Heavy downpours triggered by the arrival of a cold air front caused traffic problems early April 17 morning in Vĩnh Phúc Ward, the northern province of Phú Thọ.— VNA/VNS Photo

HÀ NỘI — The northern region is set to receive three consecutive cold spells, with meteorologists warning of a high risk of extreme weather including squalls, tornadoes and hail during the seasonal transition.

According to Nguyễn Văn Hưởng, Head of the Weather Forecasting Division at the National Centre for Hydro-Meteorological Forecasting, the first cold spell swept into the country from the night of April 16 to April 17. The second will arrive on the evening of April 18 and last until April 20, and the third will run from April 22 to April 24.

Under the influence of a low-pressure trough — formed by the boundary between a hot, humid air mass and a cooler mass moving down from the Chinese mainland — showers and thunderstorms broke out in the early hours of April 16 across northern Lào Cai and Tuyên Quang provinces, with hail recorded in Bắc Hà (Lào Cai).

Hưởng said further rounds of strong thunderstorms are likely on April 20–21 and April 22–23, with a high risk of squalls, tornadoes, hail and strong gusts, particularly across the midlands and northern mountainous areas. Vessels in the Gulf of Tonkin should also be wary of waterspouts.

From April 17 through April 22, the north will experience cool weather. Most forecast models indicate Hà Nội will remain cooler through the end of April, with little likelihood of another heatwave, though temperatures of about 32°C can still feel muggy.

Dr Nguyễn Ngọc Huy, a climate change and disaster warning expert, said that from April 20 the hot air mass will shift towards India as a cold high-pressure system from the north moves in, lowering temperatures across the northern and north-central regions. He explained that heated ground after a prolonged heatwave generates rising vapour columns which condense upon meeting cold air, with water crystals pushed upward to produce hail.

The Department of Dyke Management and Natural Disaster Prevention advised the public to reinforce houses — particularly corrugated-iron roofs — advertising signs and temporary structures, prune nearby trees and inspect electrical systems. During thunderstorms, people should stay inside sturdy buildings, avoid sheltering under large trees or power poles, and limit use of electrical appliances. In the event of hail, people should seek safe shelter immediately. After a disaster, people should remain alert to fallen power lines, toppled trees and landslide risks.

In the early hours of April 16, hail lasting 15–30 minutes struck Bắc Hà commune in the northern mountainous province of Lào Cai, with many stones five to seven centimetres in diameter. Initial reports recorded four people injured, more than 330 houses damaged and nearly 500 hectares of crops affected. — VNS