How gusty is too gusty?

Two 20-knot days can be completely different animals. What separates them is the gust spread: the gap between the average wind and the peak gusts on the forecast or the anemometer.

• Spread of 3–5 knots (18 gusting 22): smooth, laminar, easy. Typical of sea breezes and trade winds that have travelled over water.
• Spread of 8–10 knots: demanding. Constant sheeting and active kite movement.
• Spread of 10–15+ knots (20 gusting 32): unstable to dangerous, capable riders included. The square law again: 20 to 30 knots is a 2.25× jump in power, arriving in seconds.

Gusty wind comes from air that has crossed land, from frontal or unstable systems, or from mountains and cliffs upwind. Steady wind usually means a long open-water fetch, which is why beginners get sent to trade-wind and sea-breeze destinations in the first place.

Thermal winds and sea breezes

On a sunny coast the land heats faster than the sea. Warm air over the land rises, pressure drops locally, and cooler maritime air flows in to replace it: the sea breeze. It switches on in late morning, peaks mid-afternoon and dies near sunset, which is why so many famous spots are afternoon spots.

La Ventana is the textbook case: mornings are calm, the wind fills between about 11:00 and 12:30, and it fades between 16:00 and 18:00. A thermal commonly adds 5–15 knots on top of the gradient forecast in hot weather.

At Lo Stagnone in Sicily the summer thermal is worth about 5–8 knots over a plain forecast and holds strongest from 12:00 to 18:00. Because the air arrives over water it is smooth, and it is reliably cross-shore or cross-onshore.

Geography amplifies a thermal. Where wind funnels through a gap, a strait or a valley, the Venturi effect accelerates it: the same air squeezed through a smaller space has to speed up, so a 12-knot breeze on the open coast can arrive at a pinch-point spot at 20–25 knots.

Tarifa sits in the Strait of Gibraltar and gets more than 300 days a year above 15 knots, with the Levante accounting for roughly 60% of the windy days and the Poniente most of the rest. The Columbia Gorge does the same trick with a river canyon cut between two mountain ranges.

The reverse runs at night. The land cools and a weak, gusty, offshore land breeze flows out to sea, one more reason dawn sessions on thermal coasts rarely pay.