Predicting the tide
This website shows the predicted astronomic tide, for many locations.
The actual water-level depends on the astronomic tide, and on other factors; meteorologic effects, wind and waves, storm surge, atmospheric pressure; tsunami waves caused by earthquakes or underwater landslides; and long-term changes in water level, caused by land subsidence or uplift, or by sea-level rise or fall.
Only the astronomic tide is predicted here, not the effects of weather, nor long-term changes in water level.
Water level measurements
For each location we require a series of water level measurements, taken at the tide station. These historic measurements are then used to create a model, allowing prediction of water levels for the station at other times, past, present, or future.
Accurate tide predictions
Our mission is to give you accurate tide predictions for locations all over the world. However accuracy does vary a lot, depending on the characteristics of the location, and on the quality and quantity of the original water level measurements taken at the station.
Locations with a large tidal range will typically have better quality tide predictions. Where the tidal range is large, the meteorologic effects—the variations caused by wind and weather—are relatively small.
Tide stations may be located along a coast, or up-river, or in the open ocean. The adjacent body of water may be large or small, and may be connected to other bodies of water by channels, large or constricted. Large bodies of water, the oceans and the larger seas, are conducive to large tidal ranges.
Smaller seas such as the Mediterranean and the Baltic have smaller tides. In such places the effect of wind and weather is relatively large, drowning out the astronomic tide, adding noise to the signal. Similarly for tide stations any distance up-river, the effect of varying rainfall on river flow may predominate. The further up-river, the less the effect of the astronomic tide.
The original measurements
Our tide predictions are based on measurements of past water levels at each individual station. The quality of our predictions can only be as good as the quality of the original measurements.
Accuracy of the model is not affected by the age of the original measurements. Provided a sufficient number of readings were taken, and the water level and time was recorded accurately, old readings can suffice to create a good quality model.
Good quality measurements have accurate times and water levels, extending over a sufficiently long time period, with few data spikes or gaps in the data, and preferably no datum changes. While the modelling process can tolerate some data quality issues, better quality data will produce a better quality tide model.
Water-level datum
The original water level measurements for each tide station were taken relative to some vertical datum, i.e. benchmark, zero-reference level. This datum may remain the same indefinitely. If so, all the measurements for that station will be relative to the same zero-reference level.
But at some stations the datum has changed. The reason for the adjustment may be, for example, to re-align with a standard regional or national vertical datum, or to correct for vertical land motion. When this happens, all subsequent water level measurements will be offset, relative to the old measurements.
We need consistent water level measurements to create the tide model. If the set of measurements spans a change in datum, including measurements from both the old and new datum, the quality of the tide model may be impacted.
To see predicted tide heights relative to the tide station datum, select ☰ Tide height - Height datum - Gauge.
predictions last updated 2023-10-12 visit oceantide.io