August in San Antonio is the sunniest and the hottest month of the year. In August, the weather in San Antonio is typically hot. Average daily high temperature in August is about 35 degrees above zero. On average, San Antonio has 17 sunny, 7 partly cloudy, 6 rainy, and 1 cloudy day in August. The rains are usually moderate. August as well as May, June, July, and September is considered the most uncomfortable time to visit San Antonio.