September in Sihanoukville is the coldest month of the year. In September, the weather in Sihanoukville is typically warm. Average daily high temperature in September is about 27 degrees above zero. On average, Sihanoukville has 29 rainy and 1 partly cloudy day in September. The rains are usually heavy. September as well as April, May, June, and July is considered the most uncomfortable time to visit Sihanoukville.