IMPROVEMENT OF NUMERICAL PREDICTION OF TYPHOON TRACKS IN THE WESTERN NORTH PACIFIC BASIN NEAR TAIWAN

In an effort to improve the tropical cyclone track forecast, two prepr ocessing procedures are applied to an operational baroclinic forecast system at the Central Weather Bureau (CWB) in Taipei. The first replac es the environmental wind field near the storm by the previous 6-h mov ement vector of the storm. The second incorporates a wavenumber-1 asym metry constructed by matching the flow at the center of the asymmetry with the previous 6-h storm movement. Applying both processes to the 3 2 typhoon cases archived at the CWB in 1990 reduces the averaged 48-h forecast distance error from 474 to 351 km. Multiexisting typhoons may have interactions among themselves that depend on relative intensity. Proper representation of the intensities in the initial bogus is impo rtant for the track forecast. Experiments with different initial bogus intensities are conducted on a case of dual typhoons-Nat and Mireille in 1991. The forecast using different bogus vortices according to the estimated intensities of each typhoon gives substantially smaller err ors than that using identical bogus vortices. The impact of initial bo gus vortex intensity on the track forecast for single typhoon cases is also illustrated.