Early September is a transitional time of year. There is a little bit of summer and a little bit of fall in every forecast.
When cool air flows down from the north this time of year, it tends to be a bit cooler than a few weeks ago thanks to the fact that way up in the Arctic region, the nights are getting long and extremely cool. Meanwhile, south of here, summer heat and humidity continue in the southern United States with almost the intensity of midsummer. So when our weather comes from that direction, it can still be terribly warm and humid.
The biggest change this time of year is the solar angle and length of day. With less solar energy to heat air and evaporate water, there is less thermodynamic energy to create violent thunderstorms, so the storms that do form tend to be less severe than a few weeks ago. But on any given day, despite the calendar, a storm can still become dangerous.