The Cold Season, and Why It Is the Only Time to Come
There is a temperature in northern Thailand in December that people who have never felt it cannot be made to understand, and it changes what a trip is worth.
Thailand is a tropical country at sea level and a different country at 1,000 metres, and almost every piece of travel advice about the country fails because it does not distinguish between the two.
The season structure is simple once you internalise it: the monsoon arrives at different times on the two coasts, the north has a genuine winter, and the peak months differ for every region.
Last verified 15 September 2026.
The one rule that resolves most questions
The Andaman coast and the Gulf coast have opposite seasons, because they are on opposite sides of the country. The southwest monsoon hits the Andaman first, in May. The northeast monsoon hits the Gulf, in November.
So: from November to April, go west, because the Andaman, Phuket, Krabi, the Phi Phis, Koh Lanta and Khao Lak are dry. From May to October, go east, because Koh Samui, Koh Phangan, Koh Tao, Hua Hin and the Gulf islands are dry. And the central plain and the north are in between and have a monsoon that is afternoon rain rather than a washout.
This single rule answers most of the practical questions people arrive with, including the ones about which islands are open in which month.
The north, and what "cold" actually means
Chiang Mai sits at about 300 metres and the Doi mountains around it go to 1,800. In December and January the nights in the city genuinely drop to 15 to 18 degrees, and up at Doi Suthep and above it goes to single figures, and the mountains around Mae Hong Son in the far north will see frost.
This is a real winter and it is the reason the north is at its best then. It is also 20 degrees colder than Bangkok at the same moment, which trips people up constantly: they pack for a tropical country and arrive needing a jacket.
The cold season in the north is also when the air is at its clearest, because the burning season has not started. Doi Suthep from the old city on a clear December day is one of the best views in the country and you are a large majority of the way there from Bangkok by train.
Songkran, and why it is both the best and the worst time
Mid-April is the middle of the hottest period and it is also the Thai new year and the water festival. The temperatures in the north at that point routinely hit 38 to 40 degrees, and the water is the answer to that rather than an arbitrary tradition.
Songkran is the single most alive week in the country and it is also the single most physically demanding week in the country. The city becomes a water fight, the streets are unusable, and the whole country stops for three days.
For most people the right answer is: do not be in Chiang Mai for Songkran, and instead visit a week either side when you get the festival atmosphere, the flower offerings, the decorated temples, and none of the water.
Month by month, the honest version
November. The monsoon has just broken in the Gulf, so the Gulf and the south are still wet and the Andaman is starting to dry. Good for the north, excellent for the Andaman, bad for Koh Samui and Phangan. Prices are at their annual low in most places. October and November are the best-value months in the country.
December. The best month in the Andaman and the Gulf both start to be good. The Gulf's rain tapers off through the month. North is beautiful and cool. This is the month most people are aiming at and the month you should book three to four months early for the good islands.
January. Peak. Dry everywhere, cool in the north, the Gulf is genuinely good from the second half. The highest prices and the fullest planes of the year. If you want the Andaman islands, this is the month to go and it is the month to book for in July.
February. Excellent, and the end of the peak. The last dry month, hot in the south by now, still perfect in the north, and the prices start falling in the second half. February is my favourite month in the Andaman for a specific reason, which is the burning season has not started so the air is clear but the haze from the following month has not arrived.
March. Genuinely hot, 32 to 36 in most of the country, and the north starts to see the first crop burning. Still dry, still very good on the Gulf, and the last reliably dry month in the Andaman before the monsoon in May.
April. The hottest month. Songkran is in it. In the north it is 40 degrees and the air is starting to haze. The Gulf is still good. This is the month to be in the Gulf or on a beach and the month to be anywhere else in the country is a mistake.
What to pack, in a short list
November to February, north: a real jacket. A light waterproof or packable down. Not a coat, but you will want it at 6am on a mountain and at 9pm in the old city.
December to February, anywhere: a light long-sleeve for the evenings. Tropical countries cool down noticeably after dark and the air conditioning in a taxi is genuinely arctic.
November to April, anywhere: full sun protection. The sun in January at noon is stronger than most people expect and there is a genuine risk of sunburn on a boat with no shade.
Never pack only for the south if you are going north in winter. This is the single most common packing mistake and it happens every single season to people who booked the north in December in a bikini.
Where to go for what
Best winter combination: the north plus the Andaman. Bangkok or Chiang Mai, then fly down to Krabi or Phuket for the islands. It is a classic and it works because the two halves of the country are in their best condition simultaneously from December to February.
Best winter city break: Chiang Mai. Cool, clear, excellent food, cheap, and a genuine sense of a Thai city in a low season that tourists barely experience.
Best beach in February: the Gulf. By February the Andaman is still fine, but the Gulf has had two months of dry and the sea is at its calmest. Koh Samui, Koh Phangan and Hua Hin are the winter beach answer.
Best time for a budget: November and late February. Both are shoulder, both are good, and both are noticeably cheaper than January.
The thing to actually do
Stop planning by country and start planning by month, then pick the coast that month favours. Thailand is big enough and varied enough that "two weeks in Thailand in September" and "two weeks in Thailand in January" are two different countries with different seasons, and the itinerary that works for one of them will be actively wrong for the other.
