You might be pleasantly surprised with hi 70's,low 80's, but I'd pack for temps in the mid 70's and down. DW likes long pants and sweatshirts for our Dec trip. Biggest problem for her is that mid-day,sun out,no wind she's fine in shorts & tee shirts, but the drop off temp as the sun sets requires a trip back to the resort unless she suffered thru the warm part of the day in long pants and sweatshirt.
Me, I'm in shorts & tank tops regardless.