Extreme storm surges are among the most severe coastal hazards threatening low-lying areas along the Northwest European shelf and the Baltic Sea, while marine heatwaves represent oceanic temperature extremes affecting both open-ocean and coastal environments. These events result from complex interactions between hydrological and meteorological processes and are projected to intensify in several regions under climate change. However, major challenges remain in developing a comprehensive understanding of future coastal extremes and their associated risks. To address this gap, we employed a regional wave-ocean coupled model to dynamically downscale a transient regionalized REMO–MPIOM coupled model under the Representative Concentration Pathway (RCP) 8.5 scenario. Three representative ensemble members from the REMO–MPIOM simulations were selected to investigate the role of internal variability in projected extremes. Model performance was evaluated against tide-gauge observations and satellite-derived sea surface temperatures for the North Sea and Baltic Sea. We then assessed projected changes in extreme coastal events by comparing the future period (2070–2099) with the historical period (1970–1999), including the role of internal variability imposed by the parent model’s boundary conditions. The peaks-over-threshold (POT) method was applied to characterize both hazards. The results show that the coupled model reproduces key features of historical coastal extremes across both basins. Projected patterns indicate fewer but more intense storm surges along the North Sea coast, whereas marine heatwaves will occur more frequently but last for shorter periods throughout much of the North Sea. Our findings also emphasize the substantial role of internal variability in shaping future coastal extremes, underscoring the need to account for this uncertainty when interpreting regional climate projections. The insights gained from this study offer valuable guidance for enhancing coastal hazard preparedness, protecting infrastructure, and planning for long-term adaptation in vulnerable maritime regions.