Been sailin' the BVI since 1969. My own boat (11 years) and others, including many chartered boats.
Squalls in the BVI are typically very short-lived, as mentioned above. Not always, but usually.
They are easy to spot, moving in from the East and crossing to the West. You can guage their size (though not their ferocity, necessarily) by watching them.
You can often avoid them, by changing course.
If you're going to get hit, be prepared. Reef or reduce sail early. Easiest way on most boats is to simply drop the mainsail. Most boats will sail quite well with just a headsail, including to windward (close reach). All charter boats in the islands have roller-furling genoas. Easy to roll them in to any desired size.
Winds in squalls typically are 25-35 knots, but may be more occasionally. The seawater is warm, but you'll get a chill quickly as the rain falls and the wind blows.
If you're sailing the islands in winter time, beware of the Christmas winds which are VERY different from squalls. These are really fierce northers which can blow for a day or a week or more.
Be respectful and prepared, and don't worry about the squalls. They're relatively easy to weather.