A Comparison of WSR-88D Storm Total Precipitation Performance during Two Tropical Systems following Changes to the Multiplicative Bias and Upper Reflectivity Threshold

Abstract

Seventy-two hours of Melbourne, Florida (KMLB), Weather Surveillance Radar 1988 Doppler (WSR-88D) rainfall data were compared with rain gauge data during Tropical Storm Gordon as it impacted east-central Florida. Comparisons were made by centering arrays of 9 and 25 storm total precipitation (STP) data bins over corresponding rain gauge locations, then performing bias and dispersion calculations prescribed by the Operational Support Facility (OSF). Findings indicate that the STP significantly underestimated rainfall during Tropical Storm Gordon and the magnitude of error varied with range from the radar. Based on these findings, it was recommended that the upper reflectivity threshold be increased to 55 dBZ and the multiplicative bias be set to 1.4 as an immediate but interim measure to minimize the differences between the STP and surface rain gauges during tropical systems. These recommended changes were given approval by the OSF and were deployed on the KMLB WSR-88D for a 72-h period as Tropical Storm Jerry affected east-central Florida. Significant improvement was noted in the STP product during Tropical Storm Jerry. Future studies will utilize base data replay capabilities to manipulate algorithms, biases, and thresholds individually and collectively to develop better radar rainfall adjustment schemes. Future work will also involve deploying tropical rainfall Z?R relationships that should further improve on the WSR-88D?s rainfall estimation capability during tropical systems.