NOAA/NOS’ Surge and Tide Operational Forecast System (STOFS): recent upgrades and long-term hindcasts for topography of the sea surface (TSS), marine geoid validation, and accurate products

NOAA/National Ocean Service’s (NOS) Coast Survey Development Laboratory (CSDL) in the Office of Coast Survey has led research to operations (R2O) of the Surge and Tide Operational Forecast System (STOFS, formerly ESTOFS) for over a decade. NOAA STOFS provides operational model nowcast (analyses of near present conditions) and forecast guidance of water levels, water currents, water temperature, and salinity for disaster mitigation [e.g. NOAA/National Weather Service (NWS) Weather Forecast Offices (WFOs) for total water level forecasts] and marine navigation (e.g. ship pilots for maneuvering into ports) end users across the globe. CSDL has recently led annual to biannual upgrades to STOFS, which operates on NWS’s Weather and Climate Operational Supercomputing System 2 (WCOSS2).

STOFS includes a global 2D depth-averaged component [ADvanced CIRCulation (ADCIRC) core, STOFS-2D-Global] and a 3D component for the U.S. East Coast, Gulf of Mexico, and Caribbean [Semi-implicit Cross-scale Hydroscience Integrated System Model (SCHISM) core, STOFS-3D-Atlantic]. We will describe the STOFS v2.1 upgrade, implemented in mid-2024, which integrates major improvements to both STOFS components. We will also describe the next upgrade (scheduled for late 2025), including incorporation of baroclinicity via Global RTOFS for STOFS-2D-Global, as well as implementation of a new SCHISM-based STOFS-3D-Pacific.

Finally, we will detail long-term hindcast work we are doing with our STOFS-2D-Global framework. Initially 3 years hindcasts, we are building to 12 years and then 19 years to resolve the water level variability within the National Tidal Datum Epoch (NTDE) time period, as well as ENSO, interannual, seasonal, sub-seasonal, and weather time scales. This series of hindcasts, run on both on-prem and cloud sandboxes, will gradually increase the physics included:

• Barotropic with
• 8 tidal constituents
• 12 tidal constituents
• Full tidal potential based on celestial body positioning
• Baroclinic with Global RTOFS coupling
• Adding hydrology using National Water Model and USGS observations
• Adding high resolution HRRR winds and nudging on top of the standard GFS forcing

With these hindcasts, average water levels across the global grid can be computed to produce a model topography of the sea surface (TSS), or local mean sea level (LMSL) to global mean sea level (GMSL) surface. This model TSS can then be removed from water level forecast guidance to accurately vertically reference to chart datum (MLLW) for NOAA S-104 water level products for navigation. The series of model TSS products can also be used for validation of the marine geoid, which represents GMSL at a specific time. These activities support more accurate vertically controlled products for the navigational and hazard mitigation user communities, who rely on NOAA products for enhanced decision making in the coastal zone.