Official Beaufort mean-wind bands
Met Office ranges in knots; mean wind, not a gust conversion.
| Force | Mean wind (knots) | Description |
|---|---|---|
| 0 | <1 | Calm |
| 1 | 1–3 | Light air |
| 2 | 4–6 | Light breeze |
| 3 | 7–10 | Gentle breeze |
| 4 | 11–16 | Moderate breeze |
| 5 | 17–21 | Fresh breeze |
| 6 | 22–27 | Strong breeze |
| 7 | 28–33 | Near gale |
| 8 | 34–40 | Gale |
| 9 | 41–47 | Strong gale |
| 10 | 48–55 | Storm |
| 11 | 56–63 | Violent storm |
| 12 | 64+ | Hurricane |
Use the table for translation, not clearance
The table below reproduces the Met Office’s wind-force bands in knots. It helps you understand the forecast vocabulary. It does not forecast the exact waves in a particular bay or determine what your boat and crew can handle. Fetch, depth and the passage still need marine judgement.
A gust figure can fall in a higher numerical range than the mean wind without changing what the forecast’s stated Beaufort force means. Comparing the gust to a mean-wind table without saying so is a common source of false precision.
The app score answers a different question
GoNoGo combines its selected wind value with other weather penalties and caps. Its application bands are not the Beaufort scale and are not a certified definition of a gale. A code reason in a simplified scorer should never replace the marine forecast’s actual terminology.
Try the illustrative cases with a fixed mean wind and increasing gusts. The number changes because the current sailing scorer uses gusts when available. The examples do not establish sea state or a reefing point for a particular boat.
Worked examples from the existing scorer
These complete hypothetical hours run through the same scoring functions used by the live tool. They are not observations or forecasts. The displayed effective score includes any cap.
| Example | Effective score | Verdict | Model reasons |
|---|---|---|---|
| Mean 15, gusts 20 km/h | 100/100 | GO | No model penalties |
| Same mean, gusts 43 | 64/100 | MAYBE | strong — reef down · MAYBE cap |
| Same mean, gusts 53 | 40/100 | NO-GO | gale-force wind · NOGO cap |
Exact example inputs and units
temp and feels: °C; wind and gust: km/h; precipitation: mm/h; visibility: m; rain probability, cloud and humidity: %. Weather code is WMO; UV is an index. Pressure, where shown, is context in hPa and does not affect this scorer.
[
{
"example": "Mean 15, gusts 20 km/h",
"inputs": {
"temp": 15,
"feels": 15,
"precip": 0,
"pop": 0,
"wind": 15,
"gust": 20,
"vis": 20000,
"code": 0,
"cloud": 10,
"humidity": 60,
"uv": 0,
"pressure": 1010
}
},
{
"example": "Same mean, gusts 43",
"inputs": {
"temp": 15,
"feels": 15,
"precip": 0,
"pop": 0,
"wind": 15,
"gust": 43,
"vis": 20000,
"code": 0,
"cloud": 10,
"humidity": 60,
"uv": 0,
"pressure": 1010
}
},
{
"example": "Same mean, gusts 53",
"inputs": {
"temp": 15,
"feels": 15,
"precip": 0,
"pop": 0,
"wind": 15,
"gust": 53,
"vis": 20000,
"code": 0,
"cloud": 10,
"humidity": 60,
"uv": 0,
"pressure": 1010
}
}
]Planning bands and the limits of the number
The existing model starts at 100, subtracts its condition penalties and applies critical caps. GO is 70–100, MAYBE 45–69 and NO-GO 0–44. A MAYBE cap limits the effective score to 64, and a NO-GO cap to 40. These are application suitability bands, not certified safe operating limits.
Rain branches are alternatives: matching probability, intensity and weather-code triggers do not mean adding the same rain penalty repeatedly. Separate factors can combine. A cap prevents benign temperature or dry weather from cancelling a critical flagged condition. Use the reasons beside the result to understand what changed.
The model requires complete numeric weather inputs. Missing visibility, rain probability or another required value returns Insufficient data; it is never filled with an invented favourable value. Local warnings, closures, equipment instructions and actual observations can change your decision even when the model returns GO.
Read the full sailing methodology and thresholds. The model and these examples were cross-checked on 18 October 2026. No physical field-test or safety certification is claimed.
Equipment and an alternative plan
Read the official marine forecast and your boat’s own guidance, then plan the passage and return. Use the Beaufort table to interpret mean wind, and inspect gusts separately. If the forecast terminology and the app’s short reason differ, retain the precise official forecast information.
Questions about Beaufort scale for sailors: mean wind is not a gust limit
Can I convert the gust directly into the forecast force?
That would mix a gust with a scale normally describing mean wind. Label the measurement correctly.
Does force 4 suit every boat?
No. The scale is descriptive, not a universal operating limit.
Do the listed sea descriptions predict my harbour?
No. Local marine conditions still need separate assessment.
Sources and limits
The numeric application bands come from the existing GoNoGo scorer and methodology. External guidance is linked for its stated context; it is not presented as endorsement of this model.
Live forecast data is supplied by Open-Meteo. An illustrative model output is different from a live forecast, and a forecast is different from a local observation.