For fairly reliable marine forecasts, the NWS has it pretty well covered in my experience. It isn't perfect but that is why they are called forecasts.
Marine Forecasts
You would do well to checkout the regional pages as well for things like weather hazard alerts, radar and satellite imagery. NWS Regional Websites Timing the arrival of cold fronts and the time to launch can be dailed in pretty well with these aids. More about timing cold front winds CAN BE FOUND HERE and info about wind patterns in Florida in the winter CAN BE FOUND HERE
ikitesurf.com has constructed a ton of realtime weather stations all over the place in the USA and beyond. They have quite a few in Florida, along with their wind archive data provides a lot of valuable info for not only planning a kiteboarding trip but also when and where to ride once you arrive. Some of the services come with a paid membership which is cheap at the price, i.e. go for it!
ikitesurf
ikitesurf also has some powerful new tools including Windflow Viz which provides dynamic imagery of winds. It can be very helpful for estimating when the wind may turn on or off in your area.
Some averaged historical winds for a few of the many weather stations around the coast of Florida appear below. Remember these are AVERAGE data that is you can have well above and below the ranges indicated for a considerable time and portion of your trip. Also, they don't show direction which will swing clockwise as a rule with the passage of cold fronts. Westerly winds are generally good off the west coast and easterly winds off the east coast. On average stronger winds seem to come from the N to E to S much of the time however there are some epic cold front winds out of the NW to N ideal for the west coast. These plots provide limited indication of conditions, sometimes miles offshore from where you will be riding, nothing more. HINT - For more specific data be sure to visit the ikitesurf wind archives for a better idea.
St. Augustine, FL
Cape Caneral Wx Bouy off of Merritt Island/Cocoa Beach and 20 nm east of Florida. Winds are often 5 kt. or more here relative to closer to shore.
Fowry Rocks Light, 7 nm east of mainland Florida and just south of Miami. Winds are sometimes 3 to 5 kt. higher than closer to shore here.
Molasses Light, upper Florida Keys, about 5 miles offshore. Winds are sometimes 3 to 5 kt. higher here than closer to the Keys.
Sand Key about 5 miles offshore from Key West. Winds are sometimes 3 to 5 kts. higher here than closer to the Keys.
Venice in SW Florida.
The data varies up the western coast of Florida and apparently the handly graphical summaries haven't been prepared as for the other stations. There is the historical ikitesurf.com wind data for this area to look over.
Specific info and quite a few photos from past kiteboarding events around the state appear at: EVENTS AND COMPETITIONS
Wonder about water temperature? More here ...
Click for water temp map
How about air temperatures?
Try here
How to get there from here? MAPQUEST!
Anyway, that's a start, more to come.
Have a good trip!