Western North Pacific tropical cyclone wind structure and structure changes

Abstract

Subjective and objective analyses of near-surface winds are utilized to estimate tropical cyclone (TC) size over a region of the western North Pacific. An empirical outer wind profile assuming partial conservation of angular momentum is utilized to determine the radial extent of cyclonic winds, which may be defined as the TC size in four categories. The first method uses the radii of either 3O-kt or 35-kt wind in the Joint Typhoon Warning Center (JTWC) warnings during 1989-1994 to estimate the size categories each 6 h. A second subjective method based on satellite imagery has more cases of large and midget TCs than the first method. A multi-quadric interpolation (MQI) of composited wind observations over +/- 12 h is tested as a more objective method of estimating the 30-kt or 35-kt wind radii. For two case studies, these MQI-derived size estimates generally agree with the first method, although the MQI values varied more in time depending on the data distribution. It is concluded that a combination of the second and third methods could provide supporting data for estimating the outer wind profiles for the JTWC wind warnings.