Debjoe,

I go to Key West every year during that time frame; usually around Dec 11 to 18. Weather is always warm. Two years ago I was on a boat in the Lighted Boat Parade out on the water at night and was wearing only a tank top. Nights are only slightly cooler than the days. Maybe a light sweater or jacket could be in order for an air conditioned restaurant. Otherwise, bring summer clothes. After five years of going during this time frame it only rained once during the day for an hour or so. Of course, this is for Key West only. I can't speak for the upper keys and you didn't specifically mention Key West. Hope this helps.

Wayne <><