Somsak Khaosuwan said that on Thursday morning the storm was about 600 kilometres southeast of Danang, Vietnam, with wind speeds near its epicentre about 80 kilometres per hour.
It would land in central Vietnam and then cover Thailand from Friday to Sunday. He expected heavy rain throughout the country during the period, as the southwest monsoon still covered the Andaman Sea and the Gulf of Thailand would become stronger. Mr Somsak warned of flooding, runoff and strong winds.
Heavy rain was forecast on Friday for parts of the Northeast, East and the South. It would expand into the North and the Central Plains, including greater Bangkok, on Saturday and continue on Sunday, except the Northeast.
Mr Somsak said small boats should remain ashore until Sunday.