You're standing on the pier at Ocean Beach, the wind is whipping your hair, and you're suddenly realizing that the "sunny California" dream is a bit more complicated than the postcards suggested. People flock to Southern California late in the year to escape the brutal polar vortexes of the Midwest or the gray slush of New York, but San Diego temp in december is a fickle beast. It isn't exactly "winter" in the traditional sense. It's more like a long, drawn-out autumn that occasionally flirts with spring.
Honestly, if you pack nothing but shorts, you're going to have a bad time.
The numbers tell one story, but the "real feel" tells another. According to the National Weather Service, the average high in San Diego during December sits right around 65°F (18°C), while the average low dips to about 48°F (9°C). But averages are liars. They hide the days where a Santa Ana wind event pushes the mercury into the 80s, making you feel like it's mid-July. They also hide those damp, bone-chilling mornings when the marine layer refuses to burn off and 55 degrees feels like 30 because of the humidity.
The Microclimate Reality of San Diego Temp in December
San Diego isn't just one city; it’s a collection of vastly different topographical zones. This is where most tourists get tripped up. If you are staying at a hotel in La Jolla, you are dealing with the Pacific Ocean's direct influence. The water temperature is usually hovering around 58 to 60 degrees. That massive body of cold water acts as a giant air conditioner.
Move ten miles inland to El Cajon or Santee, and the script flips entirely.
While the coast might stay a steady, misty 62 degrees all day, the inland valleys can easily swing from a frosty 40 degrees at sunrise to a t-shirt-worthy 75 degrees by 2:00 PM. It's a wild ride. You basically have to dress like an onion. Layers are the only way to survive a day that spans three seasons in twelve hours.
Why the Sun is Your Best Friend (and Worst Enemy)
In December, the sun is lower in the sky, but the UV index can still be surprisingly high. On a clear day, the sun feels intense. You’ll see locals wearing hoodies with flip-flops. It sounds like a fashion disaster, but it’s actually peak efficiency. The moment you step into the shade, the temperature drops by what feels like ten degrees instantly.
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We don't get much rain, but when it happens, it's usually in December or January. The "Pineapple Express" atmospheric rivers can dump two inches of rain in a day, which, for San Diego, is basically an apocalypse. The drainage systems aren't built for it. The roads get slick because oil builds up during the dry months. If you see rain in the forecast for your December trip, expect the city to move at half-speed.
What Most People Get Wrong About the Water
You'll see surfers out there. You might even see a few brave souls in bikinis near the Hotel del Coronado. Don't be fooled. Unless you are a member of the San Diego Polar Bear Club, the ocean in December is punishingly cold.
A 4/3mm wetsuit is the standard "uniform" for anyone spending more than five minutes in the surf. The San Diego temp in december regarding the air might be pleasant, but the water is a different story. If you're planning on a surf lesson, make sure the shop provides booties. Your toes will thank you.
Interestingly, December is one of the best times for visibility if you're a diver. The summer plankton blooms are gone. The water is clear, cold, and crisp. It’s beautiful, provided you have the neoprene to withstand it.
The Santa Ana Phenomenon
Every so often, the pressure gradients over the Great Basin shift. Instead of the cool ocean breeze blowing inland, hot, dry air from the desert gets sucked toward the coast. These are the Santa Anas.
When a Santa Ana hits in December, the San Diego temp in december can skyrocket. I’ve spent Christmas Eves at the beach in 85-degree heat, sweating while wearing a Santa hat. It’s eerie. The air gets incredibly dry—your skin will crack, and your sinuses will protest. The sky turns a deep, unnatural blue because the humidity is stripped away. Then, as soon as the wind dies down, the temperature crashes back to reality.
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Planning Your Wardrobe Without Looking Like a Tourist
If you want to blend in and stay comfortable, forget the heavy parkas. You won't need them. Instead, focus on high-quality fleece, denim, and light jackets.
- Morning (6 AM - 10 AM): It’s cold. Really. It’s damp and chilly. You want a beanie and a puffer vest.
- Midday (11 AM - 3 PM): This is your window for sunshine. A long-sleeve tee or a light flannel is usually plenty.
- Evening (4 PM - Bedtime): The sun sets early, around 4:45 PM. As soon as it disappears, the heat vanishes. This is when the leather jackets and heavy sweaters come out.
I’ve seen people arrive in San Diego in December with nothing but tropical shirts. They end up spending $80 on a "San Diego" branded hoodie at a gift shop because they’re shivering by dinner time. Don't be that person.
The Impact of the Marine Layer
"May Gray" and "June Gloom" get all the press, but December has its own version of coastal clouds. It's not as persistent, but it can linger. If the marine layer stays pushed in, the San Diego temp in december will struggle to break 60 degrees. It feels "raw." It’s the kind of cold that gets into your bones because it’s wet.
However, when the sky is clear, San Diego has some of the best air quality of the year in December. The summer smog has dissipated, and you can see the snow-capped peaks of the Laguna Mountains to the east while you’re standing on the sand. It’s a stunning contrast.
Real Data: A Look at Recent Decembers
If we look at the last few years, we see a trend of increased volatility. In 2023, we saw several days where the coastal highs didn't even hit 58 degrees. Conversely, back in 2020, we had a heatwave where several records were threatened.
It's also worth noting that December is technically the start of whale watching season. The California Gray Whales are migrating south to Baja. Because the air is cool but the sun is often out, being on a boat is actually quite pleasant, provided you have a windbreaker. The lack of extreme heat makes outdoor activities like hiking Torrey Pines or walking the Zoo much more enjoyable than in the sweltering humidity of August.
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Actionable Tips for Your December Visit
To make the most of the weather, you have to play the game according to San Diego's rules. It’s a city that rewards those who are prepared for transitions.
Check the "Inland" Forecast
If you’re planning to visit the San Diego Zoo Safari Park in Escondido, do not look at the weather for "San Diego." Look at the weather for "Escondido." It can be 10 to 15 degrees different. I’ve made the mistake of dressing for the coast and roasting in the inland heat more times than I care to admit.
Monitor the Surf Reports
Even if you aren't a surfer, the surf reports (like Surfline) give you a better idea of wind direction than standard weather apps. If the wind is "Offshore," it means the air is coming from the desert—expect it to be warmer and drier. If it’s "Onshore," expect that cool, damp ocean air.
Book Outdoor Dining for Lunch
San Diego is famous for patio dining. In December, dinner on a patio can be a bit of a gamble. Most places have space heaters, but they can only do so much against a 50-degree breeze. Aim for outdoor lunches to soak up the vitamin D, and move indoors for dinner.
Don't Forget Sunscreen
It’s easy to forget because it’s not hot, but the sun is still powerful. The reflection off the water during a walk on Mission Beach can give you a nasty burn before you even realize it’s happening.
Watch the Humidity
When the humidity drops during Santa Ana events, drink twice as much water as you think you need. Dehydration hits differently in the dry cold than it does in the humid heat.
San Diego in December is arguably the city's best-kept secret. The crowds are thinner than in the summer, the air is crisp, and the sunsets are statistically more vibrant due to the way light scatters through the winter atmosphere. Just remember that "Southern California" isn't a synonym for "Tropical." It's a Mediterranean climate, and in December, that means being ready for anything.
Pack the layers, keep an eye on the specific neighborhood forecast, and accept that you might be wearing a swimsuit at noon and a down jacket at 6:00 PM. That is the true San Diego experience.