On the early morning of October 17, the capital city of Hanoi experienced a relatively dense layer of fog compared to usual, with visibility sharply reduced from midnight to early morning.
According to the National Center for Hydro-Meteorological Forecasting, the main reason is that this year’s early-season cold air mass has appeared earlier than average, beginning in mid-October and gradually intensifying from November.
A combination of weak cold air, high humidity from the Gulf of Tonkin, temperature inversion and calm winds led to fog that lingered for several hours this morning.
Meteorological experts noted that in Hanoi, fog typically occurs from October through March in the following year, peaking from December to February when cold weather and high humidity coincide. Fine dust and air pollution during this period further thicken the fog, creating a heavy, lingering effect even in light sunlight.
