In December, the weather in Koh Lanta Yai is typically hot. Average daily high temperature in December is about 29 degrees above zero. On average, Koh Lanta Yai has 23 rainy, 5 cloudy, 2 sunny, and 1 partly cloudy day in December. The rains are usually heavy. December as well as April, May, June, and July is considered the most uncomfortable time to visit Koh Lanta Yai.