Dynamical–Statistical Model Forecasts of Southern Hemisphere Tropical Cyclones

Abstract

The Navy Nested Tropical Cyclone Model (NTCM) is evaluated for performance on Southern Hemisphere storms near Australia. East of 135°E the model exhibits mean forecast errors of 246, 467, and 694 km at 24, 48, and 72 h, respectively. West of 135°E the mean forecast errors are 214, 511, and 745 km at 24, 48, and 72 h. The NTCM tends to have a poleward directional bias in the predicted tracks. This bias may be attributed to the lack of current data, which causes the analysis scheme to revert to climatological values. Storm tracks near the Australian coast also were not forecast well by the NTCM, especially in the western cases, presumably due to lack of consideration of land/sea effects. In a homogeneous sample comparison with an operational analog prediction technique (TYAN78), and with persistence of the past 12 hours motion, the NTCM performed worse in terms of forecast error at early forecast times and better at late forecast times east of 135°E. To the west of 135°E, the model performance was generally poorer than the other techniques at all forecast times. The regression post-processing technique of Peak and Elsberry (1983), when applied to the NTCM forecasts, results in a reduction of the eastern region sample forecast errors by as much as 150 km at 72 h. The western region sample forecast improvement is even greater, such that the regression-modified NTCM forecasts are superior to both TYAN78 and persistence in both test regions.