August in Bay City is the rainiest and the hottest month of the year. In August, the weather in Bay City is typically hot. Average daily high temperature in August is about 31 degrees above zero. On average, Bay City has 14 rainy, 14 sunny, and 3 partly cloudy days in August. The rains are usually heavy. August as well as June, July, September, and December is considered the most uncomfortable time to visit Bay City.