About TrueSwell

TrueSwell is an independent surf forecasting platform covering 100 spots on every US coast — Atlantic, Gulf, Pacific, Alaska, Hawaii and Puerto Rico. We build our forecasts from free public data, run them through our own wave model, and publish our measured accuracy for anyone to inspect. No resold ratings, no black box, no paywall.

The name is the promise: we'd rather show you an honest 10-day outlook than a confident-looking 16-day guess. Where the data ends, the chart ends.

Our model

Every hour at every spot, each swell train is transformed from deep water to the beach independently:

• Exposure gate — swell from outside a spot's window is blocked (land shadowing), with a small allowance for diffraction wrap.
• Refraction — Snell's law against the beach angle: swell arriving 45° off loses ~15% of its height; near-grazing swell loses most of it.
• Breaking — the Komar–Gaughan breaker formula, which is period-sensitive: longer-period swell breaks bigger. Calibrated so a 1 m @ 10 s swell breaks at roughly its deep-water height.
• Multiple swells — trains combine by energy (√ΣH²), so a secondary swell genuinely adds size.

The 0–10 score weighs size first (bigger scores higher all the way to a spot's max), then swell period (groundswell over windswell), direction fit, and wind (offshore grooms, onshore chops). Wave Hunter ranks spots with this same score for whatever time window you pick.

Data sources — all free and public

• Open-Meteo Marine — swell partitions (height, period, direction) and sea temperature, derived from NOAA WaveWatch III & ECMWF wave models.
• Open-Meteo Forecast — wind, air temperature, sky conditions, sunrise & sunset.
• NOAA CO-OPS — tide predictions for each spot's reference station.
• NOAA NDBC buoys — live observations used to verify our forecasts.
• Computed locally — moon phase and first/last light from solar geometry.

Honesty & verification

Every live forecast is logged and scored against NDBC buoy observations. Our error by forecast lead time is public at /api/skill. Skill decays with lead time — days 1–3 are solid, 4–7 useful, 8–10 a trend heads-up — and we say so rather than pretending otherwise.

Questions, corrections or a spot we should add? Get in touch.