The Meteorological Department has warned of heavy rain and runoff in many southern provinces from Wednesday night until Friday.
Wanchai Sakudomchai, director-general of the department, said on Wednesday that a depression over the lower part of the South China Sea would reach the Gulf of Thailand Wednesday night, bringing heavy rain to southern provinces.
Severe weather conditions are expected in Nakhon Si Thammarat, Narathiwat, Pattani, Phatthalung, Songkhla and Yala provinces on Wednesday night.
On Thursday and Friday, heavy rain is possible in Chumphon, Krabi, Nakhon Si Thammarat, Phangnga, Phatthalung, Phuket, Prachuap Khiri Khan, Ranong, Songkhla and Surat Thani.
Waves in the Gulf of Thailand and the Andaman Sea are expected to be 2-3 metres high. Small boats should be kept ashore and people should beware of strong waves striking the coastline during the period, Mr Wanchai said.