TMD issues alert for heavy rain and flash flood risk in upper Thailand
From Saturday (August 29) to Wednesday (September 2, 2026), isolated heavy to very heavy rain is forecast in the upper North and upper and eastern parts of the Northeast.
- The Thai Meteorological Department (TMD) has issued a warning for heavy to very heavy rain in upper Thailand from August 29 to September 2.
- The North and Northeast regions are at particular risk of flash floods and sudden run-off from forested areas.
- The severe weather is caused by a monsoon trough shifting southwards combined with a strong southwest monsoon.
- A related warning has been issued for mariners, with strong winds and waves of 2-3 meters expected in the Andaman Sea and Gulf of Thailand.
The Thai Meteorological Department (TMD) issued a warning at 5pm on Wednesday (August 26, 2026) of heavy to very heavy rain across upper Thailand from August 29 to September 2, with the North and Northeast at risk of flash floods and sudden run-off from forested areas.
Rainfall is expected to increase across Thailand, with isolated heavy to very heavy falls, particularly in the upper North, the upper and eastern parts of the Northeast, and areas facing the southwest monsoon.
The monsoon trough is forecast to shift southwards across the North and upper Northeast, extending into an active low-pressure cell over the coast of upper Vietnam and the Gulf of Tonkin.
The southwest monsoon prevailing over the Andaman Sea, Thailand and the Gulf of Thailand is also expected to be rather strong.
People in these areas are urged to beware of heavy to very heavy rain and accumulated rainfall, which may cause flash floods and sudden run-off from forested areas, particularly on foothill slopes near waterways and in low-lying areas.
Travel on routes prone to repeated flooding should be avoided, especially in low-lying areas where short-term inundation may occur.
Winds and waves in the upper Andaman Sea are expected to be rather strong, with waves of 2–3 metres and above 3 metres in thunderstorms.
Waves in the lower Andaman Sea and upper Gulf of Thailand will be about 2 metres, rising above 2 metres in thunderstorms.
Mariners in the Andaman Sea and Gulf of Thailand are advised to proceed with caution and avoid sailing in areas affected by thunderstorms.
Small boats in the upper Andaman Sea should remain ashore throughout the period.
To stay safe and minimise potential impacts, people should plan their activities and travel carefully during the period and follow TMD announcements.
Updates are available at tmd.go.th or by calling 0-2399-4012-13 or 1182, 24 hours a day.
