This report describes the typical weather at the Austin-Bergstrom International Airport (Austin, Texas, United States) weather station over the course of an average September. It is based on the historical records from 2000 to 2012. Earlier records are either unavailable or unreliable.
Austin, Texas has a warm humid temperate climate with hot summers and no dry season. The area within 25 mi of this station is covered by croplands (43%), grasslands (40%), forests (13%), and built-up areas (2%).
The month of September is characterized by falling daily high temperatures, with daily highs decreasing from 94°F to 87°F over the course of the month, exceeding 99°F or dropping below 79°F only one day in ten.
Over the course of September, the length of the day is gradually decreasing. From the start to the end of the month, the length of the day decreases by 52 minutes, implying an average day-over-day decrease of 1.7 minutes.
The shortest day of the month is September 30 with 11:53 hours of daylight; the longest day is September 1 with 12:45 hours of daylight.
The earliest sunrise is at 7:08am on September 1; the latest sunset is at 7:53pm on September 1; the latest sunrise is at 7:24am on September 30; the earliest sunset is at 7:17pm on September 30.
Daylight savings time is observed in 2012 but it neither starts nor ends in September, so the entire month is in daylight time.
The median cloud cover is 55% (partly cloudy) and does not vary substantially over the course of the month.
On September 15, a representative day, the sky is clear or mostly clear 34% of the time, partly cloudy 23% of the time, and mostly cloudy or overcast 43% of the time.
The probability that precipitation will be observed at this location varies throughout the month. Precipitation is most likely around September 26, occurring in 29% of days. Precipitation is least likely around September 3, occurring in 24% of days.
Throughout September, the most common forms of precipitation are thunderstorms, light rain, and moderate rain.
Thunderstorms are the most severe precipitation observed during 40% of those days with precipitation. They are most likely around September 23, when it is observed during 11% of all days.
Light rain is the most severe precipitation observed during 33% of those days with precipitation. It is most likely around September 14, when it is observed during 10% of all days.
Moderate rain is the most severe precipitation observed during 17% of those days with precipitation. It is most likely around September 12, when it is observed during 5% of all days.
Either snow is exceptionally unlikely to fall at this location in September or this station does not reliably report precipitation types.
The relative humidity typically ranges from 40% (comfortable) to 93% (very humid) over the course of a typical September, rarely dropping below 25% (dry) and reaching as high as 99% (very humid).
The air is driest around September 1, at which time the relative humidity drops below 47% (comfortable) three days out of four; it is most humid around September 30, rising above 90% (very humid) three days out of four.
Dew point is often a better measure of how comfortable a person will find the weather than relative humidity because it more directly relates to whether perspiration will evaporate from the skin, thereby cooling the body. Lower dew points feel drier and higher dew points feel more humid.
Over the course of a typical September, the dew point typically varies from 56°F (comfortable) to 72°F (very muggy) and is rarely below 45°F (dry) or above 76°F (very muggy).
Over the course of September typical wind speeds vary from 0 mph to 14 mph (calm to moderate breeze), rarely exceeding 19 mph (fresh breeze).
The highest average wind speed of 7 mph (light breeze) occurs around September 15, at which time the average daily maximum wind speed is 14 mph (moderate breeze).
The lowest average wind speed of 6 mph (light breeze) occurs around September 11, at which time the average daily maximum wind speed is 13 mph (moderate breeze).