The Tarutao archipelago operates on a clear two-season calendar. The dry season runs from mid-November through mid-May — this is when the boats run reliably, the water is calm, the visibility for snorkelling is good, and the park bungalows on Ko Tarutao are open. December and January are the most popular and most expensive months.
The monsoon (mid-May to mid-October) brings strong winds, heavy rain, and rough seas that close most of the archipelago. National park accommodation on Ko Tarutao shuts entirely. Ko Lipe stays partly open and a few hotels run year-round, but boat connections become unreliable and snorkelling visibility is poor. February to April is the sweet spot: calm seas, clear water, occasional cloud cover to soften the heat, and slightly thinner crowds than the December peak.