Sensitivity of storm surge to stratified coastal ocean cooling in Hurricane Irene

Global populations are increasingly concentrated along urbanized coastlines and vulnerable to tropical cyclones and associated damages from wind, surge, flooding, and inundation. Significant progress has been made in hurricane track forecasting, while improving intensity and impact predictions remains a critical next step. Recent research has connected rapid weakening of hurricanes to ahead-of-eye center ocean cooling on mid latitude continental shelves. In 2011, Hurricane Irene’s leading edge winds drove a two-layer baroclinic circulation on the shelf, rapidly mixing the stratified ocean and cooling surface temperatures by up to 11^oC. These cool ocean temperatures beneath a warmer atmosphere reversed heat fluxes into the ocean, and rapidly weakened the storm in the 12 hours before landfall. The goal this study is to assess the sensitivity of predicted storm surge heights and precipitation to this ocean cooling and rapid weakening. We utilize regional implementations of the Weather Research and Forecasting (WRF) and ADCIRC modeling systems to simulate Hurricane Irene winds, rainfall, and storm surge respectively. Twin WRF model runs are performed with only warm and cold ocean bottom boundary conditions altered, to represent the coastal ocean mixing ahead-of-eye. Both simulations have similar track and landfall times relative to NHC best track estimates. The warm case overpredicts maximum wind speeds, precipitation, and minimum sea level pressure, while the cold case mitigates the high storm intensity bias. The WRF wind fields from the warm and cold runs are then used as forcing for ADCIRC. Preliminary results show that the warm case overpredicts water level at The Battery in Lower Manhattan by 0.5 meter, while the cold case accurately matches the observations. This finding suggests that capturing shelf-scale coupled ocean-atmosphere processes is necessary to accurately predict precipitation and storm surge along the highly stratified mid latitude coastal ocean.