Photograph by Kathy Bell, owner of kbella photography.
Updated to the 1981-2010 Climate Normals
The days are considerably shorter than they were at the Summer Solstice back in June and gradually the energy budget of the atmosphere is shrinking as the sun makes less in the way of deposits and the atmosphere takes more in the form of withdrawals.
The average high in September in Birmingham is 85.1 and the average low a much more comfortable 63.4. Both averages are 5-6 degrees lower than those of August.
September 1925 is the hottest ninth month ever, with a sizzling average high of 96.1. That month featured one of the worst hot spells in Central Alabama history and the hottest reading ever recorded in the state, 112F at Centreville on September 5. There were 14 100+ days in Birmingham that September, a record that still stands. It has been 105F or hotter eighteen times in Birmingham since 1900, and four of them occurred that month including September hottest reading of 106F.
The coldest September low (37F) occurred on the 30th in 1967. September 1967 also recorded the coldest average low temperature, with an average of 57.6F.
Rainfall picks up a bit in September, generally thanks to tropical systems moving in from the Gulf. We average 3.90 inches of rain in the month. 13.19 inches fell in September 1906, the most ever in the month. 9.75 inches of rain fell on September 16, 2004 as Hurricane Ivan moved across the area; a record for any date.
Summer thunderstorms are on the way out, so we generally only see storms on four days on average, and it rains on 7.4 days on average.
The sky is clear 27% of the time, only surpassed by April, November, and October, one of the best months of the year in Alabama weatherwise.
– Bill Murray