Weather Bulletin No. 9 warns of very heavy rain in some parts of Southern Thailand. Areas at risk should beware of flooding. Small boats are advised not to sail from the Andaman coast until 20 Sep. Bangkok and vicinity have an 80% chance of thunderstorms and lightning.
On 19 Sep 2026, the Meteorological Department issued Bulletin No. 9 regarding heavy to very heavy rain in Thailand and strong waves in the Andaman Sea (effective 19-20 Sep 2026). During 19-20 Sep, Thailand will experience heavy rain in some areas, with very heavy rain in parts of the South. This is due to a high-pressure system or cold air mass from China covering upper northern and northeastern Thailand, causing the monsoon trough to shift south across lower central, eastern, and upper southern regions, combined with a fairly strong southwest monsoon over the Andaman Sea, Thailand, and the Gulf of Thailand.
The public in Thailand is advised to beware of dangers from heavy to very heavy rain and accumulated rainfall, which may cause flash floods and forest runoff, especially in foothill areas near waterways and lowlands. Avoid traveling through areas prone to repeated flooding, particularly low-lying areas where short-term waterlogging may occur.
Waves in the Andaman Sea are fairly strong, with heights of 2-3 meters and over 3 meters in thunderstorm areas. Mariners in the Gulf of Thailand and Andaman Sea should navigate cautiously and avoid sailing in thunderstorm zones. Small boats in the Andaman Sea should not sail from shore during 19-20 Sep.
Northern region: 60% chance of thunderstorms with heavy rain in some areas including Mae Hong Son, Chiang Mai, Lamphun, Lampang, Phrae, Tak, Sukhothai, Kamphaeng Phet, Phichit, Uttaradit, Phitsanulok, and Phetchabun provinces. Minimum temperatures 23-25°C; maximum 31-35°C. Easterly winds at 10-20 km/h.
Northeastern region: 60% chance of thunderstorms with heavy rain in some areas including Chaiyaphum, Nakhon Ratchasima, and Buriram provinces. Minimum temperatures 23-24°C; maximum 32-34°C. Easterly winds at 10-20 km/h.
Central region: 80% chance of thunderstorms with heavy rain in some areas including Nakhon Sawan, Uthai Thani, Chainat, Lopburi, Saraburi, Sing Buri, Ang Thong, Phra Nakhon Si Ayutthaya, Suphanburi, Kanchanaburi, Ratchaburi, Nakhon Pathom, Samut Songkhram, and Samut Sakhon provinces. Minimum temperatures 23-25°C; maximum 32-35°C. Southeasterly winds at 10-25 km/h.
Eastern region: 70% chance of thunderstorms with heavy rain in some areas including Chachoengsao, Chonburi, Rayong, Nakhon Nayok, Prachinburi, Sa Kaeo, Chanthaburi, and Trat provinces. Minimum temperatures 23-25°C; maximum 30-35°C. Southwesterly winds at 20-35 km/h. Sea waves about 2 meters high, exceeding 2 meters in thunderstorm areas.
Southern region (East coast): 60% chance of thunderstorms with heavy rain in some areas including Phetchaburi, Prachuap Khiri Khan, Chumphon, Surat Thani, Nakhon Si Thammarat, Phatthalung, Songkhla, Pattani, Yala, and Narathiwat provinces. Minimum temperatures 23-26°C; maximum 30-34°C. From Surat Thani northwards: southwest winds at 20-35 km/h, sea waves 1-2 meters high near shore and about 2 meters offshore, exceeding 2 meters in thunderstorm zones. From Nakhon Si Thammarat southwards: southwest winds at 15-35 km/h, sea waves about 1 meter high near shore and 1-2 meters offshore, exceeding 2 meters in thunderstorm areas.
Southern region (West coast): 70% chance of thunderstorms with heavy rain in some areas including Phuket, Krabi, Trang, and Satun provinces, with very heavy rain in parts of Ranong and Phang Nga. Minimum temperatures 23-25°C; maximum 28-31°C. From Phuket northwards: southwest winds at 20-40 km/h, sea waves 2-3 meters high, exceeding 3 meters in thunderstorm areas. From Krabi southwards: southwest winds at 20-35 km/h, sea waves about 2 meters high, exceeding 2 meters in thunderstorm zones.
Bangkok and vicinity: 80% chance of thunderstorms with heavy rain in some areas. Minimum temperatures 24-25°C; maximum 31-34°C. Southerly winds at 10-25 km/h.