The Meteorological Department predicted tropical storm Tembin would arrive in the Gulf of Thailand and the South on Tuesday or Wednesday and bring heavy rain to the South.
Wanchai Sakudomchai, director-general of the department, said on Monday evening that typhoon Tembin already weakened and became a tropical storm in the middle part of the South China Sea and was moving westerly.
He expected the storm to pass southern Vietnam on Tuesday and become a depression and then a low-pressure system quickly when coming into contact with a high pressure area over Thailand.
Then Tembin would enter the Gulf of Thailand and the South on either Tuesday or Wednesday, Mr Wanchai said.
He warned of heavy rain in Chumphon, Prachuap Khiri Khan and Surat Thani provinces and rain in upper Thailand.
He advised owners of small boats to remain on shore until Wednesday as waves in the gulf were likely to be 2-4 metres high.