How we know what we know
Two kinds of number appear on this site, and they behave completely differently. Telling them apart is the single most useful thing you can learn about tide forecasting.
Calculated, not fetched
Tide, sun, moon and solunar are computed from a harmonic model — the FES2022 global tide model’s harmonic constants at the nearest ocean point — plus standard astronomical formulas. They don’t depend on a network call, they’re available for any date past or future, and they never go stale.
These never carry a timestamp, because they can’t be out of date.
Fetched from a forecast service
Weather, wind, waves, sea temperature, pressure and air quality come from Open-Meteo and CAMS, refreshed while you’re online. They cover roughly a week back to two weeks ahead — outside that window we say so plainly rather than guessing.
The staleness ladder
| Age of the data | What you see | Why |
|---|---|---|
| Under 5 minutes | No badge at all | Fresh enough that a timestamp is just noise |
| 5–30 minutes | Grey timestamp, low emphasis | Normal for a marine forecast |
| 30 minutes – 24 hours | Amber accent on the card | Still usable, but worth knowing |
| Over 24 hours | “Last updated yesterday” + refresh | Treat with real caution |
Gauge vs. interpolated
Gauge station
A real instrument with a measured record, and NOAA publishes its own official predictions and datums for it. The prediction on our page is still the model’s — what the badge tells you is that a measured record exists there to check ours against.
Interpolated point
A coastal place with no gauge of its own, modelled from the same FES2022 constants at the nearest ocean point. Same mathematics, same zero — a difference of station, not of method.
Why might this differ from another app?
Two apps can both be right and still disagree. If one measures heights from Mean Lower Low Water and another from Mean Sea Level, the tide hasn’t changed — the zero point has. Ours is mean sea level, which is why a low water can read as a negative number here and as a positive one on the chart in your hand.
The rest is the model. A model cell is a few kilometres wide, and the nearest wet cell to a beach can be further off than that, so the model cannot know your estuary, a bay entrance or a lagoon: timing travels well — on an open coast our times are usually within a few minutes to a quarter of an hour of a nearby gauge — and heights travel badly, so a range inside a bay, a river or a lagoon can be wrong, occasionally by a lot. Every station page names its source and the datum its heights are counted from, so you can see what you are comparing; gauge vs. interpolated stations works through it.
A time shown as 2:15 PM might be 2:14:40 in one source and 2:15:10 in another. Both are correct to the minute.
About the fish activity rating
Solunar theory — the idea that fish and game feed more actively around sun and moon transits — is a long-standing tradition among anglers, not a scientifically proven predictor. We calculate it the standard way, from real lunar transit and moonrise/moonset times, and show it as a helpful indicator rather than a guarantee. Tide state, water temperature and local conditions matter just as much, if not more.
Data sources & licences
- Open-Meteo Weather, wind, waves, sea temperature · CC BY 4.0
- CAMS / Copernicus Air quality and pollutants
- FES2022 (CNES / AVISO+) The global tide model behind interpolated predictions
- NOAA CO-OPS US tide-gauge harmonics and current predictions · public domain
- OpenStreetMap contributors Map tiles
- GeoNames Station and place catalog · CC BY 4.0
Tide and weather predictions are estimates for planning purposes only — not for navigation or safety-critical use.
Found something that looks wrong?
Tell us which station and what looks off — a person reads every message, normally within two business days.