Coastal Downwelling Intensifies Landfalling Hurricanes

Abstract

AbstractThis study demonstrates a link between coastal downwelling and tropical cyclone (TC) intensification. We show that coastal downwelling increases air‐sea enthalpy (heat, moisture) fluxes ahead of TCs as they approach land, creating conditions conducive to intensification even in the presence of typically inhibiting factors like strong vertical wind shear. The study uses a coupled TC model (HWRF‐B) and buoy observations to demonstrate that coastal downwelling developed as three TCs in 2020 approached land. Results show downwelling maintained warmer sea‐surface temperatures over the ocean shelf, enhancing air‐sea temperature/humidity contrasts. We found that in such cases resulting air‐sea enthalpy fluxes can replenish the boundary‐layer even when cool, dry air intrudes, as in sheared storms and storms approaching continental land‐masses. The resulting warm, moist air is advected into the TC inner core, enhancing convective development, thus providing energy for TC intensification. These results indicate coastal downwelling can be important in forecasting TC intensity change before landfall.