TMD forecasts heavy rain, 2–3m Andaman waves Sept 17–20
Heavy rain is forecast in Thailand’s North and Northeast on September 17, reaching the Central region, East and South on September 18
- The Thai Meteorological Department (TMD) has forecast heavy to very heavy rain in parts of Thailand from September 17–20.
- Waves in the Andaman Sea are expected to reach 2–3 metres high, and may exceed 3 metres during thunderstorms.
- Due to the high waves, small boats in the Andaman Sea are advised to remain ashore throughout the warning period.
- The TMD warns that the heavy rainfall could cause flash floods and forest run-off, particularly near waterways and in low-lying areas.
The Thai Meteorological Department (TMD) issued a warning at 5am Thailand time on September 17, 2026, forecasting heavy to very heavy rain in parts of Thailand through September 20. Andaman Sea waves are forecast to reach 2–3 metres, exceeding 3 metres in thunderstorms.
North and Northeast face heavy rain first
According to TMD, heavy to very heavy rain will affect parts of the North and Northeast first on September 17, before reaching the Central region, East and South on September 18. The regional sequence follows the department’s earlier forecast for the September 17–20 wet spell.
TMD attributes the September 17–20 wet spell to a high-pressure system, or cool air mass, from China extending over the upper North and upper Northeast. The system is pushing the monsoon trough south across the lower Central region, East and upper South, while the southwest monsoon over the Andaman Sea, Thailand and Gulf of Thailand strengthens.
TMD warns of flash floods and flooded routes
Heavy and accumulated rainfall during September 17–20 could cause flash floods and forest run-off, TMD warns, particularly on foothill slopes near waterways and in low-lying areas.
TMD advises people travelling during September 17–20 to avoid routes that repeatedly flood, especially low-lying roads where temporary waterlogging may occur. Residents should plan daily activities and journeys carefully throughout the warning period.
Small boats in the Andaman Sea advised to stay ashore
Small boats in the Andaman Sea should remain ashore from September 17–20, TMD advises, as waves are forecast at 2–3 metres and above 3 metres in thunderstorms.
Mariners in both the Andaman Sea and Gulf of Thailand should navigate cautiously and avoid thunderstorms during September 17–20, according to TMD.
TMD urged the public to monitor weather announcements and scheduled its next bulletin for 5pm on September 17. Weather information is available around the clock through the Thai Meteorological Department website and on 02-399-4012, 02-399-4013 and 1182.
