Weather in San Jose in September

Prime time. If you get to pick your dates, September is the one. Highs average 31 °C, lows 13.6 °C, and rain falls on 1 days — nothing in the month is working against you.

September ranks 7 of 12 in San Jose: 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 1 days, so an itinerary with no wet-weather fallback is a reasonable risk. Pack for 31 °C days and 13.6 °C nights; the spread matters more here than any single number.

What the averages hide

Averages flatten a month, and this one hides a few things: 7 days clear 35 °C, so a serious heatwave is normal rather than notable; the day swings 17.3 °C from low to high, which means one bag has to cover both. Across the twenty years measured, the hottest September day reached 46.2 °C and the coldest night fell to 8.2 °C.

September is dependably dry, and that reliability is the point: across the twenty years measured, the wettest September on record still only managed 11 mm, and the driest managed 0 mm. There is no meaningful variability to plan around, which makes this one of the few months anywhere that you can build a fixed outdoor itinerary against without a fallback. The wettest single day in twenty years of Septembers brought 10 mm. Rain simply is not the variable that decides this trip — heat, crowds and cost are.

Wind is light at 7.7 km/h, so the temperature on the page is close to the temperature on your skin, and humidity is unremarkable at 60%.

How September sits in the year

Temperatures hold steady either side: 31.6 °C in August, 31 here, 26.6 in October. Nothing about the timing within the month matters much.

Daylight in September

12.5 hours of daylight, losing 1.2 hours across the month. That is between San Jose's extremes of 14.7 and 9.6 hours, so days are long enough not to constrain the plan.

Sea temperature

The sea sits at about 15.4 °C in September — cold — a quick dip rather than a swim, and a wetsuit if you are in for longer. This is the warmest the water gets all year.

How busy it gets

Shoulder. The value months — prices ease off and you get the place closer to itself.

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

September in San Jose versus nearby

If San Jose is one option among several, the nearby comparison is worth making. San Francisco is a better bet in September — 6.5 °C cooler, the same number of rain days. Napa is close enough to be a coin toss — within a degree on temperature, the same number of rain days.

So: September works, with May the better month by 15 points if the dates can move. If they cannot, nothing here should stop you booking.

Every month in San Jose

See all twelve months in San Jose, or where else to go in September.