Previous studies have shown that insufficient local information in Initial Conditions may lead to a reduced accuracy in the model response for the precipitation forecast. In order to improve the moisture field in the mesoscale I.C., new generation data from the GPS satellite system is used. Evaluation of the GPS PW impact using 3DVAR technique is performed for a few MAP IOPs. High resolution simulations, using the MM5V3, are performed to forecast the rainfall. The results are compared with both the observations and a model simulation performed without using the 3DVAR.