How To Read A Tide Chart

A NOAA tide prediction estimates the regular astronomical tide caused mainly by the gravitational relationships among Earth, the moon, and the sun. It is calculated for a specific station. Wind, barometric pressure, river flow, storm surge, seiches, and other short-term effects can make the water that actually occurs higher or lower than the predicted curve.

TideAhead labels its chart as a prediction and identifies the NOAA station behind it. If a page also contains weather observations, those measurements remain a separate layer. Do not read a smooth tide curve as proof that a sensor measured that exact height at that moment.

1. Station: The name and NOAA ID identify the precise prediction location. A city page may use a disclosed nearby station; it is not a new prediction at the city coordinate.
2. Local time: TideAhead displays prediction times in the place or station timezone. This avoids asking visitors to convert a UTC feed while making a plan.
3. Datum:Tide height is measured relative to a vertical reference surface. TideAhead uses NOAA's MLLW predictions, where zero is the station's Mean Lower Low Water datum—not the seafloor and not an absolute depth.
4. Units: Confirm feet before comparing a chart with a rule, ramp, trail, or chart that may use meters or a different datum.
5. Source status: An official NOAA curve differs from a TideAhead-derived curve between official extrema. The visual style and source badge identify which one is present.

High and low tides are turning points. Between them, the slope of the curve is a practical picture of how fast the predicted level is changing: a steeper segment means a larger predicted height change over the same amount of time, while a flatter segment occurs near a turn. This does not directly give current speed. Current timing and direction can lag the tide and vary with channel geometry.

For a beach walk, launch, shoreline crossing, or tide-pool visit, look at the whole time window: the height on arrival, the direction of change, the next turn, and the predicted height when you expect to leave. A single "low tide at 2:00" label omits most of that context.

NOAA reference stations can publish the continuous six-minute prediction series used for a solid TideAhead curve. For many subordinate stations, NOAA publishes official high and low events but not an equivalent six-minute series. TideAhead keeps those extrema and may connect adjacent events with a dashed half-cosine estimate so the direction of change is easier to inspect.

That dashed segment is bounded by the two official extrema. TideAhead does not extend it before the first event or after the last event, and it does not present an interpolated point as a NOAA observation or official six-minute prediction. When the surrounding extrema are not available, the continuous estimate remains unavailable.

1. Confirm that the station represents the shoreline or waterway you intend to visit.
2. Confirm local date, time, datum, and units.
3. Read arrival and departure heights, not only the nearest extreme.
4. Note whether the water is predicted to rise or fall during the visit.
5. Check current NWS observations and official forecast guidance.
6. Check marine hazards, local closures, access rules, and daylight.
7. At the site, treat signs, barriers, surf, weather, and water behavior as more immediate than a web page.

• Comparing heights from two stations without checking whether their datums are equivalent.
• Assuming a negative MLLW height means there will be no water.
• Treating tide height as charted water depth over a particular rock, bar, or channel.
• Using a station because its town name looks nearby without checking the actual map and water connection.
• Ignoring the return window when a route can be cut off by a rising tide.
• Treating astronomical predictions as storm-surge, wave-runup, or rip-current forecasts.

NOAA CO-OPS explains tide predictions, datums, and station metadata in its Tides & Currents service. Before a trip, pair the tide chart with the National Weather Service forecast and warnings for the destination. If you are unsure whether TideAhead selected an appropriate station, continue with our station-selection guide.