Fetch‐Dependent Surface Wave Responses to Offshore Wind Farms in the Northeast U.S. Coast

Abstract Large‐scale offshore wind farms are expected to influence surface waves by modifying local wind forcing through wake effects. We use regional coupled ocean‐atmosphere‐wave model simulations to investigate a realistic large‐scale offshore wind development scenario in the northeastern U.S. during boreal summer. Near‐surface wind speeds are reduced by 10% over lease areas and within downstream wake regions, leading to decreases in significant wave height (3%) and wave‐supported momentum flux (30%). This further leads to reductions in surface roughness length (16%) and near‐surface ocean turbulent kinetic energy (20%). Spectral analysis shows a clear reduction in wind‐sea energy, indicating suppressed local wind‐wave growth near the wind farms. Weaker winds favor the development of longer‐period waves, increasing dominant wave phase speed by 3% and suggesting a transition to an older sea state. Modern bulk flux algorithms often parameterize surface roughness using inverse wave age and/or wave slope. This raises the question of whether wake‐driven reductions in inverse wave age and wave height impact air‐sea momentum exchange. To assess this, we compare fully coupled simulations with an atmosphere‐only run excluding wave coupling. Results show that about one‐third of the reduction in roughness length can be attributed to sea state changes, while two‐thirds result from lower friction velocity due to lower wind speeds. However, the impact of sea state on the drag coefficient and momentum flux is negligible (1%), suggesting that wake‐induced wind speed reductions are the primary driver, with sea state changes playing a secondary role.