Amphidrome: Tide Almanac

Amphidrome is a harmonic tide and current almanac that does its math entirely on your device. Every prediction is computed from bundled tidal harmonic constituents — the same physics professional almanacs use — so it works exactly where cell service dies: a back-bay cove, an offshore bank, a canyon river mouth, or airplane mode. Most tide apps quietly fail without a signal because they fetch predictions from a server. Amphidrome never does. The full constituent dataset ships inside the app, and the prediction engine runs locally for any date, past or future. WHAT IT DOES • Harmonic tide-height prediction for any date, referenced to the chart datum (MLLW) where published • Tidal-current speed and direction with flood/ebb axis and slack timing • High and low tide tables, plus slacks and maximum currents • A day-by-day almanac spanning up to two weeks, with a shareable day sheet • Sun and moon rise, set, and transit, plus moon phase and illumination • An interactive tide and current graph you can scrub to read the exact value at any minute • Datum reference lines (MHHW, MHW, MSL, MLW, MLLW) drawn right on the curve FULLY OFFLINE MAP • A vector coastline and bathymetry map rendered from bundled geometry — no map tiles, no connection • Coastlines, minor islands, reefs, lakes, and five bathymetric depth contours • Every station plotted; tap to open its predictions THOUSANDS OF STATIONS • 1,300+ tide stations and 2,200+ current stations with full harmonic constituents • Search by name, ID, or state; sort by distance; save your regular spots THE ENGINE Amphidrome sums up to 37 tidal constituents with Schureman nodal corrections and an on-device astronomical ephemeris. Predictions are validated against published reference values to within minutes and centimeters. PRIVATE BY DESIGN • No account and no sign-in • No ads and no tracking • If you choose to share your location, it is used only on your device to sort stations by distance — never stored, never transmitted Built for anglers, sailors, kayakers, surfers, clammers, paddlers, and coastal photographers who need reliable tides and currents exactly where the signal ends. Tide and current predictions are approximations for planning and must not be the sole basis for navigation or safety-of-life decisions. Always consult official sources and observe local conditions.