Thailand's climate is decidedly tropical in nature. With the exception of areas in the far north, Thailand is warm throughout the year. Overall, there are three distinct seasons: a hot season, a hotter season and a rainy season. Weather in the south of Thailand varies considerably less than weather in central areas, and, because of the high elevation, a cool breeze can almost always be found in the northern mountains.

From November through February, rain is less common and temperatures are typically a bit cooler than normal. Consequently, this time of the year is considered to be "high season" for tourism. Expect tourist areas to be more crowded and the prices for travel and accommodation to be considerably more expensive than other times of the year.

March through June are typically the hottest months of the year in Thailand, with temperatures as high as 40°C not being out of ordinary. Be sure to bring plenty of sunblock, as the sun can be unforgiving during this time of the year.

Thailand's monsoon season, also known as rainy season, lasts from July through October, typically peaking in September. In recent years, partly to boost tourism, rainy season has begun to be referred to as "green season" by the Thai Tourism Authority. Although it may seem like a sales gimmick, there is some truth to it. Visitors during this time will notice that foliage is noticeably more vibrant than other times of the year. This gives the entire country a slightly more "tropical" feel. Consequently, when the weather is good during rainy season -which it can be- it's actually the most beautiful time of the year.

The biggest holiday of the year in Thailand is Songkran, or Thai New Year. Based on the Thai lunar calendar, it's typically held mid-April and lasts from one to three days. The name "Songkran" comes from the Sanskrit word meaning “passing” or “approaching”. Water plays an important part during the holiday and symbolizes cleansing or renewal. Families traditionally spend the holiday together visiting local temples and enjoying quality time together. While the festival retains its genuinely spiritual roots, it has also taken on a slightly more raucous character in recent years. These days, Songkran is also characterised by a good deal of partying, and the practise of cleansing has turned into all-out water gun fights that take places on streets throughout Thailand. It's great fun, but be prepared for getting wet!

The next biggest holiday in Thailand is Yi Peng (in the north) and Loi Krathong (in the rest of the country). Together, these holidays comprise Thailand’s Festival of Lights, which is one of Southeast Asia's most photogenic occassions. During the Festival of Lights, which takes place on the evening of the full moon of the 12th month in the traditional Thai lunar calendar, people release khom loi (lit lanterns) into the night sky or krathong (small floating vessels made of banana stalks and decorated with flowers and candles) into bodies of water. The effect is extraordinary, as thousands of lit-up vessels float across the waters or up into the air.

Other important holidays include:

Chulalongkorn Day, 23 October
Constitution Day, 10 December
Makha Buddha, 4 March