Measurements of the Advanced Microwave Scanning Radiometer 2 (AMSR2) onboard GCOM-W1 satellite at 6.925 and 7.3 GHz and both linear polarizations over tropical cyclones (TCs) during 2012 – 2014 are used to derive a new geophysical function relating the brightness temperature to the sea surface wind speed (SWS) in extreme conditions. . Similar sensitivity to SWS at close C-band frequencies allowed to correct for the atmospheric contributions to the microwave radiance and estimate the brightness temperature (TB) at the surface under the TCs, combining theoretical modeling and measured TB analyses. Estimated oceanic TBs were regressed against the wind speeds from the Best Track Archive to derive the new geophysical model function (GMF) for the wind speed excess emissivity at AMSR2 C-band microwave frequencies.