The added value of IMERG in characterizing rainfall in tropical cyclones

Heavy rainfall associated with landfalling tropical cyclones (TCs) is responsible for significant societal and economic impacts. Improved characterization and description of how rainfall during these storms changes as a function of distance from the center of circulation are critical to increase our preparedness against this natural hazard. Since March 2014, the hydrometeorological community has benefitted from the Global Precipitation Measurement mission (GPM), especially with its gridded-rainfall product IMERG (Integrated Multi-satellitE Retrievals for GPM), which offers global rainfall estimates with a spatiotemporal resolution of 0.1 degrees x 0.1 degrees every 30 min, on a near-real time basis. We analyze here 166 TCs worldwide from March 2014 through March 2016. For every TC, we extract from IMERG V04 a 2000 km rainfall swath along the TC track. This allows us to characterize with great accuracy the spatial structure of TC-rainfall, from its development all the way to its landfall and dissipation. We stratify the analyses by basin of origin, intensity of the storm, and whether the TC was over ocean or land. We find that the South Pacific, West Pacific, and North Indian basins yield (median) rainfall intensities between 6 and 7.5 mm.h(-1) at radii similar to 50 km. These intensities are for TCs over ocean, and in most cases they are twice (or more) as high as the median intensities for TCs over land (similar to 3.0 mm.h(-1)). For the North Atlantic, South Indian, and East Pacific basins the oceanic (median) rainfall intensities are between 4 and 5 mm.h(-1). Upscaled IMERG estimates (0.25 degrees x 0.25 degrees every 3 h) do not capture the rainfall structure within the eyewall (i.e., for radii < 50 km), especially for the South Pacific, West Pacific, and North Indian basins.