Tide Hours support
Tide Hours is an iPhone app that shows predicted high and low tides for more than 3,200 US tide stations. It computes the predictions on your phone, so it works with no signal.
What the numbers are
Every height and time in Tide Hours is a prediction of the astronomical tide, computed from NOAA's published harmonic constants. It is not an observed water level, and it is not for navigation.
Wind, storms, river flow and air pressure can move the real water level well above or below the prediction. Heights are in feet (or meters) above mean lower low water (MLLW), the datum on NOAA charts, and times are shown in each station's local time.
Free features and the one-time unlock
Free: every station, today's tide graph with high and low times, Near Me, and one favorite station.
A one-time in-app purchase adds unlimited favorites, the 7-day table, and Home Screen and Lock Screen widgets. There is no subscription. If you reinstall or get a new iPhone, open the unlock screen and tap Restore Purchase.
Near Me
Near Me asks for your location only when you tap it, uses it once to sort stations by distance, and then drops it. If you turned location access off, you can turn it back on in the Settings app under Privacy & Security, Location Services, or search by station name instead.
How accurate it is
Before release, the app's predictions were compared with NOAA's own published predictions at 16 stations, from Anchorage to San Juan. High and low times matched within 3 minutes and heights within 0.05 ft.
Some stations are marked as using offsets. NOAA predicts their highs and lows from a nearby reference station with published time and height adjustments, and Tide Hours does the same. The curve between those highs and lows is an estimate, drawn as a dashed line.
Where the data comes from
Tide predictions are computed from NOAA CO-OPS harmonic constants, datums and station offsets, which are U.S. Government data in the public domain. Tide Hours is not a NOAA product and is not endorsed by NOAA.
Questions
Email me about Tide Hours, including a station that looks wrong, at chelsea@chelseakr.com.