Performance of the ECMWF model in forecasting the tracks of tropical cyclones in the South China Sea and parts of the western North Pacific

The performance of the European Centre for Medium-Range Forecasts model in forecasting the tracks of tropical cyclones in the South China Sea and part s of the western North Pacific for the years 1991-8 was assessed using 2.5 degrees resolution data transmitted operationally over the WMO Global Telec ommunication System. Minimum mean sea level pressure centres were used to i dentify and track the positions of tropical cyclones, and in 1998 the posit ions of the centre of maximum 850 hPa relative vorticity were also used. Th e model's performance was compared with that of subjective forecasts made b y the Hong Kong Observatory and with no-skill forecasts as represented by a climatology-persistence method in the 1990s. Significant improvements in t he model forecasting of tropical cyclone tracks were identified towards the end of that period. The model mean forecast errors for 24-hour, 48-hour an d 72-hour positions were 215 km, 340 km and 453 km in the early 1990s (1991 -3) respectively, compared With 155 km, 244 km and 292 km in the late 1990s (1996-8).