|Koh samet weather is like the rest of Thailand, Koh samet is subject to the annual monsoon rains, which are heaviest from June to September. The coolest and driest time of year is December to February. While I generally emphasize that the rainy season is not an entirely good time to visit Thailand, it really isn't so bad to visit koh samet because when it rains it normally lasts for a short time, and there are long sunny spells. There is not a great deal of things to do on koh samet, apart from sunbathing and relaxing, so you need the sun for that. There is very little to do away from the beaches, since there are only a few historical or cultural attractions in the area.