Extreme rainfall from Hurricane Harvey (2017): Empirical intercomparisons of WRF simulations and polarimetric radar fields

Abstract

We examine extreme rainfall from Hurricane Harvey (2017) based on empirical analyses from polarimetric radar observations as well as high-resolution model simulations using the Weather Research and Forecasting model (WRF). Spatial and temporal structures of extreme rainfall from Hurricane Harvey were characterized using a dense network of rain gauges and high-resolution radar rainfall fields. Numerical simulations using two different microphysical parameterizations, the WRF 6-class single-moment (WSM6) scheme and Morrison double-moment scheme, were employed, together with an additional simulation using the hail version of the Morrison microphysical scheme. Extreme rainfall from Hurricane Harvey is closely tied to the structure and evolution of outer rainbands. Intercomparisons of the simulated and observed polarimetric radar variables show contrasts and similarities of different microphysical schemes in representing critical microphysical processes for extreme rainfall. All three WRF simulations overestimate the frequency of larger rain drops, but exhibit comparable signatures of specific differential phase to observations. The WSM6 simulation shows strong convection that leads to the largest coverage of convective rainfall over outer rainbands of all three WRF simulations. We highlight the capabilities of atmospheric model simulations and improved quantitative rainfall estimates in characterizing key features of extreme rainfall from landfalling TCs as well as critical storm ingredients that produce them.