May in Koh Lanta Yai is the rainiest and the cloudiest month of the year. In May, the weather in Koh Lanta Yai is typically hot. Average daily high temperature in May is about 29 degrees above zero. On average, Koh Lanta Yai has 30 rainy and 1 sunny day in May. The rains are usually heavy. May as well as April, June, July, and August is considered the most uncomfortable time to visit Koh Lanta Yai.