Determination of the circulation center and inner core evolution of Hurricane Danny (1997) using the GBVTD-simplex algorithm

The evolution and structure of Hurricane Danny (1997) is examined via a single-Doppler radar tropical cyclone (TC) wind retrieval technique, the ground-based velocity track display (GBVTD) algorithm. The GBVTD technique is applied to 5-hours of data gathered simultaneously by two WSR-88D radars in Mobile, AL (KMOB) and Slidell, LA (KLIX) at ~6 minute intervals. The circulation centers and the primary circulations of Danny derived from these two independent radar observations (~60 volumes from each radar) are used to evaluate the accuracy of the GBVTD algorithm and the GBVTD-simplex center finding algorithm. Other observations, such as dual-Doppler analysis, dropwindsonde, and in-situ measurements from the NOAA WP-3D and the U.S. Air Force Reserve Command WC-130 (AFRC), aircraft provide independent assessments of the TC center and structure. It is found that the GBVTD-simplex derived centers, which used only the maximum mean tangential wind as the sole criterion, were unsatisfactory and unstable. An improved algorithm is proposed to seek time continuity in RMW, maximum mean tangential wind, and the center position in order to reduce the large fluctuations experienced in this study and the results are used to quantify the accuracy of the derived circulation centers. The quality if the GBVTD-derived circulation from these new centers is assessed. Danny's kinematic structures retrieved from KLIX and KMOB data using the improved sets of centers are consistent with the structures retrieved from the dual-Doppler analyses. Danny evolved from a mostly axisymmetric TC into a wave number one asymmetric TC then returned to an axisymmetric TC during this five-hour period.