The Meteorological Department has forecast continuous rain, with isolated heavy rain, throughout the country in the next seven days.
With a monsoon trough lying across the lower North, the upper Central and the Northeast, continuous rain is likely over in the areas with isolated heavy rain on Oct 2-3.
During Oct 4-8, moderate high pressure areas from China covering Laos and Vietnam will cause more rain with isolated heavy rain in the North and the Northeast.
During the same period, the monsoon trough that lies across the Central, the East and the lower Northeast will cause more rain with isolated heavy to very heavy rain.
A southwest monsoon will prevail over the Andaman Sea, the south and the Gulf of Thailand throughout the week. So isolated heavy rain is likely in the southwest coast and the East.
Wanchai Sak-udomchai, director-general of the Meteorological Department, said his office has exchanged weather information with the Royal Irrigation Department for effective water management.
He said heavy rain is expected to continue in the next two weeks, especially in the upper Central Region, that will also be affected by run-off from the North.
Provinces under special watch are Ayutthaya, Ang Thong and Sing Buri.
Lertchai Sri-anan, director of the office of water management and hydrology of the Royal Irrigation Department, said despite the forecast of rain until the middle of this month, he believed Bangkok would not be affected as the volume of run-off from the North had begun to decrease.
Water dischaged from the Chao Phraya Dam in Chai Nat province has been reduced to 1,786 cubic metres per second while the Chao Phraya River below the dam is capable to taking up to 3,500 million cubic metres of water.
The Royal Irrigation Department is carefully managing water in Pasak Jolasid Dam, which is now holding 860 million cubic metres of water, while its full capacity is only 960 million cubic metres.
The water levels in Bhumibol, Sirikit and Kwae Noi Bamrung Daen are still manageable, Mr Lertchai said.