It can be lower and higher, too.
A little over a week starting Jan 4 this year, one day was 21 with windchill. Sadly that was the day we took the boat to DTD. I'm certain I was a shade of blue by the time we got there.
It was SO cold at certain points this Jan. After our WDW time was done we went to Daytona, where it was just as cold. Thank goodness we had packed somewhat correctly and had our puffy coats from home, so we could walk along the beach a couple times.
Then we were back in Orlando for Universal and it had *started* to warm up, but we spent one hour by the pool getting some vitamin D, wearing long pants, puffy coats, and scarves.
(should mention that I was dreadfully sick starting on the 6th, DS got it on the 11thish, and we were utterly miserable until the last week of the trip, when we just barely were able to get onto a cruise ship ("just barely" meaning the health questionnaire was able to be answered correctly, but if it had been a day earlier we would have gotten to see a doctor before being allowed, or not, to board))
We're having a re-do of that trip (and of my Half marathon that I run so so so sick) and I WILL be packing two pairs of longjohns for me and DS, I will have proper pants and long sleeved shirts, I will ALSO have shorts and tees and bathing suits and flipflops and wool socks and proper shoes. I will pack everything, LOL.
And yes, swimsuits. It was in the higher 70s before it got SO cold, and it was 80ish on the day DS ran his Mickey Mile. It can be all over the place.
People reported that for either the Half or Full marathon in January of 2010 it was actually sleeting at the start.