The short answer
A tide prediction estimates the astronomical tide; an observation measures water at a station. Weather and other effects can make the two differ, so check the matching station, datum and current forecasts.
Three products, three different questions
A NOAA tide prediction estimates the timing and height of astronomical tides at a specified station. An observed water level is a measurement from a station at a particular time. A forecast or nowcast can combine models and observations to estimate conditions beyond a pure astronomical prediction.
Those products are related, but they are not interchangeable. The predicted high water in tomorrow’s table is not an observation of tomorrow’s water. A current water-level measurement also is not, by itself, a forecast of the next high tide.
Why the water can differ from the table
Wind, atmospheric pressure, river flow and other weather effects can raise or lower water relative to the predicted astronomical tide. The effect depends on location and conditions. NOAA explicitly notes that short-term weather cannot be predicted by the tide table alone.
A difference from the table is not necessarily a failure of either source. It may reflect factors outside the tide prediction, a mismatch in station or timing, or a measurement issue. Compare like with like before drawing a conclusion, and use current official forecasts and warnings for time-sensitive decisions.
Make the station and reference match
Find the station identifier and the physical waterway it represents. A station inside an inlet, at a pier, or on a tidal river may not describe a beach or channel with a similar place name. Distance on a map is not the only consideration; the water connection and local geography matter too.
When comparing observed and predicted heights, use the same station, time basis, unit and vertical datum when the source makes them available. A height relative to mean lower low water is not automatically comparable with a number relative to another datum. Read the station’s own metadata and conversion guidance.
A worked example: a fictional 0.7-foot difference
Imagine that a station predicts 3.2 feet at 2:00 p.m. and an observation at the same station and time is 3.9 feet, using the same datum and unit. The observed-minus-predicted difference is 3.9 − 3.2 = +0.7 feet. This is a fictional calculation, not a NOAA observation or a forecast.
The arithmetic tells you the size and direction of the difference at that time. It does not establish why it occurred, whether the difference will persist, or conditions at another beach. Look at the source’s quality flags, weather and forecasts before interpreting the result.
A checklist for a tide-day plan
Write down the date, local time zone, station ID, high and low predictions, height unit and datum. Note the time you checked the table. Then look up the latest available observation and its timestamp; an old observation is not live conditions just because the page refreshed.
Check the marine forecast, weather advisories, local beach or harbor notices, and any relevant access restrictions. High and low water times do not provide current speed, wave height or a continuous water-level curve. Get the separate official products needed for your activity.
Leave room for change
Conditions can change quickly, particularly around storms, inlets and exposed coastlines. A tide table is a planning aid, not permission to enter a hazardous area. If official warnings or local conditions conflict with a personal plan, follow the current instructions from responsible authorities.
Save the station and source link so you can check again before leaving. If an observation or prediction is missing, describe it as missing rather than assuming calm or safe conditions.
Put the checklist into practice
Suppose you plan a morning visit to a coastal access point. The day before, select the official reference station and record the predicted high and low times in local time. Next, note whether the source supplies observations at that station and how recently those measurements were recorded.
Before leaving, review the latest observation, marine weather forecast and any local closures or warnings. Ask whether wind, waves, current and the approach route matter to the activity. If the information is missing or a warning is in force, a tide-table time does not resolve the gap; change the plan or seek current local guidance.
What to save for the next visit
A reusable note is more useful than a saved screenshot alone. Record the access point, station identifier, local date, time zone, datum, predicted high and low times, and the time you retrieved the information. Add the observation’s timestamp separately. Make clear which numbers are predictions and which are measurements.
Conditions on a future visit may differ. Do not reuse a prior day’s observation as a current reading. Refresh the relevant source and check current forecasts and local notices each time, especially if a planned route can be cut off by rising water. A saved note is an aid to planning, not a hazard warning.
Your next steps
- Choose the appropriate station and date.
- Match station, time, unit and datum before comparing.
- Check the observation timestamp, marine forecasts and local notices.
- Use separate current, wave and weather products when needed.
Common questions
is low tide the same as slack current?
No. Tide describes vertical changes in water level, while a tidal current describes horizontal movement of water. The time of high or low water is not automatically the time of slack current at a different place. In channels, inlets and tidal rivers, local geography matters. NOAA provides separate current-prediction products where available. If the activity depends on current speed or direction, find the appropriate current station and check its context; a high-and-low tide table alone does not supply that information. Also check weather, waves and local navigation notices.
can I subtract two heights at different stations?
Not safely without understanding their references and locations. Even if both values are expressed in feet, the stations may use different datums, sit in different waterways or experience different weather and river effects. A subtraction can produce a number without producing a meaningful comparison. For a like-for-like observed-minus-predicted example, start with the same station, same time, same datum and same unit, and check quality flags. When a different comparison is necessary, consult the official metadata and any appropriate datum-conversion tool. Explain remaining differences rather than implying one station measures the other.
Sources and editorial record
- NOAA: Tide predictions and weather effects
- NOAA: How water levels are monitored
- NOAA: Operational forecast systems
Prepared with AI assistance from the linked sources. Independent human review pending. “Public Atlas Editorial” is a publication label. First edition: 2026-10-28. Scheduled source review: 2027-01-28. Data examples update with their source snapshots; the guide text is versioned separately.
Changes to this guide
- 2026-10-28 — First AI-assisted edition published after source checks, with human review pending.