Bangkok’s seasons can be determined by the level of heat: very hot, really wet, warm and sticky, or reasonably hot. The high season from November through March claims the latter description. Many from the northern hemisphere swap winter for the Southeast Asian shores (with the requisite stopover in Bangkok). In general, Bangkok’s high season stretches till May.
November evening skies sparkle with the brilliant displays of the Loi Krathong Festival of Light. Based on 13th-century Brahmin origins, locals give thanks to the Goddess of Water and seek forgiveness for naughty deeds. You’ll find Thais and foreigners alike out by the Chao Phraya riverside setting candlelit floats into the water with a prayer. The festival is celebrated at various points along the river so that everyone has the chance to set his or her own krathong into the water.
Mid-April signals the Thai New Year, or Songkran, a nonstop, three-day festival where revelers take to the streets with water guns and buckets—a modern-day interpretation of when a Buddhist monk sprinkled water on people as a token of good luck. This also comes at the start of the shoulder season—and the start of monsoons, reinforcing the fact that the high point of Songkran is getting wet (literally, like you have just spent the day at a water park).
The really rainy months of June through October indicate low season in Bangkok. Let’s just say it seems like the Songkran on steroids during the monsoons. There have been recorded episodes of near-constant rains for two months straight. Lots of rain and humidity can make for a miserable combination for some people, but the Thais just let it roll off their backs. August and September generally get the wettest, sometimes with floods reaching knee-deep depths in busy town streets. Pack an umbrella and a light trash-bag-like poncho; the muggy temps will prove a heavy raincoat useless.