Heavy rain forecast as monsoon strengthens; Typhoon Ragasa set to hit northern Vietnam

The Thai Meteorological Department reported on Tuesday that the monsoon trough lies across the upper North, while the moderate southwest monsoon prevails over the Andaman Sea, the South, and the Gulf of Thailand.

Isolated heavy rain is expected nationwide. Residents in affected areas should remain alert, as accumulated rainfall may cause flash floods and river overflows, particularly along foothills and low-lying areas near waterways.

Sea conditions are expected to be rough. Waves in the upper Andaman Sea may reach around 2 metres, while in the lower Andaman Sea and upper Gulf, waves are forecast at 1-2 metres, rising above 2 metres during thundershowers. All vessels are urged to exercise caution and avoid thundershower areas.

The department added that as of 4:00 a.m. on September 23, Typhoon Ragasa was located over the upper South China Sea at 19.7°N, 118.9°E, with maximum sustained winds of approximately 195 km/h. The storm is moving west at 20 km/h and is expected to pass near Hong Kong before approaching China’s southern coast, crossing Hainan Island into the Gulf of Tonkin by September 25. It is forecast to weaken into a tropical storm before making landfall in northern Vietnam. Ragasa is expected to rapidly downgrade due to the influence of China’s extended high-pressure system during September 25-26.

Ragasa is expected to intensify the monsoon trough across northern and upper northeastern Thailand and strengthen the southwest monsoon over the country. Heavy to very heavy rainfall is likely in the North, Northeast, Central region, and East, including Bangkok and surrounding areas, from September 23-26. Residents are advised to be cautious of flooding and river overflows, particularly near waterways, foothills, and low-lying areas. Waves in the Upper Andaman Sea could rise to 2-3 metres high, exceeding 3 metres during thundershowers. All ships should navigate with caution, and small boats are advised to remain ashore from September 24-26.

The weather forecast for the next 24 hours is as follows:

North: Fairly widespread thundershowers and isolated heavy rain in Mae Hong Son, Chiang Mai, Lampang, Lamphun, Tak, Sukhothai, Kamphaeng Phet, Phitsanulok, Phichit and Phetchabun. Minimum temperature 23-25 °C. Maximum temperature 30-33 °C.

Northeast: Fairly widespread thundershowers and isolated heavy rain in Bueng Kan, Sakon Nakhon, Nakhon Phanom, Kalasin, Mukdahan, Roi Et, Yasothon, Amnat Charoen, Surin, Sisaket and Ubon Ratchathani. Minimum temperature 23-25 °C. Maximum temperature 30-33 °C.

Central: Scattered thundershowers mostly in Nakhon Sawan, Uthai Thani, Kanchanaburi and Ratchaburi. Minimum temperature 23-26 °C. Maximum temperature 33-35 °C.

East: Fairly widespread thundershowers and isolated heavy rain in Nakhon Nayok, Chanthaburi and Trat. Minimum temperature 23-27 °C. Maximum temperature 31-34 °C. Wave height 1-2 metres and above 2 metres in thundershowers.

South (East Coast): Isolated thundershowers mostly in Phetchaburi, Prachuap Khiri Khan and Yala. Minimum temperature 22-25 °C. Maximum temperature 34-36 °C. Wave height about 1 metre, 1-2 metres offshore and above 2 metres in thundershowers.

South (West Coast): Isolated thundershowers mostly in Ranong and Phang Nga. Minimum temperature 23-26 °C. Maximum temperature 32-34 °C. Wave height 1-2 metres and above 2 metres in thundershowers.

Bangkok Metropolitan: Fairly widespread thundershowers and isolated heavy rain. Minimum temperature 25-26 °C. Maximum temperature 33-35 °C.