Been to CC in early February. Water was cold but it was one of those where you just needed to get into the water quickly and get it over with and then you were fine. Did some snorkeling and the hardest part was that initial shock of sticking your face in the water. After that, I was able to swim for a good hour and could have gone longer.
Weather on the beach was absolutely perfect! I know the two days previous to us the Wonder and Dream were not able to dock due to rough seas so we may have gotten lucky with the weather. CC is far enough north that weather systems coming of the US coast can still have an affect on the island.