Understanding the impacts of unsteady flows on tidal turbine performance and loadings prior to device deployment is essential for mitigating the effects of large hydrodynamic forces and avoiding premature fatigue. High-frequency velocity measurements from an energetic tidal channel were fed into a model that couples Blade Element Momentum (BEM) theory with dynamic stall and rotational augmentation corrections. A model turbine operating in real-world conditions was used to investigate different hub submergence depths and also extreme wave conditions. Mean turbine coefficients were more affected by varying levels of shear than by waves while standard deviations were more sensitive to shear than to the proximity of surface waves. Under long waves, power and thrust coefficients reached more than twice the average values and standard deviations are enhanced by over 70%. Waves moved the separation point towards the leading edge in over half the blade span and thus impacting the stall behaviour. These outcomes contribute to the understanding of power extraction and hydrodynamic forces around turbine blades in real-world conditions. This analysis is important for turbine developers to design resistant structures and thus extend device durability, but also to improve turbine performance.