Numerical study of the effect of Warm-Core Ocean Eddies on Tropical Cyclone Intensity in the Northwest Pacific

It is well recognized that evaporation from the sea surface, primarily within a tropical cyclone’s core, provides heat energy required to intensify and maintain the storm. The sea surface temperature (SST) typically decreases within the storm core due to the mixing and upwelling processes in the upper ocean thereby limiting the storm’s intensity. This negative feedback to the TC intensity depends on the oceanic thermal conditions ahead of the storm. Upper oceanic heat content (OHC) has become widely accepted as a measure of the ocean energy available to the TC. Observational and modeling studies note that some tropical cyclones rapidly intensify while passing over warm ocean eddies because of their high OHC. There is abundance of eddies in the western North Pacific of different sizes and OHC. However, not always these eddies favor storm’s intensifications. The aim of this numerical modeling study is to investigate and quantify the conditions when a warm-core eddy can cause rapid intensification of a tropical cyclone. In this study, we applied the Hurricane Weather Research and Forecast (HWRF) v.4.0 system coupled to the Message Passing Interface Princeton Ocean Model (MPIPOM). The ocean model is initialized with the U.S. Navy's Generalized Digital Environmental Model (GDEM) of ocean temperature and salinity with 0.25° grid spacing. We conducted numerical experiments in which idealized warm-core eddies were embedded in front of three typhoons in the Northwest Pacific occurred in 2018 - Jebi, Kong-rey and Trami. The eddies were placed at various locations along the TC tracks. Depending on the eddy size, location and the ocean heat content (OHC) we have quantified the changes in the air-sea heat fluxes and the corresponding impact on the TC intensity.