The Meteorological Department has warned that the incoming tropical storm Sonca will bring heavy rain to most parts of the country from Tuesday to Friday.
It reported that the storm was about 350 kilometres east of Vinh, Vietnam, on Monday morning, with winds of about 65 kilometres an hour near its centre.
The storm was slowly moving west and was expected to make landfall in Vietnam on Tuesday. It is then expected to become a depression before entering Laos, the upper Northeast and the North.
The department predicted that on Tuesday and Wednesday heavy rain would hit the North in Mae Hong Son, Chiang Mai, Chiang Rai, Lamphun, Lampang, Phayao, Phrae, Nan, Uttaradit, Sukhothai, Phitsanulok and Phetchabun provinces.
Heavy rain is also expected in the northeastern provinces of Nong Khai, Bung Kan, Udon Thani, Nong Bua Lam Phu, Khon Kaen, Chaiyaphum, Nakhon Ratchasima, Sakon Nakhon, Kalasin, Mukdaman, Amnat Charoen, Yasothon, Surin, Si Sa Ket and Ubon Ratchathani.
In the East, downpours are expected in Prachin Buri, Sa Kaeo, Chon Buri, Rayong, Chanthaburi and Trat.
Map via Weather Underground
On Thursday and Friday, more rain is likely in the northern provinces of Mae Hong Son, Chiang Mai, Lamphun, Lampang, Phayao, Phrae, Nan, Sukhothai, Kamphaeng Phet and Tak provinces.
In the Northeast, downpours are predicted in Loei, Nong Bua Lam Phu, Chaiyaphum and Nakhon Ratchasima.
In the East, heavy rain is forecast in Chon Buri, Rayong, Chanthaburi and Trat.
The Meteorological Department warned that flooding is a serious possibility.
Suchart Charoensri, irrigation director in the central plain province of Chai Nat, said that water dumped by Sonca would reach the Chao Phraya river basin next week, and the Chao Phraya dam in Chai Nat was discharging more water to offset the storm's impact.
The faster discharge would raise the level of the Chao Phraya River downstream in Ang Thong and Ayutthaya province by 15-25 centimetres, he said
In the northeastern province of Nakhon Phanom, local authorities warned residents of possible flooding from the Mekong River, which was rising 20-30cm a day. The level stood at 10 metres on Monday while its overflow level is at 13 metres.
In Kalasin province, also in the Northeast, governor Suwit Khamdee said irrigation officials had increased the discharge rate at the Lampao dam to prepare its reservoir to cope with the impact of storm Sonca.