San Antonio Weather in September

September sees an easing of the hot weather for San Antonio, Texas. The transition to fall also means a little more cloud and rain.

This page gives detailed information on the typical September temperature, precipitation, sun, humidity, wind and storms for San Antonio. The numbers here are historical averages based on climate data gathered at the San Antonio International Airport, located a few miles north of the city center.

Temperature Weather iconTemperature

90 °F September average high 32 °C
70 °F September average low 21 °C
20 days 90 °F max. or more (32 °C)
13 days 70 °F min. or less (21 °C)

Nearly every day in September warms to over 80 degrees Fahrenheit (27 degrees Celsius) in San Antonio. The city averages one day this month when the thermometer reaches into the 100s °F (over 38 °C).

The thermometer dips to 60 °F (16 °C) or below on an average of 3 nights. Only in some years does September get as cold as 50 °F (10 °C).

Rainy Weather iconRain

3.9 in total precipitation 99 mm
7 days of rain

Half the time, San Antonio receives 1.5 to 5.3 inches (38 to 134 mm) of rainfall in September. One in four years has drier weather, while another one in four is wetter.

Sunny Weather iconSun

67 % sunshine
9 days clear skies

The sun's rays reach the ground in San Antonio during 67 percent of daylight hours on average in September, for a total of 247 hours in the month. Typically on 9 days this month the sky is mainly clear, with at most 30 percent cloud cover.

Sunlight in September at San Antonio lasts for 12 hours and 18 minutes a day on average. The longest day of the month is the 1st with 12 hours and 44 minutes of daylight. By the end of the month, the days have shortened to 11:54 from sunrise to sunset. These durations can vary by a minute or two from year to year.

Humid Weather iconHumidity

68 % September average humidity

The relative humidity in San Antonio during September usually peaks at 86 percent in the morning then drops to 48 percent by mid afternoon.

Local Time12 am3 am6 am9 am12 pm3 pm6 pm9 pm
Humidity % 78 83 86 74 56 48 52 68

Windy Weather iconWind

8.3 mph September wind speed average 13.4 kph

September is one of the least windy months for San Antonio.

Stormy Weather iconStorms

3 days rainfall of 0.5 inches (13 mm) or more
4 days with thunderstorms in September
6 % chance a named storm approaches

There's a 2 percent probability that a hurricane will approach within 100 miles (165 km) of San Antonio during September. The chance of a major category 3 to 5 hurricane reaching the area is 1 percent.


The weather data here are long-term averages provided by the US National Centers for Environmental Information (NCEI). Temperature and precipitation are 1991-2020 normals while humidity and thunderstorms are 1961-1990 normals. The named storm probabilities come from the Atlantic Oceanographic and Meteorological Laboratory, Hurricane Research Division.

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