May in Hayward is the rainiest month of the year. In May, the weather in Hayward is typically warm. Average daily high temperature in May is about 16 degrees above zero. On average, Hayward has 15 rainy, 6 sunny, 6 cloudy, and 4 partly cloudy days in May. The rains are usually heavy. May as well as January, March, April, and October is considered the most uncomfortable time to visit Hayward.