According to the National Centre for Hydro-Meteorological Forecasting, the cold air mass will affect northeastern Vietnam on the evening and night of October 4 before spreading to other parts of the north and the area from Thanh Hoa to Hue.
In Hanoi, the cold air will arrive from the night of October 4. From the evening of October 4 to the morning of October 5, the capital is expected to experience rain, moderate rain and thunderstorms, with some areas receiving heavy downpours.
From the early hours of October 5, Hanoi will turn cold, with the maximum temperature falling to about 26 degrees Celsius.
The cold spell is expected to bring minimum temperatures of 19 to 22 degrees Celsius across northern Vietnam and Thanh Hoa, falling to 14 to 17 degrees Celsius in high mountainous areas.
Under the combined influence of the cold air mass and the tropical convergence zone, northern Vietnam will experience rain, moderate rain and thunderstorms from the evening of October 4 to the morning of October 5. Rainfall is expected to reach 20-40mm, with some areas receiving more than 130mm.
From the night of October 5 through October 6, areas from Ha Tinh to Hue are forecast to see moderate to heavy rain and thunderstorms, with rainfall of 40-80mm and isolated areas receiving more than 150mm.
The weather agency warned that rainfall could exceed 100mm within three hours in some areas, increasing the risk of flash floods, landslides and localised flooding.