May in Perth is the sunniest month of the year. In May, the weather in Perth is typically warm. Average daily high temperature in May is about 12 degrees above zero. On average, Perth has 13 rainy, 8 partly cloudy, 6 sunny, and 4 cloudy days in May. The rains are usually moderate. May as well as January, February, April, and June is considered the most uncomfortable time to visit Perth.