TROPICAL CYCLONES IN 2011
2.1 Review of tropical cyclones in 2011
2.1.1 Tropical cyclones over the western North Pacific (including the South China Sea)
In 2011, only a total of 22 tropical cyclones occurred over the western North Pacific and the South China Sea bounded by the Equator, 45?N, 100? and 180?E, less than the long term (1961-2010) average figure of around 30. This was the fifth lowest on record since 1946. During the year, eight tropical cyclones attained typhoon intensity or above, seven less than the long term (1961-2010) average of 15.
The first tropical cyclone of the year formed in May and the last one in December. Figure 2.1 shows the monthly frequencies of the occurrence of tropical cyclones in the western North Pacific and the South China Sea in 2011.
During the year, seven tropical cyclones made landfall over Mainland China, with one of them making landfall over the south China coast within 300 km of Hong Kong. One tropical cyclone crossed Taiwan, one made landfall over the Korean Peninsula, three made landfall over Japan, seven traversed the Philippines and another four made landfall over Vietnam.
The most intense tropical cyclone in 2011 was Super Typhoon Songda (1102). Songda had an estimated maximum sustained wind speed of 205 km/h and a minimum sea-level pressure of 920 hPa ( Table 4.1) when it was located over the western North Pacific about 520 km east-northeast of Manila( Figure 2.3).
The track of Roke (1115) was the most complicated in 2011. After forming over the western North Pacific to the east-southeast of Okinawa on 13 September, Roke moved towards the Ryukyu Islands and gradually strengthened. On 16-17 September, Severe Tropical Storm Roke made a loop in its track and lingered to the east of Okinawa, during which Severe Tropical Storm Sonca (1116) made its way through the western North Pacific to the east of Roke (Figure 2.4)
2.1.2 Tropical cyclones in Hong Kong's area of responsibility
Amongst the 22 tropical cyclones in 2011, 12 occurred inside Hong Kong's area of responsibility (i.e. the area bounded by 10?N, 30?N, 105?E and 125?E), less than the long term annual average figure of 15.6 (Table 2.1).Three of these 12 tropical cyclones developed within Hong Kong's area of responsibility. Altogether, 333 tropical cyclone warnings to ships and vessels were issued by the Hong Kong Observatory in 2011 (Table 4.2).
2.1.3 Tropical cyclones over the South China Sea
Eight tropical cyclones affected the South China Sea bounded by 10?N, 25?N, 105?E and 120?E in 2011. Two of them formed over the area. Six moved into the South China Sea from the western North Pacific.
2.1.4 Tropical cyclones affecting Hong Kong
In 2011, the typhoon season in Hong Kong started on 10 June when Tropical Storm Sarika (1103) moved across the South China Sea and necessitated the issuance of the Standby Signal No.1. The typhoon season ended on 3 October as Severe Tropical Storm Nalgae moved away from Hong Kong and all tropical cyclone warning signals were cancelled.
Five tropical cyclones affected Hong Kong during 2011 (Figure 2.2), slightly less than the long term (1961-2010) average figure of 6 (Table 2.2). These five tropical cyclones were Tropical Storm Sarika (1103) and Tropical Storm Haima (1104) in June, Severe Tropical Storm Nock-ten (1108) in July, Typhoon Nesat (1117) in September and Severe Typhoon Nalgae (1119) in October. The No. 8 SE Gale or Storm Signal was issued during the passage of Nesat, which was the highest tropical cyclone warning signal in 2011. Haima, Nock-ten and Nalgae necessitated the issuance of the No. 3 Strong Wind Signal while Sarika only necessitated the issuance of the Standby Signal No. 1 in Hong Kong.
2.1.5 Tropical cyclone rainfall
Tropical cyclone rainfall (the total rainfall recorded at the Hong Kong Observatory from the time when a tropical cyclone is centred within 600 km of Hong Kong to 72 hours after it has dissipated or moved farther than 600 km away from Hong Kong) in 2011 was 185.8 mm (Table 4.8.1). This was 75% below the normal of 745.5 mm and accounted for some 13% of the years total rainfall of 1 476.7 mm.
Typhoon Nesat (1117), which affected Hong Kong on 27 - 30 September, brought 53.3 mm of rainfall to the Hong Kong Observatory Headquarters, and was the wettest tropical cyclone in 2011.
A monthly overview of tropical cyclones is given in this section. Detailed reports on tropical cyclones affecting Hong Kong are presented in Section 3.
No tropical cyclone occurred over the western North Pacific and the South China Sea in January to April.
Aere (1101) formed as a tropical depression over the western North Pacific about 660 km east-southeast of Manila on 7 May. Moving west-northwestwards, it intensified into a tropical storm that afternoon. Aere moved northwestwards on 8 May and reached its peak intensity with an estimated maximum sustained wind of 85 km/h near its centre. It moved northwards across the northeastern part of Luzon on 9 May, turned to move northeastwards and then weakened into a tropical depression over the seas to the southeast of Taiwan on 10 May. Aere moved across the Ryukyu Islands the following day and dissipated over the seas south of Japan on 12 May. According to press reports, Aere triggered landslides in the northeastern part of Luzon, where at least three people were killed and over 100 000 people evacuated.
Songda (1102) formed as a tropical depression over the western North Pacific about 300 km east-southeast of Yap on 20 May and moved generally west-northwestwards. It intensified into a tropical storm on 22 May and a severe tropical storm the next day. Songda intensified gradually into a severe typhoon and turned to move northwestwards on 25 May. It further intensified into a super typhoon over the Pacific to the east of the Philippines on 26 May, reaching its peak intensity with an estimated maximum sustained wind of 205 km/h near its centre. Songda turned to move northwards over the seas to the southeast of Taiwan and weakened into a severe typhoon on 27 May. It moved northeastwards across the Ryukyu Islands, weakening first into a typhoon the next day and became extratropical over the seas south of Japan on 29 May. According to press reports, one person was killed, one missing and 67 people injured in Japan during the passage of Songda. Electricity supply to a total of 270 000 households was interrupted in Okinawa.
Sarika (1103) formed as a tropical depression over the central part of the South China Sea about 650 km south-southeast of Dongsha on 9 June and moved northwestwards. It tracked north-northwestwards and intensified into a tropical storm on the morning of 10 June, reaching its peak intensity with an estimated maximum sustained wind of 65 km/h near its centre. Sarika turned to move northwards across the northeastern part of the South China Sea that afternoon. It made landfall near Shantou on the morning of 11 June and dissipated over Fujian that afternoon.
Haima (1104) formed as a tropical depression over the western North Pacific about 420 km east of Manila on 18 June and moved generally northwestwards, crossing the Luzon Strait in the following evening. Haima moved west to west-southwestwards across the northern part of the South China Sea for the following two days. It turned to move west-northwest to northwestwards on 22 June and intensified into a tropical storm, reaching its peak intensity with an estimated maximum sustained wind of 85 km/h near its centre. Haima made landfall over the coast of western Guangdong on 23 June and moved west-southwestwards across the coastal region of western Guangdong subsequently. It moved across Beibu Wan on 24 June and made landfall over the northern coast of Vietnam that evening. Haima dissipated inland over Laos on 25 June.
Meari (1105) formed as a tropical depression over the western North Pacific about 1 160 km east-southeast of Manila on 21 June and moved northwestwards. It intensified into a tropical storm on 22 June and moved north-northwestwards the following day. Meari intensified into a severe tropical storm on 24 June and turned to move generally northwards across the East China Sea on 25 June, reaching its peak intensity with an estimated maximum wind of 110 km/h near its centre that day. It skirted the coast of Shangdong Peninsula in the evening on 26 June. Meari weakened into a tropical storm on 27 June, turned to move northeastwards and dissipated over the Korean Peninsula subsequently. Meari brought flooding to the Philippines where 15 people were missing. It also affected 33 000 hectares of farmland and destroyed 400 houses in the provinces of Liaoning, Zhejiang and Shangdong.
Ma-on (1106) formed as a tropical depression over the western North Pacific about 1 430km east-northeast of Guam on 11 July and moved west to west-northwestwards. It gradually intensified and became a typhoon on 14 July and a severe typhoon on the following day. Ma-on intensified into a super typhoon over the western North Pacific about 530 km southwest of Iwo Jima on 16July, reaching its peak intensity with an estimated maximum sustained wind of 185 km/h near its centre. Ma-on moved northwestwards and weakened into a severe typhoon on 17 July, and turned to move northwards on 18 July. It weakened into a typhoon and turned to move northeastwards on 19 July, crossing the seas south of Shikoku, Japan. Ma-on made landfall over southern Honshu on 20 July and weakened into a severe tropical storm, but turned to move southeastwards across the seas south of Japan. It weakened into a tropical storm on 21 July. Ma-on turned to move north-northeastwards on 22 July and became an extratropical cyclone over the western North Pacific east of Japan on 24 July. At least one person was killed and 60 injured in Japan during the passage of Ma-on.
A tropical depression formed over the western North Pacific about 1 340 km east of Manila on 15 July and was named Tokage (1107). The estimated maximum sustained wind near its centre was about 45 km/h. Moving eastwards, the tropical depression dissipated over the western North Pacific on 16 July.
Nock-ten (1108) formed as a tropical depression over the western North Pacific about 790km east-southeast of Manila on 25 July and moved generally west-northwestwards. Nock-ten intensified into a tropical storm and turned to move northwestwards the next day. It intensified into a severe tropical storm on 27 July, crossing Luzon that afternoon. Nock-ten moved generally west to west-northwestwards across the northern part of the South China Sea for the following two days, reaching its peak intensity with an estimated maximum sustained wind of 105 km/h near its centre. It made landfall over Hainan Island on 29 July. Moving across Beibu Wan on 30 July, Nock-ten weakened into a tropical storm. It made landfall again over the coast of northern Vietnam that evening and subsequently dissipated inland over Laos on 31 July.
Muifa (1109) formed as a tropical depression over the western North Pacific about 500 km south of Guam on 26 July and moved west-northwestwards. It intensified into a tropical storm on 28 July and turned to move northwards on 29 July. Muifa became slow moving and intensified gradually into a severe typhoon on 30 July. It intensified further into a super typhoon over the western North Pacific to the south-southeast of Okinawa on 31 July with an estimated maximum sustained wind of 185 km/h near its centre, while moving generally northwards across the western North Pacific. Muifa weakened into a severe typhoon on 1 August, turned to move west-northwestwards on 3 August and passed to the southwest of Okinawa on 5 August on a northwesterly track. It weakened into a typhoon on 6August and turned to move north- northwestwards across the East China Sea. Muifa weakened into a severe tropical storm on 8 August and made landfall over the northwestern coast of DPR Korea. It became an extratropical cyclone over northeastern China on 9 August. According to press reports, at least four people were killed and two others missing in the Republic of Korea during the passage of Muifa. Electricity supply to 320 000 houses were also interrupted. In eastern and northeastern China, over 1 800 houses collapsed and 12 500 houses were damaged. The direct economic losses amounted to 4 235 million RMB.
Merbok (1110) formed as a tropical depression over the western North Pacific about 660 km northwest of Wake Island on 3 August. Moving west-northwestwards, Merbok intensified into a tropical storm that afternoon. It turned to move northwestwards on 5 August. Merbok moved northwards and intensified into a severe tropical storm to the east-northeast of Iwo Jima on 6 August, reaching its peak intensity with an estimated maximum sustained wind of 90 km/h near its centre. It turned to move northeastwards on 7 August. Merbok weakened into a tropical storm on 9 August and became an extratropical cyclone to the east of Hokkaido over the western North Pacific on 10 August.
A tropical depression formed over the western North Pacific about 1 080 km south of Nagoya on 10 August. The tropical depression remained weak with an estimated maximum sustained wind of 45 km/h near its centre. Moving northeastwards for the following two days, the tropical depression dissipated over the western North Pacific southeast of Tokyo on 12 August.
Nanmadol (1111) formed as a tropical depression over the western North Pacific about 700 km east of Manila on 23 August and was almost stationary. It intensified into a tropical storm that evening. Moving westwards, it intensified into a severe tropical storm on 24 August and further into a typhoon on the following day. Nanmadol moved northwestwards and intensified gradually into a super typhoon over the Pacific to the northeast of Manila on 26 August, reaching its peak intensity with an estimated maximum sustained wind of 195 km/h near its centre. It crossed the northeastern tip of Luzon on a north-northwesterly track on 27 August and weakened into a severe typhoon, and subsequently crossed southern Taiwan and weakened into a severe tropical storm on 29 August. Nanmadol weakened into a tropical storm over the Taiwan Strait on 30 August and became slow moving. It made landfall over Fuijian on the morning of 31 August and weakened into a tropical depression, dissipating inland over Fuijian in the evening. During the passage of Nanmadol, at least 15 people were killed, six others missing and over 20 people injured in the Philippines. One person was killed in Taiwan. Nanmadol brought rainstorms to Fuijian where about 70 houses collapsed, over 12 000 hectares of crops were damaged and the direct economic losses amounted to 532 million RMB.
Talas (1112) formed as a tropical depression over the western North Pacific about 480 km northwest of Guam on 24 August and moved north-northwestwards. It intensified into a tropical storm on 25 August and further into a severe tropical storm on 26 August. For the following three days, Talas became slow-moving but generally travelled northwards and continued to intensify, with the estimated maximum sustained wind near its centre reaching 110 km/h. Talas turned to move west-northwestwards across the seas south of Japan on the last two days of the month. It moved northwestwards towards Japan on 1 September. Talas turned to move northwards across Shikoku and Honshu, Japan on 3 September. It entered the Sea of Japan on the following day and weakened into a tropical storm. Talas became an extratropical cyclone over the Sea of Japan on 5 September. According to press reports, torrential rain brought about by Talas triggered flooding and landslides in Japan, where at least 46 people were killed and some 50 people missing.
Noru (1113) formed as a tropical depression over the western North Pacific about 1 030 km east-southeast of Iwo Jima on 2 September and moved west to southwestwards. It took up a north-northeasterly track on 3 September. Noru intensified into a tropical storm to the east-northeast of Iwo Jima on 4 September, reaching its peak intensity with an estimated maximum sustained wind of 75 km/h near its centre and moved north-northwestwards. Noru resumed moving north-northeastwards and became an extratropical cyclone over the western North Pacific to the east of Japan on 6 September.
Kulap (1114) formed as a tropical depression over the western North Pacific about 960 km southeast of Okinawa on 7 September and moved generally northwestwards. It intensified into a tropical storm that evening, reaching its peak intensity with an estimated maximum sustained wind of 65 km/h near its centre. Kulap weakened into a tropical depression to the east of Okinawa on 8 September. It weakened further into an area of low pressure over the East China Sea southwest of Kyushu, Japan on 10 September.
Roke (1115) formed as a tropical depression over the western North Pacific about 1 140 km east-southeast of Okinawa on 13 September and moved north-northwestwards. It turned to move west-northwestwards the following day and intensified into a tropical storm on 15 September. Roke lingered near Okinawa for the following two days and intensified into a severe tropical storm. It took up a northward track on 18 September and intensified to a typhoon to the northeast of Okinawa on 19 September. Roke speeded up to move northeastwards on 20 September and intensified into a severe typhoon over the seas south of Japan, reaching its peak intensity with an estimated maximum sustained wind of 155 km/h near its centre. It crossed eastern Honshu, Japan and weakened into a typhoon on 21 September. Roke became an extratropical cyclone over the seas east of Hokkaido on 22 September. Roke brought torrential rain to many parts of Japan triggering landslides. At least 12 people were killed, another five missing and over 300 people injured in Japan.
Sonca (1116) formed as a tropical depression over the western North Pacific about 1 420 km east-southeast of Iwo Jima on 14 September and moved generally northeastwards. It turned to move northwestwards and intensified into a tropical storm on the following afternoon. Sonca intensified into a severe tropical storm on 17 September. While moving generally on a northward track, it further intensified into a typhoon to the south-southeast of Tokyo on 18 September. Sonca reached its peak intensity with an estimated maximum sustained wind of 130 km/h near its centre on 19 September and turned to move northeastwards. Sonca weakened into a severe tropical storm on 20 September and became an extratropical cyclone over the western North Pacific to the east of Japan that evening.
Nesat (1117) formed as a tropical depression over the western North Pacific about 1 840 km east of Manila on 23 September and moved west-northwestwards. It gradually intensified over the western North Pacific and became a typhoon about 560 km east of Manila on 26 September, reaching its peak intensity with an estimated maximum sustained wind of 145 km/h near its centre. On 27 September, Nesat crossed Luzon and entered the South China Sea in the afternoon. It moved across the northern part of the South China Sea for the following two days and made landfall over the northeastern part of Hainan Island on the afternoon of 29 September. On 30 September, Nesat first moved across Beibu Wan, then made landfall again over the coast of northern Vietnam in the afternoon and weakened gradually into a tropical storm. It then moved across northern Vietnam that evening. Nesat dissipated over northern Vietnam on 1 October.
Haitang (1118) formed as a tropical depression over the central part of the South China Sea about 140 km south of Xisha on 25 September and moved slowly. Haitang intensified into a tropical storm that afternoon, reaching its peak intensity with an estimated maximum sustained wind of 65 km/h near its centre. Haitang moved westwards across the seas south of Hainan on 26 September. It made landfall over the coast of Vietnam on 27 September and weakened into a tropical depression, dissipating over Indochina that evening. Four people were killed and another four missing in Vietnam during the passage of Haitang.
Nalgae (1119) formed as tropical depression over the western North Pacific about 1 850 km east-northeast of Manila on 27 September and moved generally westwards. It intensified into a tropical storm on the following day and moved west to west-southwestwards. Nalgae intensified into a severe tropical storm on 29 September. It gradually intensified into a severe typhoon on 30 September and attained its peak intensity with an estimated maximum sustained wind of 175 km/h near its centre over the seas about 300 km northeast of Manila on the morning of 1 October. Nalgae then crossed Luzon and entered the South China Sea in the late afternoon. It moved west to west-northwestwards across the northern part of the South China Sea for the following two days. Nalgae weakened into a typhoon in the early hours on 2 October and a severe tropical storm that afternoon. It weakened further into a tropical storm on 4 October and crossed the southern part of Hainan Island that afternoon, entering Beibu Wan and weakening further into a tropical depression at night. Nalgae moved southwestwards across the southern part of Beibu Wan on 5 October and dissipated over the seas near Hainan that day.
Banyan (1120) formed as a tropical depression over the western North Pacific about 1 420 km east-southeast of Manila on 10 October and moved west-northwestwards, reaching its peak intensity with an estimated maximum sustained wind of 55 km/h near its centre on the following day. It crossed the central part of the Philippines on 12 October and turned to move northwestwards across the central part of the South China Sea on the following day. Banyan moved north-northwestwards on 14 October and dissipated over the northern part of the South China Sea about 160 km south of Dongsha on 15 October.
No tropical cyclone formed over the western North Pacific and the South China Sea in November.
Washi (1121) formed as a tropical depression over the western North Pacific about 500 km south-southeast of Yap on 14 December and moved west-northwestwards. It intensified into a tropical storm on 15 December, reaching its peak intensity with an estimated maximum sustained wind of 85 km/h near its centre on the following day and crossed the southern Philippines that evening. Washi entered the southern part of the South China Sea on a westward track on 18 December. It turned to move west-southwestwards on 19 December and dissipated over the southern part of the South China Sea to the southeast of Vietnam that evening. According to press reports, Washi brought flash floods and landslip to the Philippines where 1 010 people were killed, over 1 600 people injured and around 50 people missing. Some 4 000 houses were also damaged or destroyed.
Note: Casualties and damage figures were compiled from press reports.
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