Thailand Weather by Month

Thailand's rainy season runs from mid-May to October across Bangkok, the north, Isan and the Andaman coast (Phuket, Krabi, Koh Lanta), with the first storms in late April and the heaviest rain in August and September. The Meteorological Department declares the start each year once the southwest monsoon establishes itself, usually in the third week of May. Bangkok records 336 mm in September against 12 mm in December; Phuket 350 mm against 24 mm in February; Chiang Mai peaks earlier, at 223 mm in August. The Gulf islands run on a different clock. Koh Samui, Koh Phangan and Koh Tao stay mostly dry through the southwest monsoon (100–135 mm a month from June to September) and take their rain from October to early December, with 445 mm in November.

Rainy season rarely means all-day rain. The pattern is a bright morning, a heavy downpour of one to two hours in the afternoon or evening, then clearing skies, which is why the wet months still work for city and temple trips. The practical costs are rougher seas (Andaman ferries face cancellations in August–September, and Maya Bay closes for August and September), higher humidity (Bangkok 79% in September against 66% in December), and occasional street flooding in Bangkok. The rewards are 30–50% lower prices, thin crowds and the greenest landscapes of the year. I'd take that trade.

January is the best all-round weather month of the Thai year. Bangkok averages a 33°C high with 24 mm of rain over two days, Phuket and the Andaman coast are dry (50 mm) with calm, clear seas, Chiang Mai has warm 30°C days and genuinely cool 16°C nights, Hua Hin and Pattaya are dry at 30–31°C, and Isan wakes to 18°C mornings under cloudless skies. Even Koh Samui, fresh out of its short wet season, is drying fast (127 mm on eight days). Humidity is at its annual low, which makes temple days and city walking dramatically more pleasant.

The catch is that everyone knows it. January is peak season, with peak-season prices (hotels 30–50% above low season) and peak crowds at the headline sights. Book accommodation 2–3 months ahead, especially for the islands over the New Year window.

The Thailand in January guide breaks the month down region by region, with where to go, events and what to pack.

February matches January's dry, sunny formula, with Bangkok at 34°C with 21 mm, Phuket 34°C in its driest month of the year (24 mm) with flat seas, Samui fully dry at 29°C (64 mm, its driest month too), Hua Hin's driest month at 14 mm, and Koh Chang dry at 32°C. Crowds ease slightly after the New Year rush. It's arguably the single best month for an islands-focused trip. Both coasts are swimmable, dive visibility on the Andaman side peaks, and ferry schedules run at full capacity.

One regional caveat begins now, northern Thailand's burning season. By late February, agricultural fires start degrading Chiang Mai's air quality, usually still moderate this month but trending worse, and the north's humidity falls to 58%, the driest air of the year. If the north is the heart of your trip, January is safer. If you go in February, I'd keep plans flexible and check AQI forecasts.

The Thailand in February guide breaks the month down region by region, with where to go, events and what to pack.

March is the last fully dry month on both coasts. Phuket holds at 34°C with good seas, Samui at 30°C, Pattaya and Hua Hin at 32°C, but the heat is building fast. Bangkok hits 35°C with rising humidity, and afternoons reward pool time over sidewalk. Beach trips are still excellent. City sightseeing starts demanding early starts and air-conditioned retreats.

The north is the month's real problem. Burning season peaks in March, and Chiang Mai's AQI regularly exceeds 150 (sometimes 300+), hazardous territory that cancels the mountain views entirely. I'd skip Chiang Mai, Pai and Chiang Rai in March, and Isan is little better, with Khon Kaen at 35°C under the same haze. Chiang Mai reaches 35°C with 8.6 hours of sun a day and 54% humidity, and it's the single worst month of the northern year.

The Thailand in March guide breaks the month down region by region, with where to go, events and what to pack.

April is Thailand's hottest month. Bangkok's average high is 36°C and 40°C days are normal, Chiang Mai bakes at 37°C and Khon Kaen at 36°C under burning-season haze, and even the islands run hot, though sea breezes keep Phuket (34°C) and Samui (32°C) livable, and the Gulf coast stays dry (83 mm on Samui, 47 mm in Hua Hin). Pre-monsoon storms start on the Andaman coast (135 mm in Phuket) and on Koh Chang (196 mm). This is resort-and-pool weather, not temple-marathon weather.

April's saving grace is cultural. Songkran, the Thai New Year water festival, runs April 13–15, three days of nationwide water fights that make the heat suddenly make sense. It's a genuine bucket-list experience (Chiang Mai's moat circuit and Bangkok's Silom Road are the epicenters), but book transport and hotels months ahead and expect nothing practical to function during the holiday. See our full Songkran guide for planning detail.

The Thailand in April guide breaks the month down region by region, with where to go, events and what to pack.

May is the turning point, when the southwest monsoon arrives, in 2026 on May 15 by TMD's declaration. Phuket drops to 33°C with 237 mm, building afternoon storms and choppier seas, Bangkok's first real rains (217 mm) break the April heat, Koh Chang tips into its wet season at 420 mm, and Chiang Mai's showers (168 mm) clear the burning-season haze. The north becomes beautiful and breathable again. The Gulf coast barely notices, and Samui stays mostly dry at 33°C (132 mm), Hua Hin gets 96 mm and Pattaya 121 mm.

For travelers, May is the value play, because flights and hotels drop 30–50% from peak, crowds thin dramatically, and the rain is still mostly short afternoon downpours rather than washouts. My advice is to aim the beach leg at the Gulf coast or Hua Hin, keep Andaman plans flexible, and enjoy having the temples closer to yourself.

The Thailand in May guide breaks the month down region by region, with where to go, events and what to pack.

June settles into the monsoon rhythm. Phuket and the Andaman coast see regular rain (249 mm on 16 days, 33°C) with rough seas curbing boat trips, Bangkok gets brief daily showers (198 mm) around a still-hot 34°C, Isan turns green (146 mm), and Chiang Mai is lush with rainfall you can work around (118 mm on 12 days, its lightest monsoon month). Koh Samui, sitting in its rain shadow, delivers the country's best June beaches, with sunny spells, warm seas and 33°C days on 134 mm. Hua Hin (82 mm) and Pattaya (132 mm) are the mainland alternatives. The one coast to avoid is the eastern seaboard, where Trat, the station facing Koh Chang, averages 777 mm on 23 days.

June is also when European summer crowds start arriving on the Gulf islands, so Samui and Phangan prices firm up even as the rest of the country discounts. Book Gulf accommodation a month or two out. Everywhere else, you can be spontaneous.

The Thailand in June guide breaks the month down region by region, with where to go, events and what to pack.

July continues June's split. The Gulf trio (Samui, Phangan, Tao) enjoys its sunniest stretch, 32°C and 117 mm on 11 days with calm seas, while the Andaman side stays wet and rough (240 mm), Bangkok alternates hot sun with afternoon downpours (190 mm), and Chiang Mai is green, misty and quietly lovely between showers (149 mm), with waterfalls at full flow. Hua Hin (90 mm) is the driest coast in the country this month. Koh Chang has its wettest, and Trat averages 1,024 mm in July, more than Bangkok gets in six months.

If your dates are fixed to July (school holidays), the itinerary writes itself, Bangkok → Chiang Mai → Gulf islands, skipping the Andaman coast and Koh Chang entirely. It's also Full Moon Party high season on Koh Phangan, so book that week early.

The Thailand in July guide breaks the month down region by region, with where to go, events and what to pack.

August is deep monsoon on the Andaman coast. Phuket's wettest stretch begins (309 mm on 17 days), seas turn genuinely rough, island ferries face cancellations, and Maya Bay closes for its annual August–September ecological recovery. Chiang Mai has its wettest month (223 mm on 17 days), Isan is close behind (222 mm), Koh Chang is still under 970 mm, and Bangkok is rainy but functional (33°C, 227 mm as afternoon storms).

The Gulf islands remain the honorable exception. Samui and Phangan average decent sun at 32°C on 102 mm, their driest monsoon month, and Hua Hin's 67 mm is the driest of any coast. August works, but only if you build it around the Gulf coast and keep mainland plans city-focused. My advice is to take it, because it's the last month before Bangkok and the Andaman tip into their wettest weeks.

The Thailand in August guide breaks the month down region by region, with where to go, events and what to pack.

September is the wettest month of the year in Bangkok, on the Andaman coast and in Isan. Bangkok floods its sois in afternoon deluges (336 mm on 18 days, 33°C), Phuket sees its heaviest rain and roughest seas (350 mm on 19 days), Khon Kaen peaks at 246 mm, and even the Gulf's rain shadow starts leaking, with Samui at 118 mm and Hua Hin at 130 mm. Chiang Mai is past its August peak but still wet (207 mm), and Koh Chang stays under 816 mm. Maya Bay stays closed all month.

If September is your only window, it's still workable. Prices are the year's lowest, crowds vanish, and rain mostly falls in intense 1–2 hour bursts rather than all day. Base the trip on Bangkok, the central plains (Ayutthaya, Kanchanaburi) and Koh Samui, buy travel insurance that covers ferry cancellations, and treat any Andaman plans as a bonus rather than the backbone. That's my advice, anyway.

The Thailand in September guide breaks the month down region by region, with where to go, events and what to pack.

October is transition month, when the monsoon retreats northward, so Chiang Mai clears first (32°C, 124 mm, lush post-rain landscapes, and October's end is gorgeous), Isan dries out (102 mm), Bangkok's storms taper through the month (289 mm, mostly in the first half), and Phuket steadily improves (336 mm on paper, but the last week is often fine). Late October on the Andaman coast can be excellent, with pre-season prices. The Gulf swings the other way, since October opens Samui's short wet season (295 mm), which runs through early December, and it is the wettest month of the year in both Hua Hin (250 mm) and Pattaya (225 mm).

It's a savvy traveler's month, with near-peak northern scenery and drying Andaman beaches at shoulder-season rates. The Vegetarian Festival (usually early October, biggest in Phuket) adds one of Thailand's most theatrical cultural spectacles. My advice is to aim beach time west, not east.

The Thailand in October guide breaks the month down region by region, with where to go, events and what to pack.

November is the sweet spot. The rains have just ended across Bangkok (33°C, 45 mm), Isan (22 mm), the Andaman coast (32°C, 178 mm and falling, seas calming, full ferry schedules resuming), and especially the north. Chiang Mai at 31°C with 20°C nights, clean air and landscapes still green from the monsoon is arguably Thailand at its absolute best. Koh Chang reopens (85 mm). Prices sit just below December's peak, and crowds are still building rather than built.

The one exception is Koh Samui and the Gulf islands, now in their wettest weeks. November is Samui's rainiest month at 445 mm on 16 days, the heaviest monthly total at any station on this page except Trat in summer. If November is your window, this is the year's clearest coast call. Go Andaman. As a bonus, the Yi Peng lantern festival and Loy Krathong (November full moon) make Chiang Mai magical, and booked out, so reserve early.

The Thailand in November guide breaks the month down region by region, with where to go, events and what to pack.

December delivers the postcard. Bangkok sits at a relatively gentle 32°C with 12 mm of rain and the year's lowest humidity, Phuket dry with glassy seas (82 mm), Hua Hin, Pattaya and Koh Chang at their driest (12–28 mm), and Chiang Mai at its coolest, 29°C days and 17°C nights, perfect trekking weather. Isan is the same story, with 30°C days, 18°C nights and 5 mm of rain. Koh Samui spends early December finishing its wet season (263 mm) and usually clears by mid-month, just in time for the holidays.

It's also the most expensive, most crowded month, and the two weeks over Christmas and New Year are the single priciest window of the Thai year. Island hotels enforce minimum stays and 'compulsory gala dinners'. Book 3+ months ahead for the holidays, or aim for the first half of December, which offers nearly identical weather at noticeably kinder rates. That's what I'd do.

The Thailand in December guide breaks the month down region by region, with where to go, events and what to pack.