Average Weather in September in San Antonio Texas, United States
In San Antonio, the month of September is characterized by falling daily high temperatures, with daily highs decreasing by 7°F, from 93°F to 87°F over the course of the month, and rarely exceeding 98°F or dropping below 80°F.
Daily low temperatures decrease by 7°F, from 74°F to 67°F, rarely falling below 56°F or exceeding 78°F.
For reference, on August 6, the hottest day of the year, temperatures in San Antonio typically range from 76°F to 96°F, while on January 6, the coldest day of the year, they range from 43°F to 63°F.
Average High and Low Temperature in September
The figure below shows you a compact characterization of the hourly average temperatures for the quarter of the year centered on September. The horizontal axis is the day, the vertical axis is the hour of the day, and the color is the average temperature for that hour and day.
Average Hourly Temperature in September
The month of September in San Antonio experiences decreasing cloud cover, with the percentage of time that the sky is overcast or mostly cloudy decreasing from 42% to 31%.
The clearest day of the month is September 30, with clear, mostly clear, or partly cloudy conditions 69% of the time.
For reference, on January 3, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 46%, while on June 11, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 73%.
Cloud Cover in September
A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. In San Antonio, the chance of a wet day over the course of September is gradually decreasing, starting the month at 24% and ending it at 21%.
For reference, the year's highest daily chance of a wet day is 31% on May 27, and its lowest chance is 13% on December 16.
Probability of Precipitation in September
To show variation within the month and not just the monthly total, we show the rainfall accumulated over a sliding 31-day period centered around each day.
The average sliding 31-day rainfall during September in San Antonio is gradually increasing, starting the month at 2.4 inches, when it rarely exceeds 5.6 inches or falls below 0.4 inches, and ending the month at 2.7 inches, when it rarely exceeds 5.7 inches or falls below 0.4 inches.
Average Monthly Rainfall in September
Over the course of September in San Antonio, the length of the day is decreasing. From the start to the end of the month, the length of the day decreases by 50 minutes, implying an average daily decrease of 1 minute, 44 seconds, and weekly decrease of 12 minutes, 11 seconds.
The shortest day of the month is September 30, with 11 hours, 54 minutes of daylight and the longest day is September 1, with 12 hours, 44 minutes of daylight.
Hours of Daylight and Twilight in September
The earliest sunrise of the month in San Antonio is 7:11 AM on September 1 and the latest sunrise is 15 minutes later at 7:26 AM on September 30.
The latest sunset is 7:55 PM on September 1 and the earliest sunset is 35 minutes earlier at 7:20 PM on September 30.
Daylight saving time is observed in San Antonio during 2017, but it neither starts nor ends during September, so the entire month is in daylight saving time.
For reference, on June 21, the longest day of the year, the Sun rises at 6:34 AM and sets 14 hours, 2 minutes later, at 8:36 PM, while on December 21, the shortest day of the year, it rises at 7:24 AM and sets 10 hours, 16 minutes later, at 5:40 PM.
Sunrise & Sunset with Twilight in September
We base the humidity comfort level on the dew point, as it determines whether perspiration will evaporate from the skin, thereby cooling the body. Lower dew points feel drier and higher dew points feel more humid. Unlike temperature, which typically varies significantly between night and day, dew point tends to change more slowly, so while the temperature may drop at night, a muggy day is typically followed by a muggy night.
The chance that a given day will be muggy in San Antonio is very rapidly decreasing during September, falling from 81% to 49% over the course of the month.
For reference, on July 1, the muggiest day of the year, there are muggy conditions 89% of the time, while on January 23, the leasy muggy day of the year, there are muggy conditions 2% of the time.
Humidity Comfort Levels in September
This section discusses the wide-area hourly average wind vector (speed and direction) at 10 meters above the ground. The wind experienced at any given location is highly dependent on local topography and other factors, and instantaneous wind speed and direction vary more widely than hourly averages.
The average hourly wind speed in San Antonio is essentially constant during September, remaining within 0.1 miles per hour of 4.4 miles per hour throughout.
For reference, on April 2, the windiest day of the year, the daily average wind speed is 5.6 miles per hour, while on September 5, the calmest day of the year, the daily average wind speed is 4.3 miles per hour.
The lowest daily average wind speed during September is 4.3 miles per hour on September 6.
Average Wind Speed in September
Wind Direction in September
This section discusses the total daily incident shortwave solar energy reaching the surface of the ground over a wide area, taking full account of seasonal variations in the length of the day, the elevation of the Sun above the horizon, and absorption by clouds and other atmospheric constituents. Shortwave radiation includes visible light and ultraviolet radiation.
The average daily incident shortwave solar energy in San Antonio is essentially constant during September, remaining within 0.2 kWh of 5.6 kWh throughout.
Average Daily Incident Shortwave Solar Energy in September
For the purposes of this report, the geographical coordinates of San Antonio are 29.424 deg latitude, -98.494 deg longitude, and 663 ft elevation.
The topography within 2 miles of San Antonio contains only modest variations in elevation, with a maximum elevation change of 151 feet and an average elevation above sea level of 657 feet. Within 10 miles contains only modest variations in elevation (577 feet). Within 50 miles contains significant variations in elevation (1,831 feet).
The area within 2 miles of San Antonio is covered by artificial surfaces (100%), within 10 miles by artificial surfaces (65%) and shrubs (23%), and within 50 miles by shrubs (38%) and cropland (25%).
This report illustrates the typical weather in San Antonio year round, based on a statistical analysis of historical hourly weather reports and model reconstructions from January 1, 1980 to December 31, 2016.
Temperature and Dew Point
There are 3 weather stations near enough to contribute to our estimation of the temperature and dew point in San Antonio.
For each station, the records are corrected for the elevation difference between that station and San Antonio according to the International Standard Atmosphere , and by the relative change present in the MERRA-2 satellite-era reanalysis between the two locations.
The estimated value at San Antonio is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between San Antonio and a given station.
The stations contributing to this reconstruction are: Stinson Municipal Airport (38%, 10 kilometers, south); Kelly Field Annex (39%, 10 kilometers, southwest); and San Antonio International Airport (23%, 13 kilometers, north).
All data relating to the Sun's position (e.g., sunrise and sunset) are computed using astronomical formulas from the book, Astronomical Tables of the Sun, Moon and Planets , by Jean Meeus.
All other weather data, including cloud cover, precipitation, wind speed and direction, and solar flux, come from NASA's MERRA-2 Modern-Era Retrospective Analysis . This reanalysis combines a variety of wide-area measurements in a state-of-the-art global meteorological model to reconstruct the hourly history of weather throughout the world on a 50-kilometer grid.
Land Use data comes from the Global Land Cover SHARE database , published by the Food and Agriculture Organization of the United Nations.
Elevation data comes from the Shuttle Radar Topography Mission (SRTM) , published by NASA's Jet Propulsion Laboratory.
Names, locations, and time zones of places and some airports come from the GeoNames Geographical Database .
Time zones for aiports and weather stations are provided by AskGeo.com .
Maps are © Esri, with data from National Geographic, Esri, DeLorme, NAVTEQ, UNEP-WCMC, USGS, NASA, ESA, METI, NRCAN, GEBCO, NOAA, and iPC.