Monsoon brings heavy rain to North, Northeast; thunderstorms in Bangkok

According to the advisory, the storm’s centre remains over the Pacific Ocean, east of Luzon in the Philippines, and is moving west-northwest at a speed of 10 km/h. It is forecast to enter the upper South China Sea on September 22, 2025.

The TMD emphasised that Ragasa currently has no impact on Thailand. The rainfall experienced in recent days is due to the prevailing monsoon and monsoon trough across the country.

TMD forecasts heavy rain in northern and northeastern regions

The TMD on Sunday (September 21, 2025) forecast heavy rainfall across 70% of the northern and northeastern regions, while Bangkok and surrounding provinces can expect scattered thunderstorms.

For the next 24 hours, heavy rain is likely in some areas, particularly Mae Hong Son, Tak, Chanthaburi, and Trat. The TMD urged residents in these provinces to beware of flash floods and runoff caused by continuous downpours.

The monsoon trough is currently lying across the North and the upper Northeast, reinforced by a moderate southwesterly monsoon prevailing over the Andaman Sea, Thailand, and the Gulf of Thailand.

Wave conditions remain moderate, with waves up to 2 metres high in the upper Andaman Sea, and 1–2 metres in the lower Andaman Sea and the upper Gulf of Thailand. Thunderstorm areas may see waves exceeding 2 metres. Mariners are advised to proceed with caution and avoid sailing in stormy areas.

Thai Meteorological Department weather forecast for Thailand from 6am Sunday (21 September) to 6am Monday (22 September).

Bangkok and surrounding areas

Thunderstorms are expected over 60% of the area.

Minimum temperature: 25–27°C

Maximum temperature: 32–35°C

Southwesterly winds 10–15 km/h

North

Thunderstorms are forecast for 70% of the area, with heavy rain in Mae Hong Son, Chiang Mai, Chiang Rai, Phayao, Nan, Lampang, Lamphun, Tak, Sukhothai, Kamphaeng Phet, Phitsanulok, Phichit, and Phetchabun.

Minimum temperature: 23–25°C

Maximum temperature: 32–34°C

Variable winds 5–15 km/h

Northeast

Thunderstorms are expected in 70% of the area, with heavy rain in Loei, Nong Khai, Bueng Kan, Udon Thani, Nong Bua Lamphu, Chaiyaphum, Khon Kaen, Kalasin, Maha Sarakham, Roi Et, Yasothon, Amnat Charoen, Nakhon Ratchasima, Buri Ram, Surin, Si Sa Ket, and Ubon Ratchathani.

Minimum temperature: 23–24°C

Maximum temperature: 32–34°C

Variable winds 10–15 km/h

Central region

Thunderstorms are forecast for 60% of the area, with heavy rain in Nakhon Sawan, Lop Buri, Saraburi, and Kanchanaburi.

Minimum temperature: 24–26°C

Maximum temperature: 34–35°C

Variable winds 10–15 km/h

East

Thunderstorms are expected in 70% of the area, with heavy rain in Nakhon Nayok, Prachin Buri, Sa Kaeo, Chanthaburi, and Trat.

Minimum temperature: 24–26°C

Maximum temperature: 32–34°C

Southwesterly winds 15–35 km/h

Wave height 1–2 metres, exceeding 2 metres in stormy areas

South (east coast)

Thunderstorms are forecast for 10% of the area, mostly in Phetchaburi, Prachuap Khiri Khan, and Narathiwat.

Minimum temperature: 23–25°C

Maximum temperature: 33–35°C

Southwesterly winds 15–35 km/h

Wave height about 1 metre, 1–2 metres offshore, exceeding 2 metres in stormy areas

South (west coast)

Thunderstorms are expected in 20% of the area, mostly in Ranong and Phangnga.

Minimum temperature: 23–26°C

Maximum temperature: 32–34°C

From Phangnga northwards: southwesterly winds 20–35 km/h, wave height around 2 metres, exceeding 2 metres in stormy areas

From Phuket southwards: southwesterly winds 15–35 km/h, wave height 1–2 metres, exceeding 2 metres in stormy areas