The recently developed MM5 three-dimensional variational (3DVAR) assimilation system at NCAR has been used to investigate influences of ingested sounding and ship observation data on numerical simulations of severe weather in the vicinity of Taiwan. Three weather events were simulated in this study, which include a Mei-Yu front in June 1998, Supertyphoon Bilis in August 2000 and Typhoon Nari in September 2001. Fir tge Mei-Yu front, the simulated low-pressure system northeast of Taiwan is stronger when the 3DVAR is performed during initialization. The simulated patterns of heavy rainfall just off th southern tip of Taiwan are also closer to observation s for the run with 3DVAR. For the second case of Typhoon Bilis, both runs with and without 3DVAR show a northward bias in track upstream of eastern Taiwan. However, due to less northward track deflection, the simulated heavy rainfall in Taiwan for the 3DVAR runs is in better agreement with observations.