12WXCLIMATE Subseasonal Ocean Forecast Along US West Coast in NCEP/EMC's UFS-based Global Coupled Modeling System

ENSO dominates predictability of sea surface temperature (SST) along the US West coast across timescales through its atmospheric and oceanic teleconnection pathways. Subseasonal-to-seasonal (S2S) efforts include providing reliable forecasts of the ocean conditions along the US West coast as needed by the community to develop actionable plans for coastal and fisheries management. NOAA’s next generation operational forecast system involves community-wide collaborations in developing a fully coupled Unified Forecast System (UFS) towards seamless predictions across timescales. Towards that aim, subseasonal forecast prototypes are being developed, latest of which is demonstrated here in the context of subseasonal-scale predictions along the US West coast over a span of April, 2011-Mar, 2018 covering the super El Niño of 2015/16. Compared to observed phenomena, UFS subseasonal forecasts demonstrate weaker ENSO teleconnections. Beyond ENSO impact, mean state biases of SST and physical processes feeding to the biases along the US west coast are discussed. One of the prominent physical processes includes poleward propagation via coastal kelvin waves. With a speed of 2m/s these waves can influence ocean conditions up to ~ 6048 km downstream on subseasonal time-scales (~35-days). The present study also explores its effect on sea surface height (SSH) variation, as well as in depth variation of isopycnals (layers of constant density). However, given that both remotely and locally generated coastal kelvin waves leave very similar footprints, it is difficult to delineate one from the other, i.e one that is generated in the equatorial Pacific (during ENSO) versus one that is generated due to local alongshore winds.