Astronomical fall begins on Monday at 10:29 PM ET. This year, the start of fall is coinciding with the passage of a cold front through the area tonight into Monday. Behind the front we can expect to see cooler and less humid air which should make weather conditions across most of the Southeast cool and pretty for the next few days. Once the front passes, the chances of rain should hold off until the end of the week.
For an explanation of the difference between astronomical and meteorological seasons, check out this explanation from NOAA at https://www.ncdc.noaa.gov/news/meteorological-versus-astronomical-summer.