Total Water Level Twelve Year Hindcast Validation of STOFS-2D-Global, NOAA’s Fast Integrated Global Multi-Scale Multi-Process Operational Water Level Model

The operational version of NOAA’s Global Surge and Tide Operational Forecast System (STOFS-2D-Global) has been running with variable finite element resolution between 80m and 24km. The model incorporates optimized high resolution along all U.S. coastlines and extends onto the coastal floodplain and is driven by tides and NOAA’s Global Forecast System (GFS-FV3) winds, sea ice, and atmospheric pressure. Resolution is critical in complex inlet systems with jetties such as the St. Johns River entrance and Sabine Lake entrance, intricate shoal systems such as in Shinnecock Bay, and complex intra-tidal cross cut shoals such as the Biscayne Flats in Florida. In addition, as both inlet connections to the ocean and upland dendritic floodplain channel systems narrow, increased resolution becomes increasingly important. Further mesh developments include an optimized global shell and improvements in regional and global bathymetry. Bathymetry in key locations both globally and locally remain the most important controls of model fidelity. Overall STOFS-2D-Global is the most accurate global non-data-assimilated model with an M2 tide mean absolute error in deep water of 1.95 cm. Along the U.S. East/Gulf of Mexico coast the M2 tide errors at available NOS tidal stations are summarized as R2 = 0.9848, an mean absolute error = 2.5 cm, and a normalized RMS error = 0.089. STOFS-2D-Global incorporates 13.6 million finite element nodes and is fast, running at 2.4 wall clock minutes per day of simulation on 2400 TACC Frontera cores.

Process integration advances have now been implemented include coupling with NOAA’s global ocean circulation model, Global RTOFS, in order to incorporate the impact of the ocean’s thermohaline drivers including large current systems such as the Gulf Stream, warm and cold core eddies impinging on the coast, and seasonal steric expansion and contraction, all significantly affecting coastal water levels. In addition, coupling to the National Water Model accounts for upland hydrology and stream flows into the coastal zone. With these drivers in place, STOFS-2D-Global is a total water level model and mean water levels will balance locally to correct local mean sea levels with respect to a geodetic vertical reference. A 12 year hindcast driven by CFSv2 and GOFS3.1 is compared to measured water levels and tidal constituents at all continental US NOAA water level gauges.