From Chesapeake Bay to a national network
NOAA's National Ocean Service (NOS) started forecasting coastal waters with a model in the summer of 2001, when its Chesapeake Bay Operational Forecast System (CBOFS), developed by the Coast Survey Development Laboratory with the Center for Operational Oceanographic Products and Services (CO-OPS), was declared operational and its results released to the public. Until 2011 CBOFS was a two-dimensional model run on NOS's own computers, aimed at water levels and reaching 30 hours ahead.
On 29 March 2011 a new, three-dimensional CBOFS replaced it, built on the Regional Ocean Modeling System (ROMS) of Rutgers University, with currents, temperature and salinity as well as water levels, a horizon extended to 48 hours, and a run on NOAA's central computers operated by NCEP Central Operations (NCO). The same day, two sister systems went operational on the same model: DBOFS for Delaware Bay and TBOFS for Tampa Bay.
The network then grew coast by coast. The San Francisco Bay system, SFBOFS, built on the unstructured-grid FVCOM model, went live on 11 March 2014 on NOAA's Weather and Climate Operational Supercomputing System (WCOSS); the Gulf of Maine's GoMOFS followed on 3 January 2018, with a 72-hour horizon, and Cook Inlet's CIOFS, in Alaska, on 23 July 2019. On 22 March 2021 NGOFS2 merged three earlier northern Gulf of Mexico systems (NGOFS, NEGOFS and NWGOFS) into a single grid reaching the Mexican coast.
The latest of the eight used here, SSCOFS for the Salish Sea and the Columbia River, became operational on or about 9 September 2024: an FVCOM model of Puget Sound, the Strait of Georgia and the Columbia River up to the Bonneville Dam, which retired the older Columbia River system CREOFS, built on the SELFE model. Besides these, CO-OPS runs a West Coast model (WCOFS), systems for New York Harbor and the St. Johns River, and four Great Lakes systems.
Two model cores: ROMS and FVCOM
Every OFS solves the same physics: the primitive equations of a free-surface ocean, hydrostatic, with water levels, three-dimensional currents, temperature and salinity, so that tide, wind, river runoff and the density of the water all move the current. In the vertical, both cores use terrain-following (sigma) layers, which stretch and squeeze with the depth: from 10 layers in DBOFS and SSCOFS to 41 in NGOFS2.
Five of the eight run ROMS, the Regional Ocean Modeling System supported by Rutgers University, on a structured grid of curved or orthogonal quadrilaterals that can be tightened where it matters: CBOFS goes down to about 30 m along the bay's main channels and stretches to nearly 5 km offshore, while GoMOFS keeps about 700 m over the whole Gulf of Maine.
The other three run FVCOM, the Finite Volume Community Ocean Model developed by the University of Massachusetts Dartmouth with the Woods Hole Oceanographic Institution. Its horizontal grid is made of unstructured triangles, which can follow a jagged coastline and shrink into narrow passages without refining the whole domain: NGOFS2's triangles range from 45 m in tidal creeks, inlets and intracoastal waterways to 10 km along the open boundary, and SSCOFS has 239,734 nodes, 100 m apart inside the estuaries.
All of them run inside the same software, the Coastal Ocean Modeling Framework (COMF) written by CO-OPS, in which every OFS runs, from preparing its forcing to writing its output files; in September 2024 it moved to version 3.6, with new file names for all the systems.
How a cycle is computed
Each OFS runs four times a day, every 6 hours. A cycle starts with a nowcast over the 6 hours just past, driven by what actually happened: analysed winds (NCEP's Real-Time Mesoscale Analysis in the nowcasts of some systems), observed river flows and, for some systems, the water levels measured at NOS gauges. From that state, the forecast then runs 48 hours ahead, or 72 hours for SSCOFS and GoMOFS.
In the forecast, the wind and heat fluxes come from NCEP's North American Mesoscale model (NAM), with the global GFS as a backup when NAM is late. River discharge comes from the U.S. Geological Survey's real-time gauges, held at its last observed value for the whole forecast; SSCOFS instead takes its river flows from the National Water Model.
At the open sea boundary each model needs what lies beyond it. Temperature, salinity and the non-tidal water level come from NOAA's global ocean model, G-RTOFS, or from the Extra-Tropical Storm Surge model (ETSS) for the sea level of some systems; the tide is added from tidal databases, such as ADCIRC's, which gives NGOFS2 thirty-seven constituents. The tide then propagates into each bay and strait by the model's own physics.
NCEP Central Operations and CO-OPS monitor the runs around the clock. The fields are written in NetCDF, hourly at the surface, and published on NOAA's NOMADS server, on CO-OPS's THREDDS server and through the NOAA Open Data Dissemination programme on Amazon's cloud, in the bucket noaa-nos-ofs-pds, which keeps the history. NOAA states that these data are open to the public and can be used as desired, asking only for attribution and that no NOAA endorsement be implied.
At sea
In bays, sounds and straits, the current a sailor meets is mostly the tide, squeezed and steered by the shape of the coast: it runs hardest at an entrance or between headlands, and a river's outflow adds to the ebb. These are features of a few hundred metres, which a global ocean model, with cells of about 9 km, smooths into a single value or misses altogether. An OFS draws them, hour by hour, with the wind and the rivers of the day on top of the astronomical tide.
Each system is checked against the NOS standards for navigation: water levels, current speed and direction compared with observations, slack water defined as a current below half a knot. They are tuned for the main channels and for shipping, which is where the grids are finest; between a beach and a channel, close to a rock or in a narrow cove, the grid can still be coarser than the place.
Their forecasts are only as good as the NAM wind they are driven by, and a river flood that builds after the run starts is not in the forecast, which holds the last measured discharge. NOAA also warns that the OFS are not storm surge models and may be inaccurate in extreme weather events: in a hurricane or a strong storm, the official warnings come first.
For a sailor these models answer practical questions: when the ebb turns at a bay's entrance, whether the stream in a strait will be with or against the boat, how far a river plume pushes offshore. They are guidance from a model, not measurements, and are best read next to NOAA's tidal current predictions.
NOAA OFS in Saily WR
Saily WR uses eight OFS: SSCOFS, CBOFS, DBOFS, TBOFS, SFBOFS, CIOFS, GoMOFS and NGOFS2. For each, a server downloads the freshest complete run, four runs a day, every forecast step NOAA publishes (hourly, every three hours for GoMOFS and NGOFS2), from NOAA's public bucket noaa-nos-ofs-pds; it takes the regular-grid files, in which NOAA has interpolated the model onto a grid of longitude and latitude from 0.0025° to 0.01° (about 250 m to 1 km), and keeps only the surface current. The model's land and the sea outside its domain are marked as having no water.
There is nothing to choose: a route sails in an OFS's current wherever that OFS has water at that point, with no corner of the grid cell on land, and a forecast step at that time. Elsewhere, and past the system's last step, H+48 or H+72, it sails in SMOC, the global current, with tide. Where two OFS overlap, the finer one is taken, and of two with the same step, always the same one.
Close to the shore, a cell of the OFS's regular grid with water at one corner only still gives the OFS current, drawn from its points with water; the route takes the global current only where none of the four points around it has water, in a harbour or a pass the grid does not see. The route's summary names each current it crossed, in order, for instance "NOAA SSCOFS, then SMOC"; on a route sailed in several, the route log, on screen and printed, names the source of each leg, and the CSV has a "Current source" column. On the routing map, the Current layer shows the OFS current inside its waters and the global one around it.
Not every OFS is in yet. WCOFS, along the whole US West Coast, is published only on its curvilinear grid; NYOFS and SJROFS use older formats; CREOFS and NECOFS are not on the bucket. The four Great Lakes systems, LEOFS, LMHOFS, LOOFS and LSOFS, will come once routes can sail on lakes.
The domains
NOAA SSCOFS, Salish Sea and Columbia River
SSCOFS covers the inland seas shared by Washington State and British Columbia: Puget Sound down to its southern inlets, Admiralty Inlet, the San Juan Islands, the Strait of Juan de Fuca and the Strait of Georgia, then the Pacific coast south to the Columbia River, which it follows up to the Bonneville Dam. It is an FVCOM model, operational since September 2024, whose 239,734-node triangular mesh is 100 m fine in the estuaries, 500 m in the deep basins of Puget Sound and the Strait of Georgia, and coarsens to 10 km over the continental shelf.
Saily WR takes its runs of 03, 09, 15 and 21 UTC, hourly from H+0 to H+72, on a 0.005° grid. These are waters where the tide decides: the stream through Admiralty Inlet, which a route from Seattle to the San Juan Islands crosses, reaches 2 to 3 knots, and passing it with or against the flood makes a large difference to the arrival. At the Columbia River's mouth, the river's outflow and the tide meet over the bar, which the model resolves at 100 to 200 m.
NOAA CBOFS, Chesapeake Bay
CBOFS covers the whole of Chesapeake Bay, from the Chesapeake Bay Bridge-Tunnel at its mouth between Cape Henry and Cape Charles up to Baltimore and the mouth of the Susquehanna, with its tidal rivers, and a piece of the Atlantic shelf so that the bay and the ocean exchange water realistically. The oldest OFS, operational in two dimensions since 2001, it has run since March 2011 on ROMS, on a grid that is about 30 m fine along the bay's main channels and nearly 5 km on the shelf, with 20 layers.
Saily WR takes its runs of 00, 06, 12 and 18 UTC, hourly from H+1 to H+48, on a 0.005° grid. Chesapeake Bay is long, and its tidal stream does not turn everywhere at once: on a passage down the bay, the model shows where the ebb or the flood is running and how a steady wind along the bay adds to it. In the main channel and at the entrance between the capes, the current is worth timing.
NOAA DBOFS, Delaware Bay and River
DBOFS covers Delaware Bay, between Cape May and Cape Henlopen, the tidal Delaware River past Wilmington up to Philadelphia, and a piece of the continental shelf off New Jersey and Delaware, where its sea boundary is adjusted to the water levels measured at Ocean City Inlet and Atlantic City. A ROMS model operational since March 2011, it has a grid of 100 m to 3 km and 10 layers.
Saily WR takes its runs of 00, 06, 12 and 18 UTC, hourly from H+1 to H+48, on a 0.005° grid. The bay's entrance and its main shipping channel concentrate strong tidal streams, and against a fresh wind an ebb running out of the bay raises a short, steep sea. For a passage up or down the bay, or round Cape May, the tide is the first thing to plan for.
NOAA TBOFS, Tampa Bay
TBOFS covers Tampa Bay, from its entrance near Egmont Key and the Sunshine Skyway Bridge to Tampa, St. Petersburg and Old Tampa Bay, and a piece of the Florida shelf in the Gulf of Mexico, where its sea level is adjusted to the gauge at Clearwater Beach. A ROMS model operational since March 2011, it has a grid of 100 m to 1.2 km and 11 layers.
Saily WR takes its runs of 00, 06, 12 and 18 UTC, hourly from H+1 to H+48, on a 0.0025° grid, the finest of the OFS in Saily WR with San Francisco Bay's. The bay fills and empties through its entrance, so its stream runs hardest in the shipping channel under the bridge and at the mouth, while over the shallower parts of the bay the wind weighs more; a summer squall or a cold front can drive the current for a few hours as much as the tide does.
NOAA SFBOFS, San Francisco Bay
SFBOFS covers the whole bay system, South Bay, Central Bay, San Pablo Bay and Suisun Bay, the Golden Gate and the near shelf from Point Reyes to Point San Pedro. Operational since March 2014, it runs FVCOM on 54,120 nodes whose triangles are about 100 m apart near the coast and down to about 10 m along the navigation channels, driven by the 4 km NAM winds.
Saily WR takes its runs of 03, 09, 15 and 21 UTC, hourly from H+0 to H+48, on a 0.0025° grid. The whole bay fills and empties through the Golden Gate, where the stream runs hardest, then fans out between the islands and the shallows of the Central Bay; on a summer afternoon, when the westerly fills in through the Gate, an ebb against it makes a steep sea, and the turn of the tide shifts the best lane across the bay.
NOAA CIOFS, Cook Inlet
CIOFS covers Cook Inlet in Alaska, a 180-mile-long arm of the sea from its mouth near Kennedy Entrance and Kachemak Bay up to Anchorage, Knik Arm and Turnagain Arm, with the waters of Shelikof Strait and around Kodiak Island, where it is checked at Kodiak and Alitak. Operational since July 2019, it runs ROMS on an orthogonal grid that goes from 10 m in the upper inlet's estuaries and channels to 3.5 km offshore, with 30 layers, and wets and dries its mudflats with the tide.
Saily WR takes its runs of 00, 06, 12 and 18 UTC, hourly from H+1 to H+48, on a 0.005° grid. With tide ranges of some thirty feet, mudflats, large glacial rivers and, in winter, sea ice, Cook Inlet has strong, complex tidal currents that change hourly, daily and with the seasons: in the upper inlet, a passage is planned around the tide rather than the wind, and a boat that misses its stream can spend hours making no ground.
NOAA GoMOFS, Gulf of Maine
GoMOFS covers the Gulf of Maine as a whole: the coasts of Massachusetts, New Hampshire and Maine from Cape Cod to the Canadian border, the Bay of Fundy, Georges Bank and the waters off Nantucket, and the deep water beyond the shelf, down to 4,500 m along its southern open boundary. Operational since January 2018, it is a ROMS model on an orthogonal grid of about 700 m with 30 layers, forecasting 72 hours ahead.
Saily WR takes its runs of 00, 06, 12 and 18 UTC, every 3 hours from H+3 to H+72, on a 0.01° grid. A strong tide dominates most of the gulf, and grows towards the Bay of Fundy, where its range reaches nearly 15 m: there, over Georges Bank and off Cape Cod, the tidal stream can turn a fair passage into a foul one within a few hours, and the model shows when.
NOAA NGOFS2, northern Gulf of Mexico
NGOFS2 covers the US coast of the Gulf of Mexico from the Mexican border to the western Florida Panhandle, with Corpus Christi Bay, Galveston Bay, the Louisiana marshes and Barataria Bay, Lake Pontchartrain, the lower Mississippi up to Baton Rouge and Mobile Bay, then the Mexican coast to the south and the deep gulf offshore. Operational since March 2021, it replaced three earlier systems with one FVCOM grid of 303,714 nodes, from 45 m in tidal creeks, inlets and intracoastal waterways to 10 km on the open boundary, and 41 layers.
Saily WR takes its runs of 03, 09, 15 and 21 UTC, every 3 hours from H+0 to H+48, on a 0.01° grid. Near the coast and over the shelf, the current comes from the tide, the wind and the Loop Current's influence offshore, and in the bays and estuaries from the rivers too: it runs hardest in the passes and inlets of the barrier islands and at the mouth of the Mississippi. In a tropical storm, NOAA's warnings, not this model, come first.
Sources
- Operational Forecast Systems, NOAA Center for Operational Oceanographic Products and Services (2026)
- Chesapeake Bay Operational Forecast System: Skill Assessment for 2001 and Improvements, NOAA Technical Memorandum NOS CS 1, NOAA Office of Coast Survey (2002)
- Technical Implementation Notice – Implementation of the new Oceanographic Forecast Modeling System for Chesapeake Bay, effective March 29, 2011, NOAA National Ocean Service (2011)
- Technical Implementation Notice – Implementation of the new Oceanographic Forecast Modeling System for the Delaware Bay, effective March 29, 2011, NOAA National Ocean Service (2011)
- Technical Implementation Notice – Implementation of the new Oceanographic Forecast Modeling System for the Tampa Bay, effective March 29, 2011, NOAA National Ocean Service (2011)
- Technical Implementation Notice 13-41 Amended – Implementation of the new Oceanographic Forecast Modeling System for the San Francisco Bay, delayed until March 11, 2014, NOAA National Ocean Service (2013)
- Service Change Notice 17-108 Updated – Implementation of new Oceanographic Forecast Modeling System for the Gulf of Maine, effective January 3, 2018, NOAA National Ocean Service (2017)
- Implementation of the Gulf of Maine Operational Forecast System (GoMOFS) and the Semi-Operational Nowcast/Forecast Skill Assessment, NOAA Technical Report NOS CO-OPS 088, NOAA Center for Operational Oceanographic Products and Services (2018)
- Service Change Notice 19-51 – Implementation of new Oceanographic Forecast Modeling Systems for the Cook Inlet and Lake Michigan and Lake Huron, effective July 23, 2019, NOAA National Ocean Service (2019)
- Service Change Notice 21-14 Updated – Implementation of new Oceanographic Forecast Modeling System for the U.S. West Coast (WCOFS) and the Upgraded Northern Gulf of Mexico (NGOFS2), effective March 22, 2021, NOAA National Ocean Service (2021)
- Service Change Notice 24-77 – NOS OFS Framework Version Updates and Implementation of Oceanographic Forecast Modeling Systems for the Salish Sea and Columbia River, effective on or about September 9, 2024, NOAA National Ocean Service (2024)
- NOAA Operational Forecast System (OFS), Registry of Open Data on AWS (2026)