Anomalous ocean conditions along the US Pacific coast in 2014: analyses using the West Coast Operational Forecast System (WCOFS)

In winter 2013-14, areas of anomalously high sea level pressure and warmer SST formed in the Northeast Pacific Ocean. How these influenced coastal ocean conditions along the US West Coast is studied using outputs from the 2-km resolution West Coast Operational Forecast System (WCOFS), being developed at the National Oceanic and Atmospheric Administration. Here, continuous multiyear WCOFS runs without assimilation are utilized. Oceanic conditions and circulation for years 2009-11 are compared to the anomalous 2014. In winter 2014, downwelling in the Northeast Pacific was anomalously weak resulting in weaker transport of surface waters of the Northern Pacific Current (separating the subpolar and subtropical gyres) toward the Oregon and Washington coasts, as confirmed by the analysis of the model surface Lagrangian drifters. Due to weaker wind conditions shelf waters are more stratified in winter 2014, in contrast to the other winters. Hence, response of shelf currents to episodic northward wind events is stronger and has a different structure. In summer 2014, anomalously warm temperatures are registered in all the areas along the US West Coast. The volume-averaged heat balance analysis, performed for three different geographical areas over the shelf (inshore of the 200 m isobath), suggests that off Oregon both increased atmospheric heat flux and reduced advective cooling through the side boundaries of the control volume contribute to anomalously warm conditions that set up in summer 2014. In Central and Southern California, shelf waters are warmer mostly due to the reduced advective cooling.