Initial reports show the storm, the 8th of its kind to hit Vietnam this year, was downgraded quickly when it moved near the central coast.
The storm, sustaining gale-force winds of 74kmp near its centre, caused little damage to localities when it moved further inland.
However, heavy rains over the past few days have triggered water levels to rise quickly in major regional rivers.
Violent floodwaters on September 18 swept away 12 residents working on a rice field in Ea Sup border district of Dak Lak province. One dead body was found in the evening while 11 others remain missing.
Rescue forces are working around the clock to search for the missing, but the raging torrent hampered the rescue work.
Severe flooding was also reported in many places in Ea Sup district, prompting local armed forces to evacuate 180 residents from the isolated areas to safe grounds.
Floodwaters also submerged more than 800ha of crops and 24 fishing ponds in the district.
Although the storm did not bring heavy rains and strong winds to Danang, the city still allowed all students off school on September 19 for safety reasons.
In Quang Nam province, floods left one missing in Dong Giang district, triggered landslides in some parts of communal roads, and isolated 6 remote communes.
Dai Loc district urgently evacuated more than 1,300 households from low-lying areas to safer grounds.
Heavy downpours flooded sections of a key road from Hue City to A Luoi district in Thua Thien-Hue province and Highway 24 from Quang Ngai to Kon Tum provinces, disrupting traffic.
River levels from Quang Binh to Quang Nam provinces are forecast to rise to the second alert level on September 19.
Some images of local residents coping with storm No 8: