In the harsh weather of the North Sea, offshore wind turbines are frequently subjected to extreme loads resulting from the combined aero-hydrodynamic forces acting on the turbines. Modelling these forces often rely on simplistic and approximate approaches that tend to either overestimate or underestimate structural forces. This study examines the aero-hydrodynamic behavior of a fixed-bottom NREL 5 MW offshore wind turbine subjected to normal and extreme wave conditions of the North Sea. Computational Fluid Dynamics (CFD) based transient multiphase solver has been used for this purpose employing Volume of Fluid (VOF) and Sliding Mesh approach to accurately modelling water waves and rotor rotation. The numerical model has been validated against the analytical data for turbine’s rated power. The results obtained in this study show a highly turbulent area between the rotor wake and the free surface of water, where low and high pockets of flow velocity are observed. As the ocean condition switches from normal waves to extreme waves, mean velocity fluctuations of up to 6 m/s in this region have been observed, while the turbulent kinetic energy increase by up to 21 m2/s2. Drag force and torque exerted by the extreme waves on the tower have been calculated to increase by 52% and 113% respectively compared to normal waves. The results indicate higher risk of fatigue damage and could impact the operational lifetime of key structural components such as the tower and the monopile. The findings emphasise the need for efficient structural monitoring systems to strengthen offshore wind farms in this rapidly growing industry.