I am originally from Northern California but have lived in Atlanta, Georgia for 18 years, and actually found the climate to be quite pleasant here. Anywhere in the U.S. east of the Rockies will have high humidity during the summer, but Atlanta is in the foothills of the Appalachians at about 1000' feet of elevation. That means about half as many 90+ degree days (32) as in other southern cities like Houston (74), Miami (56), or Orlando (65).
However if you don't like hot weather, check out the North Georgia mountains, where it's significantly cooler than in the rest of the state. (The highest temperature ever recorded on Brasstown Bald, GA was only 84 degrees Farenheit.) Many retirees choose to live in areas like Helen, Elijay, Blue Ridge, or Big Canoe (elevation 3,200') for the cooler temperatures and beautiful scenery. You also have easy access to Atlanta (<2 hours) and all the amenities of a major city like world-class medical care.