If your flights are already booked, skip to the month-by-month table further down — it's arranged by month rather than by region, which is the order you need it in. If you're still choosing, read the regions first. Most people book the wrong fortnight because they picked a month before they picked a coast.
The short version, by region
If you only read one thing, read this table. It converts "when should I go to Thailand?" into "which part of Thailand am I going to, and when is that part dry?"
| Region | Best months | What to watch |
|---|---|---|
| Bangkok and central | November to February | March to May is genuinely hot. September is usually the wettest month. |
| Andaman coast Phuket, Krabi, Khao Lak, Phi Phi |
November to April | May to October is the wet season. August and September are the wettest. |
| Gulf islands Koh Samui, Koh Phangan, Koh Tao |
February to August | The rain pattern is reversed here. October to December is the wet stretch. |
| Chiang Mai and the north | November to February | Burning season smoke from late February to April. April is the hottest month. |
Bangkok and central Thailand
Bangkok has three seasons and they behave the way the guidebooks say. November through February is the cool dry season: daytime temperatures around 30°C, evenings that are genuinely pleasant, and almost no rain. This is the window to book if you want to walk the city rather than hide from it.
March to May is the hot season. It isn't a dealbreaker, because Bangkok is a city you experience indoors as much as out — malls, museums, markets under cover — but the heat changes what you can do between 11am and 4pm. April is usually the hottest month.
June to October is the wet season, and it is not the washout people fear. Rain tends to arrive in the late afternoon and last an hour or two, then stop. September is the wettest month on average, and it's also when hotel prices soften most. If you're travelling on a budget and can tolerate a wet afternoon, this is the cheapest time to see the city.
The Andaman coast
Phuket, Krabi, Khao Lak, Railay and Phi Phi all sit on the Andaman side, and they share one weather pattern. November to April is the dry season, with the most reliable conditions from December to March. This is when the sea is calm enough for diving and the longtail boat trips to the islands run on schedule.
May to October is the southwest monsoon. Rain is heavier here than in Bangkok and can last for days rather than hours, particularly in August and September. Some smaller islands effectively close, ferry schedules thin out, and dive operators move to the Gulf side.
The shoulder weeks are the value play. Late November and early April often give you dry weather at pre-peak prices, with fewer people on the beaches. If your dates are flexible, aim there rather than at the middle of high season.
The Gulf islands
This is where most guides get it wrong. Koh Samui, Koh Phangan and Koh Tao are on the eastern side of the peninsula and their monsoon arrives at a different time. The wettest stretch is October to December, which is exactly when the Andaman coast is drying out.
February to August is the better window here, with March to May usually the driest and sunniest. If you're planning a trip that combines both coasts, that difference is the single most useful thing on this page: go to the Gulf early in the year and the Andaman in the first half of the year, and you can string together two dry stops in one trip.
One practical consequence: Full Moon Party dates fall on the lunar calendar, so they move through the year. If a specific party is the reason for your trip, check the date before booking flights, not after.
Chiang Mai and the north
The north has a real cool season, which is why people go there in December. November to February brings temperatures that can drop to single digits at night in the mountains, and clear skies for the most part. This is comfortably the best window.
Then comes the part that matters more than temperature: burning season. From late February, agricultural burning and forest fires across the region push PM2.5 particulate levels up, often peaking in March and April. It doesn't just look hazy. It can reach levels where outdoor exercise is genuinely unwise, and it lasts weeks.
If Chiang Mai is on your list, put it in November, December or January. If you're already there in March, check live air quality readings daily and be ready to move. Booking a mountain trek for early April is the single most common north-Thailand planning mistake.
Songkran and dates that change your trip
Songkran, the Thai New Year water festival, runs 13 to 15 April. It is enormous fun and it will disrupt your plans. Roads close for water fights, long distance buses and trains sell out days ahead, some businesses shut entirely, and anything you're carrying is going to get wet. Prices rise around the dates.
Other dates worth knowing: Loy Krathong and Yi Peng in November bring crowds and higher room rates in Chiang Mai. New Year is peak pricing almost everywhere. And Thai public holidays generally mean domestic tourists fill the islands, so a hotel that was cheap on Tuesday can be full on Saturday.
Month by month
The same information as the table above, but arranged by month so you can work backwards from dates you already have.
| Month | Bangkok | Andaman | Gulf | North |
|---|---|---|---|---|
| January | Dry, mild | Best | Drying out | Cool and clear |
| February | Dry, warming | Best | Dry | Warm; smoke starts late month |
| March | Hot | Hot but dry | Driest | Hot; smoke |
| April | Hottest | Hot, drying | Dry | Hottest; smoke; Songkran 13–15 |
| May | Rain begins | Wet season starts | Dry | Rain begins |
| June | Wet | Wet | Mostly dry | Wet |
| July | Wet | Wet | Mostly dry | Wet |
| August | Wet | Wettest | Mostly dry | Wet |
| September | Wettest | Wet | Drying | Wettest |
| October | Wet, easing | Wet | Rain peak | Easing |
| November | Drying, mild | Drying | Rain easing | Cool and clear |
| December | Dry, cool | Best | Rain easing | Cool and clear |
Who this is for, and who should skip it
This is written for someone planning a trip who hasn't locked in dates, or who has and wants to know which coast to point at. If you're choosing between two weeks in February and two weeks in July, it will settle that.
It won't help with live conditions. These are long-run patterns, and any individual year can break them — a November that rains for a week, an August that stays dry. If your trip is close, use the Thai Meteorological Department for forecasts and a live air quality map for the north between February and April. And if someone tells you they know what the weather will do in three months, they don't.
Questions people ask
What is the best month to visit Thailand?
January, if you want one answer. It's the most reliable month nationwide and the north is still clear. It's also peak season, so expect to pay more than in November or February.
What is the cheapest month to visit Thailand?
September and October, generally. Accommodation rates drop during the rainy season, but the Andaman coast is at its wettest and some island services run reduced schedules.
Should I avoid the rainy season?
No. Rain in Thailand is usually short and heavy rather than constant. The two periods worth avoiding are the Gulf islands in October to December and the Andaman coast in August and September.
When is the burning season in Chiang Mai?
Smoke typically builds from late February and peaks in March and April, clearing with the first real rain in May. Check live air quality readings rather than relying on averages.
Can I visit both coasts in one trip?
Yes, and the weather gap makes it worthwhile. Do the Gulf islands between February and August, or the Andaman coast between November and April, and you can cover both without hitting a monsoon.
Sources
- Thai Meteorological Department, seasonal and rainfall records — tmd.go.th, checked 20 October 2026.
- Tourism Authority of Thailand, festival dates — tourismthailand.org, checked 20 October 2026.
- Live air quality for northern Thailand — iqair.com, checked before publication.
Weather patterns are described from long-run averages plus my own trips. Where I haven't been somewhere in a given month, the page says so rather than asserting it.