An Experiment on the Impact of Initial Fields and Boundary Conditions on the Typhoon Track Simulation in the Northwest Pacific Ocean

Taiwan was affected by several typhoons each year that caused significant economic losses. Timely forecast of the typhoon movement and rainfall is one of the most important tasks at the Central Weather Bureau in Taiwan (CWB). To provide guidance for the forecasts, a nonhydrostatic region forecast model (NFS) was developed and installed in the Bureau. To improve the performance of the NFS model is one of the key elements to advance the typhoon forecast of the Central Weather Bureau. The typhoon track forecast error of the NFS in 2005 typhoon season will be presented in the conference. During the operation, the initial fields of NFS were from the 6 hours forecast update cycle, the boundary conditions were from the CWB global model forecasts. Experiments of using CWB and NCEP global model results as initial fields and boundary conditions for NFS were examined. For cases of large NFS errors during operation, results showed that the typhoon track forecasts were sensitive to the initial fields and boundary conditions. For track before 36 hours, NFS forecast is sensitive to the initial fields. The effects of boundary conditions are shown gradually increase after 36 hours forecast. Discuss of the effect of the initial fields and boundary conditions to NFS forecasts will be addressed. Analysis through potential vorticity distribution will also be discussed.