I was just wondering what the weather would be like at the end of december in San Juan, St Thomas and St marteen?
All of these ports are in the tropics, so the climate is pretty constant with typical high temperatures in the mid-80's and typical low temperatures around 70. About the only variation is humidity, which is oppressive in the summer and not a problem in the winter. You are also well outside of hurricane season, so severe storms should not be a factor. It's always wise to be prepared for an occasional shower, but most days are sunny.