Intermediate 8 minutes
Wind: speed, direction and fetch
The weather data point that decides your dive more than any other
If you had to pick a single number to decide whether the dive day is going to go well, don't pick temperature or cloud cover: pick the wind. It's the only data point that affects the entry, the swell, the visibility, the surface current, and whether the boat can pick you up, all at once.
In this article you'll see how wind is measured and named, why its speed alone isn't enough without duration and fetch, what windward and leeward mean in practice, and what wind does to the water beneath the surface.
Almost every dive-day cancellation comes down to wind. Understanding the three factors that turn wind into sea state lets you anticipate that decision, and choose the right site on days when diving is still possible.
How it's measured and, above all, how it's named
There's a convention that confuses a lot of people the first time.
Wind speed at sea is expressed in knots: one nautical mile per hour, about 1.85 km/h. Forecasts that use km/h aren't wrong, but marine bulletins, boat captains, and dive centers speak in knots, so it's worth thinking in that unit.
The Beaufort scale translates that speed into an observable sea state, which is what actually matters to you. Broadly speaking, up to about 10 knots the sea stays rippled and comfortable; between 11 and 16, whitecaps appear widely; from 17-21 knots onward, the swell starts making any operation from a small boat uncomfortable. These are indicative ranges, not guarantees: the same wind produces very different seas depending on the article's other two factors.
And now the convention that needs to be firmly fixed: wind is named for the sector it comes from, not the one it's heading to. A north wind blows from the north toward the south. Currents work exactly the opposite way (they're named for the direction they're heading toward) and mixing up the two conventions when reading a forecast leads to choosing the wrong dive point.
That distinction isn't a technicality: it's the mistake that makes someone read "east wind" and plan the dive right on the coast that's about to be exposed.
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