Utility of the WSR-88D Default and Tropical Z/R Relationships over South Texas during Hurricane Bret

The WSR-88D Algorithm Testing and Display System (WATADS) was used to analyze rainfall data over south Texas from Hurricane Bret. The precipitation algorithms used in WATADS produce rainfall accumulations in 2km by 1 degree quasi-horizontal "bins". Comparisons were made between the National Weather Service Corpus Christi (NWS CRP) WSR-88D radar accumulations and the corresponding rain gage accumulations for the 24 hour period ending August 23, 1999 1200 UTC. Two sets of calulations were made: one with the Z-R relationship set to the WSR-88D default values; and the other set to the tropical Z-R default values. Total rainfall was underestimated using the default Z-R relationship. Rainfall was overestimated using the tropical Z-R relationship. It is hypothesized that the overestimation is due mainly to strong horizontal wind associated with the hurricane that carried away rain that otherwise would have fallen into the raingages.