Wave climate and tidal modulation in a macrotidal gulf: Insights from long-term observations and coupled wave–current modeling

This study investigates wave climate and associated tidal modulation in the macrotidal Gulf of Maine (GoM) using 48 years (1978–2025) of buoy observations and a coupled wave–tide–circulation model. The GoM wave climate is dominated by Atlantic swells and exhibits strong seasonality, with quiescent, directionally coherent summer waves and energetic, variable winter seas. Observed frequency spectra deviate from the deep-water JONSWAP formulation and closely match the depth-limited TMA spectrum. The wave spectra exhibit flatter profiles and a lower fitted Phillips parameter (0.003 versus 0.0081), reflecting fetch limitation and wave dissipation across shallow banks. At tidal timescales, significant wave height (SWH) and mean wave period exhibit robust semidiurnal modulation governed primarily by current-induced refraction from along-crest gradients and wavenumber shifting due to along-wave gradients. These interactions produce alternating zones of wave convergence and divergence over Georges Bank that reverse with the flood-ebb tidal cycle and produce oscillations in wave probability distributions. Importantly, this study establishes a process-to-climate connection between wave–tide interactions and long-term extremes. This tidal modulation increases the estimated 100-year return SWH by 6.0%–8.1% across the gulf. These findings highlight the importance of wave–tide interactions for reliable hazard assessments and engineering design in macrotidal basins.