YuSMP Travel Editorial Team
The best overall window for Thailand is November to February, when the cool dry season covers most of the country. But Thailand isn't climatically uniform: while Phuket and Krabi are dry and sunny, Koh Samui and Koh Phangan can be getting rain at the very same time — the west and east coasts run on different monsoon cycles. Here's the month-by-month, region-by-region breakdown so you don't accidentally land in a rainy season you weren't expecting. If you're still choosing the destination itself, start with our Thailand overview.
Thailand's three seasons: how it works
Thailand's meteorological department officially splits the year into three seasons. The hot (summer) season runs from mid-February to mid-May — the harshest heat in the country, especially in Bangkok and the inland provinces. The rainy season runs mid-May to mid-October — in 2026 it began on 15 May, with monsoon rains covering nearly the whole country. From mid-October to mid-February comes the cool dry season, also the peak tourist season: the least rainfall, the most comfortable temperatures, calm seas.
Over the year, the countrywide temperature range runs 18-38°C. During the cool season (November-February), cities and the north sit around 15-25°C — the most pleasant stretch for sightseeing, temples and trekking. During the hot season (March-May), Bangkok and the central provinces regularly push past 35°C.
Those are the country-wide boundaries. In practice, southern Thailand splits into two coasts with their own, quite different weather cycles — and that gap is exactly why the "general" dry season doesn't always match what's happening at a specific resort. For a fuller country breakdown, see our complete Thailand guide.
The Andaman coast: Phuket, Krabi, Phi Phi
The west-coast resorts — Phuket, Krabi, the Phi Phi islands — sit under the influence of the southwest monsoon. Their dry season runs November to April, and the best months for beaches and diving are January, February and March: minimal rain, calm seas, the clearest underwater visibility. May through October brings rain to the Andaman coast — though that doesn't mean non-stop downpours: it's usually rain in 30-60 minute bursts, often in the afternoon, with sun the rest of the day.
The shoulder months — October and April-May — are less predictable: the season hasn't fully settled, so you can get sunny stretches and sudden storms alike. If Andaman is your target, plan around November-March, and it's worth reading our dedicated guide — Thailand in winter: where to go and what to know.
What to watch out for on Andaman
At the peak of the rainy season (May-September), some boat and ferry routes to the islands get cancelled because of rough seas — worth factoring in if the trip centres on island-hopping. September is typically one of the wettest months on this coast.
The Gulf of Thailand: Koh Samui, Koh Phangan, Koh Tao — a different monsoon
The Gulf resorts — Koh Samui, Koh Phangan, Koh Tao — sit on the opposite side of the peninsula and run on a different schedule entirely. Their weather is driven not by the southwest monsoon but by the northeast monsoon, which arrives later in the year. So the "peak dry season" for Andaman and for the Gulf are, in effect, two different calendars.
Why Koh Samui gets wet when Phuket is dry
The wettest months on Koh Samui and Koh Phangan are October, November and December, with the peak falling in November specifically: expect prolonged rain and a rougher sea, right as Phuket is deep into its own dry season. The reverse is also true: from June to September, when the Andaman coast is getting soaked, Koh Samui is usually fairly dry — noticeably better than the Gulf's own peak wet months. For a side-by-side comparison, see Phuket or Koh Samui: which to choose, and for the broader monsoon mechanics across the region, Monsoons in Asia: how to pick rain-free months.
The practical takeaway: if your travel dates are fixed, the coast you pick should follow the calendar, not the other way round. Travelling in November? Andaman will almost certainly be more comfortable than the Gulf.
Bangkok and central Thailand
For sightseeing, temples and shopping in Bangkok, November to February is most comfortable: temperatures sit around 24-32°C, with humidity noticeably lower than the rest of the year. From March to May, the capital enters its hot season — daytime temperatures regularly top 35°C, and long walks around the city get much harder to manage. During the rainy season (May-October), central Thailand sees short downpours that usually don't derail plans, though heavy rain occasionally causes local street flooding.
Chiang Mai and the north
In the north, around Chiang Mai, the best window is also November to February: cool, dry, clear skies — great conditions for temples, markets and mountain trekking. The climate here is gentler than Bangkok or the south, though mornings and evenings can get noticeably cooler.
Worth knowing separately: the so-called "burning season" — a few weeks at the tail end of the dry season when agricultural burning in the region and neighbouring countries sends a haze into the air. Exact dates shift year to year, so if your trip is built around views and clean air, it's better to check current air-quality conditions closer to your travel dates than to plan around it in advance.
Table: when to go, by region
When to go, by Thailand region
| Region | Best months | Watch out for | Season type |
|---|---|---|---|
| Phuket / Krabi (Andaman) | January-March | Rain and rough seas May-October, especially September | Southwest monsoon |
| Koh Samui / Phangan (Gulf) | February-August | Peak rain October-December, worst month November | Northeast monsoon |
| Bangkok (central) | November-February | Heat above 35°C March-May, short downpours May-October | General country cycle |
| Chiang Mai (north) | November-February | Burning-season haze at the end of the dry season | General cycle, cooler than the south |
Frequently asked questions
When is the dry season in Thailand?
According to Thailand's meteorological department, the cool dry season runs from mid-October to mid-February, followed by the hot dry season to mid-May. But the Andaman coast and the Gulf don't share the same dry months: Phuket is driest November to April, while Koh Samui is driest from late December to September.
Can I visit Phuket in September?
You can, but it's the peak of the rainy season on the Andaman coast: rain falls nearly every day, the sea gets choppy, and some island ferry routes get cancelled. If your dates are flexible, shift the trip to November-April instead.
What's the weather like on Koh Samui in December?
December is one of the wettest months on Koh Samui and Koh Phangan because of the northeast monsoon: expect downpours and a rougher sea. November is usually the wettest month, and conditions improve noticeably by January.
When is the best time to visit Bangkok?
November through February: temperatures sit around 24-32°C and humidity is lower than the rest of the year. From March to May the city regularly climbs above 35°C.
Should I avoid Thailand during the rainy season?
It shouldn't be a reason to cancel the trip outright: rain in Thailand usually falls in 30-60 minute downpours, not all day. But it's worth factoring in when you pick a region and dates.
If your travel month is fixed but the region isn't, compare options in the destinations catalogue or try our season-based match tool.
Climate figures are long-term averages and vary from year to year. Before you travel, check the current forecast on the official Thailand government tourism portal.
