We used the pool at least three times last January, as well as our two previous December trips. It was hot, but not blazing, and the water was a comfortable temperature, even at night.
On these same trips, we also needed warm clothes - I wore a sweater and Uggs on our last day during the day, and the previous day was warm enough for t shirts. It's quite variable, but you should experience pool weather once or twice during your trip if you decide to go in January.