The Meteorological Department warned Monday that tropical storm Sonca will trigger torrential rain in most parts of Thailand Tuesday and Wednesday, while the Department of Disaster Prevention and Mitigation (DDPM) warned 43 provinces in upper Thailand to brace for the impact of the storm.
Centred in the South China Sea close to Vietnam Monday, Sonca was expected to taper into a tropical depression and then a low pressure cell as it moves past neighbouring Laos into Thailand's North and the Northeast, said the department.
Sonca is the fourth tropical storm in the South China Sea so far this year.
Certain provinces in the North, Northeast and the East were likely to be hit by Sonca Tuesday and Wednesday.
- Earlier report: Storm set to soak most of Thailand
A smaller number of them will still be affected on Thursday and Friday, the department said.
They are Mae Hong Son, Chiang Mai, Lamphun, Lampang, Phrae, Nan, Sukhothai, Kamphaeng Phet, Tak, Loei, Nong Bua Lam Phu, Chaiyaphum, Nakhon Ratchasima, Chon Buri, Rayong, Chanthaburi and Trat.
People living in these provinces are being advised to prepare for possible flash floods.
The DDPM also warned 43 provinces to stay on high alert around the clock for possible natural disasters that may occur until Thursday as a result of Sonca.
People living at the foot of a hill, in low-lying areas and in coastal areas are being warned to prepare for evacuation when necessary, said Chatchai Phromlert, director-general of the DDPM.
Meanwhile, water in the Mekong River in many districts of Nakhon Phanom, Bung Kan and Kalasin was diverted to smaller waterways Monday, to prepare for more rain from the tropical storm. Those living near river banks are advised to keep a close watch for rising water levels.
In Chiang Rai, certain parts in Muang, Mae Fa Luang and Phan districts have already experienced flooding and landslides. Floods about 20 centimetres to 1 metre deep were reported in tambon Bua Sali in Muang district as run-off continued to flow into those districts.
A man carries his daughters to higher ground as heavy rains in Chiang Rai province cause landslides and floods. (Post Today photo)
A road leading up to Doi Tung in Mae Fa Luang district became impassible Monday following a landslide that blocked access.
About 70 households in tambon Charoen Muang of Phan district were forced to move their rice to higher ground after the Mae Khao Ton River overflowed its banks, said Woraphan Lamphongnua, president of tambon Charoan Muang administration organisation.
Suchat Charoensri, director of the 12th Royal Irrigation Office in Chai Nat, said a rise in water coming into the Chao Phraya dam pointed to the need for the dam to release water at a higher rate. That is expected to lead to a rise in water levels downstream of between 15cm and 25cm.
People living in Ang Thong and Ayutthaya provinces in particular are being warned to prepare to deal with possible flooding.