Monsoon trough shift brings heavy rain and flood risk to Thailand
The Thai Meteorological Department expects downpours in several regions through Sunday (September 13, 2026), while a low-pressure system may develop into a tropical cyclone.
- A southward shift in the monsoon trough, caused by a high-pressure system from China, is bringing heavy to very heavy rain across Thailand from September 8 to 13.
- The Thai Meteorological Department warns that the heavy and accumulated rainfall creates a significant risk of flash floods and rapid run-off, particularly in hilly and low-lying areas.
- The severe weather will initially impact northern and central regions before shifting to affect the lower Central region (including Bangkok), the East, and the South from September 10.
Thailand is bracing for another spell of heavy rain.
At 5pm on Tuesday (September 8, 2026), the Thai Meteorological Department (TMD) issued its fourth advisory on heavy to very heavy rain across the country, covering the period from September 8 to 13.
The fourth advisory said isolated heavy to very heavy rain was expected on September 8 and 9, particularly in the North, Northeast, Central region and East.
A high-pressure system or cold air mass had spread over southern China, Vietnam and upper Laos, pushing the monsoon trough southwards across the North, upper Central region and Northeast.
A moderate southwest monsoon was also prevailing over the Andaman Sea, Thailand and the Gulf of Thailand.
From September 10 to 13, rain will continue in the lower Northeast, the Central region, including Bangkok and its vicinity, the East and the South, with heavy to very heavy rain in some areas.
Rain will ease in the North and upper Northeast.
This is because a high-pressure system or cold air mass from China will extend over the upper North and upper Northeast, pushing the monsoon trough southwards across the lower Central region, lower Northeast and East into an active low-pressure cell over the central South China Sea.
The southwest monsoon over the Andaman Sea, the South and the Gulf of Thailand will also strengthen.
People in upper Thailand and the upper South are advised to beware of heavy to very heavy rain and accumulated rainfall, which could cause flash floods and rapid run-off, particularly on hillsides near waterways and in low-lying areas.
They should avoid routes prone to repeated flooding, especially in low-lying areas where temporary flooding could occur.
From September 11 to 13, the low-pressure cell over the central South China Sea is likely to intensify into a tropical cyclone.
People are advised to follow weather forecasts closely during this period.
For safety and to minimise potential impacts, people are urged to plan their daily activities and travel carefully during the period and monitor announcements from the Thai Meteorological Department.
Updates are available 24 hours a day at www.tmd.go.th or by calling 0-2399-4012-13 or 1182.
