Ocean Model Impact Tiger Team: Ocean Model Impact Study for Hurricane Forecasting

Although ocean provides the thermal energy required for Tropical Cyclone (TC) intensification via the heat and moisture fluxes, a widespread belief exists in the operational forecasting community that two-way or three-way, high-resolution, data assimilated ocean coupling is not required to produce credible TC intensity forecasts. These opinions arise because most coupled TC forecast systems presently used by Regional Specialized Meteorological Centers are uncoupled, and fully coupled models sometimes display equal or reduced intensity skill compared to uncoupled models. One factor responsible for this situation is that previous generations of coupled prediction systems may not have represented the impact of ocean coupling on intensity forecasts with sufficient accuracy. The present generation of coupled prediction systems, along with next-generation systems under development, all contain major improvements to the atmospheric model, surface flux parameterizations, and to the ocean model. These latest systems can all be coupled to advanced three-dimensional Ocean General Circulation Models initialized by data-assimilative ocean analysis products. Given these advancements, questions concerning the necessity and required complexity of ocean coupling need to be revisited.

The Ocean Model Impact Tiger Team (OMITT) was formed in December 2014 as part of the NOAA Hurricane Forecast Improvement Project (HFIP) to investigate the need of ocean coupling, and to demonstrate the degree of complexity required for ocean coupling to optimize TC intensity forecasts. Teams of research and operational scientists from various institutions serve to coordinate these investigations on operational and developmental modeling systems. Our initial results show that modern data assimilation techniques properly depicting pre-existing ocean conditions, as well as dynamic coupling are key in capturing the TC intensity response to mixing and upwelling during passage. Future operational coupled modeling efforts, including wave coupling, will be presented. We also find that a lack of observations limit evaluation and validation, and conclude that systematic upper ocean measurements are needed to make further improvements to coupled forecasting intensity skill.