Cyclone Gonu (June 2007) was the strongest tropical cyclone in the Arabian Sea as well as in the northern Indian Ocean on record. At first, Gonu developed in the eastern Arabian Sea on 1 June, then rapidly intensified to 150 mph on 3 June and touched the eastern tip of Oman on 5 June. The simulation was carried out for 96 hours using Weather Research and Forecast (WRF2.2) model, starting from 0000 UTC 3 June 2007 with assimilation of the satellite data such as GPS radio occultation (RO) refractivity from FORMOSAT/COSMIC and precipitable water and near-surface oceanic wind speed from Special Sensor Microwave Imager (SSMI) using three dimensional variational data assimilation (3DVAR). A bogus vortex was also implanted to study the intensity and track of the cyclone Gonu. There are 56 GPS RO refractivity soundings assimilated into the model. A total of six experiments were carried with CTL (the control run without data assimilation) and the assimilation runs including COSMIC, SSM/I, GTS, SGC ( SSM/I + GTS + COSMIC) and the run with the bogus vortex. Both CTL and GTS give the simulated tracks close to the best track. The track for COSMIC in general is comparable with those for both CTL and GTS, but is further improved at the latest stage of simulation. The track for the run with the bogus vortex was close to the observation till day 2 but drifts away to the east of the best track afterwards. The track for SSM/I was also away from the best track at later time, but to the west. The performance of SGC was between COSMIC and SSM/I. All the assimilation runs have better agreement with the observations in day 1 and day 2 compared to day 3 and only COSMIC produces the track closest to the observation at day 4.