Charleston summer
One of the big misconceptions about summer in Charleston is how humid it is. Let's clear this up quickly.
The humidity can never be higher than 100%. 
Many people who are considering relocating to Charleston are concerned with summer heat and humidity. I remember many years ago when I first moved to the Carolinas, friends and family asked me if I was concerned with how humid it was. The interesting thing is that it is very humid in the Northeast and Midwest during the summer also and in my opinion, even more humid and uncomfortable than here in Charleston.
You might be wondering why I might say that but understand, I've been fortunate enough to live in many places in the country and have traveled just about everywhere (46 states so far, missing only North and South Dakota, Alaska and Hawaii - BTW, I really would love to visit Alaska).
Humidity is usually (well OK, always) very high overnight so when you wake up in the morning during the summertime, it could be 100%. But as the sun bakes the temperatures during the day, the humidity drops and another real benefit is that we consistently enjoy a nice breeze off the Atlantic Ocean while more inland areas will feel a little warmer during the summer.
You can be sure it will be hot during the summer in Charleston but don't worry about the humidity.
Anyway, air conditioners and swimming pools were invented just to make summer more enjoyable.