Impacts of Ocean Initialization and Three-Way Atmosphere-Wave-Ocean Coupling on Hurricane Forecasting

Tropical cyclones (TCs) are strongly coupled to ocean mixed layer and sea surface waves through air-sea momentum, heat, and moisture fluxes, as well as other air-sea-wave interaction processes. As NCEP/EMC’s primary operational hurricane model, the Hurricane Weather Research and Forecast (HWRF) modeling system is a sophisticated, high-resolution, atmosphere-ocean coupled model designed to resolve inner-core features of hurricanes and to improve our understanding of multi-scale, spatial-temporal interactions between the storm and large-scale environment, as well as the air-sea interaction processes between the atmosphere and the ocean. Currently, the operational HWRF is coupled to the Princeton Ocean Model (POM), which is typically initialized from the GDEM climatology temperature and salinity data and GFS sea surface temperature (SST) data, together with spin-up processes for the cold wake associated with the storm. With recent developments, the ocean model cannow utilize the NCEP’s global eddy resolving 1/12° operational Real-Time Ocean Forecast System (RTOFS) data for initialization, which provides more realistic upper ocean structure with detailed mesoscale features. Experiments are conducted to investigate the impact of using RTOFS data for ocean initialization on hurricane forecasting. Results show that the POM RTOFS initialization improves HWRF intensity forecasting, especially for rapid intensification storms. Additionally, in order to demonstrate the impact of air-sea-wave coupling on hurricane forecasting, we discuss results from a recently developed three-way coupled atmosphere-wave-ocean HWRF system. As compared to the two-way coupled atmosphere-ocean model, the three-way coupled atmosphere-wave-ocean HWRF system is shown to be capable of further improving hurricane forecasting.