A ride-hailing driver in Huế City drinks water while travelling on the road to stay hydrated amid scorching heat. — VNA/VNS Photo Nguyên Lý

HÀ NỘI — An unusual June cold air mass is expected to sweep into northern Việt Nam from Monday evening, triggering widespread heavy rain, cooler temperatures and bringing relief from a prolonged heatwave that has gripped much of the country since late May.

According to the National Centre for Hydro-Meteorological Forecasting, the cold air system is currently moving southward from China and is forecast to begin affecting northern mountainous areas on the evening of June 8 before expanding across the northeast, parts of the northwest and the north-central region.

Meteorologists said cold air intrusions in June have become increasingly rare. Data collected between 1979 and 2025 show 25 cold-air events occurred during June. Since 1991, however, only seven such events have been recorded, while none were observed between 2014 and 2025, indicating a warming trend linked to climate change.

The incoming weather system, combined with upper-level wind convergence at around 5,000m, is expected to generate widespread moderate to heavy rainfall across northern Việt Nam from the evening of June 8 through June 9.

Authorities warned that severe thunderstorms, heavy rain and strong winds could damage crops, trees, homes and infrastructure, while increasing the risks of flooding in low-lying areas, flash floods along small rivers and streams, and landslides in mountainous terrain. Rough seas and strong winds may also disrupt maritime activities.

The heaviest rainfall is forecast in the northwestern region and northern parts of Phú Thọ and Tuyên Quang provinces, where rainfall totals could reach 80-160mm, with some isolated areas receiving as much as 250mm.

Rainfall in Thanh Hóa and Nghệ An provinces in central Việt Nam is forecast at 50–100mm of rain, with some localities likely to record more than 150mm.

Elsewhere across the north, rainfall totals of 20-50mm are expected, although some areas could receive more than 100mm. Forecasters warned of intense downpours exceeding 100mm within three hours in some locations.

Thunderstorms accompanying the rain may bring lightning, hail and strong winds, while mountainous areas face heightened risks of flash floods and landslides.

The cold air mass is also expected to bring a sharp drop in temperatures. In the northeast and Thanh Hóa Province, daytime temperatures on June 9 are forecast to fall by 5-7 degrees Celsius, with highs remaining below 31 degrees Celsius.

Overnight temperatures are expected to range between 22 and 25 degrees Celsius, while some mountainous areas could see temperatures fall below 21 degrees.

In Hà Nội, moderate to heavy rain and thunderstorms are forecast from Monday evening through Tuesday morning, with some districts potentially experiencing very heavy rainfall. The capital is expected to turn noticeably cooler overnight, with minimum temperatures ranging between 23 and 25 degrees Celsius.

At sea, the cold air system is forecast to strengthen northeasterly winds in the northern Gulf of Tonkin from Monday night. Winds could reach force 4-5, occasionally force 6, with gusts up to force 7 and waves of 1.5-2.5 metres, creating rough conditions for vessels. — VNA/VNS