A Generalized Potential Intensity Formulation for Statistical Tropical Cyclone Intensity Models

The National Hurricane Center (NHC) runs several simplified track and statistical intensity forecast models as guidance for their official forecasts, as baselines for measuring forecast skill, and for providing model diagnostics. This model set is referred to as the NHC guidance suite. One of the most significant predictors for the statistical intensity models is the potential intensity (PI). A highly simplified empirical PI formulation that is only a function of the sea surface temperature (SST) is currently used in the guidance suite, where the SST is estimated from a static analysis at positions along the NHC forecast track. Theoretical studies have shown that the PI also depends on the atmospheric temperature and moisture profiles in the near-storm environment. In addition, the SST near the storm center cools due to upwelling and mixing, especially for slow moving storms, which impacts the PI. A generalized PI formulation based on the theoretical formulation of Bister and Emanuel (2002) is adapted for use in the NHC guidance suite. A method to incorporate SST cooling is included by replacing the SST with a depth-averaged ocean temperature. The effects of atmospheric entrainment are also included by modifying the convective available potential energy (CAPE) terms in the PI formulation using an entraining plume model. The new PI formulation and impacts on statistical intensity forecast models will be described.