Bangkok and 70 provinces warned of flash floods and rough seas

The Department of Disaster Prevention and Mitigation (DDPM) has warned Bangkok and 70 provinces to prepare for flash floods, forest run-off, landslides, waterlogging and rough seas during September 23-27, 2026.

The department issued the warning on Wednesday (September 23), coordinating preparations with provincial authorities and regional disaster prevention and mitigation centres nationwide.

Heavy rain expected as low-pressure system approaches

The Thai Meteorological Department forecasts heavy rain across many areas and very heavy rain in some places during September 23-27. The lower Northeast and East are expected to be affected first, followed by other regions.

A strong low-pressure system near the coast of central Vietnam is expected to move over the lower Northeast, East and Central region, including Bangkok and surrounding provinces. Meanwhile, the south-westerly monsoon over the Andaman Sea, Thailand and the Gulf of Thailand will strengthen.

Strong winds and high waves are also expected in the Andaman Sea and Gulf of Thailand. Waves in the upper Gulf are forecast to reach 2-3 metres, exceeding 3 metres in areas affected by thunderstorms.

The Office of the National Water Resources has separately identified areas requiring close monitoring during September 22-26 for flash floods, forest run-off, landslides and urban flooding, particularly in communities where drainage systems regularly struggle to cope with rainfall.

Areas under flood and landslide watch

For the September 23-27 monitoring period, the DDPM notice lists all provinces in the North, Northeast and Central region as areas requiring vigilance for flash floods, forest run-off, landslides and waterlogging.

In the South, the warning covers seven provinces: Chumphon, Surat Thani, Songkhla, Ranong, Phang Nga, Phuket and Narathiwat.

Coastal and island districts warned of rough seas

The strong-wind and high-wave watch covers the following areas.

Six central and eastern coastal provinces

• Chonburi: Mueang Chonburi, Si Racha, Koh Si Chang, Bang Lamung and Sattahip districts.
• Rayong: Mueang Rayong, Ban Chang and Klaeng districts.
• Chanthaburi: Na Yai Am, Tha Mai, Laem Sing and Khlung districts.
• Trat: Mueang Trat, Laem Ngop, Khlong Yai, Koh Chang and Koh Kood districts.
• Phetchaburi: Mueang Phetchaburi, Ban Laem, Tha Yang and Cha-am districts.
• Prachuap Khiri Khan: All districts.

Three southern provinces

• Chumphon: Mueang Chumphon, Pathio, Sawi, Thung Tako, Lang Suan and Lamae districts.
• Surat Thani: Mueang Surat Thani, Chaiya, Tha Chana, Tha Chang, Phunphin, Don Sak, Kanchanadit, Koh Samui and Koh Phangan districts.
• Nakhon Si Thammarat: Mueang Nakhon Si Thammarat, Khanom, Sichon, Tha Sala, Pak Phanang and Hua Sai districts.

Emergency teams and equipment ordered into risk areas

DDPM has instructed authorities to assign personnel to monitor weather conditions, rainfall and local water levels closely. Response teams and disaster-response machinery must be stationed in at-risk areas so they can respond immediately and assist affected residents.

Particular attention must be given to locations with recurring floods and areas that remain inundated. Authorities have been told to maximise drainage efforts to minimise the impact of further flooding.

At natural attractions, particularly caves, waterfalls and caves with waterways running through them, officials must issue warnings and close access if conditions pose a danger.

Coastal authorities have also been instructed to issue announcements or install warning signals during periods of strong winds and high waves. Tourists must be strictly prohibited from entering the sea to swim in such conditions.

Mariners, vessel captains and passenger boat operators must be warned to exercise greater caution. If conditions appear likely to become severe, authorities should consider suspending boat operations entirely.

Relevant agencies have also been asked to prepare temporary shelters, food, drinking water and other essential supplies to accommodate evacuees in the event of flooding.

DDPM urged residents to continue monitoring weather forecasts, disaster warnings, local water conditions and official announcements.

Warnings are available through the Thai Disaster Alert application. Emergencies and requests for assistance can be reported through the department’s LINE emergency-reporting account, @1784DDPM, or by calling the 1784 hotline, available around the clock.