The floods killed one student in Narathiwat province and have displaced more than 2,700 people, Wasan Chaitaweewong, the head of the local department of disaster prevention and mitigation, told AFP.
Prolonged rain has also forced the suspension of 65 local schools, he said.
A heavy rain warning remains in effect, with continuous rain forecast across 70% of the province until early December, according to the Thai Meteorological Department.
More than 500 soldiers and volunteers have been deployed to distribute relief kits and assist in evacuating residents to safer areas.
Narathiwat governor Trakul Totham said a team has been set up to accelerate water drainage in affected areas.
An employee at a clothing shop said floodwater had ruined her inventory.
"The water came from the back and it took us off guard," she told local media Amarin TV.
While Thailand experiences annual monsoon rains, scientists say man-made climate change is causing more intense weather patterns that can make destructive floods more likely.
Widespread flooding across Thailand in 2011 killed more than 500 people and damaged millions of homes around the country.