These conditions are brought by the weakening active low-pressure cell over the western part of the North and the monsoon trough lying across upper Thailand, the department said.
The severe conditions may cause flash floods and overflows, especially along foothills near waterways and lowlands. Drivers should proceed with caution.
Meanwhile, the rather strong southwesterly wind prevailing across the Andaman Sea, the South, and the Gulf of Thailand will cause waves to rise to about 2 metres and over. The upper Andaman Sea could see waves over 3 metres high in thundershowers. All ships should proceed with caution and keep away from storms. Small boats in the upper Andaman Sea should stay ashore, the department advised.
The affected areas are as follows:
Thursday
North: Mae Hong Son, Chiang Mai, Chiang Rai, Lamphun, Lampang, Phayao, Phrae, Uttaradit, Sukhothai, Tak, Kamphaeng Phet, Phichit, Phitsanulok and Phetchabun
Northeast: Loei, Nong Khai, Nong Bua Lamphu, Udon Thani, Chaiyaphum, Khon Kaen and Nakhon Ratchasima
Central: Nakhon Sawan, Uthai Thani, Chainat, Singburi, Ang Thong, Phra Nakhon Si Ayutthaya, Kanchanaburi, Suphanburi, Ratchaburi, Nakhon Pathom, Samut Songkhram, Samut Sakhon and Bangkok metropolitan area
East: Nakhon Nayok, Prachinburi, Sa Kaeo, Chachoengsao, Chonburi, Rayong, Chanthaburi and Trat
South: Phetchaburi, Prachuap Khiri Khan, Ranong and Phang Nga
Friday
North: Mae Hong Son, Chiang Mai, Lamphun, Lampang, Sukhothai, Tak, Kamphaeng Phet, Phichit, Phitsanulok and Phetchabun.
Northeast: Loei, Nong Bua Lamphu and Chaiyaphum.
Central: Nakhon Sawan, Uthai Thani, Kanchanaburi and Ratchaburi.
East: Chanthaburi and Trat.
South: Ranong.