Water levels in oceans, seas, bays, and rivers fluctuate with the tides due to the gravitational pull of the sun, moon, and other planets. We can predict future water levels based on past observations because the frequencies of gravitational forces are well known.
WorldTides™ uses several public and licensed sources for tidal predictions. In most cases, observations are made from tide gauges at land-based stations to ensure accuracy. When station data is not available, we use satellite data. Satellite predictions are less accurate, but you can choose whether or not to include them depending on the application.
Note: Because these predictions do not include weather conditions or seismic activity, they should not be relied upon to aid in navigation or other critical tasks involving personnel or property safety.