What this research grades
This research note grades one forecast for one reef on one day: Macaronis, a left-hand reef in the Mentawai Islands, Indonesia, on Sunday 13 September 2026. The call was sent to the operator at the break two days in advance, with a written list of what would make it wrong, and it is scored here against the model at the corrected reef cell, win or lose.
Two things happened before the call was made. The operator corrected where AYON thought the reef was, and the operator's own rules for the break were written into the AYON Wave spot record. Both change how the grade should be read, so they come first.
The point sat 8.3 km from the reef, in a different model cell
The operator received AYON's free forecast widget after an outreach e-mail on 4 September 2026. They asked for it to carry the break's name, then asked for proof of accuracy against Surfline and Windy, and whether the forecast was a subscription. The answers were that the forecast is free, since AYON charges for the school operating layer and not for the weather, and that AYON would not claim to beat Surfline.
On 10 September the operator sent the exact reef position. AYON's point for the break sat 8.3 km to the south-east of it, and the two positions resolve to different marine model cells: -2.875/100.042 for the old point, -2.792/99.958 for the reef.
Most hours the difference between the cells is small. At times it reaches 0.40 m in height, 2.55 s in period and 12° in direction, which at a reef that cares about a ten-degree window is not small. The record now carries the reef at -2.783948, 99.972289.
The operator's rules, encoded, and why the record still says unverified
With the position came the operator's rules, in their words. Best swell is "SW around 210 to 220 degrees. S swell also works but the wave gets shorter and heavier at the takeoff". On wind, the break "handles almost every direction except NW, which is our devil wind and shuts it down".
Two edits followed in commit ccfbd8d on 10 September. The swell window was recentred to 195–225°, so that a south swell still scores through the taper instead of being cut off at the edge, which is how the operator describes it working. The offshore wind bearing was set to 135°, the exact reciprocal of north-west, so the devil wind sits at the bottom of the wind score.
The record's verified flag stays false, because in AYON's evidence vocabulary the operator's e-mail is a field observation: one timestamped human report with legitimate provenance. Verified means evidence reviewed against source and context, with repeat observations. One e-mail is a single observation, not yet reviewed against source or repeated, and no one from AYON has reviewed the reef in the water. The operator's reply on 11 September, "That is a level of care we did not expect from a free tool", is welcome and changes nothing about the flag.
The operator asked for one thing on the product: swell direction and wind direction on the widget. That shipped, on the widget and in the app spot card, as a line of the form "2.8 m · 13 sec · SSW 209°".
A call sent on Friday, with its own miss condition
On 11 September AYON sent the operator a call for Sunday 13 September: peak around 2.2 m at 14 s from 213°, wind light ESE to SE at 7–11 kn, and no north-west wind for seven days. The message carried an explicit written list of what would make the call wrong. The operator said they would grade it against Surfline and Windy.
Before Sunday, live model runs began arriving with direction at 195–209°, south of the operator's window. Rather than adjust the call, AYON wrote to the operator: "if it stays south of 210 through Sunday … that's a miss on our side and I'll say so." The call was left as sent.
How Sunday scored
The grade is against Open-Meteo at the corrected reef cell on 13 September. It is a modeled verification, not a beach observation.
Four hits, two misses. The peak day was right, and 06:00 on Sunday was the true peak of the whole 11–16 September window. The height was under-called by about 30%: 2.86 m arrived against 2.2 m called. The direction stayed south of the operator's 210–220° window all day, 194–202° with 201° at the peak, a miss of about 12° that had been declared before Sunday.
- Peak dayHit
- Called
- Sunday 13th
- Model at the reef cell
- Sunday 13th, peak 06:00 — the true peak of the 11–16 Sep window
- Peak heightMiss
- Called
- ~2.2 m
- Model at the reef cell
- 2.86 m — under by ~30%
- PeriodHit
- Called
- 14 s
- Model at the reef cell
- 15 s at peak, 12–15 s across the day
- DirectionMiss
- Called
- 213° (inside the operator's 210–220° window)
- Model at the reef cell
- 194–202°, peak 201° — south of the window all day, ~12° off
- WindHit
- Called
- Light ESE/SE, 7–11 kn
- Model at the reef cell
- 3–10 kn, 117–169°, drifting SSE/S in the afternoon — speed hit, direction wider
- No NW wind for 7 daysHit
- Called
- None
- Model at the reef cell
- Zero NW hours
Both misses point the same way, and one answer decides what they mean
The two misses are not independent. The swell came in bigger and further south than called. By the operator's own description, a south swell at Macaronis "gets shorter and heavier at the takeoff". So the model, at its own cell, is describing a Sunday that should have broken shorter and heavier than the call implied.
That leaves one question with two very different answers, and it has been sent to the operator: did it actually break shorter and heavier on Sunday? If yes, the model at the reef cell carries a measurable direction bias that can be corrected in the record. If no, AYON's read of this reef is wrong at a level deeper than a few degrees, and the correction is to the understanding, not to a number.
At publication the answer has not been received. This note will be updated when it arrives, whichever way it goes.
What the grade is, and what it is not
It is a model scored against a model at the same cell, after the position was corrected. That answers whether the call held against the best available estimate at the reef; it does not say what a person on the reef saw. The operator's report, if it comes, is the only beach-level evidence in this test, and it is a field observation, not a verification.
The record stays unverified. The direction miss was pre-declared. The result is published with the misses at full weight because that was promised to the operator in writing before the swell arrived, and a verification that reports only when it wins is not one.
This is research. Estimates are models, not guarantees; a model is never an observation, and a machine estimate is never “confirmed” — only a human reviewing it in the field makes it verified. Nothing on this page is an operational-capability claim, a safety promise, or a prediction of a specific event at a specific place.
References & data
- 1.Open-Meteo Marine API — Verification source: hourly swell height, period and direction and wind at the corrected reef cell -2.792/99.958 for 13 September 2026. A modeled estimate, not a measurement.
- 2.Operator field report, e-mail 2026-09-10 — Reef position and local rules from the operator at the break, quoted in the article. A field observation; the operator is not named.
- 3.AYON Wave spots.ts — Macaronis record (commit ccfbd8d) — The 10 September 2026 edits: reef position -2.783948, 99.972289; swell window 195–225°; offshore wind bearing 135°; verified flag left false.