The rainy season in Thailand typically runs from May to October, with the heaviest rainfall occurring in September and October.

During this time, monsoon winds bring moisture from the Indian Ocean and the Gulf of Thailand, resulting in frequent thunderstorms and heavy rain. The rain often falls in the late afternoon or evening and can last for several hours.

This season can cause some flooding and travel disruptions, especially in low-lying areas. However, the rains also bring relief from the hot and dry weather that prevails for the rest of the year.

In addition to preparing for potential transportation disruptions and bad weather, travelers should also be aware that many popular tourist destinations and beaches in Thailand can become overcrowded during this time, and accommodations can be more expensive.