Weather in San Antonio in September

Shoulder season. September is shoulder season in San Antonio — cheaper, quieter, and a genuine gamble. Highs average 32.8 °C, lows 21.6 °C, and rain falls on 10 days — nothing in the month is working against you.

September ranks 9 of 12 in San Antonio: past the worst of the year but short of February, which is the month to book if the dates are open.

Rain on 10 days, 3 of them heavy. Enough to need a plan B, not enough to need a plan around it. Pack for 32.8 °C days and 21.6 °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: 9 days clear 35 °C, so a serious heatwave is normal rather than notable. Across the twenty years measured, the hottest September day reached 42.9 °C and the coldest night fell to 11.2 °C, and the wettest single day dropped 91 mm — roughly 96% of the month's rain in one day.

September is moderately variable: 11 mm in the driest year against 248 mm in the wettest, around an average of 95 mm. Roughly two Septembers in three land near that average, and the third does something else entirely.

Wind is light at 8.7 km/h, so the temperature on the page is close to the temperature on your skin, and humidity is unremarkable at 68%.

How September sits in the year

The month is on the way down: 3.9 °C cooler than August, with October dropping another 3.9 °C. The first week and the last are not the same trip.

Daylight in September

12.4 hours of daylight, losing 0.9 hours across the month. That is between San Antonio's extremes of 14 and 10.3 hours, so days are long enough not to constrain the plan.

An inland climate

With no coast nearby, the year swings a fair way — 31.5 °C between the warmest afternoons and the coldest nights, wider than any coastal city at this latitude would manage.

How busy it gets

Off season. The genuine off season: cheapest by a distance, with the caveat that some tours and restaurants close entirely.

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

September in San Antonio versus nearby

If San Antonio is one option among several, the nearby comparison is worth making. Corpus Christi is close enough to be a coin toss — within a degree on temperature, 4 days more rain. Laredo is the weaker option in September — within a degree on temperature, 3 days more rain.

So: September is a compromise. February is 37 points better and is what San Antonio is actually like at its best — worth moving the trip for if that is possible, and worth adjusting expectations for if it is not.

Every month in San Antonio

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