The department said the conditions were due to the strong monsoon trough lying across the North, Central and Northeast regions and the strong southwest monsoon prevailing across the Andaman Sea, Thailand and the Gulf.
The severe conditions could cause flash floods and overflows, especially along waterways and lowlands. Caution is advised.
Wave height in the upper Andaman Sea and the upper Gulf could rise to 2-3 metres and more than 3 metres in thundershowers. Small boats in these areas should keep ashore until Sunday and stay tuned for weather updates, the department said.
The areas to be affected by heavy to very heavy rains are as follows:
Tuesday
North: Chiang Rai, Lampang, Phayao, Nan, Phrae, Uttaradit, Phitsanulok and Phetchabun
Northeast: Loei, Nong Khai, Bueng Kan, Nong Bua Lamphu, Udon Thani, Sakon Nakhon, Nakhon Phanom, Khon Kaen, Kalasin, Mukdahan, Maha Sarakham, Roi Et, Yasothon, Amnat Charoen, Sisaket and Ubon Ratchathani
East: Chanthaburi and Trat
South: Ranong, Phang Nga and Phuket
Wednesday
North: Mae Hong Son, Chiang Mai, Chiang Rai, Lamphun, Lampang, Phayao, Nan, Phrae, Uttaradit, Tak, Sukhothai, Kamphaeng Phet, Phitsanulok, Phichit and Phetchabun
Northeast: Loei, Nong Khai, Nong Bua Lamphu, Udon Thani, Sakon Nakhon, Nakhon Phanom, Chaiyaphum, Khon Kaen, Kalasin, Mukdahan, Maha Sarakham, Roi Et, Yasothon, Amnat Charoen, Nakhon Ratchasima, Buriram, Surin, Sisaket and Ubon Ratchathani
Central: Nakhon Sawan, Uthai Thani, Chainat, Lopburi, Saraburi, Singburi, Angthong, Ayutthaya, Suphanburi, Kanchanaburi, and Bangkok metropolitan area
East: Nakhon Nayok, Prachinburi, Sa Kaeo, Chachoengsao, Chonburi, Rayong, Chanthaburi and Trat
South: Ranong, Phang Nga, Phuket and Krabi
Thursday
North: Mae Hong Son, Chiang Mai, Lamphun, Lampang, Nan, Phrae, Uttaradit, Tak, Sukhothai, Kamphaeng Phet, Phitsanulok, Phichit and Phetchabun
Northeast: Loei, Chaiyaphum, Khon Kaen, Maha Sarakham, Roi Et, Yasothon, Amnat Charoen, Nakhon Ratchasima, Buriram, Surin, Sisaket and Ubon Ratchathani
Central: Nakhon Sawan, Uthai Thani, Chai Nat, Lop Buri, Saraburi, Sing Buri, Ang Thong, Phra Nakhon Si Ayutthaya, Kanchanaburi, Suphan Buri, Ratchaburi, Nakhon Pathom, Samut Songkhram, Samut Sakhon, and Bangkok metropolitan area
East: Nakhon Nayok, Prachinburi, Sa Kaeo, Chachoengsao, Chonburi, Rayong, Chanthaburi and Trat.
South: Chumphon, Surat Thani, Ranong, Phang Nga, Phuket and Krabi
Friday to Sunday
North: Mae Hong Son, Chiang Mai, Lamphun, Lampang, Phrae, Uttaradit, Tak, Sukhothai, Kamphaeng Phet, Phitsanulok, Phichit and Phetchabun
Northeast: Nakhon Ratchasima, Buriram, Surin, Sisaket and Ubon Ratchathani
Central: Nakhon Sawan, Uthai Thani, Chai Nat, Lop Buri, Saraburi, Sing Buri, Ang Thong, Phra Nakhon Si Ayutthaya, Suphan Buri, Kanchanaburi, Ratchaburi, Samut Songkhram, Samut Sakhon, Nakhon Pathom and Bangkok metropolitan area
East: Nakhon Nayok, Prachinburi, Sa Kaeo, Chachoengsao, Chonburi, Rayong, Chanthaburi and Trat
South: Prachuap Khiri Khan, Chumphon, Surat Thani, Nakhon Si Thammarat, Ranong, Phang Nga, Phuket, Krabi, Trang and Satun