Ocean Model Impact Study for Coupled Hurricane Forecasting: An HFIP Initiative

Established in 2009, the NOAA Hurricane Forecast Improvement Project (HFIP) is a ten-year project to promote accelerated improvements hurricane track and intensity forecasts (Gall et al. 2013). The Ocean Model Impact Tiger Team (OMITT) consisting of model developers and research scientists was formed as one of HFIP working groups in December 2014, to evaluate the impact of ocean coupling in tropical cyclone (TC) forecasts. The team investigated the ocean model impact in real cases for Category 3 Hurricane Edouard in 2014, using simulations and observations that were collected for different stages of the hurricane. Two Eastern North Pacific Hurricanes in 2015, Blanca and Dolores, are also of special interest. These two powerful Category 4 storms followed a similar track, however, they produced dramatically different ocean cooling, about 7.2^oC for Hurricane Blanca but only about 2.7^oC for Hurricane Dolores, and the corresponding intensity changes were negative 40 ms^-1 and 20 ms^-1, respectively. Two versions of operational HWRF and COAMPS-TC coupled prediction systems are employed in the study. These systems are configured to have 1D and 3D ocean dynamics coupled to the atmosphere. The ocean components are initialized separately with climatology, analysis and nowcast products to evaluate the impact of ocean initialization on hurricane forecasts. Real storm forecast experiments are being designed and performed with different levels of the ocean model complexity and various model configurations to study model sensitivity. In this talk, we report the OMITT activities conducted during the past year, present preliminary results of on-going investigation of air-sea interactions in the simulations, and discuss future plans toward improving coupled TC predictions. Gall, R., J. Franklin, F. Marks, E.N. Rappaport, and F. Toepfer, 2013: THE HURRICANE FORECAST IMPROVEMENT PROJECT. Bull. Amer. Meteor. Soc., 329-343.