Altimeters can measure sea surface height first and foremost the waves height, which is of prime importance to marine weather forecasters in terms of maritime safety. Wave heights from altimetric measurements are assimilated into sea state forecast models, and improve significantly their predictions.

A wave model describes and predicts sea state in terms of wave height, period and direction. Combined with atmospheric measurements, altimetric data are vital to obtain a precise picture of sea state that closely matches observations. First, these data are fed into wave models to generate forecasts. Then, model results are compared to real altimetric measurements of sea-surface height and corrected in real time where errors are detected. 

The model at national weather service Meteo-France provides sea-state parameters every 3 hours and forecasts out to 5 days. Using these outputs, forecasters draw up daily bulletins for their area of responsibility. The level of confidence for 5-day forecasts is better than 90%. Beyond 5 days, it is still good at around 75%. These data are crucial to maritime safety, not only to give early warning to populations living near coasts in the event of a storm but also for ships so they can change course to avoid very-low-pressure zones. The current model warns ships of the risk of encountering rogue waves, which can be detected by altimetry satellites. Such waves are most likely to occur in the North Atlantic. For example, during the winter storms of 2014, the SARAL-AltiKa satellite measured waves as high as 18 metres.