The Thai Meteorological Department said the rain will be brought by the active monsoon trough over the Central region and low-pressure cell over the lower Northeast. Meanwhile, a moderate southwest monsoon is also prevailing over the Andaman Sea, the South and the Gulf.
These conditions will result in torrential rains across the country until Friday evening, with heavy to very heavy rain in the North, Northeast, East and Central region including Greater Bangkok.
People have been warned of severe conditions causing flash floods and runoffs, especially along the foothills near waterways and lowlands, the department said.
The department also warned that strong winds will create 2-metre high waves in the upper Andaman Sea and the Gulf, which will become higher in thundershowers. Ships have been warned to proceed with caution and small boats are urged to keep ashore on Friday.
The affected provinces are as follows:
North
Mae Hong Son, Chiang Mai, Chiang Rai, Lamphun, Lampang, Phayao, Phrae, Nan, Sukhothai, Uttaradit, Tak, Kamphaeng Phet, Phichit, Phitsanulok and Phetchabun.
Northeast
Loei, Nong Bua Lamphu, Nong Khai, Bueng Kan, Udon Thani, Sakon Nakhon, Nakhon Phanom, Chaiyaphum, Khon Kaen, Kalasin, Maha Sarakham and Nakhon Ratchasima.
Central
Nakhon Sawan, Uthai Thani, Kanchanaburi, Lopburi, Saraburi including Greater Bangkok.
East
Nakhon Nayok, Prachinburi, Chonburi, Rayong, Chanthaburi and Trat.