A friend of mine spent a season teaching in Miami for Miami Kiteboarding: miamikiteboarding.com/pages/how-to-ride-in-crandon

Crandon is not the only kite spot around but definitely the best one.

Get in touch with those guys as they are probably the best resource for local info there. They hire equipment as well.

Kiteboarding in places like Miami in the US is heavily regulated, so you need to make sure you abide by all those rather strict rules. Based on stats: www.windfinder.com/windstatistics/miami_airport it looks like September would be the least windy month of the year.

Christian