Typhoon Yagi Rapidly Intensifies Unusually, Reaching the Strongest Levels in 30 Years, Partly Due to Rising Sea Temperatures in the South China Sea.
Typhoon Yagi (also known as Typhoon No. 3 or Typhoon Enteng) is a powerful tropical storm that has impacted the Philippines, China, and Vietnam. It is the eleventh named storm of the season and the first super typhoon of the annual typhoon season. Yagi is one of the four Category 5 super typhoons recorded in the South China Sea according to the Saffir-Simpson Hurricane Wind Scale, following Typhoon Pamela in 1954, Typhoon Rammasun in 2014, and Typhoon Rai in 2021.
Yagi originated from a low-pressure area formed on August 30, approximately 540 km northwest of Palau. On September 1, this system was classified as a tropical storm and named Yagi by the Japan Meteorological Agency (JMA).
Satellite image of Typhoon Yagi on September 4. (Photo: NOAA).
After making landfall in Casiguran, Aurora in the Philippines on September 2, Yagi weakened as it moved inland through the rugged Cordillera Central in Luzon. It later entered the South China Sea and merged with a secondary circulation system west of Lingayen Gulf, causing deep convection to begin swirling and developing convective cloud bands extending westward and southward.
On September 5, Yagi intensified into a super typhoon at Category 16, with gusts exceeding Category 17, and wind speeds ranging from 184 to 201 km/h. After weakening during a cyclone replacement cycle, Yagi regained strength before making landfall near the city of Wenchang, Hainan Province, China on September 6. Yagi passed north of Hainan Island and directly impacted the provincial capital Haikou. The storm made landfall in Quang Ninh and Hai Phong on September 7, then moved southwest deep inland. After more than 15 hours overland in Vietnam, Typhoon Yagi weakened to a tropical depression in the Northwest region.
Previous super typhoons primarily formed in the Northwest Pacific Ocean before entering the South China Sea, usually weakening in intensity; it is rare for a super typhoon to form directly in the South China Sea. Statistics indicate that no storm has entered the South China Sea, intensified into a super typhoon, and directly affected Vietnam. Only two storms from the Northwest Pacific reached super typhoon status in this area but did not impact Vietnam’s mainland. These are Typhoon Rai in December 2021, which reached Category 16 in the South China Sea, aimed at Central Vietnam but then veered away, dissipating in the North of the South China Sea. The second is Typhoon Saola in August 2023, which reached super typhoon status in the South China Sea and moved into southern China. Yagi is the strongest super typhoon to have operated in the South China Sea in the last 30 years.
Another distinguishing feature of Typhoon Yagi is its unusual rapid intensification. On September 2, the storm was only at Category 8, but just two days later, it had intensified by eight categories. This is relatively rare for storms in the South China Sea. The duration of Category 16 for over a day is also quite long for a storm in this region.
According to Wired, the Northwest Pacific region is the birthplace of some of the strongest storms on Earth. This area, known as the Northwest Pacific Basin, is the most active tropical cyclone basin on the planet, accounting for nearly one-third of the world’s annual tropical cyclones. Super typhoons are quite common in the Northwest Pacific. Meteorologists have recorded hundreds of super typhoons in the region from 1945 to 2022. In 2021 alone, there were four super typhoons in the Northwest Pacific, including Typhoon Rai, which resulted in over 400 fatalities when it made landfall in northern Philippines.
The reason the Northwest Pacific region generates so many strong storms is that the nature of tropical cyclones requires several key conditions for development. Warm sea water is an essential factor. This is particularly concerning as, similar to many places around the world, Southeast Asia has recorded significantly high sea surface temperatures over the past 12 months. Sea temperatures above 29 degrees Celsius can provide all the energy necessary for a storm to reach its maximum strength. Currently, the sea water around the Philippines has an average temperature exceeding 31 degrees Celsius.
High humidity in the atmosphere is also another essential condition for storm development. Dry air prevents storms from intensifying. A developing tropical cyclone also requires calm winds in the surrounding atmosphere. If there is too much wind shear, the winds will displace the upper part of the storm, causing them to dissipate before stabilizing.
Strong storms are relatively rare in the Pacific due to the absence of these factors on a regular basis. Additionally, dry air masses from the Sahara Desert in Africa can extinguish a developing storm. Cold air masses moving across the United States can render the atmosphere above the Pacific completely unsuitable for tropical storm development. However, conditions in the Northwest Pacific are entirely different. Cold air masses, strong wind shear, and dry air are very rare in this tropical sea region. High temperatures and humidity year-round in Southeast Asia and island nations like the Philippines create favorable conditions along the Northwest Pacific that can lead to the formation of dozens of storms in one season. The large number of storms developing also increases the likelihood that some of them reach maximum strength, becoming super typhoons that cause significant damage upon landfall, like Yagi.
