UPDATE: TMD extends rain warning as very heavy rain is forecast in Ubon Ratchathani and Trat

The Thai Meteorological Department (TMD) has extended its recent rain warning beyond September 12-13, forecasting isolated very heavy rain in Ubon Ratchathani and Trat during the 24-hour period from 6am on September 14 to 6am on September 15, 2026, Thailand time. It warned that heavy and accumulated rainfall elsewhere could cause flash floods, forest run-off and mudslides.

The two-province forecast applies specifically to the later September 14-15 period and does not replace the earlier warning for 37 provinces on September 12-13. The TMD advised people in affected areas to remain alert on foothill slopes, near waterways and in low-lying areas, and to avoid routes repeatedly affected by flooding.

The earlier Warning No. 12, issued at 5pm on September 12, put 37 provinces on alert for heavy to very heavy rain. It covered parts of the lower North, Northeast, Central region, Bangkok and surrounding provinces, the East and the South, with possible flash floods and run-off in vulnerable areas.

At the time of that warning, the TMD said an active low-pressure cell along the coast of central Vietnam was forecast to strengthen into a tropical cyclone and move closer to the coast of upper Vietnam between September 13 and 14. The department urged people to follow further weather updates and plan travel and daily activities carefully.

For the subsequent forecast period, the TMD attributed the unsettled weather to a monsoon trough extending across the upper South, the East and the lower Northeast towards a strong low-pressure area over central Vietnam. A moderate south-westerly monsoon was also continuing across the lower Andaman Sea, the lower South and the lower Gulf of Thailand.

On the southern west coast, the September 12-13 forecast put thunderstorms across 70% of the area, with heavy rain in Phuket, Krabi, Trang and Satun and very heavy rain in Ranong and Phang Nga. For September 14-15, thunderstorms were again forecast across 70% of the west coast, with isolated heavy rain in Ranong and Phang Nga. The later forecast singled out Ubon Ratchathani and Trat for isolated very heavy rain.

For the original period, westerly winds from Phuket northwards were expected to reach 20-35 kilometres per hour, with waves about two metres high and higher during thunderstorms. From Krabi southwards, northwesterly winds were forecast at 15-35 kilometres per hour, with waves of one to two metres and higher in stormy areas. The later bulletin retained the same wind ranges, describing winds as variable from Phuket northwards and south-westerly from Krabi southwards.

The earlier forecast also warned of heavy rain on the southern east coast, with very heavy rain possible in Prachuap Khiri Khan and Chumphon. In the September 14-15 outlook, thunderstorms were forecast across 70% of the east-coast area, with isolated heavy rain in Phetchaburi, Prachuap Khiri Khan, Chumphon, Surat Thani, Pattani, Yala and Narathiwat. Thunderstorms were forecast across 60% of the North and East, 70% of the Northeast and Central region, and 60% of Bangkok and surrounding provinces.

The TMD expects waves above two metres during thunderstorms in the Andaman Sea and Gulf of Thailand and advised mariners to navigate cautiously and avoid thunderstorms. From Phuket northwards, waves in the upper Andaman Sea are forecast at about two metres and above two metres in storms. From Krabi southwards, waves are expected at one to two metres and higher during thunderstorms. Along the South's east coast, waves should be about one metre, increasing to one to two metres offshore and above two metres in storms.