Typhoon forecast with the GFDL hurricane model: Forecast skill and comparison of predictions using AVN and NOGAPS global analyses

A hurricane model developed at GFDL, NOAA, was combined with each of AVN an d NOGAPS global analyses to construct typhoon prediction systems GFDS and G FDN, respectively. The CFDS system performed 125 (178) forecast experiments for 16 (24) storms in the western North Pacific basin during 1995 (1996). It exhibited considerable skill in the forecast of tropical cyclone tracks. The average forecast position errors at 12, 24, 36, 48 and 72 h in 1995 (1 996) were 95 (108), 146 (178), 193 (227), 249 (280), and 465 (480) km. The improvement with GFDS in the typhoon position forecast over CLIPER was roug hly 30 (ro. The reduction of position errors in both average and standard d eviations indicates superior forecast accuracy and consistency of GFDS, alt hough there existed systematic northward bias in the forecast motion at low latitudes. On the other hand, intensity forecast was not satisfactory, sho wing a tendency to overpredict weak storms and underpredict strong storms, similar to the tendency in the Atlantic. Two sets of forecasts performed in the 1996 season, the one by GFDS and the other by GFDN, were compared with each other. Forecast skills of the storm position with the two systems were comparable. However, the two forecast p ositions tended to be systematically biased toward different directions. As a result, when the two forecasts were averaged, the mean error was 10 % sm aller than that of each forecast. Also, overall improvement in track foreca st was obtained in supplemental experiments in which individual forecasts w ere corrected for systematic biases. Though systematic bias is not steady, there may be ways to utilize it for improvement of tropical cyclone forecas ts.