CBLAST Wind-Wave Parameterization for Coupled Atmosphere-Wave-Ocean Models in Hurricane Research and Prediction

Improving intensity forecast is the most important issue for hurricane prediction today. The lack of skill in the intensity forecast may be attributed in part to deficiencies in the current prediction models: insufficient grid resolution, inadequate surface and boundary layer formulations, and no full coupling to the ocean. The extreme high winds, intense rainfall, large ocean waves, and copious sea spray in hurricanes push the surface-exchange parameters for temperature, water vapor, and momentum into untested new regimes. The CBLAST-Hurricane program is aimed to develop new coupling parameterizations, using the observations collected during the CBLAST-Hurricane field program, for the next generation hurricane prediction models. Hurricane induced surface waves (that determine the surface stress) are highly asymmetric, which can affect storm structure and intensity significantly. The stress is supported mainly by waves in the wavelength range of 0.1-10 m, which are unresolved by wave models. The CBLAST modeling team developed a wind-wave parameterization that includes effects of the wave spectral tail on drag coefficients using a fully coupled atmosphere-wave-ocean model with 1-2 km resolution that can resolve the extreme high winds in the eyewall. The coupling parameterization has been tested in a number of storms including Hurricane Frances (2004) that is one of the best observed storms during the CBLAST-Hurricane 2004 field program. Model simulations are evaluated with observations of directional wave spectra, air-sea fluxes, profiles of atmospheric boundary layer, ocean temperature and salinity, and SST from various in-situ, airborne, and satellite data during CBLAST-Hurricane. The fully coupled model with the new wind-wave parameterization improves the overall storm intensity forecast and produces a realistic surface wind-pressure relationship, which is sensitive to the treatment of surface stress, whereas the uncoupled atmospheric model over-predicts the minimum sea-level-pressure and under-predict the surface wind.