A Preliminary Report on Intensity Forecasting Using the TYFOON Analog Computer Program.
FLEET WEATHER CENTRAL/JOINT TYPHOON WARNING CENTER FPO SAN FRANCISCO 96630
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The computerized TYFOON analog program has been used by the JTWC as an aid in forecasting tropical cyclone movement since 1970. This study investigated the usefulness of the TYFOON program for forecasting tropical cyclone intensities at 24-, 48-, and 72-hours. Three parameters which are available on the basic climatological data tape used in TYFOON were selected to determine their usefulness in intensity forecasting The minimum sea level pressure, the 12-hour change in minimum sea level pressure, and the maximum sustained surface and wind speed. Based on selected values of these criteria, current and analog tropical cyclones were separated into two classes deepening or weakening and analog forecasts were computed. During the testing several changes were made to the classification criteria to obtain better results. The program was modified so that each succeeding intensity forecast used the previous intensity forecast as an input, i.e., initial conditions for the 48-hour forecast would depend on the 24-hour forecast, etc. Verification results based on selected cases from the 1972 tropical cyclone season showed the analog program produced intensity forecasts that were slightly better than the official JTWC forecasts for the 24-hour period but were slightly worse than the official forecasts at 48 and 72 hours.