By a whopping 1.4 F over Sep's of 1921's 79.5, KATL easily gets the 2nd hottest Sep on record back to 1879 with 80.9, an amazing 7.9 warmer than normal! Only the historic Sep of 1925's 83.0 (no, that's not a typo) was hotter! Even more amazingly, Sep barely beats out July's 80.8 to be the hottest month of the year! The only other times since 1879 Sep was the warmest month of the year: you guessed it, 1925 and 1921.
The lowest temp was only down to 69, which is THE highest Sep monthly minimum on record, beating the old record of 66 from 1925! Since 1926, the warmest minimum was 62.