P65  Evaluation of the Typhoone Track Forecast in WRF-Based     Mesoscale Ensemble Prediction System

Li, Chih-Hsin and Jing-Shan Hong, Central Weather Bureau, Taiwan

This research evaluates the performance and the uncertainty of typhoon track forecast in a mesoscale ensemble prediction system based on the WRF model. This system was designed to generate the model uncertainty, including the initial perturbation from random error seeding in the WRF VAR background error covariance and the model physics perturbation. MORAKOT and FANAPI typhoon forecast experiments were conducted for all the members run and applied several verification schemes to evaluate the spread and accuracy of the track forecast.

The evaluation results show that the ensemble typhoon track forecast of MORAKOT case performs very well in terms of the ensemble mean and the spread, but the track of typhoon FANAPI case doesnŐt. The forecasting track of FANAPI case has southern bias, and it makes the bad spread.

The bogus scheme might bring about the same initial typhoon structure, and that would cause the bias of the forecasting tack of FANAPI case. To improve the track forecast, the typhoon initial vortex perturbation in WRF 3DVAR was applied. Using different setting of variance and length scale in WRF 3DVAR to conduct new forecast experiment. The track forecast of new experiment performs well in terms of the ensemble mean and the spread.