Thailand’s weather agency warns of flash floods as heavy rain targets 21 provinces, while a Hainan depression strengthens but stays outside Thailand
Heavy rain is forecast for 21 provinces in Thailand, with the Thai Meteorological Department warning of potential flash floods, rapid run-off, and overflowing rivers.
The weather is caused by a monsoon trough and a strong south-westerly monsoon, influenced by a strengthening depression over China's Hainan Island.
The depression is expected to intensify into a tropical storm and make landfall in China, but it will not directly enter or affect Thailand.
Hazardous marine conditions are expected, with waves reaching 2-3 meters in the upper Andaman Sea, and small boats are advised to remain ashore.
Heavy rain is forecast in 21 provinces on Saturday (August 22, 2026), with the Thai Meteorological Department (TMD) warning that accumulated rainfall could trigger flash floods, rapid run-off and overflowing rivers.
Thunderstorms will affect large parts of Thailand during the 24-hour period from 6am on Saturday to 6am on Sunday. Heavy rain is most likely in western areas of the North and Central region, as well as parts of the East.
A monsoon trough has shifted northwards across the upper North and upper Laos towards a depression over China’s Hainan Island. A rather strong south-westerly monsoon is also prevailing over the Andaman Sea, Thailand and the Gulf of Thailand.
Hainan depression will not enter Thailand
The strong depression over Hainan is forecast to intensify into a tropical storm before making landfall in southern Guangxi, China, on August 24-25.
The system is not expected to move into Thailand and will therefore have no direct effect on the country’s weather, the TMD said.
Travellers planning to visit the affected area of China during that period should check the latest weather conditions before departure.
Flood and marine warnings
People in areas facing heavy or accumulated rain should remain alert for flash floods, rapid run-off and river overflows, particularly on foothill slopes near waterways and in low-lying locations.
Marine conditions remain hazardous:
Waves in the upper Andaman Sea will reach 2-3 metres and exceed 3 metres during thunderstorms.
Waves in the upper Gulf of Thailand will be about 2 metres high and exceed 2 metres in thunderstorms.
Mariners in the Andaman Sea and Gulf of Thailand should proceed with caution and avoid thunderstorm areas.
Small boats in the upper Andaman Sea should remain ashore.
Regional forecast
North: Thunderstorms are forecast across 60% of the region, with isolated heavy rain in Mae Hong Son, Chiang Mai, Chiang Rai, Lamphun, Lampang, Kamphaeng Phet, Phitsanulok, Phetchabun and Tak. Temperatures will range from lows of 22-26°C to highs of 31-34°C. South-westerly winds will reach 10-20 kilometres per hour.
Northeast: Thunderstorms are forecast across 40% of the region, with isolated heavy rain in Nong Khai, Bueng Kan and Nakhon Phanom. Temperatures will range from lows of 23-24°C to highs of 31-33°C. South-westerly winds will reach 10-20km/h.
Central region: Thunderstorms are forecast across 60% of the area, with isolated heavy rain in Nakhon Sawan, Uthai Thani, Ratchaburi and Kanchanaburi. Temperatures will range from lows of 23-25°C to highs of 32-34°C. South-westerly winds will reach 10-25km/h.
East: Thunderstorms are forecast across 60% of the region, with isolated heavy rain in Nakhon Nayok, Prachin Buri, Chanthaburi and Trat. Temperatures will range from lows of 23-27°C to highs of 31-33°C. South-westerly winds will reach 20-35km/h. Waves will be about 2 metres high and exceed 2 metres during thunderstorms.
South, east coast: Thunderstorms are forecast across 30% of the region, mainly in Phetchaburi, Prachuap Khiri Khan, Chumphon and Surat Thani. Temperatures will range from lows of 23-25°C to highs of 30-37°C.
From Surat Thani northwards, south-westerly winds will reach 20-35km/h. Waves will be 1-2 metres high, about 2 metres offshore and above 2 metres during thunderstorms.
From Nakhon Si Thammarat southwards, south-westerly winds will reach 15-35km/h. Waves will be about 1 metre high, rising to 1-2 metres offshore and above 2 metres during thunderstorms.
South, west coast: Thunderstorms are forecast across 30% of the region, with isolated heavy rain in Ranong. Temperatures will range from lows of 22-25°C to highs of 30-35°C.
From Phang Nga northwards, south-westerly winds will reach 20-40km/h. Waves will reach 2-3 metres and exceed 3 metres during thunderstorms.
From Phuket southwards, south-westerly winds will reach 15-35km/h. Waves will reach 1-2 metres and exceed 2 metres during thunderstorms.
Bangkok and surrounding provinces: Thunderstorms are forecast across 60% of the area. Temperatures will range from lows of 25-26°C to highs of 32-33°C, with south-westerly winds of 10-25km/h.
