Koh Lanta in August

November through April delivers the perfect Koh Lanta experience — dry skies, calm seas, and temperatures that hover around 30°C without the crushing humidity. December and January see the biggest crowds and highest prices, but the weather stays consistently gorgeous. February and March offer the sweet spot with fewer tourists and still-excellent conditions. April gets hot (think 35°C by midday) but the beaches empty out and resort rates drop by 40%. Avoid May through October completely — the monsoons turn roads into rivers and most beachfront restaurants simply close. The ferry service becomes unreliable, and you'll spend your vacation watching rain pound your bungalow roof.