During October 2009, Typhoon Parma struck the northern Philippines, killing hundreds of people and causing hundreds of millions of dollars in damages. Nearly two dozen WRF simulations of Parma were performed to assess the model's sensitivity of the simulated track, maximum 10 meter wind speed, minimum sea-level pressure, and accumulated rainfall to various model configurations, mostly variations in the physics schemes (microphysics, convective, and PBL). This case is particularly interesting because of the forecast challenges this storm presented as a result of its unusual, weakly-forced track. The goal of our study was to identify potential improvements to the operational configuration of the WRF model used within the Philippine Atmospheric, Geophysical, and Astronomical Administration's (PAGASA) Mesoscale Forecast Decision Support System (MesoDSS).

We found that the model track of Parma was more sensitive to changes in the convective scheme than to changes in the microphysics or PBL schemes. In addition, differences in the maximum 10 meter wind speed were quite sensitive to both the microphysics and convective schemes and much less sensitive to the choice of the PBL scheme. Other results to be discussed at the Symposium include the sensitivity to the number of vertical levels, differences between one- and two-way nesting simulations, and the performance of the WRF's tropical cyclone “bogusing” capability. Additionally, a brief update on PAGASA's MesoDSS will be provided.