Overview of Bering/Chukchi Sea Wave States for Selected Severe Storms

Strong storms are regular features over the ocean west of Alaska. These systems often loiter, generating moderate to severe marine states which can exhibit persistence, maximizing damage and hazard potential. This analysis presents the wave states associated with selected storms over the Bering and Chukchi Seas. These include the damaging events of October 2004, September 2005, and November 2009, along with a strong event from September 2011 that exhibited north winds. For each event a brief synoptic overview is presented followed by consideration of the resultant wave state, including parameters such as wave steepness. Wave data come from NOAA’s WAVEWATCH III operational global ocean wave model, implemented locally on the Arctic Region Supercomputing Center at University of Alaska Fairbanks. Comparison with observational data gathered by a wave buoy, funded by the US Environmental Protection Agency/NOAA and deployed in 2011, is also undertaken.NOAA Grant NA08OAR4600856, “Social Vulnerability to Climate Change in the Alaskan Coastal Zone

North Atlantic storm driving of extreme wave heights in the North Sea

The relationship between storms and extreme ocean waves in the North Sea is assessed using a long-period wave dataset and storms identified in the Interim ECMWF Re-Analysis (ERA-Interim). An ensemble sensitivity analysis is used to provide information on the spatial and temporal forcing from mean sea-level pressure and surface wind associated with extreme ocean wave height responses. Extreme ocean waves in the central North Sea arise due to intense extratropical cyclone winds from either the cold conveyor belt (northerly-wind events) or the warm conveyor belt (southerly-wind events). The largest wave heights are associated with northerly-wind events which tend to have stronger wind speeds and occur as the cold conveyor belt wraps rearwards round the cyclone to the cold side of the warm front. The northerly-wind events provide a larger fetch to the central North Sea to aid wave growth. Southerly-wind events are associated with the warm conveyor belts of intense extratropical cyclones that develop in the left upper-tropospheric jet exit region. Ensemble sensitivity analysis can provide early warning of extreme wave events by demonstrating a relationship between wave height and high pressure to the west of the British Isles for northerly-wind events 48 hours prior. Southerly-wind extreme events demonstrate sensitivity to low pressure to the west of the British Isles 36 hours prior