The provinces that would be affected are: Nakhon Phanom, Sakon Nakhon, Mukdahan, Amnat Charoen and Ubon Ratchathani.
"Saudel", located near the southern part of Vietnam, has already weakened into a category-2 tropical depression, the department said.
The storm is moving westwards at 15 kilometres per hour, and will reach upper Vietnam on Monday, before it gradually weakens and influences rains in the Northeast of Thailand.