TMD warns of heavy rain and rough seas through September 20

The Thai Meteorological Department (TMD) issued Weather Advisory No. 7 (211/2026) on Friday (September 18, 2026), warning of heavy to very heavy rain across parts of Thailand and strong wind-waves in the Andaman Sea from September 18-20.

Heavy to very heavy rain is expected in some areas during the period, with the North and Northeast affected first before the rain extends across the Central region, East and South on Friday.

The conditions are being driven by a high-pressure system or cold air mass from China extending over the upper North and upper Northeast. This will push the monsoon trough southwards across the lower Central region, East and upper South, while the south-westerly monsoon over the Andaman Sea, Thailand and the Gulf of Thailand strengthens.

Residents are advised to remain alert for heavy to very heavy rain and accumulated rainfall that could trigger flash floods and forest run-off, particularly near foothills, waterways and low-lying areas.

People should also avoid travelling along routes prone to repeated flooding, particularly in low-lying areas where short-term flooding may occur.

Rough seas in the Andaman

Conditions in the Andaman Sea are expected to remain relatively rough, with waves of 2-3 metres and more than 3 metres in thunderstorms.

Mariners in both the Andaman Sea and Gulf of Thailand should proceed with caution and avoid areas affected by thunderstorms.

Small boats in the Andaman Sea should remain ashore from September 18-20.

TMD urged the public to plan travel and daily activities carefully during the period and continue monitoring official weather advisories. Updates are available through the department or by calling 0-2399-4012-13 and hotline 1182 around the clock.

Areas at risk of heavy to very heavy rain on September 18

Very heavy rain

• North: Uttaradit, Phitsanulok and Phetchabun.
• Northeast: Loei, Nong Bua Lamphu, Chaiyaphum, Khon Kaen and Nakhon Ratchasima.
• East: Nakhon Nayok, Prachin Buri, Chanthaburi and Trat.
• South: Ranong, Phang Nga, Phuket, Chumphon and Surat Thani.

Heavy rain

• North: Chiang Mai, Chiang Rai, Lampang, Phayao, Nan, Phrae, Tak, Sukhothai, Kamphaeng Phet and Phichit.
• Northeast: Nong Khai, Bueng Kan, Udon Thani, Sakon Nakhon, Nakhon Phanom, Kalasin, Mukdahan, Maha Sarakham, Roi Et, Yasothon, Amnat Charoen, Buri Ram, Surin, Si Sa Ket and Ubon Ratchathani.
• Central: Nakhon Sawan, Uthai Thani, Chai Nat, Lop Buri, Saraburi, Sing Buri, Ang Thong, Phra Nakhon Si Ayutthaya, Suphan Buri, Kanchanaburi, Ratchaburi, Nakhon Pathom, Samut Songkhram and Samut Sakhon, including Bangkok and surrounding provinces.
• East: Sa Kaeo, Chachoengsao, Chon Buri and Rayong.
• South: Phetchaburi, Prachuap Khiri Khan, Nakhon Si Thammarat, Songkhla, Krabi, Trang and Satun.

Areas at risk on September 19

Very heavy rain

• Central: Ratchaburi.
• East: Rayong and Chanthaburi.
• South: Ranong, Phang Nga, Phuket, Krabi, Phetchaburi, Prachuap Khiri Khan, Chumphon and Surat Thani.

Heavy rain

• North: Tak.
• Central: Nakhon Sawan, Uthai Thani, Chai Nat, Lop Buri, Sing Buri, Ang Thong, Phra Nakhon Si Ayutthaya, Suphan Buri, Kanchanaburi, Nakhon Pathom, Samut Songkhram and Samut Sakhon, including Bangkok and surrounding provinces.
• East: Nakhon Nayok, Prachin Buri, Chachoengsao, Chon Buri and Trat.
• South: Nakhon Si Thammarat, Phatthalung, Trang and Satun.

Areas at risk on September 20

Very heavy rain

• Central: Ratchaburi, Nakhon Pathom, Samut Songkhram and Samut Sakhon, including Bangkok and surrounding provinces.
• East: Chachoengsao, Chon Buri, Rayong, Chanthaburi and Trat.
• South: Phetchaburi, Prachuap Khiri Khan, Chumphon, Ranong and Phang Nga.

Heavy rain

• North: Tak and Kamphaeng Phet.
• Northeast: Nakhon Ratchasima.
• Central: Nakhon Sawan, Uthai Thani, Chai Nat, Lop Buri, Saraburi, Sing Buri, Ang Thong, Phra Nakhon Si Ayutthaya, Suphan Buri and Kanchanaburi.
• East: Nakhon Nayok, Prachin Buri and Sa Kaeo.
• South: Surat Thani, Phuket and Krabi.