The interaction between a hurricane and the ocean is largely controlled not only by the sea surface temperature, but also by other properties of the upper ocean, such as the mixed layer depth, the stratification in the upper thermocline, and upper ocean currents. Therefore, accurate forecasting of the coupled hurricane-ocean system requires realistic initialization of the sub-surface ocean structure.

A new numerical procedure is suggested to assimilate subsurface temperature and velocity data together with the stream position to initialize the realistic structure of the Gulf Stream. The procedure utilizes a) the natural Gulf Stream temporal and spatial stability in stream coordinates; b) a limited number of observed cross-stream sections obtained in historic observations; c) a satellite-derived GS path provided by the U.S. Navy daily.

This procedure has been successfully implemented into the GFDL/URI coupled hurricane system and tested for real-case hurricanes in the Atlantic. In particular, some results will be presented for 7 forecasts of Hurricane Erin (2001) when the storm approached and crossed the Gulf Stream.