The Phuket Marine Office has warned boats to be careful when going to sea until September 18 due to Typhoon Mangkhut.
It said Mangkhut in the Pacific Ocean is likely to move through the Philippines and Taiwan on Friday and Saturday.
It will then move into the South China Sea and move towards Hong Kong before making landfall over southern China by September 16-18, the agency forecast.
The strong southwest monsoon will continue over the Andaman Sea and the Gulf of Thailand.
Downpours are forecast for the country, especially on the southwest coast.
The Andaman Sea could see waves up to 2-3 metres high and all boats should proceed with caution and small boats stay ashore until September 18, the warning said.
"Passengers should wear life jackets at all times they are on boats and captains must follow the directions from officers at each pier,” it added.