Evaluation of TRMM Daily Precipitation Estimates of Tropical Cyclone Rainfall using PACRAIN Data

This study evaluates the latest release TRMM 3B42 version 7 (V7) estimates of daily rainfall in tropical cyclones (TCs) using the Comprehensive Pacific Rainfall Database (PACRAIN) of 24h rain gauge observations. The evaluation is performed on two different terrain types: low-lying atoll sites (assumed to represent open-ocean conditions) and coastal and island sites (over land). The results show that TRMM 3B42 (V7) has good skill at detecting intense TC rainfall. It has good correlation and pattern matching with PACRAIN observations. However, it tends to overestimate heavy rain frequency on atoll sites, but tends to underestimate heavy rain frequency on coastal and island sites. In addition, TRMM is better able to estimate the intensity of TC heavy rain over ocean than over land. TRMM 3B42 is least skillful at coastal and island sites with high elevation, where it most significantly underestimates TC heavy rainfall and has the poorest skill scores, suggesting that TRMM 3B42 is unable to capture orographic enhancement during TC landfall. Finally, results from V7 were compared with results from its predecessor, Version 6, showing that Version 7 of TRMM 3B42 improves skill scores at high elevated sites. Version 7 also has higher bias on average for TC rain. The reason for this bias discrepancy requires further study. a) POD, b) FAR, c) BIAS, and d) ETS on atoll (red solid line with open circle), and coastal and island sites (blue solid line with triangle), at different rain threshold. Coastal and island sites were further separated into three subgroups according to their elevation: elevation <100m (black dotted line with open circle), elevation 100-200m (black dotted line with open square), and elevation >200m (black dotted line with cross). The error bars indicate 95% confidence intervals.