May is the hinge month: the first rain arrives, crowds drop by half, and prices have not yet fallen to green-season levels. The Andaman still works in the first half; the Gulf starts its season.
The short version
- Rain arrives mid-to-late May, usually as short afternoon storms.
- Prices 25–35% below high season and hotels are easy to book.
- The Andaman is still swimmable for the first two weeks.
- Visakha Bucha, the Buddha's birthday, falls in May — temples are busy and alcohol is restricted.
Weather
Hot and humid, with the first real rain of the year arriving mid-month. The Andaman starts to get squally in the last week; the Gulf stays calm for another month.
Why it is underrated
Hotel prices drop sharply after Songkran, temples are quiet, and the countryside turns green. You get high-season comfort at low-season prices until about the 20th.
What to book
The Gulf (Samui, Phangan, Tao) is the safer coast. In the north, the rain clears the smoke — Chiang Mai in late May is far more pleasant than in March.
Where to go in May
The first half of May is effectively still dry season on the Andaman, and it is the best-value fortnight of the year: high-season weather at falling prices, because the bookings have not caught up with the rain. Phuket and Krabi in early May are noticeably emptier than April at the same temperature minus two degrees.
By the last week the monsoon has usually arrived, which means short afternoon storms rather than all-day rain. The Gulf is starting its season and Koh Samui gets progressively better through the month.
Visakha Bucha falls in May — the Buddha's birth, enlightenment and death — and it is the most strictly observed Buddhist holiday in Thailand. Temples are busy, alcohol sales are restricted for 24 hours, and it is genuinely worth seeing if you are in Chiang Mai or Bangkok on the day.
