National Water Resources Office warns of flash floods September 26-30, 2026, with many provinces nationwide on alert

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The National Water Resources Office, or ONWR, has issued a warning to monitor areas at risk of flash floods, forest runoff, mudslides and waterlogging from September 26 to 30, 2026, after tracking weather forecasts that show heavy to very heavy rain in many areas, particularly the North, the lower Northeast, the Central region, the West, Bangkok and its vicinity, the East and the South. During September 28 to 30, 2026, rain in the Northeast and the East will begin to ease, while the North, Central region and South will still see heavy rain in some areas on the western side of each region. At present, runoff from the upper Chao Phraya River basin is increasing the volume of water flowing into the basin. ONWR said the at-risk areas requiring monitoring cover the provinces of Mae Hong Son, Tak, Kamphaeng Phet, Phitsanulok, Uthai Thani, Nakhon Sawan, Nakhon Ratchasima, Surin, Sisaket, Chai Nat, Lopburi, Suphan Buri, Saraburi, Pathum Thani, Nonthaburi, Bangkok, Samut Prakan, Kanchanaburi, Ratchaburi, Phetchaburi, Prachuap Khiri Khan, Chachoengsao, Nakhon Nayok, Prachin Buri, Sa Kaeo, Chonburi, Rayong, Chanthaburi, Trat and Narathiwat. Authorities are also to monitor sudden rises in water levels and overtopping of riverbanks in low-lying areas along major rivers and their tributaries, such as the Moei River, the Yuam River, the Wang Thong River, the Sakae Krang River, the Pa Sak River, the Nakhon Nayok River, the Prachin Buri River, Khlong Phra Sathueng and Khlong Phra Prong, the Chanthaburi River, the Trat River, Khlong Bang Saphan, the Sai Buri River and the Kolok River. For the area downstream of Chao Phraya Dam, runoff from the upper basin is expected to increase the volume of water flowing into the Chao Phraya basin, with discharges through Chao Phraya Dam expected to be around 2,000 cubic metres per second, which would affect low-lying areas outside the flood barriers in Chai Nat, Sing Buri, Ang Thong, Phra Nakhon Si Ayutthaya, Pathum Thani and Nonthaburi. The flow through Chao Phraya Dam will be kept at no more than 1,750 cubic metres per second for as long as possible, while water will be diverted into canals on the west and east banks above Chao Phraya Dam and spread into low-lying areas and already-harvested rice fields to reduce downstream impacts. ONWR asked relevant agencies to continuously monitor weather and water conditions, especially in areas with more than 90 millimetres of accumulated rainfall within 24 hours, to inspect and repair riverbank embankments, clear waterway obstructions, and manage water in reservoirs and sluice gates in a coordinated way from upstream to downstream, as well as to prepare flood response plans, personnel and machinery, and to issue advance public warnings so people can evacuate in time.

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