Thailand only has three seasons…damn hot, not so hot and humid (sometimes torrential). The wet period of the year is variously referred to as the rainy season, the green season, or the monsoon season in Thailand. While some view the sometimes heavy rain as a disturbance, others embrace the annual downpours and enjoy the break from the warm weather. It depends if you ride a motorcycle without a raincoat when it starts!
Unlike much of the rest of the world, north and south of the equatorial regions with four reliable seasons of winter, spring, summer and autumn, Thailand has only three types of weather driven by a annual monsoon that sweeps across the northeast Indian Ocean. in the land mass of Southeast Asia. Besides the pressure systems descending from China, the tropical monsoon is the dominant feature of the Thai climate.
It should also be noted that in the far north of Thailand there is also a noticeable, but short, cold season. During this season, morning temperatures can drop to 10 degrees Celsius. Mountain areas even have frosts.
What caused the monsoon season in Thailand
The Thai monsoon season is caused by the southwest monsoon which escapes from the Indian Ocean with moist air heading northeast across Thailand from the Andaman Sea and being sucked into the void left by rising warm air over the Southeast Asian landmass. The monsoon also coincides with Thailand’s location in Southeast Asia’s tropical rain belt, the Intertropical Convergence Zone.
The timing of the Thai rainy season is not the same across the country and is not exactly the same each year, although it is reliably consistent. Chiang Mai does not have the same rainy season as the islands in the Gulf of Thailand. Koh Samui’s rainy season is a month after the islands on the other side of the Malay Peninsula (the Isthmus of Kra). The wettest months in Phuket are September and October. Koh Samui has its biggest rains and storms 2 months later.
The annual celebration of Songkran, the Thai New Year on April 13, is usually timed to coincide with both the end of the hot season and the start of the annual rainy season. The center of the festival revolves around “water”, traditionally the gentle washing of Buddha images and the hands of the elderly. It’s become something of an all-out water fight since then in tourist areas, but the symbolism of water remains the focus. In most provinces, the onset of the monsoon is usually about a month later after Songkran.
Some places can be much wetter than others. Ranong in southern Thailand, just north of Phuket facing the Andaman Sea, is the wettest province in the country with a rainy season that runs from April to November. But the resort town of Hua Hin on the Gulf of Thailand only really experiences two particularly rainy months, September and October.
Rain during monsoon is more of a relief than a hassle
The strength and intensity of the rains vary considerably. But, in general, monsoon rains tend to be short, intense bursts of rain. They could last a few hours in the middle of the day. However, they could just as well be finished in about 15 minutes in the morning or evening. But torrential rains are always accompanied by warm temperatures. That’s why it can be more of a relief than a hassle.
Then again there are always the people who have to move from place to place during a rain storm and there are thousands of photos of people negotiating a Thai rain storm, knee deep in the rain monsoon. The monsoons do little to stop locals who are used to plugging in, despite occasional downpours and flooding.
Help is never too far away with the ubiquitous 29-baht ‘poncho’ available at any 7-Eleven or Family Mart. Weakened and available in a variety of old-fashioned colors, they’ll keep at least part of your body dry if you get caught in a downpour. If you find yourself in Thailand during the rainy season, we recommend keeping one in your bag as the rain can start anywhere, anytime, but it will always dissipate quickly.
Flooding is common during the monsoon season in Thailand
It is very easily flooded in Thailand, as the intensity and suddenness of the monsoon rains are important. Bangkokians will be content to roll up their pants or hold up their skirts, kick off their shoes, and wade through the floodwaters. It’s part of life when you live in Thailand. Every year, millions of baht are spent to improve drainage and prevent flooding everywhere, but nothing seems to improve the situation.
The best thing about the monsoon season in Thailand is that the rains are never freezing and usually provide a pleasant respite from the heat. There is also poetic drama and the beauty of the Thai monsoons as we enjoy and celebrate the annual rains which provide water for crops and fill dams.
Bangkok and Central Provinces
The Thai capital can usually schedule the start of the rainy season from June or early July, peaking in September and starting to dry out in September and October.
The rains could start with unexpected storms with some notable overnight discharges, before changing to more regular almost daily rains in July and August. It will not necessarily rain every day and very rarely all day. But sometimes it’s torrential. Bangkok, although built to cope with heavy rains, has closed many canals and natural means of escape have been blocked over the years.
Bangkok also sinks, slowly, so there are frequent floods in some lower coastal communities when a high tide and torrential downpour coincide.
Chiang Mai and Northern Thailand
The northern capital, Chiang Mai, is mostly flat within the city and surrounded by hills. It attracts many tourists and travelers all year round, regardless of the weather. Chiang Mai is also the starting point for visiting Pai, Mae Hong Son, Lampang and Chiang Rai.
The monsoon season lasts longer in the North than in Bangkok. It usually starts around May and continues until November. July and August are particularly wet.
As tourism plunges, regardless of the rains, there will be occasional disruptions to some of the outdoor activities during the peaks of the northern rainy season. The northern regions of Thailand have noticeably cooler weather during the dry season – from December to the end of February. During this season, there is even a morning frost in the mountains of the region.
The northeastern provinces (called Isaan) are further away from the Indian Ocean. Therefore, the monsoon has lost some of its power by the time it reaches this region. The rainy season would extend from May to October but 80% of the rains generally fall in August and September.
The region’s northern and eastern borders are the mighty Mekong River which depends on a decent annual rainfall. In recent years, the Mekong has recorded lower levels. This is due to changes in rainy season rainfall and the construction of dams upstream in Laos and China.
East of Thailand
Koh Chang and the other islands off Trat Province are beautiful and mostly unspoiled by mass tourism. However, they can be very humid during the monsoon season which generally runs from late May to late October. In June, July and August it is likely to rain at some point just about every day.
The moist air was sucked in from the Indian Ocean, passed through Thailand’s thin southern peninsula, then replenished as it passed over the Gulf of Thailand.
Storms and choppy offshore waters mean diving and snorkeling can be limited. But the islands will be much calmer and prices lower during the rainy season.
Phuket, Krabi and the Andaman Coast
Gorgeous beaches, tropical life and beautiful islands. Once upon a time, this region had a distinct high and low tourist season. However, changes in international tourist mixes have made many Andaman Sea destinations busy all year round, rain or shine. Phuket, Krabi, Koh Lanta, Khao Lak, Koh Phi Phi are just some of the popular destinations in this postcard region.
It will usually start raining from mid-April through October and November. September and October are the wettest. And when it rains, it rains. Strong southwesterly winds generally make west-facing beaches unsuitable for swimming for the duration of the monsoon. Many tourists drown off these shores every year, so take the red flags and warnings from lifeguards seriously.
Some of the smaller islands and dive sites are closed during the monsoon season in Thailand.
Koh Samui and the Gulf Islands
Koh Samui, Koh Phangan and Koh Tao in the Gulf of Thailand are a popular triad of islands off Surat Thani. These islands have their own annual weather patterns.
The monsoon season does not hit Koh Samui until later in the year. The rains generally arrive from October to December, with peaks in November and tapering off at the start of the new year. But, like the Andaman Coast destinations, it remains hot and mostly humid throughout the year.
And it gets wet. Here’s what you can do to cope Thailand humidity.