December is the month the island turns over. The heat of late summer lets go, the trade winds come back, and the first proper high-season crowd arrives. It's the most reliable weather of the year and the most expensive week of the year, and those two facts are the same fact.
The weather
Daytime settles into the mid-seventies to mid-eighties, which is about as good as this island gets — warm enough that you're in the water by nine, cool enough that the walk back up the hill isn't punishing. The sea stays in the high seventies to low eighties all year, so nobody stands at the edge working up to it.
Rain doesn't stop in December, it just gets shorter. You'll still get a squall or two crossing the island in an afternoon. Fifteen minutes, then the sun dries everything, including you.
The one real change is wind. December brings the Christmas winds, and the east-facing beaches feel them. Sapphire can run choppy for a few days in a row — not a bad beach, just a bad snorkel day. That's the week you drive fifteen minutes to the protected sand at Lindquist or head over the ridge to the north side.
The crowds, honestly
Peak season here runs December through April. The first half of December is quietly one of the best-value stretches on the calendar: high-season weather, shoulder-season prices, and beaches that still feel like yours on a weekday morning.
Then the week before Christmas arrives and the island fills. Cruise traffic peaks, Magens Bay has a genuine crowd by eleven, Red Hook restaurants want reservations, and the rental cars sell out. None of it is unpleasant. It's just a different island than the one in early December, and worth knowing which one you booked.
Booking: how far ahead
Christmas and New Year's weeks get claimed six to twelve months out, and they're the two weeks where waiting does not get you a deal. If you have a fixed date in that window, book it as early as you can live with.
Everything else in December has more give. Early-December weeks often sit open into the fall, which is where the current discounts usually live.
Two practical notes: reserve the rental car when you book the villa, not after — peak-season inventory genuinely runs out, and December is not the month to find out you needed one. And if you're weighing whether you do, we wrote up the car question in full.
Which side of the island in December
This is the month the difference between our two places is most obvious.
Sapphire Beach is on the east end: direct beach access, snorkel gear in the closet, and the shortest possible distance between waking up and being in the ocean. On a windy December stretch you'll trade a few choppy mornings for the rest of it being exactly what you came for.
Mahogany Seaview sits up in the hills on the north side. It's a few degrees cooler, breezier, and you watch the weather arrive over the water instead of having it arrive on you. Magens Bay is about fifteen minutes down the ridge, and the sunsets from the deck are the December argument all by themselves.
New Year's
Worth its own mention: the harbor fireworks are a real event, and the island treats the whole week as one long celebration. We wrote about New Year's Eve here if that's the trip you're planning — the short version is book early, eat early, and pick your viewing spot before dark.
December is the month that makes people come back. It is also the month everyone else figured out. Both of those are true, and neither should stop you.