The Office of National Water and Flood Management Policy and the Meteorological Department are keeping an eye on the movements of Typhoon Nari, which hammered the Philippines on Saturday and is expected to move inland from Vietnam next week.
Nari is expected to hit Vietnam on Tuesday and Wednesday before weakening to a tropical storm and depression, causing light to moderate rainfall in Thailand, the department said on Saturday. (Story continues after graphic)
The current projection by the weather forecast agency is that it will enter Thailand over the Northeast sometime on Wednesday as a tropical storm, quickly deteriorating to a depression.
Supoj Tovichakchaikul, secretary-general of the water management agency, said he hoped that Nari would move toward the North and help fill the Bhumibol Dam in Tak, which is currently only 47% full capacity.
But if the typhoon approaches the East and Central Plains regions, it will worsen flooding and force the Pasak Jolasid Dam in Lop Buri to release more water. This would affect already at-risk areas downstream of the Pasak and Chao Phraya rivers.
Water at Pasak Jolasid is already at 112% of its full capacity and additional rainfall would compel operators to discharge more water, the official said.
However, Mr Supoj dismissed talk of any repeat of Great Flood that severely damaged central provinces and Bangkok two years ago.
Pasak Jolasid can hold 960 million cubic metres of water but was holding 1.076 million cubic metres now, according to a Royal Irrigation Department statement on Wednesday.
Mr Supoj's remarks on Saturday indicated that the water volume in the reservoir now was even higher.
"(Nari) will fill more water but it must go to the North and Northeast. Don't come to the East," he said on a nationally televised programme.
Floods have hit 42 provinces since Sept 17 and 28 of them remain inundated, three of them seriously - Sa Kaeo, Prachin Buri and Chachoengsao, the Disaster Prevention and Mitigation Department said. The conditions have affected 3.5 million people.
Mr Supoj said expected conditions in the three provinces would be back to normal at the end of this month as water is drained out and flows naturally to the Bang Pakong River out to the sea in the Gulf of Thailand.
Disaster Prevention and Mitigation Department director-general Chartchai Promlert promised financial compensation of 33,000 baht per household for all those affected by floods, regardless of the scale of the damage.
In the Philippines, Nari arrived with a vengeance on Saturday, ripping roofs off buildings, killing eight people and leaving more than 2 million people without electricity.
Nari slammed into the east coast around midnight (1am Thailand time), toppling trees and pylons as it cut a westward swathe through the farming regions of the main island of Luzon.
"A lot of big trees have fallen down. Clean-up crews with chainsaws are out to clear the roads," British journalist James Reynolds told AFP from the coastal town of Baler, near where Nari had hit land.
"The wind picked up very quickly, very dramatically. We had the wind coming right off the ocean for four hours, very strong, typhoon-force winds," said Mr Reynolds, who had checked into a hotel two hours before the typhoon struck.
As Nari moved inland, dumping rain, a wall of mud fell on a police barracks near the town of Magalang, killing an officer awaiting deployment to rescue typhoon victims.
Another person was electrocuted by a loose power line in nearby Candaba town, while trees fell on a house and a vehicle in Nueva Ecija province, killing three people.
Two children and an elderly person drowned in the province of Bulacan, which suffered widespread flooding, provincial governor Wilhelmino Alvarado told ABS-CBN television.
The typhoon blacked out 37 towns and cities across central Luzon, according to a tally by the civil defence office in the region.
Road and utility crews were out clearing roads and restoring power, but it could take up to two days before electricity is restored and major highways are reopened to traffic, Nigel Lontoc, a disaster official for the region, told AFP by telephone.
A total of 2.1 million people live in the areas now without electricity, according to official population figures.
The typhoon spared the capital Manila, where the state weather service had warned on Friday about possible widespread flooding.