IMPROVEMENTS TO THE EXPERIMENTAL TROPICAL RAINFALL POTENTIAL (TRaP) TECHNIQUE

As discussed by Kidder et al. (2001), heavy rainfall from landfalling tropical cyclones is a major threat to life and property. Rappaport (2000) found that in the contiguous United States during the period 1970–1999, freshwater floods accounted for more than half of the 600 deaths directly asso-ciated with tropical cyclones. Forecasting rainfall from landfalling tropical cyclones is a difficult task. While the storm is off-shore, few rainfall observations are possible, and initializing NWP models with sufficient details of the storm so that accurate rainfall forecasts can be made is extremely difficult. Radar observations of storm rain rate and rain area are valuable, but only when the storm is within radar range of the coast. Since 1992, the Satellite Services Division (SSD) of the National Environmental Satellite, Data and Information Service (NESDIS) has x- eperimentally used the operational Defense Mete-orological Satellite Program (DMSP) Special Sen-sor Microwave Imager (SSM/I) rain rate product (Ferraro 1997) to produce a rainfall potential for tropical disturbances expected to make landfall within 24 hours. The launch in 1998 of the first Advanced Microwave Sounding Unit (AMSU) on the NOAA-15 satellite provided an additional rain-fall data source. The NESDIS/SSD technique (Kidder et al. 2000) was performed manually by an analyst and resulted in a single number called the tropical rain-fall potential, defined as TRaP =