I go to beautiful Turks and Caicos for one week every Jan or Feb. I bring two kites, usually 13 and 9.5. I get to kite 3-5 times in winds mostly 15-20.
I have been to St. Martin (both sides) and it is similar.
Here are a couple of links about kiting in Turks and Caicos:http://kiteprovo.com/http://www.sbckiteboard.com/travel_article?news_id=1218