May in Grasonville is the rainiest month of the year. In May, the weather in Grasonville is typically warm. Average daily high temperature in May is about 22 degrees above zero. On average, Grasonville has 15 rainy, 9 sunny, 5 partly cloudy, and 2 cloudy days in May. The rains are usually heavy. May as well as January, February, March, and December is considered the most uncomfortable time to visit Grasonville.