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How we score surf windows

swelltrip.now doesn't try to forecast every wave. It looks at 11 European regions every 3 hours and flags the moments when conditions line up — so you know whether it's worth booking a flight.

Data sources

Open-Meteo Marine API — swell height, period, and direction.
Open-Meteo Weather API — wind speed, wind direction, surface pressure.
We fetch 10 days ahead, hourly, for multiple grid points per region (to average out local noise).

The score (0–100)

For every hour and every grid point in a region, we compute a 5-component score:

Swell height in the region's comfort zone35%

Swell period (longer = cleaner, more power)25%

Wind: offshore is good, onshore penalised20%

Swell direction vs. the region's working window10%

Pressure trend (rising pressure = cleaning up)10%

Per hour we take the average of the top 30% of grid points — the idea is "somewhere in this region is firing", not "everywhere at once".

What the numbers mean

65+ — Perfect. Clean, sized swell with cooperating wind.

55–65 — Good. Worth a trip if the window is long enough.

45–55 — Mixed. Surfable if you're already there.

Below 45 — Skip. Small, blown out, or both.

Surf windows

A window is a continuous stretch of at least 4 hours at score 50+. Short gaps (under 8 hours) between two good stretches get stitched — a bad night between two great days doesn't break the trip.

Confidence

After each forecast day passes, we re-fetch the actual weather for that day, score it with the same formula, and compare to what we predicted. The rolling average of those errors becomes a per-region confidence:

≥ 60% — history says this region's forecast is usually close to reality.
30–60% — patchy track record, treat as a hint.
We hide confidence entirely when we don't have enough validation samples yet — better no number than a fake one.

Update cadence

Forecasts rebuild every 3 hours.
Learning pipeline runs once a day and retires expired forecasts from the archive.
The "last updated" timestamp at the bottom of the map is the most recent forecast write.

What this is not

This is not a spot-by-spot forecast app. Before you paddle out at a specific break, check a local source (Windguru, Surfline, Windy) that models micro-bathymetry and nearshore effects. swelltrip.now is a trip trigger — a way to find out whether the coast is worth the flight.

Built by a solo surfer in Graz. Feedback and pull requests welcome at hello@swelltrip.now.