Some major dams have been told to discharge water to make room for heavy rain expected from an upcoming storm this week, according to the Office of the National Water Resources (ONWR).
The ONWR and the Thai Meteorological Department are keeping watch on a storm brewing from a low-pressure front.
If it develops into a tropical storm, it is expected to unleash heavy rain in parts of the country from Oct 29-31, said the ONWR deputy spokesman Thanaroj Woraratprasert.
It would be the seventh storm to hit the country this rainy season. The previous storm, Kompasu, drenched much of the Northeast after making landfall in Vietnam in the middle of this month.
With the latest storm alert, the Royal Irrigation Department (RID) has been asked to release some water from large dams in preparation for the forecast downpours, he said.
Rainfall has generally increased throughout the country, Mr Thanaroj said.
The rainy season is predicted to wind down this month or early next month.
Water in dams and reservoirs nationwide stand at a combined 59,920 million cubic metres, with 17 dams and reservoirs 80% above-capacity. They are being closely monitored.
The ONWR's advance team was out inspecting the water situation in the Tha Chin River through which floodwater was being emptied into the sea.
To alleviate the effects of floods, the RID is diverting excess water from the river to the large Pho Phraya field covering U Thong and Muang district of Suphan Buri, which has been set aside as a water catchment area.
Also, discharges from the Pasak Joasid dam in Lop Buri were being carefully regulated to minimise flooding on downstream residents.
At present, floods remain in 15 provinces: Khon Kaen, Chaiyaphum, Maha Sarakham, Nakhon Ratchasima, Buri Ram, Si Sa Ket, Lop Buri, Sing Buri, Suphan Buri, Ang Thong, Ayutthaya, Pathum Thani, Nakhon Pathom, Prachin Buri and Sa Kaeo.
According to the ONWR, floods triggered by the overflowing Chao Phraya River, which receives water from the North, have shown sign of easing in the next few days.