Yeah, I do live in Atlanta and it is getting warmer.

 

Pretty good bet that's the cause of your declining fuel economy; once things cool off this fall you should see your mileage right back up to normal; errr, that is if the traffic in the greater Atlanta area cooperates.

 

My fuel economy can drop from 6.9ltrs / 100kms to 7.7 ltrs/100kms during the summer.
& loose about 25 - 30kms fuel range per tank.

I'm loving the cooler weather right now, & so is my car.