Landfalling Tropical Cyclone Rainfall Distributions

Rainfall-induced freshwater flooding associated with landfalling tropical cyclones (TCs) is one of the major threats to both life and property along coastal regions of the world. It accounted for about 27% of the total fatalities caused by TCs in the United States during 1963-2012. Landfalling TC rain magnitude and distribution is affected by many factors such as track, translation speed, and the TC’s interaction with synoptic and mesoscale features. The interaction of TCs with baroclinic systems and their transition to extratropical status (ET) are also processes that can produce asymmetries in the rain field of TCs moving poleward. Strong flow ahead of the storm that interacts with frontal boundaries can produce uplift and torrential rainfall in much the same way as topographical barriers can. TCs undergoing ET typically experience strong vertical shear, leading to the development of pronounced azimuthal asymmetries. Often these asymmetries extend several hundred kilometers ahead of the TC. Rainfall well in advance of these TCs can sometimes cause significant death and damage. Since the landfall of Tropical Storm Agnes in 1972 Lance Bosart and his students were key players in our improved understanding of these impacts on the landfalling TC rain distribution and amount. Discussion is presented on Lance and his student’s contributions to understanding these physical processes that modulate landfalling TC rainfall distributions. A review of our current state of the art in landfall TC rainfall forecasting and an outlook for improvement will be presented.