August in Guaymas is the rainiest and the hottest month of the year. In August, the weather in Guaymas is typically hot. Average daily high temperature in August is about 33 degrees above zero. On average, Guaymas has 17 sunny, 9 partly cloudy, 4 rainy, and 1 cloudy day in August. The rains are usually heavy. August as well as July and September is considered the most uncomfortable time to visit Guaymas.