The province of Narathiwat, where hundreds of villages have been evacuated, was said to be hardest hit.
A reservoir has filled to capacity, prompting warnings about possible landslides, officials told the Bangkok Post.
Waves from 6 to 9 feet have been reported in the Gulf of Thailand, prompting a small boat advisory through Sunday night. A 36-foot fishing boat sank in the area Saturday, officials said.
No reports of casualties resulting from the weather had been compiled.