TMD warns of heavy rain and 2–3m Andaman waves September 17–20
Thailand’s North and Northeast face heavy rain from September 17, followed by the Central region, East and South on September 18, forecasters warn
- The Thai Meteorological Department (TMD) has issued a warning for heavy to very heavy rain across parts of Thailand from September 17–20, which may cause flash floods and forest runoff.
- Waves in the Andaman Sea are forecast to be 2–3 metres high during this period, potentially exceeding 3 metres in areas with thunderstorms.
- As a precaution, the TMD has advised that all small boats in the Andaman Sea should remain ashore from September 17–20.
The Thai Meteorological Department (TMD) warned on September 15, 2026, that parts of Thailand face heavy to very heavy rain from September 17–20, bringing risks of flash floods and forest runoff. The warning also forecasts rough conditions in the Andaman Sea.
North and Northeast face heavy rain from September 17
The North and Northeast will be the first regions affected on September 17, according to the TMD. Heavy to very heavy rain is then expected in some areas of the Central region, East and South from September 18.
Heavy and accumulated rainfall during September 17–20 could trigger flash floods and forest runoff, the TMD warned. Particular caution is needed on foothill slopes near waterways and in low-lying areas.
People travelling during September 17–20 should avoid routes with recurring flooding, particularly low-lying roads where short-term waterlogging could develop, the TMD advised.
Andaman waves forecast at 2–3 metres
The TMD forecasts fairly strong winds over the Andaman Sea and waves of 2–3 metres during September 17–20. Waves could exceed 3 metres in thunderstorms.
Small boats in the Andaman Sea should remain ashore from September 17–20, the TMD advised. Mariners in both the Andaman Sea and Gulf of Thailand should navigate cautiously and avoid areas with thunderstorms.
China’s cool air mass to push monsoon trough south
A high-pressure system, or cool air mass, from China is expected to extend over the upper North and upper Northeast, the TMD said. The advancing air mass will push the monsoon trough south across the lower Central region, East and upper South.
The southwest monsoon over the Andaman Sea, Thailand and Gulf of Thailand will also strengthen, contributing to the wet conditions, according to the TMD.
The TMD issued its first warning for the September 17–20 period, No. 1 (205/2569), at 5am Thai time (UTC+7) on September 15. The announcement was signed by Nattawut Dandee, deputy director-general for technical services, acting on behalf of the TMD director-general.
The TMD urged the public to plan daily activities and travel carefully during September 17–20 and follow further announcements. Weather information is available around the clock through the TMD website and on 02-399-4012, 02-399-4013 or 1182.
The TMD scheduled its next announcement for 5pm Thai time on September 15.
