It will be hot in Atlanta, but you could still enjoy it. My family purchased an Atlanta. City Pass
http://ww.citypass.com which saves you money at the attractions. We purchase our pass at the CNN building, but you could purchase the pass either on-line or at either of the attractions that are included on the City Pass. The pass it worth it especially if you plan to visit The Aquarium. Our pass came with free admission to the Dolphin Show at the Aquarium too.