Weather in San Diego in December

Prime time. If you get to pick your dates, December is the one. Highs average 19.9 °C, lows 11 °C, and rain falls on 5 days — nothing in the month is working against you.

December ranks 8 of 12 in San Diego: past the worst of the year but short of May, which is the month to book if the dates are open.

Rain falls on only 5 days, so an itinerary with no wet-weather fallback is a reasonable risk. Nothing specialised needed — this is the month you pack for the trip rather than for the weather.

What the averages hide

Averages flatten a month, and this one hides a few things: it never really gets hot: not one day in an average December reaches 30 °C. Across the twenty years measured, the hottest December day reached 29.6 °C and the coldest night fell to 4.2 °C, and the wettest single day dropped 54 mm — roughly 106% of the month's rain in one day.

December is moderately variable: 1 mm in the driest year against 126 mm in the wettest, around an average of 51 mm. Roughly two Decembers in three land near that average, and the third does something else entirely.

Wind is light at 9 km/h, so the temperature on the page is close to the temperature on your skin, and humidity is unremarkable at 64%.

How December sits in the year

Temperatures hold steady either side: 23.9 °C in November, 19.9 here, 20.4 in January. Nothing about the timing within the month matters much.

Daylight in December

December sits at the dark end of San Diego's year — 10 hours of daylight against 14.3 at midsummer, holding steady all month. Sightseeing days are genuinely shorter, and an itinerary built for summer will not fit.

Sea temperature

The sea sits at about 16.4 °C in December — cold — a quick dip rather than a swim, and a wetsuit if you are in for longer. The sea peaks at 20.3 °C in September and bottoms out at 15.3 °C — water lags the air by a month or two, which is why the best swimming often comes after the best weather.

How busy it gets

Busy. Popular without being frantic; book the things you care about, improvise the rest.

Crowd levels are estimated from climate desirability and school-holiday calendars, not from visitor numbers.

December in San Diego versus nearby

If San Diego is one option among several, the nearby comparison is worth making. Irvine is the weaker option in December — 2.4 °C cooler, 1 day more rain. Riverside is close enough to be a coin toss — within a degree on temperature, 1 day more rain.

So: December works, with May the better month by 9 points if the dates can move. If they cannot, nothing here should stop you booking.

Every month in San Diego

See all twelve months in San Diego, or where else to go in December.