Ha Tinh, Quang Tri, Hue and Danang are expected to bear the brunt of the downpours, driven by strengthening easterly winds.
Rainfall of 50-120 mm is forecast across the four localities from Wednesday morning through Thursday, with isolated areas receiving more than 250 mm. Northern Quang Tri, formerly Quang Binh Province, could see the heaviest rainfall.
Overnight on October 27 and early October 28, moderate to heavy rain was recorded in Quang Tri, Hue, Danang, eastern Quang Ngai and eastern Gia Lai.
Between 7 pm on October 27 and 3 am on October 28, rainfall reached 65.2 mm at Duong Hoa in Hue and 62.6 mm at Hoa Trung Reservoir in Danang.
The heavy rain is expected to ease gradually from late October 29.
Elsewhere, Thanh Hoa, Nghe An, eastern Quang Ngai, eastern Gia Lai, eastern Dak Lak and Khanh Hoa could receive 20-40 mm of rain on October 28, with isolated areas exceeding 80 mm.
Northern Vietnam remains unusually hot
Northern Vietnam is experiencing an unusually prolonged spell of warm October weather, with daytime temperatures reaching 30-33 degrees Celsius and overnight lows of 22-25 degrees.
Hanoi is forecast to remain sunny and dry, with temperatures ranging from 23 to 33 degrees Celsius.
Scattered showers and thunderstorms could return to northeastern Vietnam between late October 29 and October 30.
The Central Highlands, meanwhile, are expected to remain largely dry, with daytime temperatures of 28-31 degrees Celsius and lows of 20-23 degrees. Mostly dry conditions are forecast to continue in much of the region, excluding Lam Dong.
In Lam Dong and southern Vietnam, scattered showers and thunderstorms are expected during the afternoon and evening of October 28, bringing rainfall of 10-30 mm and locally more than 60 mm.
Thunderstorms could be accompanied by lightning, hail, strong gusts and whirlwinds.
Ho Chi Minh City is forecast to see scattered afternoon and evening thunderstorms, with temperatures ranging from 24 to 34 degrees Celsius.
Similar weather is expected to persist across southern Vietnam and Lam Dong over the coming days, with locally moderate to heavy rain.
