May in Dehiwala-Mount Lavinia is the rainiest and the cloudiest month of the year. In May, the weather in Dehiwala-Mount Lavinia is typically hot. Average daily high temperature in May is about 28 degrees above zero. On average, Dehiwala-Mount Lavinia has 30 rainy and 1 sunny day in May. The rains are usually heavy. May as well as March, April, June, and July is considered the most uncomfortable time to visit Dehiwala-Mount Lavinia.