Source: China Meteorological Administration
On June 30, the tropical depression in the South China Sea strengthened to typhoon Siamba (tropical storm level) (English name: Chaba; Name origin: Thailand; Meaning of the name: Tropical Flower).
As of June 30, in the first half of this year, only three typhoons were generated in the northwest Pacific Ocean and the South China Sea: Maleka, Catfish, and Siamba. According to the National Meteorological Center's Typhoon and Ocean Weather Forecasting Center, there were 4.6 typhoons generated in the same period of history (1949 to 2021), and the number of typhoons generated in the first half of this year was 1.6 less.
01
Will La Niña continue, will there be fewer typhoons?
According to Wang Hao, senior engineer of the Typhoon and Marine Meteorological Forecasting Center of the National Meteorological Center, since 1949, the number of typhoons generated in the first half of the year has not exceeded 3 years, accounting for more than 30%, and in 1973, 1998 and 2016, there was even a phenomenon of "empty stations" from January to June. From this point of view, the lack of typhoons in the first half of this year is not extreme.
The main reason for the low number of typhoons generated in the first half of this year is related to the ongoing La Niña incident.
Han Rongqing, a researcher and chief of the flood season typhoon prediction class of the National Climate Center, pointed out that the La Niña incident began last autumn, the winter reached its peak, and this spring not only did not decay, but also strengthened in stages, which is very rare in history. The continued development of the La Niña event will trigger a pair of abnormal anticyclonic circulation symmetrical to the equator in the lower tropical atmosphere on the west side of cold water, with the anticyclone on the north side of the equator just controlling the main source of typhoons in the northwest Pacific Ocean, that is, the waters east of the Philippines. This large-scale circulation anomaly is very unfavorable to typhoon generation, resulting in less typhoon generation in the first half of this year.
Han Rongqing believes that the interannual change in the number of typhoons generated in the first half of the year is very closely related to the development and evolution trend of SST in the tropical Middle East And Pacific. When the surface temperature of the Equatorial Middle East Pacific Ocean warms up from January to June (in the past 5 years such as 2018 and 2021), it is easy to lead to the development of large-scale atmospheric circulation cyclones at the source of typhoon generation in the northwest Pacific Ocean and the South China Sea, which is conducive to typhoon generation; On the other hand, when the sea surface temperature becomes cold (in the past 5 years, such as 2020 and 2022), it is easy to cause the large-scale atmospheric circulation of the source of typhoon generation to develop in an anti-cyclone, which is not conducive to typhoon generation.
02
Will the typhoons pile up in the second half of the year?
There are fewer typhoons in the first half of the year, will the typhoons in the second half of the year come in groups? According to the statistics of the best path of typhoons compiled by the China Meteorological Administration, from 1949 to 2021, the number of typhoons generated in the first half of the year and the second half of the year is basically uncorrelated. According to the statistical results, an average of 14.8 typhoons were generated from July to September, which is an active typhoon season and a period of active landfall typhoons.
The National Climate Center predicts that this year's typhoon generation is small and the overall intensity is weak, but it is possible that the landfall typhoon will affect the northern region (referring to the north of 30° north latitude). Tropical cyclone generation in the northwest Pacific Ocean and the South China Sea is expected to be 15 to 18 from July to December, which is less than the usual (21); The frequency of tropical cyclones on the continent is 4 to 6, close to the perennial (6.4) to less.
03
When does the first stage generally come?
Chutai generally refers to the first typhoon that made landfall on the mainland that year.
The initial stages are mainly concentrated in June and July. In the past 30 years (1991-2020), the average landing time of the first platform is June 28. The highest number of months of initial occurrence was June (14), followed by July (12). Typhoon Raccoon made landfall on April 18 in Longlou Town, Wenchang City, Hainan Province, making it the earliest landfall in the past 30 years. Typhoon Pabou made landfall in Hengchun, Taiwan, on August 8, 2007, the latest landfall in nearly 30 years.
The average landfall intensity of the initial platform was 28.8 m/s (severe tropical storm level) and the average peak intensity was 33.6 m/s (typhoon level).
From 1991 to 2020, the initial landing areas covered Guangdong, Hainan, Taiwan, Fujian and Hong Kong. The first taiwan generally landed in low-latitude coastal areas such as south China, and the most common landing places were Guangdong, Hainan and Taiwan, of which the most years landed in Guangdong were 11.
04
Why are tropical cyclones rarely experienced in Europe and South America?
Tropical cyclones are called differently in different parts of the world. Tropical cyclones active in the northwest pacific ocean are called typhoons, hurricanes in the northeast and north Atlantic, cyclonic storms in the northern Indian Ocean, and tropical storms or tropical cyclones in the southern Indian and south Pacific Oceans. Tropical cyclones are often attacked in Asia, North America and even Africa, while Europe and South America are rarely affected by tropical cyclones.
Map of the path of tropical cyclones around the world from 2001 to 2020 Courtesy of the Central Meteorological Observatory
According to Wang Hao's analysis, tropical cyclones are catastrophic weather systems that affect tropical and subtropical seas and regions around the world, and tropical cyclone generation and development requires warm and deep seawater layers, high low and medium-low layer humidity, convective unstable stratigraphic knots, certain geostationary bias forces, and low vertical wind shear. Due to the low surface temperature of the south-east Pacific Ocean and the South Atlantic Ocean, the shallow warm water layer, and the large vertical wind shear in the environment, there is a lack of conditions for tropical cyclone generation and maintenance, so tropical cyclone generation is rare. In addition, although there is a deep warm water layer near the equator, tropical cyclones generally do not generate in the sea near the equator within 5° north and south latitudes due to the extremely small geodesic deflection force.
Most of Europe is located in the middle and high latitudes north of 40° north latitude, and tropical cyclones are no longer the "protagonists" of the weather stage. However, some North Atlantic hurricanes interact with the mid-latitude system as they move to the middle and high latitudes, turning northeast and gradually converting into extratropical cyclones, which can also bring strong winds and precipitation to Western Europe. In South America, because the surrounding oceans are not conducive to tropical cyclone generation and development, tropical cyclone effects are rare.
The global average is about 80 tropical cyclones per year, with the Northwest Pacific being the most numerous, about one-third of the global generation. About 15 are generated in the northeast Pacific, the waters near Australia and the southwest Pacific Ocean each year; In other seas, such as the North Atlantic Ocean, the North and South Indian Oceans generate about 10 per year. Tropical cyclone landings affect the coastal areas of East Asia, Southeast Asia, South Asia and North America, and the continent is one of the few countries in the world that are most affected by tropical cyclones.
As of June 30, a total of 29 tropical cyclones have been generated worldwide this year, of which 8 have been generated in the northern hemisphere, 2.1 less than in the same period of the year; 21 in the southern hemisphere, 1.6 more than the same period of the year; and from late January to late February, 4 rare tropical cyclones ("Anna", "Bazire", "Dumako" and "Emnati") have landed in Madagascar and severely damaged many countries such as Madagascar, Mozambique and Malawi; In April, Tropical Storm Catfish hit the Philippines hard in the Northwest Pacific; In May, Category 2 Hurricane Agatha in the northeast Pacific severely affected Mexico.
Produced by china meteorological administration propaganda center (China Meteorological News).
Author: Zhang Minglu Wang Meili
Draft: Zhao Miao
Source: Central Meteorological Observatory