"Meteorological Department" issued the first announcement warning of heavy to very heavy rain in upper Thailand, affecting the period from 18 to 21 August 2026, especially in the northern and northeastern regions.
On 15 August 2026, the Meteorological Department issued the first announcement regarding heavy to very heavy rain in upper Thailand (effective 18-21 August 2026). It stated that during 18-21 August, some areas in Thailand, particularly in the North and Upper Northeast, will experience heavy to very heavy rain. This is due to a monsoon trough passing through the North and Upper Northeast, combined with a fairly strong southwest monsoon covering the Andaman Sea, Thailand, and the Gulf of Thailand. Residents in these areas are advised to be cautious of dangers from heavy and accumulated rainfall that may cause flash floods and mountain runoff, especially in foothill areas near waterways and low-lying zones. Travelers should avoid routes prone to repeated flooding, particularly low-lying areas where short-term flooding may occur.
Regarding sea conditions, the upper Andaman Sea will experience fairly strong winds from 19-21 August 2026, with wave heights of 2-3 meters. Areas with thunderstorms may see waves exceeding 3 meters. The lower Andaman Sea and upper Gulf of Thailand will have waves around 2 meters, with thunderstorms causing waves over 2 meters. Boaters in the Andaman Sea and Gulf of Thailand are advised to navigate cautiously and avoid areas with thunderstorms. Small boats in the upper Andaman Sea should refrain from leaving shore during this period.
For safety and to minimize potential impacts, the public is urged to plan daily activities and travel with caution during this time. They should follow announcements from the Meteorological Department and can access information at the department’s website http://www.tmd.go.th or by calling 0-2399-4012-13 and hotline 1182, available 24 hours a day.
24-hour weather forecast Thailand will continue to experience heavy rain in some areas, with very heavy rain in the Eastern region. This is due to a monsoon trough passing through Myanmar and the Upper North, entering a low-pressure area over Upper Vietnam. Combined with a fairly strong southwest monsoon covering the Andaman Sea, Thailand, and the Gulf of Thailand, residents in these areas are advised to be cautious of dangers from heavy and accumulated rainfall that may cause flash floods and mountain runoff, especially in foothill areas near waterways and low-lying zones, including riverbank overflow in the Northeast.
The upper Andaman Sea will have fairly strong winds, with waves 2-3 meters high. Areas experiencing thunderstorms may have waves exceeding 3 meters. Boaters are advised to navigate cautiously and avoid areas with thunderstorms. Small boats in the upper Andaman Sea should refrain from leaving shore.
From 06:00 today until 06:00 tomorrow
There will be thunderstorms in 60% of the area, with some heavy rain in Mae Hong Son, Chiang Mai, Chiang Rai, Phayao, Nan, and Tak provinces. Minimum temperatures range from 23-28°C, maximum temperatures from 32-35°C. Southwest winds blow at 10-20 km/h.
There will be thunderstorms in 60% of the area, with some heavy rain in Udon Thani, Nong Khai, Bueng Kan, Sakon Nakhon, Nakhon Phanom, Mukdahan, Amnat Charoen, and Ubon Ratchathani provinces. Minimum temperatures range from 24-26°C, maximum temperatures from 33-35°C. Southwest winds blow at 10-20 km/h.
There will be thunderstorms in 40% of the area, with some heavy rain in Saraburi and Kanchanaburi provinces. Minimum temperatures range from 25-27°C, maximum temperatures from 34-36°C. Southwest winds blow at 10-25 km/h.
There will be thunderstorms in 60% of the area, with some heavy rain in Nakhon Nayok and Prachinburi provinces, and very heavy rain in Chanthaburi and Trat provinces. Minimum temperatures range from 25-28°C, maximum temperatures from 31-34°C. Southwest winds blow at 20-35 km/h. Sea waves are about 2 meters high, with waves over 2 meters in areas with thunderstorms.
There will be thunderstorms in 40% of the area, mostly in Chumphon, Surat Thani, Nakhon Si Thammarat, Songkhla, Yala, and Narathiwat provinces. Minimum temperatures range from 23-26°C, maximum temperatures from 33-35°C. Southwest winds blow at 20-35 km/h. Sea waves are 1-2 meters high near shore, about 2 meters offshore, and over 2 meters in areas with thunderstorms.
There will be thunderstorms in 60% of the area, with some heavy rain in Trang and Satun provinces. Minimum temperatures range from 24-28°C, maximum temperatures from 32-34°C. From Phang Nga northward: southwest winds blow at 20-40 km/h, with sea waves 2-3 meters high, and waves exceeding 3 meters in areas with thunderstorms. From Phuket southward: southwest winds blow at 15-35 km/h, with sea waves 1-2 meters high, and waves over 2 meters in areas with thunderstorms.
There will be thunderstorms in 60% of the area, with some heavy rain. Minimum temperatures range from 26-27°C, maximum temperatures from 33-35°C. Southwest winds blow at 10-25 km/h.