"Meteorological Department" issued its 6th announcement warning of heavy to very heavy rain in upper Thailand, effective from 18 to 21 August 2026, especially in the northern and northeastern regions.
On 18 August 2026, the Meteorological Department announced its 6th notice regarding heavy to very heavy rain in upper Thailand, effective from 18 to 21 August 2026. It states that during this period, heavy to very heavy rain is expected in some areas, particularly in the northern and upper northeastern regions. This is due to a monsoon trough crossing northern and upper northeastern Thailand, combined with a relatively strong southwest monsoon covering the Andaman Sea, Thailand, and the Gulf of Thailand. Residents in these areas are urged to beware of dangers from heavy and very heavy rain, as well as accumulated rainfall, which may cause flash floods and flash floods from mountain streams. Especially those in foothill areas near waterways and lowlands should avoid travel through frequently flooded routes, particularly low-lying areas prone to short-term flooding.
Regarding sea conditions, the upper Andaman Sea will experience relatively strong winds from 19 to 21 August 2026, with wave heights
of 2-3 meters; in areas with thunderstorms, waves may exceed 3 meters. The lower Andaman Sea and upper Gulf of Thailand will have wave heights around 2 meters, with waves over 2 meters in thunderstorm areas. Mariners in the Andaman Sea and Gulf of Thailand are advised to navigate cautiously and avoid sailing in thunderstorm zones. Small boats in the upper Andaman Sea should refrain from departing during these days for safety.
To ensure safety and minimize potential impacts, the public is advised to plan their activities and travel cautiously during this period. People should follow updates from the Meteorological Department and can access information on their website http://www.tmd.go.th or by calling 0-2399-4012-13 and 1182, available 24 hours.
24-hour weather forecast
Thailand will experience heavy rain in some areas, with very heavy rain in parts of the upper northeastern and eastern regions. This is due to a monsoon trough shifting southward across northern Laos into a low-pressure area over northern Vietnam, combined with a strengthening southwest monsoon covering the Andaman Sea, Thailand, and the Gulf of Thailand. Residents in these areas should be cautious of heavy to very heavy rain and accumulated rainfall, which may cause flash floods, flash floods from mountain streams, and river overflows, especially in foothill areas near waterways and lowlands.
Sea conditions in the Andaman Sea and Gulf of Thailand will be moderate, with waves around 2 meters high in the upper Andaman Sea and upper Gulf of Thailand. In thunderstorm areas, waves may exceed 2 meters. Mariners in these seas should navigate cautiously and avoid sailing in thunderstorm zones.
From 06:00 today until 06:00 tomorrow
There will be thunderstorms covering 40% of the area, with heavy rain in some provinces including Mae Hong Son, Chiang Mai, Chiang Rai, Phayao, Nan, Lampang, Phrae, and Tak. Temperatures will range from 22-28°C minimum to 32-36°C maximum, with southwest winds at 10-20 km/h.
Thunderstorms will cover 60% of the area, with heavy rain in provinces including Nong Khai, Udon Thani, Sakon Nakhon, Kalasin, Mukdahan, Roi Et, Yasothon, Amnat Charoen, Surin, Sisaket, and Ubon Ratchathani. Very heavy rain is expected in Bueng Kan and Nakhon Phanom. Temperatures will range from 24-26°C minimum to 33-36°C maximum, with southwest winds at 10-20 km/h.
Thunderstorms will cover 40% of the area, mainly in Kanchanaburi and Saraburi provinces. Temperatures will range from 24-27°C minimum to 35-37°C maximum, with southwest winds at 10-25 km/h.
Thunderstorms will cover 60% of the area, with heavy rain in Nakhon Nayok and Chanthaburi provinces and very heavy rain in Trat province. Temperatures will range from 22-26°C minimum to 31-35°C maximum, with southwest winds at 20-35 km/h. The sea will have waves about 2 meters high, exceeding 2 meters in thunderstorm areas.
Thunderstorms will cover 30% of the area, mainly in Prachuap Khiri Khan, Chumphon, Nakhon Si Thammarat, Yala, and Narathiwat provinces. Temperatures will range from 23-26°C minimum to 33-36°C maximum, with southwest winds at 15-35 km/h. The sea will have waves 1-2 meters high near shore, about 2 meters further out, and exceeding 2 meters in thunderstorm areas.
Thunderstorms will cover 40% of the area, mainly in Ranong, Phang Nga, Trang, and Satun provinces. Temperatures will range from 23-26°C minimum to 31-34°C maximum. From Ranong northwards: southwest winds at 20-35 km/h with waves around 2 meters, exceeding 2 meters in thunderstorm areas. From Phang Nga southwards: southwest winds at 15-35 km/h with waves 1-2 meters high, exceeding 2 meters in thunderstorm areas.
Thunderstorms will cover 60% of the area. Temperatures will range from 25-28°C minimum to 35-37°C maximum, with southwest winds at 10-25 km/h.