The months from April to May are the hottest in the country, and if you cannot handle extreme heat, a holiday here is best avoided. July onwards starts the monsoon, and the next three months are the wettest and the least appealing ones to head to Thailand.

The best month to visit Thailand is typically January, offering the "sweet spot" of the cool, dry season with clear blue skies, manageable humidity, and comfortable temperatures ranging from 22°C to 32°C. Conversely, the worst month is often April, which marks the peak of the "hot season." During April, temperatures in Bangkok and central Thailand frequently soar to 40°C (104°F) with intense humidity that makes outdoor sightseeing physically exhausting. While April features the famous Songkran water festival, the heat can be oppressive for those not used to tropical climates. Another candidate for "worst" is September, the height of the monsoon season, which brings the heaviest rainfall and highest risk of flash flooding, particularly in the northern and central regions. For travelers seeking a balance, the "shoulder" months of November and February offer excellent weather with slightly fewer crowds than the absolute peak of the December holidays.