So, you're thinking about ditching the puffer jacket for a pair of flip-flops and heading south. Honestly, it’s a solid move. Key Largo in December is basically the "Goldilocks" zone of the Florida Keys. It’s not face-meltingly hot like August, and it’s certainly not "I can’t feel my toes" cold like the rest of the country.
But here’s the thing. Most people pack for a tropical paradise and then get blindsided by a "cold front" that makes them buy a $60 tourist sweatshirt. Let’s talk about what the weather in Key Largo Florida in December actually looks like when you’re on the ground, or more importantly, in the water.
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The Reality of December Temperatures
You’ve probably seen the averages. They say the high is 77°F and the low is about 67°F. Those numbers are technically true, but they’re also kinda misleading.
In reality, December is a tug-of-war between the Caribbean sun and Arctic fronts. On a "normal" day, you’ll wake up to a crisp 68°F morning that feels like a dream. By noon, the sun is blazing, and it’s a perfect 79°F. Then, a front hits. Suddenly, the wind whips from the north, and you’re looking at a daytime high of 64°F.
It sounds warm to a New Yorker, but with the ocean breeze? It’s chilly.
The Humidity Factor
Unlike the "soup" you breathe in July, December humidity is manageable. It usually sits around 70%. It’s enough to keep your skin from cracking but low enough that you don't feel like you're wearing a damp blanket.
Can You Actually Swim?
This is the big question. Short answer: Yes. Long answer: It depends on how much you enjoy a "refreshing" shock.
The water temperature in December generally hovers between 72°F and 76°F. If you’re from Michigan, this is basically bathwater. If you’re a local Floridian, it’s an ice bath.
Diving and Snorkeling
If you’re heading out to John Pennekamp Coral Reef State Park, listen to the dive masters. Most will tell you to wear a 3mm wetsuit. Even if the water feels okay at first, your core temp drops fast when you're 30 feet down for 45 minutes.
Visibility is a gamble. On calm days, it’s like looking through glass—you can see 80 feet out easily. But if a front just passed through, the wind "stirs the pot," and visibility can drop to 20 feet.
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- Wind direction matters more than temperature. A North wind is the enemy of clear water.
- Afternoon trips are better. The sun has had more time to warm the top layer of water.
The Dry Season Perks
One of the best things about the weather in Key Largo Florida in December is the lack of rain. This is the start of the "dry season." While the rest of the state might be dealing with gray, drizzly winter days, Key Largo averages only about 1.4 to 2.2 inches of rain for the whole month.
When it does rain, it’s usually a quick "sprinkle and it's gone" situation ahead of a cold front. You don't get those massive, world-ending 4 p.m. thunderstorms that define the Florida summer.
What to Pack (The Non-Generic Version)
Forget the "tropical vacation" Pinterest boards for a second. If you want to actually enjoy yourself, you need layers.
Basically, you’re dressing for three different climates in one day. Start with a swimsuit and a light cover-up. Keep a pair of jeans and a windbreaker in the car.
I’ve seen too many people shivering on sunset cruises because they thought "Florida" meant "No Sleeves Required." The wind on the water is significantly colder than the wind on land.
- A "Boat Coat": Even just a cheap windbreaker makes a huge difference on a moving boat.
- Polarized Sunglasses: Essential. The winter sun sits lower on the horizon and the glare off the water is brutal.
- Reef-Safe Sunscreen: Just because it’s 75 degrees doesn't mean you won't fry. The UV index still hits 4 or 5 regularly.
Fishing and Wildlife
December is a weirdly great time for wildlife. Since the water is cooling down, you start seeing the "winter locals."
Spotted eagle rays are much more common this time of year. You’ll see them gliding over the flats or near the reefs. If you’re fishing, this is the time for Sailfish, Kingfish, and Wahoo. They love the cooler water.
The mangroves are also buzzing. Since it’s not quite as buggy (the mosquitoes take a slight break, though they never truly leave), it’s the best time of year for kayaking or paddleboarding the winding creeks.
Why December Still Matters
Despite the occasional cold snap, Key Largo in December is arguably the best version of the Keys. The air is crisp, the sky is a deep, ridiculous blue, and the "Holiday Spirit" is high.
Honestly, the biggest threat to your vacation isn't the rain; it's the "Snowbirds." December is when the crowds start to swell. If you’re planning on a weekend trip, book your boat charters at least two weeks out.
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Next Steps for Your Trip:
Check the marine forecast specifically—not just the iPhone weather app—at least 48 hours before any water activities. Look for wind speeds under 15 knots if you want a smooth ride and decent visibility. If a cold front is predicted to hit on your Tuesday, move your snorkel trip to Monday. You'll thank me when you aren't bouncing over 4-foot swells.