A Statistical Tropical Cyclone Intensity Forecast Technique Incorporating Environmental Wind and Vertical Wind Shear Information

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  • 1 Department of Meteorology, Naval Postgraduate School, Monterey, California
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Abstract

An objective technique for forecasting the 24, 48 and 72 h intensity of western North Pacific tropical cyclones over the open ocean is proposed. In addition to the climatologicad and persistence information contained in present statistical intensity forecast technques environmental information is represented by empirical orthogonal functions of operationally-analyzed wind fields at 700, 400 and 250 mb and the vertical wind shears between these levels. The improvement over the conventional data only equations is small when a nonstratified dataset is used. When the sample is stratified by initial storm intensity, the separate sets of regression equations utilize more of the environmental predictors. Based on dependent sample verifications the combined results with the intensity-stratified sets appear to offer improvements relative to the Joint Typhoon Warning Center official forecasts at 48 and 72 h. Since the intensity-stratified results seem to be physically plausible, this technique appears to be an effective means of including environmental information in tropical cyclone intensity forecasts.

Abstract

An objective technique for forecasting the 24, 48 and 72 h intensity of western North Pacific tropical cyclones over the open ocean is proposed. In addition to the climatologicad and persistence information contained in present statistical intensity forecast technques environmental information is represented by empirical orthogonal functions of operationally-analyzed wind fields at 700, 400 and 250 mb and the vertical wind shears between these levels. The improvement over the conventional data only equations is small when a nonstratified dataset is used. When the sample is stratified by initial storm intensity, the separate sets of regression equations utilize more of the environmental predictors. Based on dependent sample verifications the combined results with the intensity-stratified sets appear to offer improvements relative to the Joint Typhoon Warning Center official forecasts at 48 and 72 h. Since the intensity-stratified results seem to be physically plausible, this technique appears to be an effective means of including environmental information in tropical cyclone intensity forecasts.

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