Where I used to live in San Sebastian, Spain - that region experiences a meteorological phenomena they call "Galerna". I happens only in the summer when the temperature over the water and land reach a specific temperature differential. It occurs on still, warm summer days. The geography of the region causes an inversion where suddenly, in a matter of seconds, winds go from 0 to gale force winds. It usually only lasts for 10 or 15 minutes, but occasionally it can last longer.
The worst one I ever saw there lasted close to 45 minutes. We had just put in a new anchorage behind the island and my friend Xavier and I had just taken my sail boat out and anchored it. He had a flat in the port overlooking the bay and we had just walked out onto his balcony to look at the boat when the Galerna hit. The wind whipping around the island actually flipped my boat over onto it's side with the mast hitting the water. It was amazing to watch. I've attached a photo of the city, you can see the sailboats behind the island Santa Clara. That's where my boat was at the time.
I was out in the ocean a couple times when Galerna's hit, the difficulty is it is so fast, and they occur on really calm days so one is usually got max light air sails up and then suddenly you find yourself in near hurricane force winds. Boats sink, people get hurt or die in these events. You learn fast when they may occur...
dj
