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Sunday, 8 September 2024

Passage of Typhoon Yagi kills at least 39 people across the Philippines, South China, and Vietnam.

Typhoon Yagi is now known to have killed at least 39 people as it swept across the  Philippines, South China, and Vietnam between 2 and 7 September 2024. The storm was initially detected as a low pressure system to the northwest of Palau by the Japan Meteorological Agency on 30 August 2024. By 1 September it has moved to the northeast, gaining in strength to become a tropical depression as it entered the Philippine Area of Responsibility (an area of the northwest Pacific monitored by the Philippine Atmospheric, Geophysical and Astronomical Services Administration. The system was identified as Tropical Depression 12W by the Joint Typhoon Warning Center, and named Enteng by red by the Philippine Atmospheric, Geophysical and Astronomical Services Administration, then as it intensified to become a tropical storm, formally named Tropical Storm Yagi by the Japan Meteorological Agency.

Typhoon Yagi made landfall in Aurora Province on Luzon Island, the Philippines, at about 2.00 pm local time on Monday 2 September, taking fifteen hours to move across the island before emerging over the South China Sea at about 3.00 am on Tuesday 3 September. During this time the storm lost considerable energy, particularly as it passed over the Cordillera Central mountain range, but still causing significant disruption. The storm raised the waters of the Marikana River, which flows through eastern Manila, to rise by 16 m, leading to flooding in the Metro Manila area, as well as in the provinces of Bulacan, Camarines Norte, Camarines Sur, Cavite, Laguna, Northern Samar, Pangasinan, and Rizal. A number of ships were driven aground in Manila Bay, with two colliding and catching fire. Twenty people are currently known to have died as a result of the storm on Luzon, nine of them in Rizal Province, with at least more 26 missing and at least eighteen injured. Around 28 000 people in Metro Manila, Calabarzon, and Bulacan, lost their electricity supplies during the storm, schools were closed for two days, and most flights to and from Luzon Island cancelled. About 80 000 people were evacuated from low-lying areas, with 459 homes destroyed and another 6128 damaged. Several dams had to be opened to prevent them being damaged by high waters, adding to the flooding in areas beneath them.

Flooding in Rizal Province, the Philippines, on 2 September 2024. AP

After passing over Luzon Tropical Storm passed across the South China Sea, merging with a smaller depression and gaining significantly in strength as it moved west towards China. By 5 September the storm had gained suficient energy that the Japan Meteorological Agency upgraded it to a Super Typhoon, which is to say a typhoon with windspeeds of 240 km per hour or above, the equivalent to a Category 4 or 5 storm on the Saffir–Simpson scale.

In preparation for this 420 000 people were evacuated from low-lying areas on Hainan Island, and 500 000 from low-lying areas in Guangdong Province, with widespread cancelation of flights, non-essential travel, and coastal activities in both provinces as well as Hong Kong.

Typhoon Yagi made landfall near the city of Wenchang on Hainan at about 4.20 pm local time on Friday 6 September, bringing with it sustained windspeeds of 195 km per hour, making it the strongest storm to hit the island since Typhoon Ramassun in 2014. It passed across the island making, and over the provincial capital, Haikou, before briefly making landfall in Xuwen County, Guangdong Province, then passing out over the Gulf of Tonkin. Four people are reported to have lost their lives on Hainan Island, with another 95 injured, and 1.2 million people losing electricity supplies. Aa further nine people were injured in Hong Kong.

Heavy rainfall and fallen trees in Wenchang City on 6 September 2024. Luo Yunfei/China News Service/VCG/Getty Images.

Typhoon Yaagi gained in strength again as it passed over the Gulf of Tonkin, reaching Vietnam as a Category 4 Typhoon (i.e. a storm with sustained winds in excess of 209 km per hour), making it one of the strongest storms ever to hit northern Vietnam. In preparation for the storm schools were closed and fishing and outdoor gatherings advised against, as well as most flights, ferry services, and sporting events cancelled. The storm made landfall over the city of Haiphong, binging high winds and extensive flooding to the Red River Valley. fifteen people are known to have died in Vietnam, including four people hit by flying debris, another four, described as a family, by a landslide in Hoa Binh, and another man in Hai Dong hit by a falling tree.

High winds caused by Typhoon Yagi on the shore of Phuong Luu Lake in Haiphong. Nhac Nguyen/AFP.

Tropical storms are caused by the warming effect of the Sun over tropical seas. As the air warms it expands, causing a drop in air pressure, and rises, causing air from outside the area to rush in to replace it. If this happens over a sufficiently wide area, then the inrushing winds will be affected by centrifugal forces caused by the Earth's rotation (the Coriolis effect). This means that winds will be deflected clockwise in the northern hemisphere and anti-clockwise in the southern hemisphere, eventually creating a large, rotating Tropical Storm. They have different names in different parts of the world, with those in the northwest Pacific being referred to as typhoons.

The structure of a tropical cyclone. Wikimedia Commons.

Despite the obvious danger of winds of this speed, which can physically blow people, and other large objects, away as well as damaging buildings and uprooting trees, the real danger from these storms comes from the flooding they bring. Each drop millibar drop in air-pressure leads to an approximate 1 cm rise in sea level, with big tropical storms capable of causing a storm surge of several meters. This is always accompanied by heavy rainfall, since warm air over the ocean leads to evaporation of sea water, which is then carried with the storm. These combined often lead to catastrophic flooding in areas hit by tropical storms. 

The formation and impact of a storm surge. eSchoolToday.

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