ONWR warns 28 provinces in five regions of floods on September 15–19

Thailand’s Office of the National Water Resources (ONWR) has warned of waterlogging, flash floods, rapid run-off and landslides across five regions from September 15 to 19, 2026, as monsoon conditions bring more rain and heavy to very heavy downpours in some areas.

ONWR’s Notice No. 4/2026, reported by Bangkok Biznews, calls for the highest level of vigilance and identifies districts requiring close monitoring, alongside separate watchlists for reservoirs and rivers.

Monsoon conditions raise flood risks across Thailand

ONWR said a monsoon trough was extending across the lower Central region, upper South and East towards a low-pressure area over the upper Northeast. A moderate south-westerly monsoon was also covering the Andaman Sea, Thailand and the Gulf of Thailand, contributing to increased rainfall and the risk of flooding.

ONWR assessed the risks using rainfall forecasts and information from the Thai Meteorological Department, the Hydro-Informatics Institute (Public Organization), the Department of Water Resources and the Department of Mineral Resources. The assessment identified areas vulnerable to flooding, rapid run-off and landslides during the five-day warning period.

ONWR identifies flood-risk districts in five regions

ONWR’s September 15–19 warning identifies the following districts for particular vigilance against waterlogging, flash floods, rapid run-off and landslides.

North — 12 provinces

• Mae Hong Son: Sop Moei, Khun Yuam, Mae La Noi, Pai and Mae Sariang.
• Chiang Mai: Omkoi, Mae Chaem, Chom Thong and Hot.
• Chiang Rai: Mae Suai and Mueang Chiang Rai.
• Lampang: Thoen and Chae Hom.
• Phayao: Pong, Dok Khamtai and Chiang Kham.
• Phrae: Song, Nong Muang Khai, Rong Kwang, Mueang Phrae and Wang Chin.
• Nan: Thung Chang, Mae Charim, Bo Kluea, Wiang Sa and Pua.
• Tak: Tha Song Yang, Ban Tak, Umphang, Sam Ngao, Mae Ramat, Mueang Tak and Mae Sot.
• Uttaradit: Nam Pat, Ban Khok and Laplae.
• Phitsanulok: Chat Trakan, Noen Maprang, Nakhon Thai, Wang Thong, Bang Rakam, Bang Krathum, Phrom Phiram and Mueang Phitsanulok.
• Phetchabun: Lom Sak, Mueang Phetchabun, Khao Kho, Lom Kao, Wang Pong, Nong Phai, Nam Nao, Si Thep and Chon Daen.
• Uthai Thani: Ban Rai and Lan Sak.

Northeast — four provinces

• Loei: Dan Sai, Wang Saphung, Phu Kradueng, Pha Khao and Erawan.
• Chaiyaphum: Kaeng Khro, Mueang Chaiyaphum, Phu Khiao, Kaset Sombun, Khon San, Nong Bua Rawe, Phakdi Chumphon, Nong Bua Daeng, Chatturat and Thep Sathit.
• Sakon Nakhon: Ban Muang, Wanon Niwat, Kham Ta Kla, Akat Amnuai and Khok Si Suphan.
• Nakhon Phanom: Si Songkhram, Phon Sawan, Na Kae, Tha Uthen, Pla Pak, Na Wa, Wang Yang, Na Thom and Mueang Nakhon Phanom.

East — two provinces

• Chanthaburi: Khlung, Khao Khitchakut, Makham, Pong Nam Ron and Kaeng Hang Maeo.
• Trat: Mueang Trat, Khao Saming, Bo Rai, Laem Ngop, Khlong Yai and Ko Chang.

West — one province

• Kanchanaburi: Sangkhla Buri, Sai Yok, Thong Pha Phum, Dan Makham Tia and Si Sawat.

South — nine provinces

• Ranong: Mueang Ranong, Suk Samran, Kra Buri and Kapoe.
• Phang Nga: Kapong, Khura Buri, Takua Pa, Mueang Phang Nga and Thai Mueang.
• Phuket: Thalang, Mueang Phuket and Kathu.
• Krabi: Ko Lanta, Khlong Thom and Ao Luek.
• Satun: Mueang Satun and La-ngu.
• Songkhla: Saba Yoi and Thepha.
• Yala: Betong, Bannang Sata, Raman, Than To and Mueang Yala.
• Pattani: Yarang and Thung Yang Daeng.
• Narathiwat: Sukhirin, Chanae, Si Sakhon, Rueso, Ra-ngae and Su-ngai Padi.

Reservoir and river watchlists target overflow risks

ONWR called for close monitoring and water management at small and medium-sized reservoirs holding more than 80% of their storage capacity in 14 provinces: Chiang Mai, Chiang Rai, Phayao, Nan, Phetchabun, Tak, Uthai Thani, Chaiyaphum, Sakon Nakhon, Chanthaburi, Trat, Kanchanaburi, Krabi and Ranong.

ONWR also identified the following rivers and associated waterways as requiring monitoring for possible overflows:

• Mae Hong Son: Yuam River.
• Chiang Rai: Sai and Kok rivers.
• Nan: Nan River.
• Tak: Moei River.
• Phitsanulok: Khwae Noi River.
• Phetchabun: Pa Sak River.
• Sakon Nakhon: Songkhram River.
• Narathiwat: Kolok River and Tanyong Mat canal.

ONWR sets out four flood-response measures

ONWR has coordinated with relevant agencies on four measures intended to reduce risks to lives and property during the September 15–19 warning period:

1. Maintain continuous weather and water monitoring. Agencies should pay particular attention to areas receiving more than 90 millimetres of rain within 24 hours and locations that repeatedly experience flooding.
2. Inspect embankments and coordinate water management. Agencies should inspect and repair river embankments, remove waterway obstructions and coordinate the management of large, medium and small reservoirs, river flows, barrages and sluice gates from upstream to downstream. Water management should also account for tidal conditions, with drainage accelerated and storage levels lowered ahead of the expected heavy rain.
3. Prepare personnel, equipment and flood-response plans. Agencies should ready staff, machinery and tools, clear waterway obstructions and drainage pipes, and coordinate resources so assistance can be provided immediately.
4. Provide public updates and early warnings. Agencies should keep people informed about water conditions and warn those likely to be affected in advance, allowing them to prepare for timely evacuation if the situation requires it.