Tropical Cyclone Rainfall Climatology, Extremes and Flooding Potential over the Continental U.S.

Tropical cyclones (TCs) are high-impact events responsible for devastating rainfall and freshwater flooding. Quantitative precipitation estimates (QPEs) are thus essential to better understand and assess TC impacts. QPEs based on different observing platforms (e.g., satellites, ground-based radars, and rain-gauges), however, may vary substantially and must be systematically compared. The objectives of this study are to 1) compute the TC rainfall climatology, 2) investigate TC rainfall extremes and flooding potential, and 3) compare these fundamental quantities over the continental US across a set of widely-used QPE products. We examine five datasets over an 18-year span (2002-2019). The products include three satellite-based products, CPC MORPHing technique (CMORPH), Integrated Multi-satellitE Retrievals for GPM (IMERG), Tropical Rainfall Measuring Mission - Multisatellite Precipitation Analysis (TRMM-TMPA), the ground-radar and rain-gauge-based NCEP Stage IV, and a state-of-the-art, high-resolution reanalysis (ERA5). TC rainfall is highest along the coastal region, especially in North Carolina, northeast Florida, and in the New Orleans and Houston metropolitan areas. Along the East Coast, TC can contribute up to 20% of the warm-season rainfall and to more than 40% of all daily and 6-hourly extreme rain events. Our analysis shows that the Stage IV detects far higher precipitation rates in landfalling TCs, relative to IMERG, CMORPH, TRMM and ERA5. As a result, satellite- and reanalysis-based QPEs underestimate both the TC rainfall climatology and extreme events, particularly in the coastal region. This uncertainty is further reflected in the TC flooding potential measured by the Extreme Rain Multiplier (ERM) values, whose single-cell maxima are substantially underestimated and misplaced compared to the NCEP Stage IV.