Tropical Cyclones in 2021 > Review of tropical cyclones in 2021
2.1 Review of tropical cyclones in 2021
2.1.1 Tropical cyclones over the western North Pacific (including the South China Sea)
In 2021, a total of 27 tropical cyclones occurred over the western North Pacific (WNP) and the South China Sea (SCS) bounded by the Equator, 45°N, 100°E and 180°, less than the long-term (1961 - 2020) average figure of around 30. During the year, 10 of the tropical cyclones attained typhoon intensity or above, less than the long-term average (1961 - 2020) of about 15, with five of them reaching super typhoon intensity (maximum 10-minute wind speed of 185 km/h or above near the centre).
Figure 2.1 shows the monthly frequencies of the occurrence of tropical cyclones in WNP and SCS in 2021.
During the year, seven tropical cyclones made landfall over China, with one of them crossing the south China coast within 300 km of Hong Kong. Four traversed the Philippines and five made landfall over Vietnam. With an estimated maximum sustained wind speed of 240 km/h and a minimum sea-level pressure of 910 hPa near the centre (Table 4.1), Super Typhoon Surigae (2102) and Super Typhoon Chanthu (2114) in September were the most intense tropical cyclones over the WNP and the SCS in 2021.
2.1.2 Tropical cyclones in Hong Kong’s area of responsibility
Amongst the 27 tropical cyclones in 2021, 17 of them occurred inside Hong Kong’s area of responsibility (i.e. the area bounded by 10°N, 30°N, 105°E and 125°E), slightly more than the long-term annual average (1961-2020) figure of around 16 (Table 2.1). Seven of them developed within Hong Kong’s area of responsibility. Altogether, 413 tropical cyclone warnings to ships and vessels were issued by the Hong Kong Observatory this year (Table 4.2).
2.1.3 Tropical cyclones over the South China Sea
11 tropical cyclones affected SCS bounded by 10°N, 25°N, 105°E and 120°E in 2021, slightly less than the long-term annual average (1961-2020) of around 12. Seven of them formed over the SCS.
2.1.4 Tropical cyclones affecting Hong Kong
In 2021, the typhoon season in Hong Kong started on 11 June when Tropical Depression Koguma (2104) formed over the northern part of the SCS, necessitating the issuance of the Standby Signal No. 1. It is rare to have tropical cyclones directly threatening Hong Kong in winter. However, as Severe Tropical Storm Rai (2122) gradually edged closer to the coast of Guangdong in late December, the Observatory issued the Standby Signal No. 1 on 20 December. This is the latest tropical cyclone warning signal in a year since 1946. When Rai weakened rapidly and dissipated the next day, the typhoon season ended with the cancellation of all tropical cyclone warning signals on that day.
Eight tropical cyclones affected Hong Kong during 2021 (Figure 2.2), more than the long-term (1961-2020) average of about six in a year (Table 2.2). They were Tropical Storm Koguma (2104) in June, two Tropical Depressions and Typhoon Cempaka (2107) in July, Tropical Storm Lupit (2109) in August, Tropical Storm Lionrock (2117) and Typhoon Kompasu (2118) in October, Super Typhoon Rai (2122) in December. The No. 8 Gale or Storm Signal was issued during the passage of Lionrock and Kompasu on 9 and 12 October respectively, the highest tropical cyclone warning signal issued in 2021. The time separation between these two No. 8 signals was only 60 hours 40 minutes, the shortest record of break time between two No. 8 signals for two tropical cyclones since 1946. The No. 3 Strong Wind Signal was issued during the passage of Cempaka and Lupit. The rest of the four tropical cyclones all necessitated the issuance of the Standby Signal No. 1 in Hong Kong.
2.1.5 Tropical cyclone rainfall
Tropical cyclone rainfall for Hong Kong (total rainfall recorded at the Hong Kong Observatory Headquarters from the time when a tropical cyclone comes within 600 km of Hong Kong to 72 hours after it has dissipated or moved more than 600 km away from Hong Kong) in 2021 was 980.6 mm (Table 4.8.1). This accounted for approximately 42.5 % of the year’s total rainfall of 2307.1 mm and was about 39.3% higher than the 1961-2020 long-term average of 704.2 mm.
According to the above definition, Tropical Storm Lionrock (2117) brought 369.0 mm of rainfall to Hong Kong (Table 4.8.1) and was the wettest tropical cyclone in 2021.
2.2 Monthly overview
A monthly overview of tropical cyclones in 2021 is given in this section. Detailed reports on tropical cyclones affecting Hong Kong, including reports of damage, are presented in Section 3.
JANUARY
No tropical cyclone formed over the western North Pacific and the South China Sea in January 2021.
FEBRUARY
Dujuan(2101) formed as a tropical depression over the western North Pacific about 1 520 km east-southeast of Manila on the morning of 18 February. Dujuan developed into a tropical storm that night, reaching its peak intensity the next morning with an estimated sustained wind of 75 km/h near its centre. Dujuan lingered over the seas east of the Philippines and weakened that night and on 20 February. It tracked northwestward towards the Philippines on 21 February and degenerated into an area of low pressure over the Philippines the next morning.
According to press reports, Dujuan brought squalls and torrential rain to the Philippines. More than 53 000 people were affected and over 180 houses were damaged.
MARCH
No tropical cyclone formed over the western North Pacific and the South China Sea in March 2021.
APRIL
Surigae (2102) formed as a tropical depression over the western North Pacific about 230 km south of Yap on the night of 13 April. Moving generally west-northwestwards, it intensified gradually. Surigae intensified into a typhoon on 16 April. Under favourable atmospheric conditions, Surigae started to intensify rapidly that night. It developed into a super typhoon the next day and reached its peak intensity with an estimated sustained wind of 240 km/h near its centre, making it the most intense tropical cyclone over the western North Pacific in April since 1961. It then moved north-northwestwards slowly across the seas east of the Philippines in the following four days. Surigae turned to move northeastwards across the seas south of Ryukyu Islands on 22 April and weakened gradually. It finally evolved into an extratropical cyclone over the western North Pacific south of Japan on 25 April.
According to press reports, a cargo ship ran aground over the seas of the southern Philippines during the passage of Surigae, killing four crew members on board.
MAY TO JUNE
A tropical depression formed over the western North Pacific about 1 280 km southeast of Manila on the small hours of 13 May and moved generally westwards towards the southern part of the Philippines. The tropical depression reached its peak intensity in the morning with an estimated sustained wind of 55 km/h near its centre. It weakened gradually afterwards and finally dissipated over the southern part of the Philippines in the small hours on 14 May.
Choi-wan (2103) formed as a tropical depression over the western North Pacific about 1 700 km east-southeast of Manila on the morning of 30 May and moved west-northwestwards. It intensified into a tropical storm the next day and moved across the seas east of the Philippines. Choi-wan reached its peak intensity with an estimated maximum sustained wind of 75 km/h near its centre in the small hours on 1 June. It moved across the Philippines afterwards and entered the South China Sea. Choi-wan turned to move northwards on 3 June and weakened gradually. It then moved northeastwards on 4 June and finally evolved into an extratropical cyclone over the vicinity of the Ryukyu Islands in the small hours on 5 June.
According to press reports, Choi-wan left at least 11 deaths, 3 injuries and 2 missing in the Philippines during its passage. Near 94 000 people were affected. Choi-wan also brought torrential rain and flooding to Taiwan. Electricity supply to around 50 000 households was interrupted in Taibei.
A monsoon depression developed into a tropical depression over the northern part of the South China Sea about 500 km south-southwest of Hong Kong on the afternoon of 11 June. It generally tracked west-northwestward towards Hainan Island. The tropical depression moved across Hainan Island on the morning of 12 June and was named Koguma (2104) in the afternoon. Koguma intensified into a tropical storm over Beibu Wan in that evening and reached its peak intensity with an estimated maximum sustained wind of 65 km/h near its centre. It made landfall over the northern part of Vietnam on the morning of 13 June and degenerated into an area of low pressure over inland Vietnam in the afternoon.
According to press reports, Koguma left at least 1 death and 2 missing during its passage to Vietnam. At least 130 houses were collapsed.
Champi (2105) formed as a tropical depression over the western North Pacific about 390 km east-southeast of Guam on the morning of 21 June. It generally moved northwestwards and intensified gradually. Champi intensified into a severe tropical storm in the small hours on 25 June and turned to move north or north-northeastwards. Champi further intensified into a typhoon that night and reached its peak intensity with an estimated maximum sustained wind of 120 km/h near its centre. Champi started to weaken afterwards and finally evolved into an extratropical cyclone over the seas east of Honshu, Japan on 27 June.
JULY
The area of low pressure over the western North Pacific around 740 km east-northeast of Manila developed into a tropical depression in the small hours on 5 July. The tropical depression then moved northwestwards across the Luzon Strait. It reached its peak intensity that night with an estimated sustained wind of 55 km/h near its centre. The tropical depression skirted past the southwestern coastal waters of Taiwan and weakened rapidly on the morning of 6 July. It dissipated near the Taiwan Strait shortly after noon.
Another area of low pressure over the central part of the South China Sea around 230 km south-southeast of Xisha intensified into a tropical depression on the night of 5 July. It tracked generally northwest to north-northwestwards towards Hainan Island on 6 July and reached its peak intensity that night with an estimated sustained wind of 55 km/h near its centre. After moving across the southwestern part of Hainan Island, the tropical depression entered Beibu Wan on 7 July. It made landfall over the northern part of Vietnam the next day and then weakened into an area of low pressure.
In-fa (2106) formed as a tropical depression over the western North Pacific about 1 110 km southeast of Okinawa in the small hours on 17 July. It moved north-northwestwards and intensified gradually. In-fa intensified into a severe tropical storm on the morning of 19 July, and took a west to west-southwesterly track to skirt past the vicinity of Ryukyu Islands. It further intensified into a typhoon on the night of 20 July and reached its peak intensity with an estimated maximum sustained wind of 145 km/h near its centre in the next morning. In-fa slowed down on 22 July and turned to move north-northwestwards across the East China Sea in the following three days. In-fa made landfall over the coast of the northern part of Zhejiang on 26 July and weakened gradually. It finally degenerated into an area of low pressure over Shandong on 29 July.
According to press reports, there were torrential rain and extensive flooding over the vicinity of eastern China under the persistent influence of In-fa. More than 2.7 million people were affected and around 1 100 houses were damaged.
Cempaka (2107) formed as a tropical depression over the northern part of the South China Sea about 180 km south-southwest of Hong Kong on the night of 18 July. It moved generally northwest to west-northwestwards slowly towards the coast of western Guangdong and intensified rapidly. Cempaka intensified into a typhoon in the small hours on 20 July and reached its peak intensity with an estimated maximum sustained wind of 120 km/h near its centre. It started to weaken at night and made landfall near Yangjiang. Cempaka moved across western Guangdong and inland Guangxi, and weakened into a tropical depression progressively on 21 July. It turned to move south-southwestwards the next day and entered Beibu Wan on 23 July. Cempaka finally degenerated into an area of low pressure over Beibu Wan on 24 July.
Nepartak (2108) formed as a tropical depression over the western North Pacific about 710 km east of Iwo Jima on the night of 23 July and intensified into a tropical storm in the small hours on 24 July. It generally moved north-northeastwards in the following two days, and weakened into a tropical depression. Nepartak then gradually turned to move westwards across the seas east of Japan on 26 July and re-intensified into a tropical storm that night. Nepartak reached its peak intensity with an estimated maximum sustained wind of 75 km/h near its centre in the small hours on 27 July. It then turned to move northwestwards and finally weakened into an area of low pressure over Honshu of Japan on 28 July.
AUGUST
Lupit (2109) formed as a tropical depression over the northern part of the South China Sea at about 280 km southwest of Hong Kong on the night of 2 August. It moved generally east-northeastwards across the northern part of the South China Sea and intensified gradually. Lupit slowed down on the morning of 3 August and turned to move southeastwards in the afternoon. It then turned to move northeastwards in the small hours on 4 August and intensified into a tropical storm in the morning. Lupit reached its peak intensity in the small hours on 5 August with an estimated maximum sustained wind of 85 km/h near its centre. It skirted past the coastal areas of Fujian in the afternoon and the next day, and weakened into a tropical depression. Lupit re-intensified into a tropical storm over the Taiwan Strait in the small hours on 7 August and tracked northeastwards towards Japan. It finally evolved into an extratropical cyclone over the seas north of Honshu of Japan on 9 August.
According to press reports, Lupit brought torrential rain and flooding to Kyushu of Japan and Taiwan.
Nida (2111) formed as a tropical depression over the western North Pacific about 760 km east-northeast of Iwo Jima on the afternoon of 4 August. It tracked northwards and intensified gradually. Nida intensified into a tropical storm on 5 August and turned to move east to northeastwards across the western North Pacific east of Japan the next day. Nida reached its peak intensity in the small hours on 7 August with an estimated maximum sustained wind of 85 km/h near its centre. It evolved into an extratropical cyclone over the western North Pacific east to Japan on 8 August.
Mirinae (2110) formed as a tropical depression over the western North Pacific about 60 km west-southwest of Okinawa on the morning of 5 August. It moved generally east-northeastwards and intensified gradually. Mirinae developed into a severe tropical storm in the small hours on 8 August and reached its peak intensity with an estimated maximum sustained wind of 90 km/h near its centre. It evolved into an extratropical cyclone over the seas east of Japan on 9 August.
Omais (2112) formed as a tropical depression over the western North Pacific about 1 430 km east-southeast of Wake Island on 11 August and moved westwards. It weakened into an area of low pressure over the seas east of Guam on 16 August and its remnant continued to track west-northwestwards in the following four days. The low pressure area associated with the remnant of Omais re-intensified into a tropical depression over the western North Pacific about 890 km south-southeast of Okinawa on the afternoon of 20 August. It turned to move northwestwards and intensified into a tropical storm on 21 August, reaching its peak intensity with an estimated maximum sustained wind of 85 km/h near its centre. After moving across the vicinity of Ryukyu Islands on 22 August, Omais turned to move northwards and weakened gradually. It evolved into an extratropical cyclone over the seas near Jeju Island the next day.
SEPTEMBER TO OCTOBER
A tropical depression formed over the western North Pacific about 900 km northwest of Wake Island on the night of 1 September and moved west-northwestwards. The tropical depression reached its peak intensity on the morning of 2 September with an estimated maximum sustained wind of 55 km/h near its centre. It turned to move northeastwards gradually in the following two days. The tropical depression finally evolved into an extratropical cyclone over the western North Pacific to the east of Japan on 4 September.
Conson (2113) formed as a tropical depression over the western North Pacific about 1 140 km east-southeast of Manila on the afternoon of 5 September. It moved northwestwards and intensified gradually. Conson intensified into a severe tropical storm and reached its peak intensity on the morning of 7 September with an estimated maximum sustained wind of 90 km/h near its centre. After sweeping across the central part of the Philippines on 8 September, Conson slightly weakened and turned to move westwards across the central part of the South China Sea. It re-intensified into a severe tropical storm again on the night of 9 September. Conson weakened into a tropical storm on the morning of 11 September. Conson then slowed down and lingered over the central part of the South China Sea to the east of Vietnam. Conson finally degenerated into an area of low pressure over the coastal waters of the central part of Vietnam on the night of 12 September.
According to press reports, Conson left 20 deaths, 24 injuries and at least 7 missing in the Philippines during its passage. Besides, about 9 000 buildings were damaged.
Chanthu (2114) formed as a tropical depression over the western North Pacific about 1 880 km east of Manila on the afternoon of 6 September. It moved west or west-northwestwards at first and intensified rapidly. Chanthu intensified into a super typhoon on the morning of 8 September and reached its peak intensity on the night of 10 September with an estimated maximum sustained wind of 240 km/h near its centre. Chanthu then weakened gradually and turned to move northwards across the seas east of Taiwan. It slowed down and lingered over the East China Sea on 14 and 15 September. Chanthu started to pick up speed and turned to move east to northeastwards on 16 September. It swept across Kyushu and Shikoku of Japan next day and finally evolved into an extratropical cyclone over the seas east of Honshu, Japan on 18 September.
According to press reports, there were more than 80 000 households without electricity supply in Taiwan under the influence of Chanthu. Railways and aviation services in Japan were suspended during the passage of Chanthu.
Dianmu (2115) formed as a tropical depression over the southern part of the South China Sea about 460 km south-southeast of Xisha on the night of 22 September. It moved west-northwestwards and intensified gradually. Dianmu intensified into a tropical storm on the night of 23 September and reached its peak intensity with an estimated maximum sustained wind of 65 km/h near its centre. Dianmu weakened and turned to move westwards after it made landfall over the central part of Vietnam in the small hours on 24 September. It degenerated into an area of low pressure over Indochina Peninsula during the day.
Mindulle (2116) formed as a tropical depression over the western North Pacific about 340 km southeast of Guam in the small hours on 23 September. It moved west-northwestwards and intensified gradually. Mindulle developed into a severe tropical storm on the night of 24 September. It turned to move northwestwards and intensified rapidly. Mindulle further developed into a super typhoon on 26 September and reached its peak intensity with an estimated maximum sustained wind of 220 km/h near its centre. It tracked northwards in the following three days and turned to move northeastwards towards the seas east of Japan on 30 September. Mindulle finally evolved into an extratropical cyclone over the seas east of Japan on 2 October.
A monsoon depression developed into a tropical depression over the central part of the South China Sea about 290 km east-southeast of Sanya on the afternoon of 7 October. It generally tracked northwestwards towards Hainan Island. The tropical depression was named Lionrock (2117) on the morning of 8 October and intensified into a tropical storm. Lionrock reached its peak intensity in the afternoon with an estimated maximum sustained wind of 75 km/h near its centre. When Lionrock moved across Hainan Island on 9 October, it took on an erratic track and made an anti-clockwise loop. Lionrock turned to move west-northwestwards in that afternoon and entered Beibu Wan at night. It degenerated into an area of low pressure over the coast of northern Vietnam on the night of 10 October.
According to press reports, Lionrock left six injuries in Macao. Besides, it also brought torrential rain to Zhuhai and triggered extensive flooding.
Kompasu (2118) developed as a tropical depression over the western North Pacific about 1 020 km east of Manila on the night of 8 October. It moved northwards at first and intensified gradually. Kompasu picked up speed to move westwards on 10 October. It developed into a severe tropical storm and moved across the Luzon Strait on 11 October. Kompasu moved westwards across the northern part of the South China Sea on 12 October. It further developed into a typhoon on the morning of next day, reaching its peak intensity with an estimated sustained wind of 120 km/h near its centre. Kompasu moved across Hainan Island on 13 October and weakened rapidly. It degenerated into an area of low pressure over Beibu Wan on 14 October.
According to press reports, Kompasu left 40 deaths, 5 injuries, 17 missing and over 500 000 people evacuated in the Philippines during its passage. Besides, the Yantian Port in Guangdong and 3 ports in Hainan Island were closed and the marine transportation services were suspended because of the torrential rain brought by Kompasu.
Namtheun (2119) formed as a tropical depression over the western North Pacific about 550 km west-southwest of Wake Island on the night of 9 October. It moved west-northwestwards and intensified gradually. Namtheun turned to move northwards on 12 October and drifted northeastwards the next day. Namtheun intensified into a severe tropical storm and reached its peak intensity on the morning of 16 October with an estimated maximum sustained wind of 90 km/h near its centre. It then weakened rapidly and finally evolved into an extratropical cyclone over the western North Pacific to the north of Wake Island on 17 October.
Malou (2120) formed as a tropical depression over the western North Pacific about 340 km northeast of Yap Island on the morning of 24 October. It generally moved northwards and intensified gradually. Malou intensified into a typhoon on the night of 27 October and turned to move north-northeastwards. It reached its peak intensity on the afternoon of 28 October with an estimated maximum sustained wind of 140 km/h near its centre. Malou then weakened gradually and finally evolved into an extratropical cyclone over the seas east of Japan on 29 October.
A tropical depression formed over the southern part of the South China Sea about 280 km east of Nansha on the afternoon of 24 October. It generally moved westwards or northwestwards. The tropical depression reached its peak intensity on the afternoon of 26 October with an estimated maximum sustained wind of 55 km/h near its centre. It degenerated into an area of low pressure over the southern part of Vietnam on 27 October.
NOVEMBER TO DECEMBER
Nyatoh (2121) formed as a tropical depression over the western North Pacific about 450 km northeast of Yap on the night of 29 November. It moved west-northwestwards towards the seas east of the Philippines and intensified gradually. Nyatoh intensified into a severe tropical storm on the morning of 1 December. It then turned gradually to move northeastwards towards the vicinity of Iwo Jima and continued to intensify. Nyatoh further intensified into a super typhoon in the small hours on 3 December and reached its peak intensity with an estimated maximum sustained wind of 185 km/h near its centre. Nyatoh weakened into a severe typhoon that night and finally evolved into an extratropical cyclone over the seas east of Iwo Jima.
Rai (2122) formed as a tropical depression over the western North Pacific about 2 680 km east-southeast of Manila on the night of 12 December. It moved west-northwestwards and intensified gradually. Rai started to intensify rapidly on 15 December and developed into a super typhoon on the next day. After sweeping across the Philippines, Rai weakened into a severe typhoon and moved westwards across the southern part of the South China Sea on 17 December. Rai re-intensified into a super typhoon the next day and became the first super typhoon over the South China Sea in December since 1961. It reached its peak intensity in the small hours on 19 December with an estimated maximum sustained wind of 205 km/h near its centre. Turning to move northeastwards gradually in the following two days, Rai edged closer to the coast of Guangdong and weakened rapidly. It finally degenerated into an area of low pressure over the seas south of Hong Kong on 21 December.
According to press reports, Rai left at least 409 deaths and over 100 000 people evacuated in the Philippines during its passage.
Note: Casualties and damage figures were compiled from press reports.