Extended Abstract (60K)7A.5
Monsoon depressions, monsoon gyres, midget tropical cyclones, TUTT cells, and high intensity after recurvature: Lessons learned from the use of Dvorak’s techniques in the world’s most prolific tropical-cyclone basin.
Mark A. Lander, University of Guam, Mangilao, Guam
For nearly 30 years, the techniques developed by Dvorak for determining tropical cyclone intensity from visual and infrared satellite imagery have been used across the global tropics and sub-tropics. During this long 3-decade period, over 2,500 tropical cyclones have been subjected to Dvorak’s analysis rules and guidelines. The techniques often yield the only available guidance on tropical cyclone intensity diagnosis. After such a long and hugely successful period of use, have there been any problems noted by users in the field that the techniques have specific weaknesses, or do not address all situations? The western North Pacific is the world’s most prolific tropical cyclone basin, and is home to some unusual phenomena related to the monsoonal nature of that basin. Monsoon depressions (huge cyclonic circulations that are often the low-latitude pre-cursors to tropical storm formation in this basin) have given Dvorak users problems for many years. The even larger monsoon gyres also are puzzling. The tremendous range of tropical cyclone sizes along with a similar large range in eye size (from several kilometers to several hundred kilometers) has presented some problems. Lastly, the retention of typhoon force winds after recurvature has been a problem for users of Dvorak’s techniques, and prompted an in-house development (at the Joint Typhoon Warning Center, Guam) of the “XT” technique to estimate tropical cyclone intensity during the process of extra-tropical transition. Lessons learned from many years of routine field use of Dvorak’s techniques in the western North Pacific are presented.
Session 7A, 30 years of the Dvorak technique: Part I
Tuesday, 4 May 2004, 1:30 PM-3:00 PM, Le Jardin Room
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