I've been there in June. Check out the Bermuda Kitesurfing Association at
http://www.bka.bm/index.asp for info on locations and weather.
Also, windguru has some info:
http://www.windguru.cz/int/index.php?sc=32728&wj=knots&odh=3&doh=22&go=1.
Simon runs the kite school at the 9 Beaches resort; see
http://www.surfshack.bm. Contact him at
info@bka.bm; he's a great guy and really helpful!
Enjoy!
Hannes