Heavy rain and strong seas are forecast for the South this long weekend, brought by a powerful low pressure system over the area and the annual northeastern monsoon.
Monday is a national holiday marking the birthday of the late King Bhumibol.
Powerful waves pounded the shorelines and flooding was already reported in several southern provinces on Friday.
Wanchai Sak-udomchai, director-general of the Meteorological Department, said a strong low pressure system over the lower South and Malaysia was moving slowly northwestward, adding to the effect of the northeastern monsoon.
The outlook is for heavy rain in Krabi, Nakhon Si Thammarat, Narathiwat, Pattani, Phatthalung, Phuket, Songkhla, Surat Thani including Koh Samui, Trang, Satun and Yala from Friday to Sunday.
On Sunday and Monday heavy rain is forecast for Chumphon, Krabi, Nakhon Si Thammarat, Phangnga, Phatthalung, Phuket, Prachuap Khiri Khan, Ranong, Songkhla and Surat Thani.
Mr Wanchai warned of flooding caused by runoff.
Small boats are advised to remain ashore until Monday with waves 2-3 metres high forecast in the Gulf of Thailand and the Andaman Sea. People living along the eastern coast of the southern region should take precautions.
Continuous heavy rain caused flooding 30-80 centimetres deep in Ratsada district of Trang province on Friday. Hundreds of houses were awash.
Runoff also caused flooding in Na Mom district and adjacent tambon Khor Hong of Hat Yai district in Songkhla province on Friday.
In Narathiwat, continuous rain flooded Muang Narathiwat municipality. Shops along Narathat beach in Muang district were closed and about 3,000 fishing boats were pulled ashore in Muang and Tak Bai districts as fierce seas swept along the coast.
In Surat Thani, flooding 60-150cm deep was reported in Don Sak, Kanchanadit, Khiri Ratthanikhom, Phrasaeng and Phunphin districts.