How often we refresh

Every 10 minutes while the app is open
When you reopen the app if data is more than 5 minutes old
Manually using the refresh button (⟳) next to the date

The "pulled X min ago" line tells you how stale the data is.

Where the data comes from

Tide times & heights — NOAA harmonic predictions, the same numbers the National Ocean Service publishes. These are math, not measurements, so refreshing doesn't change them.
Weather forecast — Open-Meteo's hourly model output.
Current conditions — NWS ground stations (airport ASOS/AWOS) when nearby; reports every 20 min. Falls back to model output otherwise.
Marine forecast — Open-Meteo Marine (wave height, swell, water temp), hourly.
Coastal alerts — National Weather Service Watches / Warnings / Advisories.
Beach conditions — NWS Surf Zone Forecast for your zone (East Coast / Gulf / Great Lakes in swim season). Falls back to a score computed from weather + marine data.
Air quality — Open-Meteo Air Quality (CAMS model).
Moon phase — calculated client-side; doesn't fetch.

How the beach flag works

The flag at the top combines two signals, worst wins:

Red if NWS has any active alert, or beach conditions are dangerous
Yellow if conditions are marginal (choppy surf, gusty wind, high UV)
Green when nothing meets either threshold

Not a substitute for lifeguards or local knowledge.

Tidal river accuracy

NOAA publishes tide predictions only at official stations. When you're upriver from one, Tideline applies a calibrated time shift based on the local watershed authority's field measurements. Heights upstream are the station's heights (not adjusted for upstream damping) — treat them as approximate.

If you use geolocation and you're within 1.5 mi of a station, no shift applies — Tideline trusts your position.

Limits

Informational only — not a substitute for NOAA Marine Forecasts, lifeguard flags, or official safety guidance.
Predictions can be off during storms (especially storm surge). Check NWS directly for severe events.
US-only coverage.