Soldiers assist local residents in Lạng Sơn Province to wade through flooded areas. Lạng Sơn Province is one of the hardest hit localities in the north following impacts of Typhoon Narra. — VNA/VNS Photo

HÀ NỘI — Typhoon Narra, the fourth typhoon to hit Việt Nam this year, entered the Gulf of Tonkin in the early hours of August 21 — but it did not weaken into a tropical depression until the evening of August 25, when it moved toward China’s Hainan Island. 

The typhoon set the record for the longest duration in the Gulf of Tokin.

Director of the National Centre for Hydrometeorological Forecasting Mai Văn Khiêm said Typhoon Narra has followed a relatively unusual track and displayed abnormal developments over the Gulf of Tonkin. The typhoon is moving very slowly, at an average speed of only 3-5km per hour, while changing direction several times, he said.

“Instead of quickly moving ashore or weakening as it enters the Gulf of Tonkin, as is commonly seen in many cases, Typhoon Narra has moved in loops, changed direction and, at times, moved back toward the open waters of the gulf,” Khiêm said.

Another notable feature of the typhoon was the relatively long period during which it maintained its influence over the Gulf of Tonkin, he added. 

After forming and entering the gulf on August 21, the typhoon maintained a strong circulation for several days, at times reaching gale force winds at 8-9 on the Beaufort scale (63-87kph) with gusts of up to force 11, or 104-117kph.

Its complex track, slow movement and prolonged lifespan have resulted in the typhoon's circulation affecting the Gulf of Tonkin and mainland areas for considerably longer than usual, he said.

From a meteorological perspective, Khiêm said the unusual behaviour was associated with a weak and complex steering environment in the region. The typhoon was operating within the Intertropical Convergence Zone, while the large steering flow failed to establish a stable direction of movement.

At the same time, the typhoon was subject to the combined influence of surrounding atmospheric systems and the vortex's own internal dynamics. As these influences shifted over time, the typhoon's direction and speed also changed, resulting in a curved or looping track and sharp turns.

According to Khiêm, most storms that enter the Gulf of Tonkin quickly make landfall or weaken over the gulf. In contrast, Typhoon Narra followed a winding track before turning back toward the open sea.

Its prolonged presence over the gulf has caused protracted rainfall, resulting in flooding of rivers in northeastern and north-central Việt Nam in recent days.

“Normally, a typhoon takes only about one to two days to cross or remain over the relatively narrow Gulf of Tonkin before making landfall, and some storms remain there for just around 12 hours. The fact that Narra maintained its storm structure over the gulf for several consecutive days is very rare,” he said.

He added that in other months, particularly July, there have also been storms that remained over the Gulf of Tonkin for an extended period. In 1994, Typhoon Amy remained over the gulf for four days, from July 27 to 30.

Typhoon Narra and its torrential rains left two people dead and three others injured in northern Việt Nam.

The two deaths were reported in Lạng Sơn Province, while the three injured people were in Hà Nội, and Sơn La and Quảng Ninh provinces, respectively.

More than 1,000 houses were damaged, with roofs blown off, while thousands of homes were deeply inundated and isolated. 

The typhoon also damaged more than 28,000ha of rice and other crops and over 9,000 ha of trees, as well as livestock, poultry and aquaculture. 

It also damaged irrigation and transport infrastructure and left more than 50,000 households without electricity. — VNS