Without a doubt, June is a wet, rainy month just about everywhere in the country. The heaviest rainfall occurs on the western side of the Kra Isthmus along the Andaman coast where Phuket sees about 19 rainy days per month. The eastern side by Koh Samui is slightly drier with an average of 17 days of rain. The northern part of the country is wet too, although not as intensely so as in July and August. Chiang Mai gets rain about half of the days, and Bangkok slightly less.
The temperatures are hot and humid with high-low averages ranging from 77 to 90 degrees Fahrenheit. The rainfall comes in short spurts, mostly in the afternoons and evenings. The rest of the time it's dry and you might not know it's the wet season. Just keep in mind that if you come on a week with especially heavy rainfall, it can sometimes wash out roads, especially in the south near Phuket. Storms are often accompanied by thunder and lightning, occasionally flooding areas and causing evacuations. Be sure to keep an eye on the weather to stay safe.
The upshot to the rain is that it brings an end to the smoky season (from March to May) which clears up the air as farmers stop burning sugar fields. The sky isn't as hazy and the smog doesn't seem as bad. Overall, there's less need for pollution masks this time of year.
Crowds and Costs
A major silver lining to the rainy afternoons in June is that it's both cheaper and less crowded. Due to the weather, hotels often run off-season rates that are half the price you pay in January or February. Although food and drinks are generally comparable, you can often find deals on tours and activities, too. Plus, the group sizes are much smaller. The tourist sites have fewer people and there aren't hordes of people crowding the beach resorts. Additionally, you don't have to book things as far in advance.
Where to Go
Perhaps surprisingly, Bangkok is one of the driest parts of the country in June. It gets fewer rainy days total (about 12 on average) and the storms it does get are mostly confined to the late afternoons and early evenings. Plus, most of the attractions in Bangkok are indoors anyway, so the rain is less of an inconvenience than in places like Chiang Rai or Pai where you might want to take a hike or visit an elephant sanctuary. The excitement is mainly urban so things like museums, art galleries, and restaurants aren't affected.
It's not a terrible time to head north either, you just need a good rain coat. Pai Canyon is gorgeous this time of year and, as long as you mentally prepare for some rain showers, it's a spectacular time to explore the mountains. When venturing out, just keep an eye out for places to take shelter, if needed. Also keep in mind that up north the weather is extra hot so make sure your ponchos and rain gear are lightweight and non-insulated.
The beaches along the Gulf of Thailand can be amazing this time of year, too. Although you'll unquestionably encounter some degree of rain, it won't happen all the time and when the sun is indeed out, the beaches will be less crowded. You can stay in the luxury hotels for a fraction of the price and you won't be fighting lines at the poolside bars. Just stay off the west coast as much as possible—Phuket gets more rain so your chances of nice weather will be higher on the east side.
What to Do
In Bangkok, check out places like the Grand Palace where you can learn about the history of the royal court and see where Siam kings lived in the 18th century lived, as well as where the Thai royalty called home up to 1925. At Wat Pho (also known as the "Temple of the Reclining Buddha,") observe the 150-foot-long gilded Buddha who symbolizes his entrance into Nirvana. Another idea is to stroll through some of the trendy neighborhoods like Sathorn or Thonglor where you can sample the food and nightlife scene.
In Chiang Mai, take a cooking class or check out the Elephant Valley Thailand sanctuary in Chiang Rai. The latter is a wildlife refuge that rescues elephants and rehabilitates them, using tourist dollars to help conservation efforts. Farther northwest near the border with Myanmar, the stunning Pai Canyon offers incredible hiking opportunities, as well as natural wonders like the Pam Bok Waterfall.
Down south in Koh Samui, the breaks of sunshine will offer perfect conditions for snorkeling, swimming, or sea kayaking through lush mangroves (which will be extra green this time of year). Have a massage at one of the day spas or check out the pristine Angthong Marine Park.
Events in June
Phi Ta Khon Ghost Festival: In the town of Loei in the northeastern region of Isan, villagers gather every year for the Phi Ta Khon Ghost Festival which celebrates a time when people presumed the Buddha dead after a long journey, only to celebrate when he eventually returned. During the festival, locals don masks and wigs, dressing in scary costumes and playing music to wake up the spirit of the Mun River for protection.
Hua Hin International Jazz Festival: Every June, the seaside resort town of Hua Hin, which is just three hours south of Bangkok, draws more than a hundred jazz artists from around the world to play smooth jazz by the beautiful ocean backdrop.
Traveling to Thailand in June? Check out this great itinerary
Family Adventure in Chiang Mai – 7 Days. This seven-day exploration of Chiang Mai is great for June vacations because, unlike many Thailand tours, it doesn't include a portion in Phuket which can be rainy and unpleasant this time of year. Instead, it takes you through northern wonders including hiking on Doi Suthep Mountain, kayaking in Si Lanna National Park, and biking through the Baan Tawai craft village.