May in Samui is the hottest month of the year. In May, the weather in Samui is typically hot. Average daily high temperature in May is about 30 degrees above zero. On average, Samui has 24 rainy, 3 sunny, 3 cloudy, and 1 partly cloudy day in May. The rains are usually heavy. May as well as June, July, August, and September is considered the most uncomfortable time to visit Samui.