The National Centre for Hydro-Meteorological Forecasting said a fairly strong cold air mass would move into northern Vietnam from the night of October 4 and early morning of October 5.
Under its influence, moderate rain and thunderstorms are expected across the northern region from the evening of October 4 until noon on October 5, with some areas likely to see heavy rain.
Temperatures are forecast to fall by 8-10 degrees Celsius, with the eastern part of the northern region expected to be affected most strongly.
On October 5-6, northern provinces and cities will experience cool conditions at night and in the early morning, while mountainous areas are expected to become cold during these periods.
People are advised to be alert for thunderstorms, whirlwinds, hail and strong wind gusts as the cold air moves in.
In Hanoi, temperatures on October 4 are forecast to range from 22 to 27 degrees Celsius. Minimum temperatures on subsequent days are expected to remain around 21-22 degrees Celsius.
The cold air will also bring unsettled weather to central Vietnam.
From the night of October 4 to October 6, Thanh Hoa to Quang Tri is forecast to see scattered showers and thunderstorms, with heavy rain possible in some areas.
From around October 6 to 10, Hue and the south-central coast are expected to continue experiencing scattered showers and thunderstorms, with locally heavy rain.
The US-based AccuWeather forecasts that Hanoi's temperatures on October 4-5 will be 5-6 degrees Celsius lower than current levels. Rain is expected, with highs of 28-29 degrees Celsius and lows of 22-23 degrees Celsius.
The national weather agency said average temperatures across Vietnam in October are forecast to be 0.5-1.5 degrees Celsius above the long-term average, with some areas potentially recording higher deviations.
