Rapid intensification of Hurricane Charley (2004) derived from WSR-88D data prior to landfall. Part II: HVVP adjustment for the environmental wind and central pressure retrieval

Two single-Doppler radar wind retrieval techniques are combined to estimate the central pressure of tropical cyclones: the Ground-Based Velocity Track Display (GBVTD) and the Hurricane Volume Velocity Processing (HVVP) methods. The GBVTD mean tangential wind is utilized with the gradient wind relationship and a reference pressure observation within the analysis domain to yield a central pressure estimate. However, the GBVTD mean tangential wind is biased by the unobserved transverse component of the environmental wind with respect to the radar-azimuth direction of the tropical cyclone center. HVVP provides a correction for this bias from its estimate of the environmental wind as a function of altitude.

Hurricane Charley (2004) was within range of the WSR-88D units at Key West (KBYX) and Tampa (KTBW) for about 14 hours prior to landfall in Florida. WSR-88D level II data form KBYX and KTBW for the time period 08-21 UTC Sep 13 2004 were combined with nearby pressure observations. The central surface pressure as a function of time was estimated from the combined GBVTD-HVVP algorithms with much higher temporal resolution compared to the infrequent measurements of central pressure obtained by aircraft reconnaissance. In particular, the onset of the intensification was clearly visible in the GBVTD-HVVP results yet undetected in the aircraft observations, ~6 hours before landfall. HVVP significantly improved upon the pressure estimates derived from GBVTD alone by 3-8 mb.