Offshore wind turbines are problematic for radar detection due to their large Radar Cross Section (RCS) and micro-Doppler signature, and the multiple scattering path caused by the sea surface. These problems hinder the growth of wind farms and thus our ability to combat climate change. In this paper, we build a model based on Physical Optics (PO) and an improved four-path model, which takes the sea surface randomness into account, using the K-distribution. These methods are chosen as a compromise between model realism and computational efficiency. The proposed model is then applied to an offshore wind turbine observed by an X-band radar: its monostatic RCS and its micro-Doppler signature are computed and analyzed. The obtained results are compared to similar ones obtained at lower frequencies, and show good agreement with both measurements and simulation results at lower frequencies. Emphasis is placed on the impact of the sea surface on the signal scattered by the wind turbine, and on the impact of the high frequency on the model.