18 Provinces Warned of Flash Floods August 19–21
Eighteen Thai provinces face flash flood warnings through August 21 as a monsoon trough and strengthening southwest monsoon bring heavy rainfall across the north, northeast, and eastern regions.
The National Water Resources Office warned on August 17, 2025, that 18 provinces must prepare for flash floods and flooding from August 19–21 as a monsoon trough moves across the northern and upper northeastern regions, combined with a strengthening southwest monsoon over the Andaman Sea, Thailand, and the Gulf of Thailand. The office cautioned residents in flood-prone urban areas where drainage systems may be overwhelmed, and in zones at risk of flash floods, mudslides, and riverbank overflow due to heavy and cumulative rainfall.
The 18 provinces on alert are Mae Hong Son, Chiang Mai, Chiang Rai, Lampun, Lampang, Phayao, Phrae, Nan, Uthai Thani, Tak, Nong Khai, Bueng Kan, Nakhon Phanom, Sakon Nakhon, Chanthaburi, Trat, Kanchanaburi, and areas at risk based on cumulative rainfall. (The source data lists 17 provinces—10 in the north, 4 in the upper northeast, 2 in the east, and Kanchanaburi.)
As of August 17, 2025, at 7:00 a.m., the highest rainfall recorded by region was Chiang Mai in the north at 73 mm, Bueng Kan in the northeast at 35 mm, Lopburi in the central region at 22 mm, Sa Kaew in the east at 30 mm, Kanchanaburi in the west at 19 mm, and Satun in the south at 70 mm. Heavy rain is forecast to continue on August 17 in the north, upper northeast, east, and southwestern south. From August 18–22, the north and upper northeast are expected to see increased and heavy rainfall in many areas as the monsoon trough drifts southward while the southwest monsoon remains strong over the Andaman Sea, Thailand, and the Gulf.
Nationally, water reservoirs held 48,320 million cubic meters (60% capacity) on August 17, with 24,199 million cubic meters in use (43%). By region: the north held 15,915 million cubic meters (58%), the northeast 5,803 million cubic meters (48%), the central region 641 million cubic meters (34%), the east 1,511 million cubic meters (48%), the west 19,672 million cubic meters (69%), and the south 4,778 million cubic meters (62%).
The four major dams in the Chao Phraya basin showed: Bhumibol Dam at 7,334 million cubic meters (54%), Sirikit Dam at 6,113 million cubic meters (64%), Khwae Noi Bamrung Dam at 288 million cubic meters (31%), and Pasak Chachoen Dam at 248 million cubic meters (28%). The three major reservoirs in the Eastern Economic Corridor held: Bang Phra at 54 million cubic meters (46%), Nong Plalai at 84 million cubic meters (51%), and Prasae at 196 million cubic meters (66%).
