Expert Advisor: Xiang Chunyi, Senior Engineer, Typhoon and Marine Meteorological Center, China Meteorological Administration

Wang Yongguang, Chief Forecaster, National Climate Center

Interviewer: China Meteorological News reporter Shen Minxia Wang Meili Huang Bin

　　The typhoon that was common on the weather stage in July of previous years was "absent" this year!

　　Since the formation of Typhoon No. 1 "Wasp" on May 12 and Typhoon No. 2 "Parrot" on June 14 in 2020, there have been no new typhoons in the Northwest Pacific and South China Sea. July is about to end. At present, multiple tropical disturbance "embryos" near the Philippines are also brewing, but the possibility of developing into a typhoon is unlikely.

　　As a result, will July this year be the first "empty platform" July in history? What are the main reasons for the suppression of typhoon activity so far this year? What is the trend of typhoon activity in the later period?

History is rare! No typhoon in July will break historical records

　　From a perennial point of view, July is an active typhoon period, and many typhoons even landed in my country. For example, in July 2019, there were 7 typhoons. But this year, the typhoon did not play its cards according to common sense. Not only was it "late", but its "attendance rate" was very low. As of now, only two typhoons "Wasp" and "Parrot" have been generated this year, with an average of 4.1 typhoons in July.

　　Not only that, since 1949, there has not been an "empty station" in July. Prior to this, at least one typhoon occurred in 1954, 1957, 1985, and 1998. According to statistics, 8 typhoons (appearing in 1967, 1971, 1994, and 2017) were generated in 4 years and July. If there is still no typhoon before the end of July, it is very rare.

Variation curve of the number of typhoons in the Northwest Pacific and South China Sea from 1990 to July year by year

Not active! Significantly fewer typhoons have generated and made landfall this year

　　July is very likely to be "empty," reflecting the lack of active typhoons so far this year. From a perennial perspective, with the northward movement of the subtropical high and the increase in monsoon activity, typhoon activity usually increases significantly in July.

　　In the Northwest Pacific, where typhoons are active throughout the year, typhoon activities have significant seasonal characteristics, with August having the highest frequency, followed by September, and July ranking third. According to typhoon statistics from 1949 to 2019, the number of typhoons generated in July accounted for 15.2% of the total.

The monthly average number of typhoons from 1949 to 2019

The monthly average number of typhoons from 1949 to 2019

　　However, this year, not only was the typhoon activity reduced or even "absent" in July. Since January this year, typhoon activity has been significantly less.

　　According to big data, the average number of typhoons generated from January to July in the past 30 years was 8.1, of which the most generated typhoon was in 2015 (13), and the least generated was 1998 (1). Compared with the same period in history, the total number of typhoons generated from January to July this year was 6.1 less, or about 75%, which was the year with the fewest typhoons since 1949 except 1998.

　　In addition, this year only the second typhoon "Parrot" landed in Yangjiang, Guangdong on June 14. The total number of typhoons landed from January to July this year was relatively high, and the annual average was 2.3, which was 1.3 less than that since 1949, excluding 1951, 1975 and 1997. One of the years with the least landfall typhoons (no typhoons landed in China from January to July during the same period of 1951, 1975 and 1997).

Variation curve of the number of typhoons in the Northwest Pacific and South China Sea from 1990 to January to July 2019

Why was the typhoon absent in July this year?

　　Why is the typhoon so inactive this year? Experts say that the number of typhoons is related to factors such as ocean thermal conditions, monsoon activities, and atmospheric low-frequency oscillations from a climate perspective; from a weather perspective, high sea temperature, high humidity, high convective and unstable stratification are required. Thermal conditions, a certain geostrophic deflection force, weak ambient wind vertical shear and dynamic conditions of initial dynamic disturbance.

　　But for this year, the subtropical high is the "behind-the-scenes" in restraining the formation of typhoons. The abnormally strong subtropical high is closely related to the abnormally warmer sea temperature of El Niño and the tropical ocean surface of the Indian Ocean.

　　With the occurrence of the El Niño event in the autumn of 2019, the western Pacific subtropical high is unusually strong and the area is too large. The tropical ocean surface of the Northwest Pacific and South China Sea where the typhoon is generated is controlled by the subtropical high. Because the subtropical high is generally a sinking airflow and convective activity Suppressed, the necessary conditions for typhoon generation are lacking.

　　Climate statistics show that in the past 70 years, there were 16 years with less than two typhoons in the first half of the year, and 11 of them were related to El Niño events. There were no typhoons in 1973, 1998, and the first half of 2016, all of which occurred in the context of strong or even super strong El Niño events.

　　In addition, in the summer of this year, the cold air activity in the southern hemisphere was weak and the cross-equatorial airflow was abnormally weak, making the “pushing force” insufficient; and since the second half of May, the South China Sea monsoon has been abnormally weak, and at the same time, due to the abnormal subtropical high pressure, the south side of the South China Sea has been extremely weak. The Pacific Ocean and the South China Sea are controlled by strong easterly winds, and the monsoon trough is difficult to form in the Western Pacific and South China Sea. Therefore, the South China Sea and the tropical ocean east of the Philippines have weaker current cloud clusters than usual, which is not conducive to the formation of typhoons.

High temperature and drought in many parts of South China urgently need typhoon to “extinguish”

　　The typhoon is approaching, heavy storms and rain; the typhoon is absent, high temperature and drought.

　　Generally speaking, the disasters of typhoons are mainly the accompanying torrential rains and secondary disasters. The potential benefits of typhoons are to alleviate drought conditions, alleviate heat and power demand, increase fishery production, regulate climate, and desalinate seawater. In fact, the number of typhoons is not a measure of the number of disasters, but is also related to the impact of specific typhoons and the climate background of the year.

　　From a global perspective, if there is no typhoon, more than a quarter of the precipitation will be lost along the coasts of China, the Sea of ​​Japan, India, Southeast Asia, and the southeastern United States, and the supply of fresh water may even be tight.

　　If there is no typhoon to "drive away" the high temperature, the tropical and subtropical areas close to the equator will be hotter and the surface dry will be more severe. At the same time the frigid zone will be colder and the temperate zone will disappear.

　　This year, due to the fact that there are few tourists from Taiwan, since June, many places in southern China have experienced constant high temperatures. As of July 23, 33 hot days have occurred in Fuzhou, Fujian, and 40 hot days have occurred in Haikou, Hainan.

　　According to expert analysis, until the end of July, the hot and muggy weather in South China will continue. Although the subtropical high may move northward in stages, it has little effect on alleviating the high temperature in South China. If you want to "extinguish the fire", you can only expect a typhoon or a proper soaking rain. Therefore, for some time in the future, the South China partners should also pay attention to heatstroke prevention and cooling.

The typhoon is on its way! Typhoons are the most frequent in August

　　If there is no typhoon in July, this does not mean that the typhoon activity will weaken in the second half of this year, nor does it rule out that the ocean’s accumulated energy is "stuck".

　　Today, the northern hemisphere is gradually entering the midsummer period, and the world is also entering a period of high incidence of typhoons. At present, there is a tropical storm "Douglas" in the northwestern part of Hawaii in the Central Pacific Ocean. It is expected that "Douglas" will move to the west, its intensity will gradually weaken, and it will gradually weaken and disappear this afternoon.

　　According to the latest monitoring information of atmospheric environment and ocean conditions, typhoons in the Northwest Pacific and South China Sea will gradually become active in the next 10 days. It is estimated that 1-2 typhoons will be generated, and one of them may affect the southeast coastal areas of my country.

　　Statistical analysis shows that August is the month with the most frequent typhoon activity, with an average of 5.7 typhoons generated in history. The most generated typhoons were in 1960 and 1966 (10), and the least generated was 2014 (1), of which 1998 There were 3 typhoons in August.

　　According to the forecast of the National Climate Center, the number of typhoons generated in the Northwest Pacific and South China Sea in August is 4-6, slightly less than that of the same period in normal years (6); the number of typhoons that landed in China is 2 to 3, which is more than normal. Over the same period (2) were slightly higher. The meteorological department will closely monitor the typhoon dynamics and do a good job of corresponding forecast services.