July in Charlston is the hottest month of the year. In July, the weather in Charlston is typically hot. Average daily high temperature in July is about 29 degrees above zero. On average, Charlston has 15 rainy, 8 sunny, 7 partly cloudy, and 1 cloudy day in July. The rains are usually heavy. July as well as January, February, March, and December is considered the most uncomfortable time to visit Charlston.