average weather in south carolina in august
1. Re: August weather in Charleston South Carolina. Jul 07, 2012, 6:18 PM. August is typically our hottest and most humid month, however July and Sept are about the same. Last year during August the highest daily high temp recorded downtown was 100, with the average daily high for the month 92. The lowest daily high was 83. The humidity was 85% or higher all but 5 days out of the month.