The only other thing about cruising in the summer in the Carribean is that the hurricane season runs from June 1 through November 30 ... and no one can predict where or when they will hit this far ahead. This is why so many ships reposition to Alaska and Europe in the summer.
We've had hurricanes as early as June 1 - generally they develop later - August through September sometimes into mid-October, so I don't book anything until late October or early November. There have been hurricanes every month of the year except April.
Should a hurricane develop, the cruise ship would alter it's itinerary from the Eastern Carribean to the Western.
I've personally been on the edge (because the ships alter their course) of both hurricanes and the South China Seas typhoons, but I'm fortunate enough not to get seasick.
I, too, live in Florida in the Tampa Bay area and we have never hit 100 degrees here, but I agree with Thomas's comments as to warm weather and to partying younger people in the summer.