Heavy rain on Sunday flooded many roads in Bangkok, including the major arteries of Ratchadaphisek and Ramkhamhaeng. Pictures posted on Twitter showed flooding at Rajamangala National Stadium.
The Bangkok Metropolitan Administration reported stretches of 17 different roads were underwater.
Pattaya and Bang Lamung districts in Chon Buri were also hit by torrential rain on Sunday. The downpour started around 1pm and lasted about two hours, flooding numerous roads and causing traffic congestion.
Pattaya's Beach Road, including the Walking Street section, saw water levels rise to between 30 and 50 centimetres. Officials and volunteers helped move stalled cars to higher ground.
The worst hit area of the resort city was a road running parallel to the eastern railway tracks, with water rising to one metre in places.
The flooding in most areas started to subside once the rain stopped.
Rainfall in the eastern, northeastern, central and southern regions was due to a weather system blowing into the country from the South China Sea, said Chaicharn Sitthiworranan in the Meteorological Department's daily forecast on Sunday. Rain will continue on Monday, the forecaster added.
Netizens on social media pointed to Typhoon Trami as the cause of heavy rains in the country but Mr Chaicharn dismissed the claims.
"Typhoon Tsami will have no impact on the weather in Thailand," he said, but advised travellers to Taiwan and the Chinese coast near Taiwan check weather conditions from Monday to Wednesday as Trami is approaching those areas.
