Thailand Issues Heavy Rain and Flash Flood Warning for August 18-21

The Thai Meteorological Department (TMD) has released its third announcement regarding severe weather conditions expected across upper Thailand from August 18 to 21, 2026. According to the report from Khaosod Online, a monsoon trough is expected to move across the northern and upper northeastern regions, coinciding with a strengthening southwest monsoon over the Andaman Sea and the Gulf of Thailand.

Residents and travelers in these areas should prepare for heavy to very heavy rainfall, which may lead to flash floods and forest runoff, particularly in low-lying areas and regions near hillsides or natural waterways. Authorities have advised the public to exercise caution and avoid traveling through areas prone to recurring flooding.

Marine conditions are also expected to deteriorate. From August 19 to 21, the upper Andaman Sea will experience strong winds, with wave heights reaching 2 to 3 meters, and potentially exceeding 3 meters in areas affected by thunderstorms. The lower Andaman Sea and the upper Gulf of Thailand are expected to see waves of approximately 2 meters, with higher swells during storms.

While the TMD has provided a clear forecast for the affected regions, the specific intensity of rainfall in localized areas remains subject to change. Travelers are encouraged to monitor local weather updates and follow instructions from provincial authorities before planning trips to mountainous or coastal regions during this period.