Every day of one year's tide at six American harbours, each day drawn as a ring on a 24-hour clock. Anchorage swings 11 metres; Honolulu less than one. Bright rings are the spring tides that follow new and full moons. Tap or hover any ring.
Data & source
Source: NOAA CO-OPS harmonic tide predictions for 2025,
hourly, local standard time, heights above mean lower low water · fetched
— · public domain. These are the astronomical tide — what the
Moon and Sun alone would do. Real water also answers to wind, pressure and storm surge,
so an observed day can sit well above or below its ring. Six harbours chosen for
contrast, not coverage; the character label is the standard form factor
F = (K1+O1)/(M2+S2) from NOAA's own published constituents.