m when it hits Imtin, China at 18:00 22 September.

The Typhoon developed from a tropical depression from September 16 to 18, rapidly picking up energy and moisture from the warmer than average waters before causing 8 metre waves, torrential rains, landslides as it passed between the Northern Philippines and Taiwan leaving destruction in its wake.

The typhoon is heading straight for Hong Kong and China, although has reduced slightly in intensity. It will be the strongest storm in 34 years to hit Hong Kong.


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