Southeast Asia does not have four neat seasons — it has wet and dry, and the timing shifts as you move around the region. Get the timing right and you will trade downpours and humidity for blue skies and easy travel.
The general rule: November to March
For most of the mainland — Thailand, Vietnam, Cambodia and Laos — the cool, dry season from November to March is the comfortable window. Skies are clear, humidity drops and it is the best time for temples, trekking and island-hopping. It is also the busiest and priciest, so book ahead around Christmas and New Year.
The hot season (April–May)
Temperatures soar before the rains break, often into the high 30s°C. It is a good time for bargains and for the famous water festivals — Songkran in Thailand and similar new-year celebrations across the region — but sightseeing in the midday heat is hard work.
The wet season (roughly June–October)
Don't write it off. Rain often comes in short, heavy afternoon bursts rather than all-day grey, the landscape is at its greenest, and prices are at their lowest. Bali, for instance, is still enjoyable in the shoulder months. The exception is the islands exposed to the worst storms — check the specific coast you are visiting.
Important: the coasts are split
Thailand's two coasts are on opposite schedules. The Andaman side (Phuket, Krabi) is best November–April; the Gulf side (Koh Samui, Koh Phangan) is often driest February–April and can stay pleasant later in the year. Plan island time around the coast, not the calendar alone.
Quick verdict
- Best overall: November–February (cool, dry, but busy).
- Best for value: the green shoulder months of May and October.
- Best for festivals: April, for the water festivals.
Always cross-check the individual city or island — within a single country the right month can differ by hundreds of miles.