Tides are the regular increase and decrease of the water levels of oceans, seas, bays, and rivers. Tides are caused by the gravitational pull on the water from the sun, moon, and other planets as it interacts with geography of the land. Becuase the frequencies of the gravitational pulls are well known, future water levels can be predicted based on past observations using Harmonic Analysis. However, these predictions do not take into account weather conditions and seismic activity. So, it is very important not to use these predictions for navigation or other critical tasks especially where harm can come to persons or property.
WorldTides™ uses a number of public and licensed sources for tidal predictions. When available, land-based station observations from tide gauges are used for the maximum accuracy. When station data is not available, predictions based on satellite observation are used instead. Satellite predictions are not as accurate but you can choose whether or not to include these depending on the application.