August in Grapevine is the sunniest month of the year. In August, the weather in Grapevine is typically hot. Average daily high temperature in August is about 34 degrees above zero. On average, Grapevine has 25 sunny, 3 rainy, and 3 partly cloudy days in August. The rains are usually moderate. August as well as January, July, and December is considered the most uncomfortable time to visit Grapevine.