Sammy -
We're from Nashua too and went in January. We swam in every port and everyday on the ship. We were away when it was the very cold week and they closed schools because of it, so to just be there was enough in itself. You will be fine and should be able to swim as much as you want. The only times it was even chilly was Port Canaveral when we left, 50's, but still wore shorts and short sleeves, and a couple nights on deck. Wore a sweatshirt.
So you will be fine. Have fun.....
GO SOX!