A GIS analysis of rain field size for tropical cyclones before and after landfall using data from TRMM

Previous research has demonstrated that rainfall from tropical cyclones (TCs) makes an important contribution to the hydroclimatology of Mexico and the United States. Several studies of the sizes of TC wind fields have been conducted. However, fewer researchers have looked at the sizes of the rain fields of these storms. A larger size corresponds to an event of longer duration that can affect larger areas. Therefore, it is important to calculate how rapidly TC rain areas change in size and by how much during the hours before and after landfall. The environmental conditions associated with these changes can then be incorporated into rainfall forecasts. This study examined rain-field areas during 1998-2012 for TCs affecting the U.S. and Mexico utilizing data from the Tropical Rainfall Measuring Mission's 3B42 product. A Geographic Information System was used to calculate the areas of regions delineated by 5 mm h-1 rain rates. The conditions evaluated include intensity, motion, vertical wind shear, landfall location, whether or not the TC completed an extratropical transition, month, and time of day. After dividing observations into groups for each condition, Mann–Whitney U and Kruskal–Wallis tests determined whether statistically significant differences existed among the groups for each condition. The largest rain fields occurred in the late-season months of October and November. The second largest group featured hurricanes and/or TCs that were intensifying prior to landfall. TCs nearing the end of an extratropical transition also had relatively large areas of moderate-to-high rain rates.