Evaluation of 1D and 3D ocean coupling on GFDL hurricane model forecast skill in the Western Pacific

Recent studies have indicated that coupled hurricane models that employ a one-dimensional (1D) ocean component can underestimate storm-induced sea surface temperature cooling by neglecting upwelling, a process that can only be captured with a three-dimensional (3D) ocean model. We present a study designed to investigate the operational impact of the use of one-dimensional versus three-dimensional ocean model components in a coupled tropical cyclone forecast system. A suite of forecasts of Western Pacific typhoons is carried out using the GFDL hurricane model coupled with 1D or 3D versions of the Princeton Ocean Model. The GFDL hurricane model domain consists of a triply nested grid configuration, in which two inner grids are moveable and two-way interactive. The stationary outermost grid spans 75x75º with 1/2º resolution. The moveable middle (innermost ) grid spans 11x11º (5x5º ) with resolution 1/6º (1/12º). The GFS global analysis and the storm message provided by NHC were used to generate initial conditions for the atmospheric model. An axisymmetric version of the prediction model was used to create an axisymmetric vortex based on the initial storm structure that was estimated from the data in the storm message. The initial conditions were calculated by adding back the model simulated vortex to the environmental fields that were determined from the GFS analysis. Six-hourly GFS forecasts output on 1/2 deg grid were used for lateral boundary conditions. The Princeton Ocean Model was run with a 1/6 deg horizontal grid spacing and 23 vertical sigma levels. The ocean was initialized with the Navy's NCODA daily temperature and salinity analysis. The coupled model forecast skill with 1D and 3D ocean coupling is evaluated by a variety of metrics. The impact of storm translation speed is explored, and operational implications are discussed.