Tideline pulls free public-data feeds and combines them into one dashboard. Here's what's behind the numbers and how fresh they are.
How often we refresh
- Every 10 minutes while the app is open
- When you reopen the tab if the data is more than 5 minutes old
- Manually using the refresh button (⟳) next to the date
The "pulled X min ago" line under the date tells you how stale the data is. It updates every 30 seconds.
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 they don't really "update" — refreshing just slides the countdown forward.
- Weather forecast — Open-Meteo's hourly model output. Models refresh roughly hourly upstream.
- Current conditions — NWS ground station observations (airport ASOS/AWOS) when one is nearby. Most stations report every 20 minutes, some hourly. Falls back to Open-Meteo's "current" model output when no station is close.
- Marine forecast (wave height, swell, water temp) — Open-Meteo Marine, hourly model refresh.
- Beach & coastal alerts — National Weather Service Watches / Warnings / Advisories, pushed live as forecasters issue them.
- Beach conditions card — National Weather Service Surf Zone Forecast for your zone when available (East Coast / Gulf / Great Lakes during swim season, issued daily around 4 AM local). Falls back to a computed score from the weather + marine data when no SRF exists.
- Air quality — Open-Meteo Air Quality (CAMS European Centre for Medium-Range Weather Forecasts model), updated hourly.
- Moon phase & rise/set — calculated client-side using astronomical formulas (Meeus). Doesn't fetch anything.
How the beach flag works
The flag in the top card combines two signals and shows the worst:
- Red if NWS has issued any active beach alert, OR if computed beach conditions are dangerous
- Yellow if beach conditions are marginal (choppy surf, gusty wind, high UV, etc.)
- Green when nothing meets either threshold
The flag is a guide, not a substitute for lifeguards or local knowledge. NOAA marine forecasts are the authoritative source for boating decisions.
Tide accuracy for tidal rivers
NOAA publishes tide predictions only at official stations (~210 nationwide for the NWLON plus subordinates). When you're upriver from one — say, in Pembroke on the North River — Tideline applies a calibrated time shift derived from the local watershed authority's published "Tide Math." North & South River shifts come from NSRWA field-measured offsets vs. Boston. Heights upstream are the station's heights (not adjusted for upstream damping), so treat upriver heights as approximate.
If you use the geolocation button and you're within 1.5 mi of a tide station, no upstream shift applies — Tideline trusts your precise position over the watershed rule.
Limits
- Tideline is an informational tool, not a substitute for NOAA Marine Forecasts, lifeguard flags, or any official safety guidance.
- Predictions can be affected by weather (especially storm surge) and won't reflect on-the-water reality during severe events. Check NWS directly for storm conditions.
- Coverage is US-only — outside the US the tide-station selection won't work and most data sources will be sparse or missing.
Tideline · v2026.05.31.1100 · built in Marshfield, MA