In December, the weather in Dehiwala-Mount Lavinia is typically hot. Average daily high temperature in December is about 28 degrees above zero. On average, Dehiwala-Mount Lavinia has 26 rainy, 4 sunny, and 1 partly cloudy day in December. The rains are usually heavy. December as well as March, April, May, and June is considered the most uncomfortable time to visit Dehiwala-Mount Lavinia.