August in Hilton Head Island is the rainiest and the cloudiest month of the year. In August, the weather in Hilton Head Island is typically hot. Average daily high temperature in August is about 30 degrees above zero. On average, Hilton Head Island has 22 rainy, 8 sunny, and 1 partly cloudy day in August. The rains are usually heavy. August as well as July is considered the most uncomfortable time to visit Hilton Head Island.