Weather in San Diego in January

Prime time. If you get to pick your dates, January is the one. Highs average 20.4 °C, lows 11.1 °C, and rain falls on 5 days — nothing in the month is working against you.

January ranks 6 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 January reaches 30 °C. Across the twenty years measured, the hottest January day reached 30 °C and the coldest night fell to 2.1 °C, and the wettest single day dropped 48 mm — roughly 117% of the month's rain in one day.

This is the volatile part. January rainfall has ranged from 2 mm to 128 mm across the twenty years measured — a 126 mm spread around an average of 41 mm. The average is real but almost no individual January looks like it, so treat the figure as the middle of a wide range rather than a forecast.

Wind is light at 8.6 km/h, so the temperature on the page is close to the temperature on your skin, and humidity is unremarkable at 64%.

How January sits in the year

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

Daylight in January

January sits at the dark end of San Diego's year — 10.2 hours of daylight against 14.3 at midsummer, gaining 0.5 hours across the month. Sightseeing days are genuinely shorter, and an itinerary built for summer will not fit.

Sea temperature

The sea sits at about 15.5 °C in January — 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.

January 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 January — 2.8 °C cooler, the same number of rain days. Riverside is close enough to be a coin toss — within a degree on temperature, the same number of rain days.

So: January works, with May the better month by 7 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 January.