Updated October 2026
The rainy season in most of Thailand runs from May to October, usually beginning around mid-May and easing around mid-October. The important exception is the southern Gulf coast: Koh Samui, Koh Phangan and Koh Tao have their main wet period later in the year, broadly October to December, with November particularly wet.
A July beach holiday on Samui and a July island-hopping trip around Phuket face different weather patterns. Choose the region before deciding whether the rainy season fits the trip.
Rainy-season dates by destination
Chiang Mai, Chiang Rai and northern Thailand
Expect the wet season roughly from May to October, with heavier rain towards August and September. Rain usually begins to ease as October progresses, although the change does not happen on a fixed date. Northeastern Thailand, including Isan, follows the same broad summer-monsoon pattern.
The hills turn green, but heavy rain on a mountain route can mean poor visibility, slippery paths or a cancelled outing. When choosing places to visit in northern Thailand, leave outdoor excursions movable within the stay.
Bangkok and central Thailand
Bangkok’s rainy season also falls broadly between May and October. September is typically the wettest month, and October can still bring substantial rain; arriving in October does not automatically mean arriving after the wet season.
Keep some room between an outdoor visit and a timed booking. A downpour can make a short walk unpleasant and slow road travel. For a day split between Bangkok’s temples and an indoor attraction, avoid booking both so tightly that the weather leaves no room to swap their order.
Phuket, Krabi, Phi Phi and Koh Lanta: the Andaman coast
The southwest monsoon brings the main wet season to this coast roughly from May to October, with unsettled weather possible around either end. September is often particularly wet. November to April is generally the simpler window for an Andaman beach holiday, though conditions still need checking for individual boat trips.
Sea conditions matter as much as rain on land. A hotel pool can remain usable between showers while a planned island excursion is cancelled because of rough water. A beachfront hotel does not guarantee safe swimming, either: follow the beach flags even when the sky looks clear.
Koh Samui, Koh Phangan and Koh Tao: the southern Gulf
These islands have a different calendar. Their main rainy period comes later, broadly October to December, and November is usually the wettest month. June, July and August are often a more promising beach window here than on the Andaman coast, without being reliably rain-free.
For a July beach holiday, I prefer Samui to Phuket because its heaviest rains usually arrive later in the year. That choice changes in November, when Samui’s main rains can coincide with improving weather around Phuket and Krabi. Koh Phangan and Koh Tao share the broader southern-Gulf pattern, but each boat journey still depends on the conditions at the time.
Koh Chang and the eastern Gulf coast
Do not apply the Samui calendar to every destination beside the Gulf of Thailand. Koh Chang, near Trat, has a wet season broadly from May to October and can receive very heavy rain during the southwest monsoon. It is not a summer-weather substitute for Samui simply because both islands are in the Gulf.
Pattaya and Hua Hin should also be checked as individual destinations, rather than assigned the same weather as Koh Samui. “Gulf coast” is too broad a label for choosing travel dates.
Does it rain all day?
Some days bring a sharp shower followed by dry weather; others stay wet for much longer. Persistent rain and several unsettled days are possible. The familiar promise of “an hour or two in the afternoon, then sunshine” is not a reliable basis for booking a holiday. Morning is not a guaranteed dry slot either.
The opposing coastal calendars come from the monsoons. The southwest monsoon brings moisture to much of Thailand during the middle of the year. Later, the northeast monsoon brings drier weather to much of the mainland but picks up moisture over the Gulf and brings rain to the southeast. The changeover varies from year to year.
A seasonal calendar helps choose the region. A forecast close to the travel date helps decide whether to take the boat, go into the hills or move an outing. A rain symbol on a daily forecast does not tell you how many hours the whole destination will be wet.
Is the rainy season a good time to visit?
For a food-focused wet-season trip, I prefer Chiang Mai as a base to an itinerary built around island excursions. Restaurants and cooking classes give the day a purpose even when a mountain outing falls through. That is a different holiday from travelling mainly to swim, snorkel or spend every afternoon on a beach.
In Bangkok or Chiang Mai, keep an indoor option near the area already on the day’s route: a museum, a cooking class, a massage appointment or a covered place to eat. A shopping centre can also fill a wet interval without a long transfer. Check whether a cooking class includes an outdoor market visit, and do not assume a temple visit is completely sheltered; courtyards and walks between buildings are often exposed.
Some destinations have quieter periods and lower room rates during the rains. Compare the actual dates before treating that as a saving. A discounted island room is less attractive if the activities that prompted the booking cannot run, and a holiday weekend may still be busy.
If beaches and boat trips are the whole reason for travelling, choosing a more suitable coast is worth more than filling the itinerary with rainy-day alternatives. For a mixed trip with food, city sightseeing and a few flexible outdoor days, the wet season can work well.
Book a trip that can survive a cancelled boat
Keep weather-dependent excursions movable where the booking terms allow it. Read what happens if the operator cancels and what happens if you decide not to go; those are not necessarily the same refund conditions. A flexible room rate may also be useful for a route that depends on sea crossings.
Avoid making the final available ferry the only link between an island stay and an important flight. For an international departure, spending the preceding night on the airport side of the sea crossing removes that particular connection risk.
If dates are flexible, November to February often makes a northern, Bangkok or Andaman itinerary easier to plan around rain. It is not a universal dry-season recommendation: November can be exactly the wrong choice for a Samui beach trip. The broader best-time-to-visit guide helps compare the rest of the calendar.
When rain changes the plan
Check the current weather warnings as well as the local forecast before a boat trip or an outing into the hills. Confirm that the operator is running and that the park or attraction is open. Seasonal closures and storm closures are different, so a general travel calendar cannot settle either question.
Red flags mean stay out of the sea. Follow boat cancellations and park closures. During heavy-rain or flash-flood warnings, leave river swimming, waterfalls and cave outings for another day. Rain upstream can change conditions even when it is dry beside the hotel. Do not walk or ride through floodwater to keep to an itinerary.
What to pack for wet weather
Bring quick-drying clothes, a light rain cover and footwear with grip. Heavy clothing is awkward to dry between outings. Keep the phone, passport and other travel documents in a dry pouch inside the day bag; an outer pocket is a poor place for them during a downpour.
An umbrella is useful for short town walks, while a light rain jacket or poncho leaves both hands free when carrying luggage. Footwear that slips off easily helps with temple visits, but grip matters on wet steps. Keep a dry change of clothes available for the transfer day, and use the rainy-season travel tips for the rest of the practical preparations.