A New Drag Coefficient Formulation and its Impact on the GFDL and HWRF Hurricane Model Predictions

Whereas hurricane tracks are determined mostly by their large-scale atmospheric environment, storm intensity is influenced to a greater degree by smaller-scale features in both the atmosphere and ocean. One of the critical factors that control the intensity of hurricanes is the turbulent exchange of heat and momentum at and near the air-sea interface. A new drag coefficient formulation (CD) has been developed for hurricane modeling and forecasting based on the recent observational and theoretical studies. The formulation has a different shape of the CD dependence on the wind speed at high winds compared to the formulation based on the CBLAST field observations and other studies. The new Cd formulation has been implemented into 2014 GFDL operational hurricane prediction model. Recently, the new CD has been also implemented into an experimental configuration of the HWRF operational hurricane model. Numerous forecasts from previous seasons were conducted with the GFDL and HWRF models and the impact of the new drag coefficient on the hurricane forecast skill was evaluated.