It's hard to say. I remember times when I wore shorts during Christmas. Other times, it was very cold. You can still swim in the pool since the water is heated. I'm not sure of the exact temperature, but it was pretty warm.
Just like Barry said, who knows! The last two December & Janauary's have been cool to chilly! But I have seen many times where it has been nice & warm.
When I was at HRH this year the first week of January it was freezing! I was watching the dive-in movie with the comforter from my bed & hot chocolate & some people were swiming in the pool!
Soooooo who knows!