August in Dehiwala-Mount Lavinia is the coldest month of the year. In August, the weather in Dehiwala-Mount Lavinia is typically warm. Average daily high temperature in August is about 27 degrees above zero. On average, Dehiwala-Mount Lavinia has 30 rainy and 1 sunny day in August. The rains are usually heavy. August as well as March, April, May, and June is considered the most uncomfortable time to visit Dehiwala-Mount Lavinia.