Data sources and coverage

Every number on TidalMap comes from an agency that measures the water for a living. This page says which one, what it covers, and how fresh it is when it reaches you.

The order follows the water. Rain falls, rivers rise, dams release, the tide carries it all past the inlet, and the wind decides what the ride out looks like. Wherever you look on the map, TidalMap picks the best source for that spot: the most accurate first, then the closest, then the freshest, and it shows you how old each reading is.

Rain, wind and clouds ahead

Hourly wind, gusts, rain and cloud cover

Source: NOAA's High-Resolution Rapid Refresh (HRRR, 3 km) for the next two days, then NOAA's Global Forecast System (GFS) out to 72 hours. Hawaii, Puerto Rico, Alaska and Guam use NOAA's National Blend of Models, also to 72 hours.
What you see: Animated wind streamlines, rain and cloud layers you can scrub forward hour by hour.
Coverage: HRRR covers the lower 48 states and nearby water. GFS and the National Blend fill in beyond it.
Refresh: HRRR and GFS are checked every hour, the National Blend four times a day.

Live radar

Source: NOAA's Multi-Radar Multi-Sensor (MRMS) composite reflectivity.
What you see: The latest radar loop over the map.
Coverage: The lower 48 states.
Refresh: Every 4 minutes.

Rivers

River flow and stage

Source: U.S. Geological Survey (USGS) stream gauges.
What you see: Current flow and water level at each gauge, with its trend and how it compares to normal for the season.
Coverage: All 50 states and Puerto Rico.
Refresh: Every 30 minutes.

River forecasts and flood stages

Source: National Weather Service river forecast points (the National Water Prediction Service).
What you see: The forecast stage for the days ahead, the flood categories for that gauge, and its historic crests.
Coverage: About 4,000 NWS forecast points nationwide, matched to the USGS gauge they describe.
Refresh: Fetched when you open a gauge, never more than 15 minutes old.

Dam releases

TVA generation schedules

Source: Tennessee Valley Authority.
What you see: Observed releases, the planned generation schedule and TVA's predictions for the next day, for tailwater trout and everything downstream.
Coverage: All 43 dams in TVA's index, hydro plants and the Corps projects TVA reports on.
Refresh: Hourly through the day, every 5 minutes in the late afternoon window when TVA posts the next day's schedule, and every two hours overnight.

Army Corps of Engineers releases

Source: U.S. Army Corps of Engineers water management data.
What you see: Release, pool level and tailwater at dams that publish their outflow directly.
Coverage: Starting with the Little Rock, Tulsa and Mobile districts.
Refresh: Hourly.

Tides

Tide predictions and observed water levels

Source: NOAA Center for Operational Oceanographic Products and Services (CO-OPS).
What you see: High and low times and heights, the predicted curve, and the observed water level beside it at gauges that report live, so you can see when the wind is holding water in or pushing it out.
Coverage: More than 3,000 NOAA tide stations on every US coast, Puerto Rico, the U.S. Virgin Islands and the Pacific islands. Times are given in each station's local time.
Refresh: Predictions are loaded for the year and topped up monthly. Observed water levels every 30 minutes.

Community water-level gauges

Source: Hohonu sensors on docks, bridges and pilings, republished by the U.S. Integrated Ocean Observing System (IOOS).
What you see: Observed water level in back water NOAA never gauged. These read against their own local reference, not a chart datum, and carry no predictions, and TidalMap labels them that way.
Coverage: About 86 sensors where Hohonu has installed them.
Refresh: Every 30 minutes.

Wind, waves and weather on the water

Weather stations

Source: NOAA's National Data Buoy Center (buoys and shore stations), NOAA CO-OPS weather sensors at tide stations, and NWS airport stations (ASOS).
What you see: Each pin says what kind of station it is, because that decides what it can report. Buoys give wind, waves and water temperature. Tide-station sensors give wind and water temperature inshore. Airports give wind, visibility and cloud cover, never water temperature. Near the coast the weather card prefers a marine station within 40 km over a closer airport.
Coverage: About 3,600 stations nationwide, with buoys and tide-station sensors that share a pole shown as one pin.
Refresh: Tide-station weather every 30 minutes. Buoy and airport readings are fetched when you open a station.

Wave forecasts

Source: The National Weather Service's Nearshore Wave Prediction System, run by each coastal forecast office.
What you see: Wave height and direction near the coast, hour by hour.
Coverage: 22 forecast offices on the East Coast, the Gulf and Puerto Rico.
Refresh: Twice a day.

Offshore

Sea-surface temperature and temperature breaks

Source: NOAA CoastWatch blended satellite sea-surface temperature, freshened with GOES satellite reads and NOAA's Real-Time Ocean Forecast System (RTOFS) where clouds block the view. Temperature lines are drawn from the same field.
What you see: Water temperature, isotherm lines that show where the breaks are, and a forecast of how they move over the next days.
Coverage: Worldwide between 75 degrees north and south.
Refresh: The satellite blend and the temperature lines daily, the fresher satellite reads hourly, the forecast daily.

Currents

Source: NOAA's Real-Time Ocean Forecast System (RTOFS).
What you see: Surface current speed and direction as flowing trails, like the wind layer.
Refresh: Daily.

Chlorophyll and water color

Source: NOAA CoastWatch VIIRS satellite chlorophyll.
What you see: Where blue water meets green, the edge where bait gathers.
Refresh: Daily.

Hazards and alerts

Local Notices to Mariners

Source: U.S. Coast Guard.
What you see: Discrepant and missing aids to navigation, obstructions and other notices placed on the map.
Coverage: All nine Coast Guard districts that publish them: the East Coast, the Gulf, the Great Lakes, the Pacific coast, Hawaii and Alaska.
Refresh: Every 6 hours.

Weather and flood alerts

Source: National Weather Service active alerts.
What you see: Flood watches and warnings beside river gauges. Through the TidalMap MCP connection, every active alert at a spot, including marine ones such as Small Craft Advisories and Gale Warnings.
Coverage: Everywhere the NWS issues alerts.

The chart underneath

Nautical chart, depths and seamarks

Source: NOAA Electronic Navigational Charts (Office of Coast Survey), NOAA NCEI bathymetry, and OpenSeaMap seamarks.
What you see: The official chart as a layer, depth contours, and buoys and markers.

Aerial imagery

Source: State aerial imagery programs (for example North Carolina, South Carolina, Virginia, Maryland, New Jersey, New York and Massachusetts), USDA's National Agriculture Imagery Program, NOAA Digital Coast, and Copernicus Sentinel-2 where no aerial photography exists, such as much of Alaska.
What you see: Photographs of the flats, channels and marsh, credited to the agency that flew them.
Refresh: We search for newer flights every week.

Sun, moon and feeding times

Source: Calculated on your device from the positions of the sun and moon. No network needed.
What you see: Sunrise, sunset, moon phase, and the major and minor solunar periods for the week.
Coverage: Anywhere.

What we don't cover yet

Wave forecasts for the Pacific coast, Hawaii and Alaska. The forecast offices publish them; we have not wired them in yet.
Live radar outside the lower 48 states.
Army Corps dams whose districts publish releases only as tailwater level and turbine output, such as the Nashville district.

Fishing somewhere we're thin? Tell us which water, and we'll look for the best source there.

Not for navigation

TidalMap is for information and recreation. It is not a navigational tool and should never replace official NOAA charts, proper aids to navigation, or sound seamanship. Government data is shown as published and is not an official government product. See our Terms of Service for the full disclaimer.