Feb 2012 my cousin and her family took a 3 nighter and their CC day was really cold. The kids wouldn't swim. Of course, the whole coast of FL was cold, too; we met them at their house in Daytona the day they disembarked and it was very very cold. (they are nearly-lifelong Floridians, but we certainly aren't, and it was cold in FL)
The following year we all went on the "same" sailing, and it was gorgeous. The water was chilly when you got int, but you got used to it. The kids, even the Floridians, spent most of the day in the water.
Last year in January we did an eastern Caribbean, and San Juan and Sint Maarten were hot hot hot.
This year in January we did Bahamas again and Castaway was rather warm.
Whereas in our October trips, the air at Castaway was warmer, so the water actually *felt* colder than it did during our wintertime trips. Far less pleasant for us than in winter.