A low-pressure area is being pushed from the north by a mass of cold air, which would cause rainfall of 40-150 mm in northern localities on Monday and Tuesday, the National Center for Hydro-Meteorological Forecasting said Sunday.
Starting Tuesday temperatures will drop due to the mass of cold air, and the weather thereafter will mostly be dry.
U.S. weather service AccuWeather forecast temperatures in Hanoi this week of 25-34 degrees Celsius and in high-altitude locations like Lao Cai's Sa Pa of 15-25 degrees.
In central Vietnam, only provinces between Quang Binh and Ninh Thuan will remain hot, with temperatures elsewhere declining to a maximum of 36-39 degrees during the day.
This will be due to a mass of cold air and an intertropical convergence zone, which will also bring rains of 20-100 mm to the region between Nghe An and Quang Binh. The rainfall will then gradually move to the south.
During the National Day holidays from Sept. 1 to 4 the region between Thanh Hoa and Thua Thien-Hue provinces will see little rain and have maximum daytime temperatures of 32-35 degrees.
Heavy rain is forecast however between Da Nang City and Binh Thuan Province and peak temperatures of 31-34 degrees.
The Central Highlands and southern regions will see rains at dusk until the end of the holiday, and have highest temperatures of 27-30 degrees and 29-32 degrees.