Warnings of flash floods and landslides in mountainous areas and localised flooding in low-lying and riverside areas have been issued by the national weather agency.
As of 1pm on December 18, the storm was located 650 kilometres east-southeast of the Binh Dinh-Khanh Hoa coast, sustaining 150-165 kilometres per hour winds near its centre.
Over the next 24 hours, the system will move west-northwest before changing its direction north towards Da Nang-Quang Nam in the following 24-48 hours.
Rai is then forecast to move northeast at a speed of 15-20 kilometres per hour and weaken to a tropical depression.
From December 18 night to December 19, total rainfall of 100-250 millimetres is forecast for the provinces from Thua Thien Hue to Khanh Hoa, with some places expected to receive more than 300 millimetres.
At a meeting on December 17 to respond to the storm, Deputy PM Le Van Thanh asked localities to warn fishing boats to find safe shelter, ensure safety for people and properties, and protect dykes and production facilities.
