TMD forecasts rain across 80% of Bangkok and central Thailand on September 19

The Thai Meteorological Department (TMD) forecast thundershowers across 80% of Bangkok and surrounding provinces and 80% of the central region on Saturday (September 19, 2026), with isolated heavy rain. Parts of Ranong and Phang Nga face very heavy rain as the department warns of flooding and landslides.

The TMD’s 24-hour forecast covers the period from 6am on September 19 to 6am on September 20, Thailand time.

Heavy to very heavy rain and accumulated rainfall could cause flash floods, rapid run-off and landslides, the TMD warned, particularly on foothill slopes near waterways and in low-lying areas. The department also advised travellers to avoid routes prone to repeated flooding, where water could accumulate for short periods.

Cold air from China pushes the monsoon trough south

A high-pressure system, or cold air mass, from China has extended over the upper North and upper Northeast, pushing the monsoon trough southwards across the lower central region, lower South and East, according to the TMD.

A relatively strong south-westerly monsoon is also covering the Andaman Sea, Thailand and the Gulf of Thailand, the TMD reported.

Small boats advised to stay ashore until September 20

Small boats in the upper Andaman Sea should remain ashore until September 20, the TMD advised. With winds and waves relatively strong across the Andaman Sea and Gulf of Thailand, all mariners should navigate cautiously and avoid thunderstorms.

The TMD forecast waves of 2–3 metres in the upper Andaman Sea, rising above 3 metres during thunderstorms. Waves in the lower Andaman Sea and upper Gulf of Thailand are expected to reach around 2 metres and exceed 2 metres in thunderstorms.

Regional forecasts put thundershower coverage at 60–80%

The TMD forecasts thundershowers across 60–80% of each region during September 19–20, with isolated heavy rain in every region and very heavy rain in parts of the western South.

North: The TMD’s September 19–20 forecast puts thundershower coverage at 60%, with isolated heavy rain in Mae Hong Son, Chiang Mai, Lamphun, Lampang, Phrae, Tak, Sukhothai, Kamphaeng Phet, Phichit, Uttaradit, Phitsanulok and Phetchabun. Minimum temperatures will be 23–25°C and maximum temperatures 31–35°C, with easterly winds of 10–20 km/h.

Northeast: Thundershowers will cover 60% of the region during September 19–20, with isolated heavy rain in Chaiyaphum, Nakhon Ratchasima and Buri Ram, according to the TMD. Minimum temperatures will be 23–24°C and maximum temperatures 32–34°C, with easterly winds of 10–20 km/h.

Central region: The TMD forecasts thundershowers across 80% of the region during September 19–20, with isolated heavy rain in 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. Minimum temperatures will be 23–25°C and maximum temperatures 32–35°C, with south-easterly winds of 10–25 km/h.

East: Thundershowers will cover 70% of the region during September 19–20, with isolated heavy rain in Chachoengsao, Chon Buri, Rayong, Nakhon Nayok, Prachin Buri, Sa Kaeo, Chanthaburi and Trat, according to the TMD. Minimum temperatures will be 23–25°C and maximum temperatures 30–35°C, with south-westerly winds of 20–35 km/h. Waves will reach around 2 metres and exceed 2 metres during thunderstorms.

South, east coast: The TMD forecasts thundershowers across 60% of the region during September 19–20, with isolated heavy rain in Phetchaburi, Prachuap Khiri Khan, Chumphon, Surat Thani, Nakhon Si Thammarat, Phatthalung, Songkhla, Pattani, Yala and Narathiwat. Minimum temperatures will be 23–26°C and maximum temperatures 30–34°C. From Surat Thani northwards, south-westerly winds will reach 20–35 km/h, with waves of 1–2 metres, around 2 metres offshore and above 2 metres during thunderstorms. From Nakhon Si Thammarat southwards, south-westerly winds will reach 15–35 km/h, with waves around 1 metre, rising to 1–2 metres offshore and above 2 metres during thunderstorms.

South, west coast: Thundershowers will cover 70% of the region during September 19–20, with isolated heavy rain in Phuket, Krabi, Trang and Satun and very heavy rain in parts of Ranong and Phang Nga, according to the TMD. Minimum temperatures will be 23–25°C and maximum temperatures 28–31°C. From Phuket northwards, south-westerly winds will reach 20–40 km/h, with waves of 2–3 metres and above 3 metres during thunderstorms. From Krabi southwards, south-westerly winds will reach 20–35 km/h, with waves around 2 metres and above 2 metres during thunderstorms.

Bangkok and surrounding provinces: The TMD forecasts thundershowers across 80% of the area during September 19–20, with isolated heavy rain. Minimum temperatures will be 24–25°C and maximum temperatures 31–34°C, with southerly winds of 10–25 km/h.