Rapid intensification of hurricane Charley (2004) derived from WSR-88D data prior to landfall. Part I: GBVTD retrieval of the primary circulation and pressure tendencies

Hurricane Charley (2004) made landfall in Florida on 19 UTC, 13 August 2004 as a category 4 hurricane. Charley intensified rapidly from category 2 to 4 about 7 hours before landfall. The rapid intensification process was observed by coastal WSR-88Ds in Key West (KBYX) and Tampa (KTBW) in six-minute intervals. A total of 18 hours of WSR-88D data were analyzed which covered both the rapid intensification and decaying of Charley before and after its landfall. This paper presents Charley's kinematic and dynamic structure using winds deduced from the ground based velocity track display technique (GBVTD). This single-Doppler tropical cyclone wind retrieval technique estimates the axisymmetric tangential and radial winds, the asymmetric tangential winds, and the radial component of the environmental wind with respect to the radar-azimuth direction of the tropical cyclone center. The axisymmetric vertical motion, angular momentum, vorticity and pressure gradient are then derived from these wind components.

The GBVTD analysis successfully captured the rapid intensification of Charley's tangential wind accompanied by contraction of the eyewall. The radial profiles of the axisymmetric vorticity evolved from a ring pattern (barotropically unstable) to monopole pattern (barotropically stable) before Charley reached its peak intensity. A 30 mb drop of central pressure in 5 hours was found during this period. Charley's intensity decayed rapidly after it made landfall. The pros and cons of the WSR-88D scanning strategies and lessons learned in Charley will be discussed.