Summer here is mid 70's on average - low 80's on hot days and rarely into the 90's. So FL in the winter is often like our summer, and I love it! There have been some cold days in the 60's, but overall during our 2 wk trips we can usually find at least 3 or 4 days that swimming is very pleasant.
Have fun! I'll be there Dec 1-13th, and definitely plan to swim!