August in Kumamoto is the hottest month of the year. In August, the weather in Kumamoto is typically hot. Average daily high temperature in August is about 31 degrees above zero. On average, Kumamoto has 15 rainy, 8 sunny, 5 partly cloudy, and 3 cloudy days in August. The rains are usually heavy. August as well as January, February, March, and June is considered the most uncomfortable time to visit Kumamoto.