May in Dover is the rainiest and the cloudiest month of the year. In May, the weather in Dover is typically warm. Average daily high temperature in May is about 15 degrees above zero. On average, Dover has 14 rainy, 6 sunny, 6 partly cloudy, and 5 cloudy days in May. The rains are usually heavy. May as well as February, March, April, and December is considered the most uncomfortable time to visit Dover.