This year in January (mid month) we did Aquaventure through Disney.
It was an overcast, cloudy and breezy day. Probably in the low 70's. We complained a little then remembered the weather at home was in between 10 - 15 (f) and nasty. Stopped complaining and put up with the shivers we had towards the end of the day.
We were in Nassau the prior week (a "b2b" - 4 night Wonder out of Miami, and 3 days later a 3 nighter on the Dream) and the temperature was probably 10 degrees warmer, no clouds, no breeze. So the answer might be ... It Depends.
Oh yea, we booked the excursion on the Dream on embarkation day. It was very nice at Port Canaveral, so we booked. 45 minutes afterwards, dark clouds and cool breezes decended upon us.
I would wait to book on board. I would check the weather forecast before boarding to get an idea of what the weather will be like.
Here is what the sky looked like while we were there at the water park...
This is what it looked like the prior week....