The Gridpoint Statistical Interpolation (GSI) scheme released in June 2006 from the National Center for Environmental Prediction (NCEP) and the Weather Research and Forecasting (WRF) model are used in this study for improving hurricane analysis. In addition to incorporating observations from conventional instruments and from operational satellites, Special Sensor Microwave Imager Sounder (SSMIS) measurements are assimilated through GSI. A "control-run" using current NCEP analysis field and a "test-run" using additional SSMIS data are compared. The error in forecasting the hurricane center after 30-hour grew up dramatically for the control-run while the error for the test-run remains stable for the entire 48-hour forecasting. The forecasting surface minimum pressure and maximum wind speed from the test-run generally agree with observations better. Results for the test-run also showed that the warm core at 200 hPa is strengthened and extended as Hurricane Katrina was developing toward its mature stage, which is consistent with SSMIS observations.