Upper Thailand faces heavy rain until September 2
TMD forecasts heavy to very heavy rain in upper Thailand from August 29 to September 2, raising flash-flood and landslide risks.
The Thai Meteorological Department (TMD) has warned of heavy to very heavy rain across parts of upper Thailand from Saturday (August 29) to Wednesday (September 2, 2026), raising the risk of flash floods, overflowing waterways and landslides.
The heaviest rainfall is expected mainly in the upper North, upper Northeast and East, including areas exposed to the prevailing wind.
People living near foothills, waterways and low-lying land have been advised to monitor conditions closely, particularly where rainfall accumulates over several days.
The warning was issued in Weather Advisory No. 3 (170/2026) at 5pm on Thursday (August 27, 2026).
Monsoon systems to bring widespread rain
The monsoon trough is forecast to move across the North and upper Northeast before extending into an active low-pressure system over the coast of upper Vietnam and the Gulf of Tonkin.
At the same time, a rather strong southwest monsoon will prevail over the Andaman Sea, Thailand and the Gulf of Thailand.
The combined weather systems are expected to bring more widespread rainfall, with isolated heavy to very heavy downpours in the most exposed areas.
Accumulated rain could cause sudden flooding, waterways to overflow and slopes to become unstable, the TMD said.
Waves could exceed three metres
The rather strong southwest monsoon will also generate rough conditions at sea.
Waves in the upper Andaman Sea and upper Gulf are forecast to reach 2–3 metres, rising above 3 metres in thunderstorms.
In the lower Andaman Sea, waves are expected to be about 2 metres and higher than 2 metres during storms.
All vessels in the Andaman Sea and Gulf of Thailand should proceed with caution and avoid thunderstorm areas.
Small boats in the upper Andaman Sea and upper Gulf should remain ashore during the warning period.
Forecast through Friday evening
The TMD also issued the following regional forecast for the period from 6pm on Thursday (August 27) to 6pm on Friday (August 28, 2026):
North: Thunderstorms across 60% of the region, with isolated heavy rain in Mae Hong Son, Chiang Mai, Chiang Rai, Tak, Kamphaeng Phet, Phitsanulok and Phetchabun. Temperatures will range from 24–27°C to 32–36°C. Southwesterly winds will reach 10–20km/h.
Northeast: Thunderstorms across 40% of the region, mainly in Bueng Kan, Sakon Nakhon, Nakhon Phanom, Mukdahan and Ubon Ratchathani. Temperatures will range from 24–26°C to 31–35°C, with southwesterly winds of 10–25km/h.
Central region: Thunderstorms across 60% of the area, with isolated heavy rain in Kanchanaburi and Ratchaburi. Temperatures will range from 23–26°C to 33–36°C. Southwesterly winds will reach 10–25km/h.
Bangkok and surrounding provinces: Thunderstorms across 60% of the area. Temperatures will range from 27–28°C to 33–35°C, with southwesterly winds of 10–25km/h.
East: Thunderstorms across 60% of the region, with isolated heavy rain in Nakhon Nayok, Prachin Buri, Chanthaburi and Trat. Temperatures will range from 24–28°C to 31–34°C. Southwesterly winds will reach 20–35km/h. Waves will be about 2 metres and higher than 2 metres in thunderstorms.
Southern east coast: Thunderstorms across 40% of the region, mainly in Phetchaburi, Prachuap Khiri Khan, Chumphon, Surat Thani, Yala and Narathiwat. Temperatures will range from 23–25°C to 32–37°C.
From Surat Thani northwards, southwesterly winds will reach 20–35km/h. Waves will be 1–2 metres, about 2 metres offshore and higher than 2 metres during thunderstorms.
From Nakhon Si Thammarat southwards, southwesterly winds will reach 15–35km/h. Waves will be about 1 metre, increasing to 1–2 metres offshore and more than 2 metres in thunderstorms.
Southern west coast: Thunderstorms across 30% of the region, with isolated heavy rain in Ranong and Phang Nga. Temperatures will range from 23–26°C to 31–35°C.
From Phuket northwards, southwesterly winds will reach 20–40km/h. Waves will be 2–3 metres and higher than 3 metres in thunderstorms.
From Krabi southwards, southwesterly winds will reach 15–35km/h. Waves will be 1–2 metres and higher than 2 metres during thunderstorms.
The advisory was signed by TMD Director-General Sugunyanee Yavinchan. The next advisory is scheduled for 5am on Friday (August 28, 2026).
