Thailand weather warning issued for heavy rain and flash floods

The Thai Meteorological Department has issued warnings for heavy to very heavy rainfall across much of Thailand between August 18 and 21, 2026. The weather is driven by a monsoon trough passing over upper Laos and a low-pressure area in northern Vietnam, combined with a strengthening southwest monsoon over the Andaman Sea and the Gulf of Thailand.

Extreme rainfall is expected in the upper Northeast, specifically in Bueng Kan and Nakhon Phanom, and in parts of the East, particularly Trat province. Other regions, including the North and Bangkok metropolitan areas, are expected to experience thunderstorms and significant precipitation.

Authorities have warned of potential flash floods, forest runoffs, and overflowing rivers, particularly in mountainous areas, low-lying plains, and near waterways. In maritime areas, waves in the upper Andaman Sea may reach 2 to 3 meters, with higher waves in thunderstorm zones. Small vessels in the upper Andaman Sea are advised to remain ashore.