According to the National Center for Hydro-Meteorological Forecasting, the highest temperature in the northern region on Saturday was 37 degrees Celsius, recorded at Phu Yen station in Son La Province and Mai Chau in Hoa Binh Province.

In Hanoi, five monitoring stations recorded temperatures above 35 degrees Celsius, the official threshold for heat wave classification.

On Sunday, the heat wave intensified and expanded across the north, with many locations seeing temperatures surpassing 37 degrees Celsius. In Hanoi, clear skies and strong sunlight were recorded as early as 8 a.m., with temperatures hitting 32 degrees and rising steadily at a rate of 1–1.5 degrees Celsius per hour.

A low-pressure area in the west has triggered the widespread heat wave. Temperatures are forecast to reach 35–37 degrees Celsius, and up to 38 degrees in Hanoi and some areas in the Red River Delta on Sunday, according to the national meteorological agency.

The U.S.-based AccuWeather website predicted that Hanoi will experience extreme heat ranging from 28 to 41 degrees Celsius on Sunday and Monday, before cooling slightly to 26–33 degrees starting Tuesday.

In higher-altitude areas above 1,500 meters such as Sa Pa, temperatures are expected to range from 18 to 25 degrees Celsius.

The heat wave in northern Vietnam is forecast to last until Tuesday. Starting that evening, widespread thunderstorms are expected, especially in the midlands and mountainous regions.

In the central region, the heat wave began a day earlier than in the north, due to the combined effects of the western low-pressure zone and hot, dry foehn winds. Since Sunday, temperatures have hovered around 35–36 degrees Celsius, with some areas recording higher figures, including places in Thanh Hoa, Nghe An, and Ha Tinh provinces.

The heatwaves are forecast to persist across provinces from Thanh Hoa to Binh Thuan, with temperatures ranging from 36 to 38 degrees Celsius, and some locations exceeding 39 degrees.

Meanwhile, the Central Highlands and southern regions are under the influence of a southwest monsoon. These areas will likely experience late afternoon thunderstorms, with daily high temperatures ranging from 29–32 degrees Celsius in the Central Highlands and 32–34 degrees in the south.