Upper Thailand faces flash-flood risk in TMD forecast

People in upper Thailand should remain alert to flash floods and rapid run-off as isolated heavy rain continues, with wetter conditions expected to spread across the country during September 8–13, the Thai Meteorological Department (TMD) said.

The department’s forecast for Monday (September 7, 2026) places communities in the Mekong basin, foothill areas near waterways and low-lying locations at particular risk from heavy to very heavy rain and accumulated rainfall. Nation Thailand’s preceding weather report

Residents should avoid routes repeatedly affected by flooding, especially low-lying roads where water may temporarily accumulate.

Thunderstorms are forecast across 60% of the North, Northeast, Central region and East, with isolated heavy rain in specified provinces. Bangkok and surrounding areas also face thunderstorms across 60% of the area, while coverage along both southern coasts is forecast at 40%.

Rain expected to increase from September 8

A monsoon trough extending across the North and upper Northeast, together with a moderate southwest monsoon over the Andaman Sea, Thailand and the Gulf of Thailand, is maintaining the current rainfall.

Rain will increase during September 8–13, bringing heavy falls to many areas and isolated very heavy downpours. The Northeast will be affected first, followed by other regions.

The change is expected as the monsoon trough shifts southwards across upper Thailand, while the southwest monsoon remains moderate.

Sea conditions in the Andaman Sea and Gulf of Thailand will also remain moderate. Waves in the upper Andaman Sea will reach about two metres and exceed two metres in thunderstorms.

Boat operators in both waters should navigate cautiously and avoid areas affected by thunderstorms.

Regional forecast

The forecast covers 6am on September 7 to 6am on September 8, 2026, Thailand time. Percentages refer to the proportion of each region expected to experience thunderstorms.

North

• Thunderstorms across 60% of the region, with isolated heavy rain in Chiang Rai, Nan, Tak, Phitsanulok and Phetchabun.
• Minimum temperatures of 23–27°C and maximum temperatures of 33–37°C.
• Variable winds at 10–20 kilometres per hour.

Northeast

• Thunderstorms across 60% of the region, with isolated heavy rain in Nong Khai, Bueng Kan, Udon Thani, Sakon Nakhon, Nakhon Phanom, Kalasin, Mukdahan, Roi Et, Yasothon, Amnat Charoen, Buri Ram, Surin, Si Sa Ket and Ubon Ratchathani.
• Minimum temperatures of 23–24°C and maximum temperatures of 32–35°C.
• Southwesterly winds at 10–20 kilometres per hour.

Central region

• Thunderstorms across 60% of the region, with isolated heavy rain in Nakhon Sawan, Saraburi and Kanchanaburi.
• Minimum temperatures of 25–27°C and maximum temperatures of 35–37°C.
• Southwesterly winds at 10–20 kilometres per hour.

East

• Thunderstorms across 60% of the region, with isolated heavy rain in Nakhon Nayok, Chanthaburi and Trat.
• Minimum temperatures of 23–28°C and maximum temperatures of 32–35°C.
• Southwesterly winds at 15–35 kilometres per hour.
• Waves of one to two metres, exceeding two metres in thunderstorms.

South, east coast

• Thunderstorms across 40% of the region, mainly in Phetchaburi, Prachuap Khiri Khan, Chumphon, Songkhla, Yala and Narathiwat.
• Minimum temperatures of 23–26°C and maximum temperatures of 33–36°C.
• Southwesterly winds at 15–35 kilometres per hour.
• Waves of about one metre, rising to one to two metres offshore and exceeding two metres in thunderstorms.

South, west coast

• Thunderstorms across 40% of the region, mainly in Ranong, Phang Nga, Trang and Satun.
• Minimum temperatures of 24–27°C and maximum temperatures of 31–34°C.
• From Phuket northwards, southwesterly winds at 20–35 kilometres per hour, with waves of about two metres and above two metres in thunderstorms.
• From Krabi southwards, southwesterly winds at 15–35 kilometres per hour, with waves of one to two metres and above two metres in thunderstorms.

Bangkok and surrounding areas

• Thunderstorms across 60% of the area.
• Minimum temperatures of 25–26°C and maximum temperatures of 34–36°C.
• Southwesterly winds at 10–20 kilometres per hour.