IMPROVEMENTS IN THE GFDL HURRICANE PREDICTION SYSTEM

The hurricane model initialization scheme developed at GFDL was modifi ed to improve the representation of the environmental fields in the in itial condition. The filter domain defining the extent of the tropical cyclone in the global analysis is determined from the distribution of the low-level disturbance winds. The shape of the domain is generally not circular in order to minimize the removal of important nonhurrica ne features near the storm region. An optimum interpolation technique is used to determine the environmental fields within the filter domain . Outside of the domain, the environmental fields are identical to the original global analysis. The generation process of the realistic and model-compatible vortex has also undergone some minor modifications s o that reasonable vortices are produced for various data conditions. T he upgraded hurricane prediction system was tested for a number of cas es and compared against the previous version and yielded an overall im provement in the forecasts of storm track. The system was run in an au tomated semioperational mode during the 1993 hurricane season for 36 c ases in the Atlantic and 36 cases in the eastern Pacific basin. It dem onstrated satisfactory skill in the storm track forecasts in many case s, including the abrupt recurvature of Hurricane Emily in the Atlantic and the landfall of Hurricane Lidia onto the Pacific coast of Mexico.