If you're someone who hates the rain, then May is definitely not the best time to visit Thailand. Chiang Mai averages 15 rainy days while Bangkok gets about 12. And though it rarely rains all day long, when it does come down, it comes down hard.
There's often heavy thunder and lightning that accompanies the rain and during especially intense wet seasons, it can wash out roads, flood cities, and even lead to full-on evacuations. (There have been instances of flash flooding that have killed people so if you choose to go, be sure to check the weather regularly).
In the coastal towns along the Kra Isthmus, the rain is heaviest with 16 rainy days in Koh Samui and about 19 rainy days in Phuket. Throughout all of this, however, the temperatures stay hot, averaging about 77 to 93 degrees, depending on where you are.
Crowds and Costs
The great thing about the rainy season is that there's hardly anybody there. While Bangkok and Chiang Mai always have a certain degree of crowds, the tourism numbers plummet after April, leaving much more room at places like the Grand Palace or Wat Pho. The same holds true for popular tourist draws in the Northern region including Chiang Mai, Chiang Rai, Pai, and Mae Hong So.
Not only that, the prices are cheap, too. Most hotels have completely different rate structures during the rainy season, often cutting prices by half. For these reasons, it can sometimes be worth braving the afternoon showers if you end up with a cheaper, less crowded vacation.
Where to Go
Most of the country battles significant water during the month of May. However, the east coast of the southern peninsula gets shielded from much of the monsoon activity and it's typically much drier there than in other parts of the country.
That doesn't mean it doesn't rain at all—you'll still likely have some wet days. But it's not nearly as frequent or as heavy as across the isthmus in Phuket and Phang-Nga. In fact, some days can be downright sunny and beautiful. Check out islands like Koh Samui or Koh Pha Ngan for the best weather.
Bangkok is another good place to be during the wet season. Most of the attractions are inside anyway and you don't have to worry about washed out roads or other transit issues since the public skytrain will take you almost anywhere. There are tons of great museums, theaters, art galleries, restaurants, and bars, along with world-class shopping and nightlife. Chiang Mai can be OK too, but you need to prepare for rain.
What to Do
If you end up in Koh Samui or other parts of the Gulf of Thailand, you may be surprised to find beautiful, sunny weather in May. It really depends on the season. It will definitely be hot—there's no question about that—so take advantage of the clear mornings by lying on the beach, snorkeling in the water, or lounging by the pool. If the afternoons stay dry too, continue the fun by swimming, sea kayaking, or scuba diving. There's also lots of adventure to be found with activities like surfing and kiteboarding.
In addition to beach-going activities around Koh Samui, May is a great time to take a cruise in the Gulf of Thailand because you can enjoy swimming and suntanning while still having somewhere to hunker down if the rains roll in. Another beautiful spot is the Angthong Marine Park where you can tour the pristine natural beauty.
In Bangkok, soak up the foodie scene in neighborhoods like Thonglor and Sathorn, or check out some of the trendy bars throughout the city. Learn about Thai history at the Grand Palace or discover its religious traditions at Wat Pho (the Temple of the Reclining Buddha).
You can also try indoor activities like the Royal Thai Elephant Museum or Siam Ocean World. If you brave the rains up north, try a cooking class in Chiang Mai, or a trip to the Chiang Mai National Museum. In Chiang Rai, stop by the Hill Tribe Museum or swing by the Mountain Creek Vineyard.
Events in May
Royal Ploughing Ceremony: Meant as a ritual to mark the beginning of the rice-growing season, the Royal Ploughing Ceremony (also known as Wan Phuet Mongkhon or Farmer's Day) is a public holiday in Thailand. The ceremony takes place at Sanam Luang in Bangkok, a public square in front of the Grand Palace that sometimes draws royalty as spectators.
Rocket Festival: In the northeastern part of Thailand, known as Isan, the provinces of Ubon Ratchathani, Yasothon, and Nong Khai participate in a festival involving homemade rockets called bang fai which they fire into the air. The event, which is steeped in Laotian traditions, occurs in May to kick off the wet season. The rockets are meant to encourage rain ahead of the planting season.
Buddha Day ("Visakha Bucha"): This Buddhist celebration, which occurs on the full moon day of the sixth lunar month, honors the birthday of Buddha, as well as his enlightenment. It's a public holiday during which devotees visit temples and attend a procession with flowers, incense sticks, and candles.
Chanthaburi Fruit Day: This colorful festival, which occurs in late May or early June, is a jubilant event celebrating durian and other fruits of the region. Once called the World Durian Festival, today's iteration involves fruit contests and a parade with fruit-decorated floats.
Traveling to Thailand in May? Check out this great itinerary
Ultimate Highlights of Thailand – 10 Days. This is the perfect itinerary for a May trip because it skips Phuket and the Andaman coast in favor of Koh Samui, Bangkok, and Chiang Mai. Highlights include a trip to the beautiful Angthong Marine Park, a visit to the Patara Elephant Farm, and a food and culture tour in Bangkok's historic Bang Rak.