The Tropical Rainfall Potential (TRaP) Technique. Part II: Validation

Abstract

Satellite analysts at the Satellite Services Division (SSD) of the National Environmental, Satellite, Data, and Information Service (NESDIS) routinely generate 24-h rainfall potential for all tropical systems that are expected to make landfall within 24 to at most 36 h and are of tropical storm or greater strength (Ͼ65 km h Ϫ1 ). These estimates, known as the tropical rainfall potential (TRaP), are generated in an objective manner by taking instantaneous rainfall estimates from passive microwave sensors, advecting this rainfall pattern along the predicted storm track, and accumulating rainfall over the next 24 h.In this study, the TRaPs generated by SSD during the 2002 Atlantic hurricane season have been validated using National Centers for Environmental Prediction (NCEP) stage IV hourly rainfall estimates. An objective validation package was used to generate common statistics such as correlation, bias, root-meansquare error, etc. It was found that by changing the minimum rain-rate threshold, the results could be drastically different. It was determined that a minimum threshold of 25.4 mm day Ϫ1 was appropriate for use with TRaP. By stratifying the data by different criteria, it was discovered that the TRaPs generated using Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) rain rates, with its optimal set of measurement frequencies, improved spatial resolution, and advanced retrieval algorithm, produced the best results. In addition, the best results were found for TRaPs generated for storms that were between 12 and 18 h from landfall. Since the TRaP is highly dependent on the forecast track of the storm, selected TRaPs were rerun using the observed track contained in the NOAA/Tropical Prediction Center (TPC) "best track." Although some TRaPs were not significantly improved by using this best track, significant improvements were realized in some instances. Finally, as a benchmark for the usefulness of TRaP, comparisons were made to Eta Model 24-h precipitation forecasts as well as three climatological maximum rainfall methods. It was apparent that the satellite-based TRaP outperforms the Eta Model in virtually every statistical category, while the climatological methods produced maximum rainfall totals closer to the stage IV maximum amounts when compared with TRaP, although these methods are for storm totals while TRaP is for a 24-h period.

Hurricane “Rainfall Potential” Derived from Satellite Observations Aids Overland Rainfall Prediction

“…TRaP uses the SSM/I, the Advanced Microwave Sounding Unit (AMSU), and the TMI rain rates to predict tropical cyclone rainfall potential. Ferraro et al (2005) found that the TMI TRaPs performed better than the AMSU TRaPs and SSM/I TRaPs.…”

“…Their method correctly predicted the highest actual rainfall totals for the major flood hurricanes Agnes (1972) andFifi (1974) and the lowest potentials for the relatively dry hurricanes Celia (1970) and Edith (1971). A similar technique called the tropical rainfall potential (TRaP) was developed at the National Oceanic and Atmospheric Administration/National Environmental Satellite, Data, and Information Service (NOAA/NESDIS; Kidder et al 2005;Ferraro et al 2005). TRaP uses the SSM/I, the Advanced Microwave Sounding Unit (AMSU), and the TMI rain rates to predict tropical cyclone rainfall potential.…”

On the Differences in Storm Rainfall from Hurricanes Isidore and Lili. Part I: Satellite Observations and Rain Potential

“…TRaP uses the Special Sensor Microwave Imager (SSM/I), the Advanced Microwave Sounding Unit (AMSU), and the Tropical Rainfall Measurement Mission (TRMM) Microwave Imager (TMI) rain rates to predict tropical cyclone rainfall potential. Ferraro et al (2005) found that the TMI TRaPs performed the best when compared to the AMSU and SSM/I TRaPs.…”

“…Alternatively, the physical connection between microwave observations from polar-orbiting satellites and precipitation is much better. A technique similar to Griffith et al's (1978) rain potential approach is called the tropical rainfall potential (TRaP), which was developed at the National Oceanic and Atmospheric Administration/ National Environmental Satellite, Data, and Information Service (NOAA/NESDIS; Kidder et al 2005;Ferraro et al 2005). TRaP uses the Special Sensor Microwave Imager (SSM/I), the Advanced Microwave Sounding Unit (AMSU), and the Tropical Rainfall Measurement Mission (TRMM) Microwave Imager (TMI) rain rates to predict tropical cyclone rainfall potential.…”

Long‐term rainfall risk from tropical cyclones in coastal areas

“…Under this hypothesis, the temporal variability of rainfall at a fixed location A is statistically the same as the variability that results from translating the frozen-in-time rainfield over A with the storm velocity V t . For example, Vicente et al [1998], Scofield and Kuligowski [2003], Kidder et al [2005], and Ferraro et al [2005] used Taylor's hypothesis to obtain rainfall totals at fixed locations from satellite and radar rainfall snapshots.…”