Surf Reports That Rate Themselves

Every spot gets a live rating on a six-step scale — Flat, Poor, Fair, Fair-Good, Good, and Epic — in the color language surfers already know: gray when there's nothing, blue and green as it builds, orange when it's good, purple when it's an event. The score comes from three ingredients, weighted the way surfers actually judge a day:

• Swell period — 40%. The single best signal of organized, powerful surf. A 15-second groundswell and 6-second wind chop are different oceans.
• Wave size — 30%. Chest-high to overhead scores best; tiny days and giant closeout days taper off.
• Wind — 30%, and it can veto. Every break carries its shore orientation, so we know offshore from onshore. Wind quality doesn't just add or subtract points — it gates the top tiers. A blown-out onshore day cannot rate above Fair no matter how big the swell; heavy cross-shore wind caps at Good; and Epic requires clean wind — glassy or genuinely offshore.

Epic also demands size and period at once: at least chest-high (4 ft), at least 12 seconds, and clean wind — all three, plus a near-perfect score. Purple is supposed to mean drop everything.

A worked example — Lagundri Bay, Nias, on July 3, 2026: 4.0 ft of swell at 14.8 seconds with an 8-knot offshore breeze. Period 40 + size 30 + wind 28 = 98 → Epic. Same day at Pipeline: 6 ft at 12.7 s but 16-knot cross-shore trades — the wind cap holds it at Good. That's the design working.

The data is NOAA's GFS-Wave model sampled at each break's coordinates, refreshed with every model run — four times a day, out to 16 days.

v1 (June 21, 2026) shipped as a simple weighted score: period up to 45 points, size up to 30, wind up to 25, Epic at 80. The flaw took two weeks to show itself: period and size alone could reach 75 of the 80 points, and cross-shore wind cost nothing. On an ordinary July day, v1 rated 25 of our 74 spots Epic — a third of the planet wearing purple, while Surfline called the same day Fair. Surfers know Epic is an event, and our scale was calling a normal Southern-Hemisphere week the day of the decade.

v2 (July 3, 2026) makes Epic an event: the wind gates above, a size-and-period floor for purple, and a rebalanced curve across every tier. Recalibrated against live data before shipping — the same day that produced 25 Epics under v1 produces 3 under v2 (Lagundri Bay, Macaronis, and Puerto Escondido — all long-period, chest-high-plus, and clean), with the rest of the world distributed the way a normal day should be: mostly Fair, a healthy band of Fair-Good, Good meaning genuinely good.

Every future calibration is versioned and ships as its own entry in the changelog — we tune this dial in public.

Here's the problem v3 solves. On July 3, 2026, the model showed Teahupo'o and Montañita, Ecuador nearly identical offshore swell — 3.1 ft at about 15 seconds. But Teahupo'o's reef rises out of deep water so abruptly that it focuses that energy into double-overhead slabs, while Montañita's gentler point turns it into head-high walls. Raw offshore numbers can't tell you that. Bathymetry can.

v3 estimates the breaking face height at each break in three steps, all published science:

• A physics baseline — the Komar & Gaughan (1972) breaking-wave transform, which grows waves as they shoal: long-period swell breaks meaningfully bigger than the same offshore height of wind chop.
• Each break's swell window — the compass arc of swell directions it actually receives. Swell aimed outside the window is attenuated, the way headlands and islands do it.
• A calibrated per-break factor — how this specific bathymetry amplifies or tames swell, by period band. The approach follows Caldwell & Aucan (2007), NOAA's Hawaii study that fitted exactly these coefficients against years of lifeguard observations (their reef fits reach ~2.1×). Ours are curated per break, published on each spot page, and bounded by that study.

The result — under v3, that same July day: Teahupo'o rates Epic at ~11-ft faces; Montañita rates Good at ~5-ft faces. Spot pages now lead with the face estimate ("Surf ~6–8 ft faces") and keep the raw offshore swell visible underneath.

Honest limits: ±20% is the physics floor; sandbars move, so beach calibrations are climatology, not this morning's bank; and island-shadowed coasts are the hardest problem in surf forecasting — ours included. When we tune a spot's calibration, it ships as a changelog entry.