You could probably be at
Dive Land Park in 2 hours or less (depending on ATL traffic), and about 2.5 hours to
Blue Water Park. I'm guessing both would probably be a little warmer than
Loch Lo Minn Quarry or
Philadelphia Quarry in East Tennessee (which have thermoclines down to around 55-57 degrees (at 50-60 feet deep) even in August. Loch Lo Minn does have paddlefish, which is an attraction for some. Last I checked, Philadelphia Quarry had a very reasonable $60 package which includes admission, every bit of gear you need including wetsuit, and all the tank fills you need -- just in case you didn't want to schlep your gear when visiting friends.
I believe the closest salt water diving may be around Savannah at 4 hours or less, then Charleston, though I don't know how good either place is to dive. Panama City Beach is not much farther than Charleston, and you can hit some of the
Florida Panhandle Shipwreck Trail from there -- it's not the Caribbean, but it's usually pretty warm, and there are some neat things to see (including goliath grouper).