I'm not a FL local, but do dive the Gulf and have had my trips cancelled for high seas and other weather. (FGNMS charters out of Freeport TX, 3 times over the last couple years, one June, one Aug, and one September).
There's really no 'guarantees' or odds - although in my impression there do seem to be more 'upper gulf region' storms (near US FL/AL/LA/TX coastal vs. further down into the Carribbean or out along the Atlantic seaboard) as you get later in the season in general.
One tool is of course the National Hurricane Center track summaries, but even if a track wasn't on top of where you're going, storm size and direction can mean there was still a good enough blow that boats decided not to go out due to rough seas. Link is http://www.nhc.noaa.gov/pastall.shtml#tracks_all ....pick the year you want for the Atlantic basin and it shows all the tracks overlayed for that year.
I guess my only advice would be if you have to fly down or whatnot and commit to costs before you'll know if the liveaboard has been cancelled or not, then trip insurance becomes just part of the cost of the vacation. For the Flower Gardens trips I don't have to as we just drive down, and they of course refund you if they have to call the trip and not go. But for my July trip to Puerto Rico we did buy trip insurance as we could be out at the very least by having to pay a rebooking fee on the plane flights if given long notice, and much more if the boat can't go out after we arrive.