Nguyen Duc Hoa, deputy head of the Climate Forecasting Division at the National Centre for Hydro-Meteorological Forecasting, said heavy rain was expected to be concentrated mainly in central Vietnam during the month.
Total rainfall in northern mountainous areas is forecast to be 5-20 per cent above the long-term average, while the rest of northern Vietnam and areas from Thanh Hoa to Hue are expected to receive 20-40 per cent less rainfall.
Rainfall in the south-central coast, Central Highlands and southern Vietnam is forecast to be 5-20 per cent below average.
Cold air is expected to continue affecting northern and central Vietnam. Average temperatures nationwide are forecast to be 0.5-1.5 degrees Celsius above the long-term average, with some areas seeing higher deviations.
Storms and tropical depressions in the East Sea are expected to be less frequent than average but could still affect mainland Vietnam.
Forecasters warned that the intertropical convergence zone, combined with upper-level wind convergence, the southwest monsoon and cold air, could trigger widespread rain and severe weather.
Strong winds at sea may also occur due to cold air, the southwest monsoon, tropical cyclones or local thunderstorms, posing risks to vessels.
Authorities and residents have been advised to closely follow short-term weather forecasts and warnings to adjust production and response plans.
In September, the East Sea saw one storm, SauDel, and one tropical depression.
Northern Vietnam experienced three spells of rain during the month. Heavy rain from September 14-17 brought 300-500 mm to parts of the northern delta, Phu Tho and Bac Ninh, with some areas receiving more than 600 mm.
Central Vietnam saw three widespread rain spells, with rainfall from September 9-26 reaching 300-700 mm in many areas and exceeding 1,000 mm in some places.
Northern and central Vietnam also experienced four widespread heatwaves, with highs of 35-38 degrees Celsius and above 38 degrees in some areas.
A cold spell on September 10 brought widespread heavy rain and thunderstorms to northern Vietnam, lowering average daily temperatures by 1.5-3.5 degrees Celsius across the north and from Thanh Hoa to Ha Tinh.