Chatchai Promlert, the director-general of the department, issued the warning at a press conference on Friday.
He said the provinces that are under threat of floods and mudslides are Chumphon, Surat Thani, Nakhon Si Thammarat, Phatthalung, Songkhla, Pattani, Yala, Narathiwat, Ranong, Phang Nga, Phuket, Krabi, Trang and Satun.
The department has coordinated with provincial administrations to be on standby around the clock to help people in need, Chatchai said.