Thailand in December: what to expect

December is the cool season, and it is the month most of Thailand's tourist map is built around. The northeast monsoon has arrived, so Bangkok, the central plains, the north and the Andaman coast are dry and comfortable: warm days, cooler evenings, and rain that mostly stays away. The exception is the Gulf side of the peninsula, where the same monsoon dumps rain on Koh Samui, Koh Phangan and Koh Tao, usually easing through the second half of the month.

The north is the one place to pack for cold. Chiang Mai and Chiang Rai can drop to around 15 °C at night, and hill towns such as Mae Hong Son and Pai go lower — guesthouses there are built for heat, not cold, so a layer matters. Daytime is still T-shirt weather almost everywhere.

December splits into two very different halves. Until about 20 December, Thailand is busy but manageable: hotel rates are high-season high, not yet holiday-high, and you can still find rooms on the islands with a few days' notice. From roughly 20 December to 5 January, the country runs at full capacity. Domestic flights to Phuket, Krabi, Samui and Chiang Mai sell out, island ferries fill, and beach bungalows that cost 1,200 THB in November can ask 3,000 THB or more.

If your dates are fixed over the holidays, book flights and the first two nights before you leave home, and treat everything after that as flexible. If your dates are not fixed, the single best move is to travel in the first half of the month and be somewhere quiet by Christmas Eve.

Thailand's December calendar is built around two fixed dates and one moving one. On 5 December the country marks Father's Day and the birthday of the late King Bhumibol Adulyadej, with ceremonies, lights and flags in Bangkok and most provincial capitals — a good day to be in a city rather than on a beach. New Year's Eve on 31 December brings fireworks and countdown events in Bangkok, Chiang Mai, Phuket and Pattaya, plus full hotels everywhere.

The moving date is Loy Krathong, the lantern-and-float festival that usually falls in November but occasionally lands in early December. When it does, Chiang Mai is the busiest place to see it. Note that Buddhist holidays and some royal days carry a nationwide ban on alcohol sales for 24 hours; shops and bars still open, but no drink is served.

The Andaman coast is the safest bet: Phuket, Krabi, Ao Nang, Rai Leh, Koh Lanta and the Similan and Surin island parks are all in season, with calm water and diving at its best. Book early — this is the coast everyone wants in December.

Bangkok works well as a base: dry, walkable in the evenings, and the easiest place to fly in and out of. The north is excellent for the first three weeks — Chiang Mai, Chiang Rai, Nan and Mae Hong Son are cool and clear, with none of the burning-season smoke that ruins February to April. Isaan and the central plains are quiet, cheap and dry if you want to avoid the crowds entirely.

The Gulf islands are the one place to think twice. Koh Samui, Koh Phangan and Koh Tao are still wet in early December, and ferries and diving trips can be cancelled. From mid-month conditions usually improve, but check the forecast before committing to a non-refundable booking.

Pack for warm days and cool evenings, plus one genuinely warm layer if you are going north. A light rain shell is worth the space for the Gulf islands in early December, and for the odd shower elsewhere. Beach days need reef-safe sunscreen, a hat and sandals; city days need shoes you can walk in, since Bangkok's December evenings are the most comfortable of the year.

Two practical items for the holiday period: a printed copy of your bookings, because airport and ferry staff will ask, and a little cash, because ATMs on the islands run dry when they are busiest.

November is the shoulder: the cool season has started, the Andaman coast is drying out, and prices are lower than December's. January is the mirror image of December — just as dry and cool, still peak season, but the holiday crush is over after the first week. February stays dry but the north begins to haze late in the month, so shift south if air quality matters to you.

If you are weighing the whole year, the pattern is simple: the Andaman coast runs November to April, the Gulf islands run February to September, and the north is best from November to January.