August in Hiroshima is the rainiest and the warmest month of the year. In August, the weather in Hiroshima is typically hot. Average daily high temperature in August is about 28 degrees above zero. On average, Hiroshima has 24 rainy and 7 sunny days in August. The rains are usually heavy. August as well as January, February, March, and July is considered the most uncomfortable time to visit Hiroshima.