Thailand’s two coasts have opposite seasons. Here is how to plan around it
Almost every difficult conversation we have about Thailand comes down to one fact that nobody puts on the front page of a brochure. Thailand has two coasts, they face different oceans, and they are on opposite weather calendars. When one is at its best, the other is usually not.
Get that right and Thailand works in almost any month of the year, which is genuinely unusual in Asia. Get it wrong and you spend a fortnight looking at a red flag on an empty beach, having paid high-season rates for the privilege.
The two calendars, in one table
| Andaman coast, west | Gulf coast, east | |
|---|---|---|
| Where | Phuket, Krabi, Koh Lanta, Koh Yao, Khao Lak, the Similans | Koh Samui, Koh Phangan, Koh Tao |
| Best months | November to March, and April is still good | February to September, with June to August very reliable |
| Worst months | May to October, worst in September and October | November and December, with November the wettest |
| The failure mode | Sea state. Red flags, suspended ferries, closed dive sites | A concentrated wet block at the end of the year, plus rough crossings |
There is also a third pattern, which catches people out. The eastern Gulf islands, Koh Chang and Koh Kood, near the Cambodian border, run on their own calendar again: best from November to April, wet in the middle of the year. So Thailand really has three beach seasons, not two.
Why this happens
The southwest monsoon arrives from the Indian Ocean around May and blows straight at the Andaman coast until October. It hits the west first and hardest.
The Gulf of Thailand sits in the lee of the peninsula, so it stays relatively dry through those same months. Its own wet period comes later, driven by the northeast monsoon at the end of the year, and it is short and intense: November is the wettest month on Samui by a wide margin, with December still unsettled.
The practical version: the peninsula acts as a wall, and each coast gets its weather from a different direction at a different time of year.
What this means month by month
November to February. The Andaman is at its best and so is most of the country. This is the high season and it is priced accordingly, particularly around the turn of the year. The Gulf is at its worst in November, improving through December, and reliable again by February. If you have these months, go west.
March and April. Still very good on the Andaman, hot and getting hotter, with April the hottest month of the year nationally and often above 95°F (35°C). The Gulf has come good. Both coasts work. April also carries Songkran, the Thai new year water festival, which is either the reason you are going or a thing to plan around, and it needs booking far in advance either way.
May to August. The Andaman is into its monsoon. The Gulf is at its best, and this is the answer that saves the summer holiday. A family locked to July is not choosing between Thailand and somewhere else, they are choosing Koh Samui rather than Krabi. Rates on Samui in June and July are also noticeably below the December peak.
September and October. The hardest weeks in the country. The Andaman is at the bottom of its year and the Gulf has not yet reached its wet block but is not at its best either. This is when we most often suggest a route built around the north and the interior rather than a beach, or a different country.
The mistake people actually make
It is rarely “we went to the wrong coast”. It is subtler than that. It is booking a two-week Thailand trip in July, spending the first week in Bangkok and Chiang Mai, and then adding Krabi at the end because Krabi is the place everyone has heard of. That last week is the holiday, and in July it is red flags and a ferry that does not run.
The fix costs nothing. Same trip, same dates, same budget, Koh Samui instead of Krabi. We do this reshuffle several times a month, and it is the single highest-value change we make to a Thailand itinerary.
The honest bit about the Andaman monsoon
We are not going to tell you the Andaman is impossible in the wet season, because it is not. Rain there in June is often a heavy couple of hours and then bright sun, the islands are green, and the rates are half what they are in January. Plenty of people have a very good time.
What we will say is that the sea, not the rain, is what changes the holiday. Swells build, beaches get red-flagged for days at a time, and the small boat transfers that make the Andaman islands what they are get cancelled. The Similan and Surin island national parks close for roughly half the year, generally mid-May to mid-October, which removes the best diving in the country. Long-tail boat trips to Phi Phi and Hong Island become a maybe rather than a plan.
If your Andaman trip is a hotel with a pool and a good spa, the monsoon is a bargain. If it is islands, boats and snorkelling, it is not.
The north is a separate problem, and it is not rain
Chiang Mai, Chiang Rai and the northern hills do not follow either coast. Their rainy season runs roughly June to October and it is manageable: green rice terraces, full waterfalls, fewer people.
The season to avoid in the north is the one nobody warns you about. From roughly late February to mid-April, agricultural burning fills the northern valleys with smoke, and Chiang Mai’s air quality is regularly among the worst of any city in the world during those weeks. The mountains disappear into haze and people with any respiratory sensitivity have a genuinely unpleasant time. It coincides exactly with the best beach weather in the south, which is why so many February and March itineraries pair a wonderful week on the Andaman with a disappointing few days in Chiang Mai.
Our advice: do the north in November, December or January, or from late May onwards. Not in March.
How we build around it
A few working rules from our consulting team.
- Fix the beach week first, then build the rest of the trip around it. The cultural half of a Thailand trip, Bangkok, Ayutthaya, the north, works in most months. The beach half does not. So the beach decides.
- One coast per trip, in most cases. Bangkok to Krabi to Samui in fourteen days is two internal flights and a lot of transfer time for two beaches that are more alike than they are different.
- Two beach stops, not one, if you are on the Andaman in shoulder season. A busy island and a quiet one, so a run of bad sea days does not define the whole week.
- Book the good properties on the working coast early. The problem with July on the Gulf is not weather, it is that the well-run Samui and Koh Tao hotels are finite and everybody who has read this article is aiming at them.
Our complete Thailand guide has the month-by-month detail, and the classic fourteen-day route shows how we sequence a trip that has to work in a specific window.
Plan this trip
Tell us your dates before you settle on an island. Half of what we do on a Thailand file is move the beach week to the coast that is actually working in your fortnight. Free first proposal, no obligation.
Keep reading
- Thailand, planned around which coast is working
- Thailand: the complete guide to planning your trip
- Classic Thailand in 14 days
- Romantic Thailand, 11 days
- Monsoon in Asia: which countries it actually ruins
- How far ahead to book Asia, country by country
Frequently asked questions
Which coast is better, honestly?
Can we do both coasts in one trip?
Is there a month when the whole country is good?
What about typhoons?
Do prices really change that much between the coasts?
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