Thailand's Rainy Season, Region by Region

The typical pattern is a bright, hot morning, clouds building after lunch, then a heavy downpour of an hour or two in the afternoon or evening before it clears again. Even in Bangkok's wettest month, September, rain falls on about 18 days, and most of those are a single storm rather than a washed-out day. Whole days of drizzle do happen, mostly when a tropical storm passes close by in August or September, but they are the exception.

The bigger change is the sky and the air. Bangkok averages 4.2 hours of sunshine a day in August against 7.6 to 7.7 from February to April, and humidity rises to 79% in September against 66% in December. Temperatures barely move, highs in the low 30s °C almost everywhere, so it feels sticky rather than cool. On the coasts the real difference is the sea, which turns rough on the side facing the monsoon.

Yes, if you pick the right coast, and I'd happily go in June or July. You get the greenest landscapes of the year, waterfalls at full flow, rice fields at their brightest, temples and markets without the crowds, and the lowest hotel rates of the year, with September the cheapest month. The trade is an afternoon storm most days, stickier air and less sunshine.

There are two real exceptions. The Andaman islands in August and September are hard work, with rough seas, canceled boat trips and Maya Bay closed until the end of September. And the Koh Chang islands are at their wettest from June to September, when many resorts close or cut back. Outside those two, a rainy-season trip built around Bangkok, the north and a Gulf island works well.

May, June and the first half of July are the easy months, with the rain still building. September is the hard one for most of the country, and if your dates are flexible it's the month I'd skip.

The rule is to follow the dry coast. For most of the rainy season that's the Gulf of Thailand, from Hua Hin and Pattaya to Koh Samui, and late in the year it swings back to the Andaman side.

The two coasts sit under different monsoons, which is why one of them is nearly always the better beach.

The cities handle the rainy season best, because almost everything you'd do in Bangkok works in the morning or indoors. Rain builds from May and peaks in September, with storms most afternoons and an hour or two of flooded streets after the heaviest ones. The BTS and MRT keep running through it, which makes a hotel near a station worth more than usual.

The north is at its prettiest. Chiang Mai has 12 to 17 rain days a month from May to September, wettest in August, and the mountains around it are green, misty and full of waterfalls, with Doi Inthanon and the rice terraces at their best. Trekking trails get muddy and some roads in the hills are slow after heavy rain. October is the north's turning point, and by November it's dry and cool.

Isan and the central plains follow Bangkok's pattern, wettest in September. Ayutthaya's riverside ruins can flood in wet Septembers and Octobers, so check before a day trip late in the season.

Most flooding a traveler sees is street flooding in Bangkok and other cities, ankle to shin deep after a big storm and gone within an hour or two. It's a nuisance rather than a danger, and taxis and buses slow to a crawl while it drains. Serious floods are rarer and usually come late in the season, in September and October, when a tropical storm adds to rivers that are already full.

Bangkok flooded in late September 2026. Three days of rain from 24 to 27 September dropped more than 300 mm on parts of the city in 48 hours, and the city declared all 50 districts disaster zones on 26 September. Both airports stayed open and the BTS and MRT kept running. If your trip falls in a period of heavy rain, check the official advisories and the news before you travel, and give yourself extra time to reach the airport.

The Thai Meteorological Department declared the 2026 rainy season open on May 15, 2026, and forecast total rainfall about 10% below the 30-year average and below 2025, a dry spell from late June to early July outside irrigated areas, the heaviest and most widespread rain in August and September with one or two tropical storms reaching the country, rain ending in upper Thailand around mid-October, and the Gulf coast of the south staying wet through December. In the event, late September brought the Bangkok flood described above. The monsoon usually arrives within a week of the 30-year normal either way, so the table at the top of this page is the better planning tool for 2027.