Accurate Observations of Extreme Wave Conditions with SWIFT Buoys in the Eastern North Pacific

Extreme wave conditions caused by distant cyclones and locally strong winds pose hazards to residents, recreational enthusiasts and infrastructure located along the coastline or further offshore.  Forecasts that accurately predict the expected conditions help community preparation and mitigate potential damage caused by the physical risk of large wave events. Accurate prediction includes specification of bulk wave parameters, including wave height, period and direction. The Pacific Northwest Coastline is subject to extreme wave events, with at least one 10 m wave height event occurring every year. A currently operational model consistently under-estimates large wave height events (wave heights greater than 6 m). Improvement to this model’s accuracy for extreme conditions has been made through the analysis of three historical extreme events.  This model output has been validated with observations by NDBC buoy 46050, offshore of Newport, OR.   The final model configuration includes wind input of better quality (Climate Forecast System Reanalysis from the National Center for Environmental Prediction) and implementation of the latest physics package available for WaveWatch III (Ardhuin et al ST4 physics).  Spectral analysis reveals that the superior model configuration more accurately resolves southern wave energy, which helps to distinguish which atmospheric feature is responsible for the wave event. This ultimately results in more accurate predictions of bulk parameters.

Complementing the analysis of the historical events are simulations of extreme events which occurred in December 2015. SWIFT buoys, as produced by the Applied Physics Laboratory at the University of Washington, were dispatched into the area surrounding NDBC buoy 46050 at the time of the event. Model simulations are validated not only by observations produced by the NDBC buoy, but also observations as produced by SWIFT buoys. With respect to directional resolution of the incoming wave energy, the agreement between the SWIFT buoys and model output is better than the agreement between the NDBC buoy and model output.  Therefore, tracing the specific atmospheric feature which creates the extreme wave energy could be more accurate with an observation system which can better resolve direction. Identification of hazardous atmospheric features will better aid forecasters and stakeholders.