Real-time implementation of VORTRAC at the National Hurricane Center

Under the auspices of the United States Weather Research Program's Joint Hurricane Testbed project, the Vortex Objective Radar Tracking and Circulation (VORTRAC) nowcasting system is currently being implemented and tested for real-time use at the National Hurricane Center (NHC) in Miami, Florida. Using the full-resolution coastal Weather Surveillance Radar – 1988 Doppler (WSR-88D) data, VORTRAC tracks the intensity (central pressure) and the radius of maximum wind of landfalling tropical cyclones. VORTRAC is a fusion of several single-Doppler radar data quality control and wind analysis methods. The data quality control component includes the Bargen and Brown unfolding algorithm, initialized by the gradient velocity azimuth display (GVAD) method, and simple ground clutter and noise removal techniques. The wind analysis component combines 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. This paper presents an overview of the components of VORTRAC along with a demonstration of its use on archived WSR-88D data from previous landfalling hurricanes. Tests of VORTRAC at NHC during the 2006 hurricane season have led to improvements in the system that will be implemented in time for the 2007 hurricane season.