How it works

Rosa answers one question: is it worth surfing, and when, and where?

Here is how, in plain terms.

1. We start with free, public forecasts. Rosa is built on open data that anyone can use:
   • NOAA and ECMWF open data directly, for worldwide waves: Rosa reads the two global wave models itself, blends them, and takes sea temperature from NOAA too.
   • DWD (the German weather service) open data for each swell's peak period.
   • Open-Meteo for wind and weather.
   • EOT20 tide harmonics, so every spot gets a real tide curve for the whole forecast.
   • GEBCO for the shape of the seabed near each spot.
   • Public surf buoys (NDBC and ISRAMAR) to check our forecasts against what the ocean actually did.
2. We do the maths for every spot, ahead of time. A few times a day, Rosa takes those forecasts and, for each surf spot, works out how the open-ocean waves will actually stand up and break there, using the seabed shape and the way the beach faces. It saves the result, so the app opens instantly and still works on a shaky signal.
3. We turn it into a score. Every hour gets a rating from 0 to 100. Bigger, cleaner, well-lined-up waves with friendly wind score higher; small, messy, or blown-out conditions score lower. We boil that down to a single word, from Flat to Epic, so you can read it at a glance.

We refresh the forecast several times a day, and always show when it last ran, so you know how fresh it is.