Tides and Coastal Water Levels Today

Coastal water level rises and falls with the astronomical tide, but weather, currents and local geography can move the observed water away from the prediction. This page pairs the latest verified observation with the next predicted high and low at eight NOAA stations around the United States.

Observed water level versus predicted tide

The observed level comes from a water-level sensor at the station. The predicted high and low are astronomical tide predictions calculated from long records of local tidal constituents. Predictions do not include every short-term weather effect.

Strong onshore wind and low atmospheric pressure can elevate water above the predicted tide; offshore wind can lower it. Waves and run-up can produce hazardous conditions even when the still-water level at a gauge appears unremarkable.

What MLLW means

All levels on this page are in metres relative to Mean Lower Low Water (MLLW), the average of the lower low tide on days with two low tides over an official tidal datum epoch. Nautical charts commonly use MLLW as a local reference.

MLLW is not a universal global zero. A value of 1 metre at San Francisco and 1 metre at Boston does not mean the sea surface is at the same elevation in a shared coordinate system. It means each station is 1 metre above its own local MLLW reference.

Stations represented

The table includes San Francisco, Seattle, Honolulu, Key West, Mayport, The Battery in New York, Boston and Galveston Pier 21. Together they illustrate several tidal regimes and coastlines, but they are not a complete view of U.S. coastal flooding or global tides.

How to use the page

Start with the observation time, then compare the observed level with the next predicted high or low. For local decisions, open the station link to see NOAA’s full plots, datums and quality flags. Consult National Weather Service coastal-flood products, harbor authorities and emergency managers when risk matters.

Limitations

• Preliminary observations can be corrected after quality control.
• Tide predictions describe astronomical forcing and are not storm-surge forecasts.
• Station data do not measure wave run-up at a nearby beach or property.
• Local datum values cannot be compared directly between stations.
• A sensor outage or delayed transmission is shown as missing or stale data, not as zero water level.

Methodology and source

Observed levels and high/low predictions come from the NOAA Center for Operational Oceanographic Products and Services Data API. Queries use metric units, GMT and the MLLW datum. The table links to each NOAA station page for authoritative plots and metadata.

ARGO.net validates station identity, coordinates, observation time and numerical ranges before caching a new snapshot. Predictions cover the next 72 hours so the next high and low can be selected without contacting NOAA during a visitor request.

Update log

• August 2026: Page launched with eight coastal stations, observed levels and next predicted high and low tides.