Data and methodology

How Tide Chart Now handles tide data

US tide predictions come from the National Oceanic and Atmospheric Administration’s Center for Operational Oceanographic Products and Services (NOAA CO-OPS).

Prediction settings

• Datum: Mean Lower Low Water (MLLW).
• Units: feet.
• Timezone: local standard or daylight time for the verified station.
• High/low coverage: refreshed before fewer than 14 future days remain.
• Hourly chart coverage: refreshed before fewer than seven future days remain where the station supports interval predictions.

Local storage and freshness

NOAA requests run only in background jobs or operator tasks. A production job checks coverage every day, refreshes only stale stations, and spaces station requests by at least one second. Predictions are parsed into local dates and UTC timestamps, stored in SQLite, and served from the local database. Public page requests cannot invoke the NOAA client.

How the Tide Brief is calculated

The Tide Brief is calculated only from the stored high and low predictions shown on the same page. It identifies the next predicted change, groups the next 24 hours of turns, and calculates each day’s largest predicted high minus its lowest predicted low. It does not infer currents, surf, weather, water temperature, access, or conditions between NOAA prediction points.

Location and station mapping

Location reference coordinates were derived during a one-time review using OpenStreetMap contributors. NOAA station identifiers, names, and coordinates come from the official NOAA CO-OPS tide-prediction station catalog. The distance shown on a location page is the great-circle distance between those two recorded points. That distance makes the station choice transparent; it is not a promise that every shoreline, inlet, or harbor will behave identically.

Location availability

The main directory features locations with a verified station mapping and at least seven complete days of high and low tide predictions. Search may find additional verified coastal locations. If prediction coverage becomes incomplete, a location is removed from browse pages until fresh data is available again. When a station has not published a full annual horizon, the refresh process uses the shorter available prediction window and checks it more frequently.

Attribution and safety

Tide predictions are based on NOAA CO-OPS data. Tide Chart Now is not affiliated with or endorsed by NOAA. Predictions are for general informational use only and are not intended for navigation.

Review the official NOAA CO-OPS Data API guidance and NOAA Tides & Currents disclaimer.

For data questions, contact [email protected].