We did not go on Carnival, but in January a few years ago, we went on NCL in January.
To say the least, it was "almost" a disaster when we went to Hawaii. The wind was so strong, that when going in/coming out, someone had to be on the other side of the door to open it up.
Also, there was not just a "light" rain, but a very HEAVY rain while we were there. Trying to walk the island with water 2" high sloshing in our shoes, was not fun.