BANGKOK — 18 August 2026, The Meteorological Department warned of heavy to very heavy rain in parts of Thailand on Tuesday, with thunderstorms forecast to cover up to 60% of some regions, including Bangkok and surrounding provinces.
The department’s 24-hour forecast, from 06:00 on 18 August to 06:00 on 19 August, said a monsoon trough is moving southward across upper Laos toward a low-pressure cell over northern Vietnam. Meanwhile, the southwest monsoon covering the Andaman Sea, Thailand and the Gulf of Thailand is strengthening.
Residents in affected areas were advised to beware of heavy to very heavy rainfall and accumulated rain, which could trigger flash floods, forest runoff and overflowing waterways, particularly in foothill areas, near waterways and in low-lying areas.
Winds and waves in the Andaman Sea and Gulf of Thailand are moderate. Waves in the upper Andaman Sea and upper Gulf are around 2 meters high, rising above 2 meters during thunderstorms.
Boaters were advised to exercise caution and avoid areas experiencing thunderstorms.
Regional forecasts
North: Thunderstorms are forecast over 40% of the area, with isolated heavy rain in Mae Hong Son, Chiang Mai, Chiang Rai, Phayao, Nan, Lampang, Phrae and Tak. Temperatures will range from 22-28°C, with highs of 32-36°C. Southwest winds will reach 10-20 kph.
Northeast: Thunderstorms will cover 60% of the region, with heavy rain in Nong Khai, Udon Thani, Sakon Nakhon, Kalasin, Mukdahan, Roi Et, Yasothon, Amnat Charoen, Surin, Si Sa Ket and Ubon Ratchathani. Very heavy rain is expected in Bueng Kan and Nakhon Phanom. Temperatures will range from 24-26°C, with highs of 33-36°C. Southwest winds will reach 10-20 kph.
Central: Thunderstorms will cover 40% of the area, mainly in Kanchanaburi and Saraburi. Temperatures will range from 24-27°C, with highs of 35-37°C. Southwest winds will reach 10-25 kph.
East: Thunderstorms will cover 60% of the region, with heavy rain in Nakhon Nayok and Chanthaburi and isolated very heavy rain in Trat. Temperatures will range from 22-26°C, with highs of 31-35°C. Southwest winds will reach 20-35 kph. Waves will be around 2 meters high and above 2 meters during thunderstorms.
South, east coast: Thunderstorms will cover 30% of the area, mainly in Prachuap Khiri Khan, Chumphon, Nakhon Si Thammarat, Yala and Narathiwat. Temperatures will range from 23-26°C, with highs of 33-36°C. Southwest winds will reach 15-35 kph. Waves will be 1-2 meters high offshore, around 2 meters, and above 2 meters during thunderstorms.
South, west coast: Thunderstorms will cover 40% of the area, mainly in Ranong, Phang Nga, Trang and Satun. Temperatures will range from 23-26°C, with highs of 31-34°C.
From Ranong northward, southwest winds will reach 20-35 kph, with waves around 2 meters and above 2 meters during thunderstorms. From Phang Nga southward, winds will reach 15-35 kph, with waves of 1-2 meters and above 2 meters during thunderstorms.
Bangkok and surrounding areas: Thunderstorms are forecast over 60% of the area. Temperatures will range from 25-28°C, with highs of 35-37°C. Southwest winds will reach 10-25 kph.