The capital and its vicinity should be prepared for flooding.
Residents living in areas where foothills meet the lowlands, and along waterways, are also warned of possible flash floods.
Speaking to reporters after inspecting the hardest-hit area of Uttaradit's Nampad district, Director-General Wiboon Sanguanpong of the Disaster Prevention and Mitigation Department said search teams are racing to locate four missing villagers. So far three corpses--two men and one woman--have been retrieved. About 700 households have been majorly damaged.
Abhisit Vejjajiva, opposition Democrat party leader, and key party executives brought relief supplies donated by the public to help flood victims in the province. Prime Minister Yingluck Shinawatra is scheduled to visit the villagers later in the day and will come up with measures to further help them.
In other developments, incessant downpours since Saturday night until Sunday morning raised the water level of the Chao Phraya River additional 5-7 centimetres as the river running through the central provinces of Ang Thong and Ayutthaya.
Maitri Pitinanont, chief of irrigation projects in Ayutthaya, said efforts to drain floodwaters to other fields are under way to help ease hardship of residents along riverbanks. Villagers in Bangban and Sena districts fear that this year's water volume will be much more than last year.
In its latest warning issued on Sunday, the meteorological department urged residents in much of the country to brace themselves for heavy and very heavy downpours as there is an intense monsoon trough lying across the Central, East and Lower Northeast. In addition, the strong southwest monsoon prevailing over the Andaman Sea, the South and the Gulf of Thailand are likely to cause torrential rain and isolated heavy to very heavy rail falls much of the country.
Provinces at risk are Tak, Kamphaeng Phet, Phichit, Phetchabun, Lop Buri, Saraburi, Chaiyaphum, Nakhon Ratchasima, Buri Ram, Surin, Si Sa Ket, Roi Et, Mukdahan, Yasothon, Amnat Charoen, Ubon Ratchathani, Kanchanaburi, Ratchaburi, Nakhon Nayok, Prachin Buri, Sa Kaeo, Rayong, Chanthaburi, Trat, Chumphon, Surat Thani, Ranong, Phangnga, Phuket, Krabi and Satun, according to the announcement.
Strong winds and waves in the Andaman Sea and the upper Gulf of Thailand are likely to reach 2-3 metres high. All ships should proceed with caution and small boats keep ashore during the next one to two days.