About Groundswell
What Groundswell is, where the data comes from, and who builds it.
Last updated: September 2, 2026
What Groundswell is
Groundswell is a surf-forecast service: live conditions and a 10-day wave forecast for any surf spot on earth, plus 4+ years of historical swell climatology. It covers wave height, swell period and direction, wind, water temperature, tides, and UV index.
The spot database spans more than 6,900 named breaks worldwide. Groundswell is a progressive web app (PWA), is available in five languages, and shows no ads on any tier. There is a free tier; paid subscriptions add swell alerts and extended forecast access.
Where the forecast data comes from
Live forecasts come from the Open-Meteo Marine API, which runs the ECMWF wave model. Tides and UV index come from Open-Meteo’s tidal and atmospheric models.
Historical climatology is built on ERA5 reanalysis (offshore significant wave height, Hs) for 2022–2024. Every source is open data. The Accuracy page explains the models and their limits.
How the surf rating is calculated
Each spot gets a composite rating that combines swell height, period, and direction against the break’s orientation, together with wind speed and direction.
It is not a black box: the Accuracy page breaks down how the rating is built and publishes Groundswell’s track record against observed conditions.