Recently, there has been an interest to quantitatively simulate the US summer precipitation from weekly to monthly time scale using MM5 coupled with an adequate land surface model (Zhang et al. 2003, Zheng and Zou 2004). These studies suggested that the coupled model could simulate the US summer precipitation for the interested time scales with reasonable accuracy. In these simulations, many daily characteristics of the weather evolution can be reasonably reproduced during a continuous monthly integration over the Large-Scale-Area-East (Zhang et al. 2003) and the southwestern US continent (Zheng and Zou, 2004). Such simulations greatly enhanced our understandings on the possibilities of extending the current weather prediction capabilities from a few days to the weekly scales. Encouraged by these findings, this study further examines the impact of the QuikSCAT surface wind on the simulation. Here the QuikSCAT surface wind is assimilated into MM5 using a Four-Dimensional Data Assimilation (FDDA) scheme, in which the model surface wind is continuously nudged toward the QuikSCAT wind during the integration. The assimilation of the QuikSCAT wind improves the boundary layer flow patterns over the Gulf of Mexico and changes the associated moisture flux patterns. These changes significantly affect the simulated US early summertime precipitation. Detailed results will be discussed in the extended abstract.