The typhoon was rapidly downgraded to a tropical storm, tropical depression and then a low pressure cell, the Meteorological Department announced on Wednesday.
Early Wednesday it was centred over Mukdahan, Amnat Charoen and Ubon Ratchathani, with steady rain falling throughout the day over a much wider region, including Bangkok .
More rain was expected over the Northeast and eastern provinces for the rest of today and tomorrow, particularly Mukdahan, Amnat Charoen, Nakhon Ratchasima, Buri Ram, Surin, Si Sa Ket and Ubon Ratchathani .
From Oct 16 to 19, a strong high pressure system from China will extend to cover upper Thailand. This will lead to a temperature drop of five to eight degrees Celsius in the North and upper Northeast, the weather office said.
Adisak Kanti, director of the city's Drainage and Sewerage Department, said most areas of Bangkok were hit by steady rain and flooding triggered by the storm on Wednesday morning.
Mr Adisak said the eastern part of the capital, particularly Sai Mai, Don Muang, Kanna Yao, Min Buri and Prawet districts, were expected to see more rain throughout the day.
Work crews were quickly draining water from swollen canals in Bangkok to the Chao Phraya River, he said.
"I ask the people not to be worried because Bangkok officials are doing their best, but there might be some traffic congestion and water on roads waiting to be drained," Mr Adisak said.
According to the Bangkok Flood Control Centre, the entire Bangkok area had experienced steady rainfall since about 1am.
The Metropolitan Police Bureau's traffic police division advised commuters in the city to try to avoid using nine roads due to flooding and heavy traffic congestion on Wednesday -- Suwintawong, Ratchaprarop, Chaeng Wattana, Ngam Wong Wan, Vibhavadi-Rangsit, Phahon Yothin, Prasert-Manukitch, Rama IV and Sukhumvit.
In Vietnam, at least seven people died and four remained missing after high winds and rain caused by Typhoon Nari hit the central part of the country.
Dau Minh Ngoc, chairman of Quang Son district's People's Committee, said two people were killed and 22 injured when high winds destroyed houses in Quang Binh province.
According to the National Search and Rescue Committee, five people died on Tuesday after the typhoon made landfall at around 7am, uprooting trees and causing power outages.
Around 120,000 people were evacuated to makeshift shelters.
Torrential downpours over the past 24 hours brought rainfall of between 140 and 315 millimetres to central Vietnam.