Hi Mike, I can't help you so much, but I've been in Celestun two years ago in April, just for one day. It's a really nice place if you look for relaxed and mexican atmosphere (nothing to do with Cancun and Playa del Carmen) and, most of all, I remember a good 15/18 knots side shore wind and a wide beach ... Anyway, I suggest you to bring all your kites, It's so frustrating to stay on the beach thinking about the sail you've left at home ... Further informations try 'kitesurfing yucatan' in google, for example I've found this:
http://www.kiteh2o.com/forum/msg.asp?T2=44
Bruno