Thailand has a tropical climate with a distinct monsoon season, which means that whatever time of year you visit, it’s going to be warm and humid and might be wet. There are three seasons in Thailand -- cool season between November and February, hot season between March and May and rainy (monsoon) season between June and October. Heat, humidity and rainfall vary significantly depending on where you’re traveling and what time of year you come.
Chiang Mai and the rest of the northern region of Thailand enjoy cooler, milder weather throughout the year. During the cool season, average highs are in the low 80s (Fahrenheit) but average lows will dip down into the 60s and even lower up in the mountains, making it the only region in Thailand where you’ll ever need a sweater outside!
Hot season temperatures can easily hit mid-90s or higher during the day. The weather won’t cool off much at night, either, although higher elevations in some areas make it more bearable than in the rest of the country.
The rainy season sees less rain than other parts of the country, but monsoon storms can still be dramatic and intense, especially during September, the rainiest month of the year.
Bangkok and Central Thailand
Bangkok's three seasons all share one thing in common – heat. In fact, the coldest temperature ever recorded in Bangkok was 50 degrees, and that was back in 1951. Cool season temperatures are generally in the 70s and 80s so it’s no surprise it’s such a popular time to visit.
During the hot season, expect highs in the 80s and 90s, with some days in the 100s. If you’re visiting Bangkok during hot season, make sure to plan around the weather. The heat makes it difficult to walk around outside for too long.
For most of the rainy season temperatures cool off by a few degrees and storms only last an hour or two before passing, making it a good time visit if you want to avoid crowds and don’t mind getting a little wet.
The weather in Southern Thailand follows a slightly different pattern than the rest of the country. There’s really no cool season, as temperatures only vary by about 10 degrees between the hottest and coldest months of the year.
Rainy season happens at a different time depending on whether you’re on the west side of the peninsula or the east side. If you’re on the west, where Phuket and other Andaman Coast destinations are, the rainy season starts a little earlier, in April, and lasts through October. If you’re on the east, where Koh Samui and the other Gulf Coast destinations are, most of the rainfall happens between October and January.