The dry season from November to March is the best time to visit, with calm Andaman seas, sunshine and reliable island-hopping, and it is also the busiest and priciest window, peaking around December and January. April and May are very hot before the rains. The southwest monsoon from roughly May to October brings heavier rain, rougher seas and stronger currents, when some longtail crossings and island tours are cancelled on bad days, though prices drop and the landscape turns lush and green.
During the May-to-October monsoon the Andaman Sea can turn rough with strong rip currents, and some beaches fly red warning flags. Heed the flags and lifeguards, do not swim when red flags are up, and accept that boat trips may be cancelled in bad weather for good reason.
Longtail boats are the everyday transport but vary in condition and rarely feel formal about safety. Check that life jackets are available before boarding, avoid clearly overloaded boats, and think twice about crossings in rough seas or after dark.
The tropical sun is strong, especially on open boats, beaches and the long, shadeless climb at Tiger Cave Temple. Wear reef-safe sunscreen, a hat and sunglasses, carry water, and protect children and older travellers, who feel the heat fastest.