New storm gains strength, heavy rain forecast for Thailand

The Thai Meteorological Department has issued a weather forecast for the next 24 hours, warning of increased rainfall across the country, with heavy showers in some areas, particularly in the eastern provinces. Strong rainfall is expected in Amnat Charoen, Ubon Ratchathani, Chanthaburi, and Trat. 

Authorities are advising residents in these areas to be cautious of heavy downpours and accumulated rainfall, which may cause flash flooding and runoff, especially in hillside areas, near waterways, and low-lying regions.

The increased rainfall is due to the monsoon trough extending across the lower central region, eastern region, and lower northeastern region of Thailand, coupled with a low-pressure system over the South China Sea. The southwest monsoon is intensifying over the Andaman Sea, Thailand, and the Gulf of Thailand.

In the Andaman Sea, wave heights are expected to reach around 2 metres, while in the lower Andaman Sea and upper Gulf of Thailand, waves may range from 1 to 2 metres. In areas experiencing thunderstorms, waves could be higher than 2 metres. Mariners are advised to navigate cautiously and avoid sailing in stormy areas.

Additionally, a depression near Luzon Island, Philippines, is forecast to intensify into a tropical storm, with a potential landfall in southern China between September 19 and 20, 2025.

Thailand weather forecast for the next 7 days (September 17-23, 2025)

From September 17 to 20, rain will continue across northern, central, and lower northeastern Thailand, with heavy rain expected in some areas. This is due to a monsoon trough extending across lower northern, central, and lower northeastern regions, moving into a strong low-pressure area in the central South China Sea. 

Additionally, the southwest monsoon is covering the Andaman Sea, Thailand, and the Gulf of Thailand at moderate strength.

From September 21 to 23, rainfall will increase in the northern and northeastern regions, with heavy rain expected in some areas. In the southern region, rainfall will decrease as the monsoon trough shifts northwards, affecting the northern, upper central, and northeastern areas. The southwest monsoon will continue to bring moderate rainfall to the Andaman Sea, Thailand, and the Gulf of Thailand.

Waves in the Andaman Sea and Gulf of Thailand will be moderate. In the upper Andaman Sea, waves may reach around 2 metres, while in the lower Andaman Sea and the upper Gulf of Thailand, waves will range from 1 to 2 metres. In areas experiencing thunderstorms, waves could exceed 2 metres.

Precautions:

From September 17 to 20, residents of Thailand are advised to be cautious of heavy rain and accumulated rainfall, which could lead to flash flooding and runoff, particularly in hillside areas, near waterways, and low-lying regions. 

From September 21 to 23, residents of the northern, upper central, and northeastern regions should also be alert to heavy rain and accumulated rainfall that could cause flash flooding and runoff in similar areas. 

Mariners are urged to navigate with caution and avoid sailing in stormy conditions throughout this period.

Thailand Weather Forecast from 6pm Wednesday (September 17) to 6pm Thursday (September 18)

Northern Region

Thunderstorms are expected in 60% of the area, with heavy rain in some parts, especially in Mae Hong Son, Chiang Mai, Lamphun, Lampang, Tak, Sukhothai, Phitsanulok, Kamphaeng Phet, Phichit, and Phetchabun. Minimum temperatures will range from 22°C to 24°C, with maximum temperatures between 30°C and 34°C. Winds will be variable, with speeds of 5-15 km/h.

Northeastern Region

Thunderstorms will affect 70% of the area, with heavy rain in some areas, including Loei, Nong Khai, Bueng Kan, Yasothon, Amnat Charoen, Nakhon Ratchasima, Buri Ram, Surin, Si Sa Ket, and Ubon Ratchathani. Minimum temperatures will range from 23°C to 25°C, and maximum temperatures will range from 32°C to 34°C. Winds will be variable, with speeds of 10-15 km/h.

Central Region

Thunderstorms are expected in 70% of the area, with heavy rain in some parts, including Uthai Thani, Ayutthaya, Saraburi, Kanchanaburi, Suphan Buri, Ratchaburi, Samut Songkhram, Samut Sakhon, and Nakhon Pathom. Minimum temperatures will range from 22°C to 25°C, with maximum temperatures between 31°C and 34°C. Winds will be variable, with speeds of 10-15 km/h.

Bangkok and Vicinity

Thunderstorms are expected in 70% of the area, with heavy rain in some parts. Minimum temperatures will range from 24°C to 25°C, with maximum temperatures between 31°C and 34°C. Winds will be variable, with speeds of 10-15 km/h.

Eastern Region

Thunderstorms will affect 70% of the area, with heavy to very heavy rain in some parts, especially in Nakhon Nayok, Prachin Buri, Sa Kaeo, Chachoengsao, Chonburi, Rayong, Chanthaburi, and Trat. Minimum temperatures will range from 23°C to 26°C, with maximum temperatures between 30°C and 34°C. Winds will be variable, with speeds of 15-35 km/h. In the sea, waves will be 1-2 metres high, with waves over 2 metres in areas with thunderstorms.

Southern Region (East Coast)

Thunderstorms will affect 40% of the area, with heavy rain in some parts, especially in Phetchaburi, Prachuap Khiri Khan, and Chumphon. Minimum temperatures will range from 23°C to 25°C, with maximum temperatures between 31°C and 34°C. Winds will be from the southwest at speeds of 15-30 km/h. In the sea, waves will be around 1 meter high, and waves will reach 1-2 metres further from the shore, with waves exceeding 2 metres in areas with thunderstorms.

Southern Region (West Coast)

Thunderstorms will affect 60% of the area, with heavy rain in some parts, especially in Ranong and Phang Nga. Minimum temperatures will range from 24°C to 26°C, with maximum temperatures between 29°C and 34°C.

For areas from Phang Nga upwards, Winds will be from the southwest at speeds of 20-35 km/h. Waves will be around 2 metres high, with waves over 2 metres in areas with thunderstorms.

For areas from Phuket downwards, Winds will be from the southwest at speeds of 15-35 km/h. Waves will be 1-2 metres high, with waves exceeding 2 metres in areas with thunderstorms.