The Office of National Water Resources (ONWR) is warning that the North and Northeast face a new round of floods as a low-pressure front passes across the South China Sea and a monsoon picks up over the Andaman Sea.
Its deputy secretary-general, Samroeng Sangphuwong, said current weather conditions over Thailand would result in continuous and heavy rain in some areas, particularly in the upper part of the country.
The northern provinces of Chiang Rai, Phayao and Nan saw accumulated rainfall in the past 24 hours of more than 150 millimetres and were at risk of forest runoffs, landslides and flash flooding.
Mr Samroeng said the northern and northeastern provinces should brace for possible flooding today.
In Nakhon Ratchasima, and seven other northeastern provinces, heavy rain on Thursday caused flooding on many roads and farmland.
In the inner part of the province, many main and minor roads were submerged, including Ratchadamnoen Road in front of the provincial governor's residence and Route 304, which passes the Suranaree University of Technology.
The Meteorological Department reported that Nakhon Ratchasima and many other provinces in the lower Northeast would continue to see heavy or very heavy rain, until this morning at least.
In Kalasin, Huay Pho reservoir in Muang district now has about 2.52 million cubic metres of water or 103% of its capacity.
The reservoir has received a massive amount of water from the inner part of the province, which has been deluged by heavy rain.
Villagers near the reservoir had said they wanted to rid it of weeds under the water as much as possible, so that it could store more water during this rainy season.
The villagers said they had to closely monitor the water situation since their rice fields might be inundated if there were any more downpours.
The Meteorological Department has forecast downpours for today in 39 provinces in the North, Northeast and East, as well as thunderstorms in all regions.
The heavy rains are a product of a monsoon trough in the upper part of the country passing a low-pressure system in the South China Sea and a southwest monsoon in the Andaman Sea and Gulf of Thailand.