Thailand does not have one rainy season; it has several overlapping ones. The southwest monsoon soaks the Andaman coast from roughly May to October, the northeast monsoon brings the Gulf of Thailand its heaviest rain in roughly October to December, and the north and Bangkok follow a more classic hot, rainy and cool cycle. If you match the region to the month, you can travel in almost any month and still get good weather somewhere. The ranges below are typical patterns as of 2026; any single year can run early or late, so check the Thai Meteorological Department before you commit.
The calendar at a glance
Legend: Best = reliably good conditions; Good = mostly fine with some rain or heat; Mixed = changeable, plan flexibly; Wet = frequent heavy rain or rough seas.
| Month | Bangkok | Chiang Mai and north | Andaman (Phuket, Krabi, Lanta, Lipe) | Gulf (Samui, Phangan, Tao) |
|---|---|---|---|---|
| Jan | Best | Best (cool) | Best | Good (some rain possible early) |
| Feb | Best | Best, some haze late | Best | Best |
| Mar | Good (hot) | Hot, smoky air risk | Best | Best |
| Apr | Hot | Very hot, smoke risk | Good (hot, some storms) | Best |
| May | Hot, rain begins | Hot, rain begins | Mixed (monsoon starts) | Good |
| Jun | Mixed | Green, rainy | Wet | Good |
| Jul | Mixed | Rainy | Wet | Good |
| Aug | Wet | Rainy | Wet | Good |
| Sep | Wet | Wet | Wet (peak) | Mixed |
| Oct | Wet, easing | Easing | Mixed | Wet |
| Nov | Good | Best (cool begins) | Mixed to good | Wet (often the wettest month) |
| Dec | Best | Best | Best | Mixed to good |
This table is a simplification of broad regional patterns. Weather has been less predictable in recent years, and local effects (for example the east coast of the Andaman islands) can differ.
Region by region
Bangkok and the central plains
Bangkok is hot all year, with daily highs commonly in the low-to-mid 30s Celsius. The coolest, driest, most comfortable months are roughly November to February. March to May is the hottest stretch; May to October is the rainy season, with showers typically heavy but short and often in the afternoon. Flooding in some streets can happen during the heaviest rains, particularly in September and October. For city-specific advice see Bangkok best time to visit.
The north: Chiang Mai, Chiang Rai and Pai
The north is a three-season region:
- Cool season (roughly November to February): clear skies, pleasant days and cool mornings; hill areas can be properly cold at night. This is the best and busiest time.
- Hot and smoky (roughly March to May): temperatures climb sharply. Burning of agricultural land and forest fires can produce heavy haze, generally in the dry months before the rains (often worst around late February to April). People with asthma or other breathing conditions should treat this period with caution and check local air-quality indices.
- Rainy (roughly June to October): green countryside, waterfalls at their fullest and fewer tourists, though some rural roads and trails become difficult.
Trip-specific details are in the Chiang Mai hub and the Chiang Mai 3-day plan.
The Andaman coast
This includes Phuket, Krabi, Koh Phi Phi, Koh Lanta, Koh Lipe, Khao Lak and the Similan Islands.
- High season (about November to April): calm seas, clear water, the best visibility for snorkelling and diving, and the highest prices. December to February is the busiest.
- Shoulder (about April-May and late October): hot, with occasional storms, and better value.
- Low season (about May to October): the southwest monsoon brings rain, swell and strong currents. Red flags often fly on west-facing beaches such as Phuket's Kata, Karon and Patong, and swimming can be dangerous. Some islands and national parks close or restrict boats; for example, the Similan Islands national park is generally closed to visitors for part of the low season. Ferry schedules reduce, and some routes to smaller islands may stop. Check the national park authority page for dates each year.
Read Phuket best time to visit for beach-level detail.
Rip currents are a leading danger in the low season. Obey flags and lifeguard signs, and do not swim when a red flag is flying even if the water looks calm.
The Gulf islands: Koh Samui, Koh Phangan and Koh Tao
The Gulf coast sits on a different rhythm. The driest, sunniest period is roughly January to August, with February to April especially reliable and warm. The northeast monsoon brings the heaviest rain roughly October to December, often peaking in November, with rough seas that can disrupt ferries. Mid-year (June to August) tends to be a good time for the Gulf when the Andaman coast is wet, which is why many travellers swap coasts depending on the month. See the Samui, Phangan and Tao ferry guide for crossing conditions.
The eastern seaboard: Pattaya and Koh Chang
Pattaya is accessible all year, and the sea is rarely suitable for clear-water snorkelling anyway. Koh Chang is on the Gulf of Thailand's eastern side with a wetter pattern, so the rainy months of roughly May to October are heavier there than in Samui. See the Koh Chang guide.
Choosing by priority
| If your priority is | Aim for | Consider |
|---|---|---|
| Fewest crowds and lowest prices | May-Oct on the Gulf, or Sep-Oct in the north | Accept showers and flexible plans |
| Best beach weather | Dec-Mar Andaman; Feb-Aug Gulf | Book ahead for peak weeks |
| Hiking and cool air | Nov-Feb in the north | Pack a warm layer for nights |
| Diving visibility | Nov-Apr Andaman; roughly Mar-Sep Gulf | Check park closures |
| Festivals | Songkran in mid-April, Loy Krathong around November, Yi Peng in Chiang Mai | Dates vary; check TAT |
| Budget | Shoulder months | Compare prices on operator sites |
Festivals that affect planning
- Songkran (Thai New Year, 13-15 April): nationwide water fights, many businesses closed for a day or two and transport crowded. Fun, but you will get wet.
- Loy Krathong and Yi Peng: held around the full moon of the twelfth lunar month, usually November. Dates change each year.
- Chinese New Year: local travel peaks, especially in Bangkok and Phuket.
- Christmas and New Year: highest prices and tightest booking across the country.
Sample combinations by month
- December to February: Bangkok, then Chiang Mai, then Krabi or Phuket. All three are at their best.
- March to April: Bangkok briefly, then straight to the Gulf islands. Avoid the north for smoke.
- June to August: Bangkok, then Samui, Phangan and Tao, skipping the Andaman coast.
- September to October: central Thailand and the north, which are wet but green, with shorter days at the beach.
- November: the north and the Andaman coast shoulder; avoid the Gulf islands.
See which Thai island for beach choices and Thailand 2-week itinerary for routing. The Thailand hub has the full list of destination guides.
FAQ
What is the best month to visit Thailand overall?
January and February are the safest picks for a mixed trip: they are comfortable in Bangkok and the north and good on both coasts. They are also busy and relatively expensive.
Is it worth visiting Thailand in the rainy season?
Yes, for the right region. Rain often arrives as short, heavy bursts, and prices drop. The Gulf islands are a sensible choice during the Andaman monsoon. Keep flexible plans, as heavy rain can disrupt boats and mountain roads.
When is Phuket's sea too rough for swimming?
Typically from roughly May to October on west-facing beaches. Follow red flags and lifeguard advice, since conditions can change within a day.
Does it rain all day in the monsoon?
Usually not. Most days have sunshine and cloud with downpours, though multi-day storms do happen, especially in September on the Andaman coast and in November on the Gulf.
When is the smoky season in Chiang Mai?
Generally in the dry, hot months before the rains, often most severe from late February to April. Check an air-quality app and the Thai Meteorological Department notices before you plan a northern trip in that window.
Official sources and further reading
Prices, schedules and entry rules change. Figures here are approximate as of 2026; always confirm on the official or operator page before you book. Spotted something out of date? Tell us.
