Tidal Modulation of Waves Around the Aleutian Islands

Forming a critical part of the North Pacific Great Circle Route, the narrow passes of the Aleutian Islands are considered among the United States' most treacherous waters for maritime navigation. This study investigates the tidal modulation of surface gravity waves throughout the archipelago using a high‐resolution, unstructured‐grid, coupled ocean‐wave model. Model results reveal frequent and significant bidirectional wave modulation by the tidal currents, with significant wave height regularly increasing by over 50% when waves encounter opposing currents. A power spectral density analysis confirms that this modulation is forced at the precise frequencies of the primary diurnal and semidiurnal tidal constituents. Furthermore, spatial mapping shows that the dominant modulation (diurnal or semidiurnal) varies geographically, directly corresponding to the regional patterns of the underlying tidal currents. Beyond altering wave height, we demonstrate that tidal currents fundamentally change the sea state by shortening wave periods and directionally focusing wave energy. While direct in situ wave observations at the passes are unavailable, the improved model skill of the coupled model versus wave‐only model is supported by comparisons to satellite altimetry. In high‐current regions, improvements due to the wave‐current coupling are as significant as those due to adding wave boundary conditions. The coupled model also points to the possibility of tidal modulation at a distance from the island straits, as observed in remote wave buoy data. These findings provide a quantitative basis for existing navigational warnings and demonstrate that accurate sea state predictions in this energetic environment are contingent upon the use of coupled ocean‐wave models.