In December you just have to begin checking the forecast every day beginning about a week before you dive. The best for marine information is NOAA. We can get spectacular calm spells in the winter and some of the best vis of the year between fronts, but there is no way to predict whether it will "calm down" in December because that depends completely on whether cold fronts are moving through.
I love winter diving and dive year round, but winter dives are often spontanteous, like "it's calm tomorrow, let's go."
In fact, did that yesterday (will work on Sunday to make it up) when it calmed down for the first time in about 3 weeks, and had truly excellent diving off of Jupiter, with sharks, surprising # of goliath groupers, huge stingrays, 5 turtles, lots large gag grouper, lots of tropicals, and generally good vis from 80 feet in some spots to 40' in others.
I do have to say that the long spell of windy weather we have had this Oct is pretty unusual (going to blow hard again for the next 4 days). Usually there are a few days of wind followed by a few days of calm. Hopefully that pattern will be back in December and give you a better shot at getting out.
