The tropical depression is poised to dump heavy rain on coastal localities from Thua Thien Hue to Binh Thuan, plus the Central Highlands and Southeastern regions, the NCHMF said.
At 04.00am on October 26, the depression was about 300km off the central coast of Khanh Hoa province, packing winds of 60kph near its centre.
In the 24 hours, it is forecast to move at a speed of 10kph, hit south-central localities and weaken further.
Heavy downpours will be reported in the regions, with rainfall likely to climb as high as 300mm.
Weather experts warned coastal and mountainous localities of severe flooding and landslides when the tropical depression makes landfall.