West Coast Model-Observation Biases of Remotely-Forced Swell

Remotely generated waves along the U.S. West Coast originate from two primary geographic storm regions: the Southern Ocean and the North Pacific off the coast of Japan. The energy radiated from these storms travels long distances as swell, interacting with islands and mesoscale currents before arriving at the shoreline many days later. As part of a publicly available nearshore observation system, the Coastal Data Information Program (CDIP) operates a longstanding network of moored waverider buoys and records state-of-the-art WaveWatch III numerical forecast output at each buoy location. Comparisons between modeled and observed wave spectra at buoy locations along the west coast show that modeled swell events often arrive up to 12 hours earlier with wave height biases as large as ±20%. Differences in swell arrival time are estimated by determining the maximum of the normalized cross correlation between modeled and observed significant wave height in swell bands for each event. In addition to event-based validation, regional and seasonal patterns are explored in the model bias. To better understand amplitude and timing biases in the nearshore swell arrivals, spectral wave measurements from drifting miniature wave buoys and satellite remote sensing are used to distinguish potential errors in the model wind-forcing fields from issues with propagation and dissipation in the model. Understanding patterns in the discrepancies between models and observations will inform advancements in wave forecasts and data assimilation strategies, improve coastal monitoring, motivate more detailed regional studies, and can be utilized in broader global applications.