2.1.1 Tropical cyclones over the western North Pacific (including the South China Sea)
In 2015, 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 (1961-2010) average figure of around 30. During the year, 20 of the tropical cyclones attained typhoon intensity or above, more than the long-term average (1961–2010) of about 15, with 13 of them reaching super typhoon intensity (maximum 10-minute wind speed of 185 km/h or above near the centre), more than the long-term (1961–2010) average of about five by eight, and making it the most active year for super typhoons since comprehensive record began in 1961.
The high number of super typhoons in 2015 is partly attributed to the El Niño event. The above-normal sea surface temperature over the central and eastern equatorial Pacific resulted in abnormal atmospheric circulation over the Pacific and in turn displaced the breeding ground of tropical cyclones further east. As shown in Figure 2.1, the tropical cyclone genesis positions in 2015 were mostly to the east of 140oE, including all 13 super typhoons and two crossing the dateline and entering WNP. Moving typically west to northwestwards after formation, tropical cyclones starting further east will stay over the oceans longer during their lifespan, thereby increasing the chance for them to develop into super typhoons under relatively high sea surface temperature and favourable atmospheric conditions.
Figure 2.2 shows the monthly frequencies of the occurrence of tropical cyclones in WNP and SCS in 2015. Tropical cyclone genesis occurred in the region every month throughout 2015.
During the year, five tropical cyclones made landfall over China, with one of them crossing the south China coast within 300 km of Hong Kong. Two tropical cyclones crossed Taiwan, four made landfall over Japan, six traversed the Philippines and two made landfall over Vietnam. With an estimated maximum sustained wind speed of 240 km/h and a minimum sea-level pressure of 905 hPa near its centre (Table 4.1), Super Typhoon Soudelor (1513) in August (Figure 2.4) was the most intense tropical cyclone in 2015 over the western North Pacific and the South China Sea.
2.1.2 Tropical cyclones in Hong Kong’s area of responsibility
Amongst the 27 tropical cyclones in 2015, 13 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), less than the long-term annual average figure of around 16 (Table 2.1). Two of them developed within Hong Kong’s area of responsibility. Altogether, 316 tropical cyclone warnings to ships and vessels were issued by the Hong Kong Observatory in 2015 (Table 4.2).
2.1.3 Tropical cyclones over the South China Sea
Nine tropical cyclones affected SCS bounded by 10°N, 25°N, 105°E and 120°E in 2015, less than the long-term annual average of around 12. Only two of them formed within SCS.
2.1.4 Tropical cyclones affecting Hong Kong
In 2015, the typhoon season in Hong Kong started on 21 June when Tropical Storm Kujira (1508) moved northwards and edged towards the south China coast, necessitating the issuance of the Standby Signal No. 1. The typhoon season ended on 5 October when Tropical Storm Mujigae (1522) moved away from Hong Kong and the Standby Signal No. 1 was replaced by the Strong Monsoon Signal.
Three tropical cyclones affected Hong Kong during 2015 (Figure 2.3), less than the long-term (1961-2010) average of about six in a year (Table 2.2). They were Tropical Storm Kujira (1508) in June, Typhoon Linfa (1510) in July, and Severe Typhoon Mujigae (1522) in October. The No. 8 Gale or Storm Signal was issued during the passage of Linfa, the highest tropical cyclone warning signal issued in 2015. The Strong Wind Signal No. 3 was issued during the passage of Mujigae. Kujira only necessitated the issuance of Standby Signal No. 1 in Hong Kong.
In 2015, no tropical cyclone warning signal was issued in August and September, the first time since 1946. This was mainly attributed to less tropical cyclones entering SCS from the WNP and less tropical cyclones forming within SCS. Under the influence of the El Niño, above-normal sea surface temperatures over the central and eastern equatorial Pacific displaced the breeding ground of tropical cyclones further east. This increased the chance for tropical cyclones to recurve and turn northwards when moving across WNP, resulting in less tropical cyclone entering SCS. Less tropical cyclones forming in SCS in August and September 2015 was mainly due to the weaker-than- normal southwesterly airstream over the region, leading to less moisture transport and weaker convergence in SCS and hindering the formation of tropical cyclones.
2.1.5 Tropical cyclone rainfall
Tropical cyclone rainfall (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 2015 was 346.6 mm (Table 4.8.1). This accounted for approximately 18.5 % of the year’s total rainfall of 1874.5 mm and was about 52 % below the 1961-2010 long-term average of 728.8 mm.
Severe Typhoon Mujigae (1522) brought 156.6 mm of rainfall to the Hong Kong Observatory Headquarters (Table 4.8.1) and was the wettest tropical cyclone in 2015.
2.2 Monthly overview
A monthly overview of tropical cyclones is given in this section. Detailed reports on tropical cyclones affecting Hong Kong, including reports of damage, are presented in Section 3.
JANUARY
Mekkhala (1501) formed as a tropical depression over the western North Pacific about 420 km east of Yap on the night of 13 January. Moving west-northwestwards, it developed into a tropical storm the next day. Mekkhala turned west to west-southwestwards on 15 and 16 January and continued to intensify, becoming a typhoon about 730 km east-southeast of Manila on the morning of 17 January and reaching peak intensity with an estimated sustained wind of 120 km/h near its centre. Mekkhala subsequently took on a northwesterly track across the Philippines and weakened gradually. It finally degenerated into an area of low pressure over the coastal waters off the east coast of Luzon on the morning of 19 January.
FEBRUARY
Higos (1502) formed as a tropical depression over the western North Pacific about 1 420 km east of Guam on the night of 7 February. It moved slowly at first and developed into a tropical storm the next morning. Higos moved generally northwestwards and continued to intensify in the next two days. It developed into a super typhoon on the afternoon of 10 February, reaching peak intensity with an estimated sustained wind of 185 km/h near its centre. Higos weakened rapidly thereafter and dissipated over the western North Pacific on the afternoon of 11 February.
MARCH TO APRIL
Bavi (1503) formed as a tropical depression over the western North Pacific about 2 640 km east-southeast of Guam on the night of 11 March. Moving west to west-northwestwards, it developed into a tropical storm the next morning. Bavi slightly intensified in the following two days, reaching its peak intensity on the afternoon of 14 March with an estimated sustained wind of 85 km/h near its centre. After skirting past Guam the next day, Bavi started to weaken. It finally degenerated into an area of low pressure over the western North Pacific east of the Philippines on the morning of 18 March.
Maysak (1504) formed as a tropical depression over the western North Pacific about 1 640 km east-southeast of Guam on the morning of 27 March. Moving generally westwards, Maysak intensified gradually in the next four days. It developed into a super typhoon in the early hours of 31 March and reached its peak intensity that night with an estimated sustained wind of 230 km/h near its centre. Maysak moved west-northwestwards towards Luzon in the following days, crossing Luzon on 5 April and entering the South China Sea that night. It weakened rapidly and degenerated into an area of low pressure over the northeastern part of the South China Sea the next morning.
According to press reports, Maysak wreaked havoc in the Federated States of Micronesia. At least nine people were killed and several thousand people had to be evacuated.
Haishen (1505) formed as a tropical depression over the western North Pacific about 1 220 km east-southeast of Guam on the night of 3 April. Moving generally westwards, it intensified into a tropical storm the following afternoon. Haishen reached its peak intensity that night with an estimated sustained wind of 75 km/h near its centre. It became slow-moving and weakened gradually in the next couple of days. Haishen eventually dissipated over the western North Pacific southeast of Guam on the afternoon of 6 April.
MAY
Noul (1506) formed as a tropical depression over the western North Pacific about 360 km east of Yap on the night of 3 May. It developed into a tropical storm the following morning and moved slowly westwards. Skirting past Yap on 6 May, Noul took on a west-northwesterly track towards the seas east of Luzon and continued to intensify. It developed into a super typhoon on the night of 9 May and reached its peak intensity the following morning with an estimated sustained wind of 220 km/h near its centre. After moving across the seas near the northeastern part of Luzon on the night of 10 May, Noul gradually turned northeastwards and started to weaken. It finally became an extratropical cyclone after sweeping past the Ryukyu Islands on the morning of 12 May.
Dolphin (1507) formed as a tropical depression over the western North Pacific about 2 170 km east-southeast of Guam on the morning of 8 May and generally moved northwards in the following three days. Dolphin started to turn west-northwestwards on 11 May and intensified gradually. It skirted past Guam on 15 May and became a super typhoon the following day, reaching its peak intensity with an estimated sustained wind of 205 km/h near its centre. It turned northeastwards and weakened gradually in the next three days. Dolphin eventually evolved into an extratropical cyclone over the sea areas northeast of Iwo Jima on the afternoon of 20 May.
JUNE TO AUGUST
Kujira (1508) formed as a tropical depression over the central part of the South China Sea about 190 km south-southwest of Xisha on the afternoon of 20 June. Moving slowly at first, it started to track generally northwards the next day and intensified into a tropical storm that night. It made landfall over the east coast of Hainan Island on the evening of 22 June and weakened slightly while crossing Hainan Island. Kujira re-organized and re-intensified after entering Beibu Wan the next morning. It reached its peak intensity with an estimated sustained wind of 85 km/h near its centre on the morning of 24 June. Moving northwestwards across Beibu Wan, Kujira made landfall over the coast of northern Vietnam in the afternoon and weakened gradually, before finally dissipating over northern Vietnam on the morning of 25 June.
According to press reports, Kujira severely disrupted air, sea and land transportation in Hainan Island. In Vietnam, at least seven people were killed and four were reported missing during the passage of Kujira.
Chan-hom (1509) formed as a tropical depression over the western North Pacific about 1 710 km east-southeast of Guam on the night of 30 June. It developed into a tropical storm the following morning and moved westwards. Under the influence of an area of low pressure west of Chan-hom, Chan-hom moved erratically on 2 - 3 July. It subsequently tracked generally northwestwards and intensified gradually, sweeping across the Ryukyu Islands and developing into a super typhoon on 10 July with a peak intensity of estimated sustained winds up to 195 km/h near its centre. Turning northwards the next day, Chan-hom skirted past the coastal waters of Zhejiang and weakened gradually. Chan-hom finally evolved into an extratropical cyclone near the west coast of the Korea Peninsula on 12 July.
According to press reports, at least one person was killed and about two million people were affected in Zhejiang during the passage of Chan-hom, with direct economic loss estimated to be around RMB 6 billion. In Okinawa, at least 27 people were injured and more than 40 000 households were without power supply.
Linfa (1510) formed as a tropical depression over the western North Pacific about 830 km east of Manila on the afternoon of 2 July. It moved generally westwards and intensified into a tropical storm the next morning. Moving northwestwards, Linfa headed towards the northern part of Luzon and developed into a severe tropical storm on 4 July. Linfa moved across the northern part of Luzon on 5 July and entered the South China Sea. It weakened into a tropical storm the next day. With a weaker steering flow, Linfa drifted northwards slowly on 6 - 7 July and re-intensified into a severe tropical storm. It started to take on a more westerly track and edged closer to the coast of eastern Guangdong on the afternoon of 8 July. Linfa intensified into a typhoon that night, reaching its peak intensity the next morning with an estimated sustained wind of 140 km/h near its centre. It made landfall near Lufeng in Guangdong around noon and continued to track westwards across the coastal areas of Guangdong towards the Pearl River Estuary in the afternoon. Affected by relatively dry air from the north, Linfa weakened rapidly into a tropical depression. It finally degenerated into an area of low pressure over western Guangdong on the morning of 10 July.
According to press reports, at least 700 000 people were affected and 6 700 houses were damaged in eastern Guangdong during the passage of Linfa. Transportation services were suspended and there was power outage in many places.
Nangka (1511) formed as a tropical depression over the western North Pacific about 240 km north of Marshall Islands on the night of 3 July. It moved generally west to west-northwestwards and intensified gradually. Nangka developed into a super typhoon on the night of 7 July and reached its peak intensity two days later with an estimated sustained wind of 220 km/h near its centre. Nangka weakened into a typhoon on 12 July and started to turn north towards the sea areas south of Japan. It re-intensified into a severe typhoon on 14 July and weakened gradually the following day. Nangka moved across the western part of Japan on 16 July and evolved into an extratropical cyclone over the Sea of Japan during the night.
According to press reports, Nangka left at least five people dead and several dozen injured in Japan.
Originating from the central part of the North Pacific, Severe Tropical Storm Halola (1512) crossed the International Date Line and entered the western North Pacific on 13 July. Moving generally west-northwestwards, it intensified into a typhoon the next day. Halola started to weaken afterwards and took on a more westerly track, at one stage degenerating into a tropical depression on 17 July. Halola resumed a west-northwesterly track the next few days and re-intensified on 20 July, reaching peak intensity on the morning of 23 July with an estimated sustained wind of 145 km/h near its centre. Turning northwards on 25 July, Halola skirted past the Ryukyu Islands and weakened gradually. It finally degenerated into an area of low pressure near Kyushu, Japan on 26 July.
According to press reports, heavy rain brought by Halola flooded many houses and triggered landslides on the island of Amami Oshima in the northern part of the Ryukyu Islands and over the southwestern part of Japan.
Soudelor (1513) formed as a tropical depression over the western North Pacific about 1 720 km east of Guam on the morning of 30 July. It moved west to west-northwestwards and intensified gradually in the next three days. Soudelor developed into a super typhoon on the afternoon of 3 August and reached its peak intensity the next morning with an estimated sustained wind of 240 km/h near its centre. It continued to track west-northwestwards towards Taiwan and gradually weakened into a severe typhoon in the next three days. After crossing Taiwan on the morning of 8 August, Soudelor weakened into a typhoon and made landfall over the coast of Fujian that night. It finally degenerated into an area of low pressure over Jiangxi on the morning of 10 August.
According to press reports, at least six persons were killed, four were missing and more than 4 million households were without power supply in Taiwan during the passage of Soudelor. In Fujian, Zhejiang, Jiangxi and Anhui, 21 people were killed, five were missing and about 3.4 million were affected in the fury of Soudelor.
Molave (1514) formed as a tropical depression over the western North Pacific about 550 km east of Iwo Jima on the afternoon of 7 August and moved generally northwestwards. Molave intensified into a tropical storm in the early hours of 8 August and reached its peak intensity the next afternoon with an estimated sustained wind of 85 km/h near its centre. It weakened slightly on 10 August and re-intensified the next day and turned to move in a northeast direction. It finally evolved into an extratropical cyclone over the western North Pacific east of Japan on the night of 13 August.
Goni (1515) formed as a tropical depression over the western North Pacific about 470 km east of Guam on the afternoon of 14 August. Moving west to west-northwestwards, it intensified gradually in the next five days. Goni developed into a super typhoon on the night of 19 August, reaching its peak intensity with an estimated sustained wind of 195 km/h near its centre. Weakening into a severe typhoon, it started to turn northwards over Luzon Strait on the morning of 21 August and moved towards the seas east of Taiwan. Goni re-intensified into a super typhoon about 420 km west-southwest of Okinawa on the night of 23 August. It then turned to a northeasterly course, skirting past the vicinity of Ryukyu Islands and weakening gradually. Goni moved across Kyushu of Japan on 25 August and evolved into an extratropical cyclone over the Sea of Japan the next day.
According to press reports, during the passage of Goni, at least 26 people were killed and 15 were missing in the Philippines. Goni also wreaked havoc in Okinawa, resulting in at least eight death and over 20 000 households without power supply. In Kyushu of Japan, at least 70 persons were injured, more than 600 000 people had to be evacuated, near 500 000 households were without power supply in the fury of Goni.
Atsani (1516) formed as a tropical depression over the western North Pacific about 2 510 km east-southeast of Iwo Jima on the afternoon of 14 August. Moving slowly at first, Atsani intensified gradually. It started to take on a northwestly course on 17 August and developed into a super typhoon. Atsani reached its peak intensity on 19 August with an estimated sustained wind of 220 km/h near its centre. Skirting past the sea areas east of Iwo Jima on 21 August, Atsani started to turn northeastwards and weakened gradually. It finally evolved into an extratropical cyclone over the western North Pacific east of Japan on 25 August.
SEPTEMBER
Kilo (1517) originated from the central North Pacific and crossed the International Date Line into the western North Pacific as a severe typhoon with an estimated sustained wind of 155 km/h near its centre on 2 September. Kilo subsequently weakened slightly into a typhoon and moved generally west-northwestwards. Kilo weakened further into a severe tropical storm on 9 September and started to track northwestwards. It finally evolved into an extratropical cyclone over the sea areas east of Japan in the early morning of 11 September.
Etau (1518) formed as a tropical depression over the western North Pacific about 440 km southwest of Iwo Jima on the morning of 7 September. It moved northwards towards the seas south of Japan and intensified gradually. Etau developed into a severe tropical storm on the morning of 8 September and reached its peak intensity with an estimated sustained wind of 90 km/h near its centre. It moved across Honshu, Japan on the morning of 9 September and weakened gradually. Etau finally evolved into an extratropical cyclone over the Sea of Japan that afternoon.
According to press reports, Etau triggered heavy rain and flooding in Japan during its passage. At least three persons were killed, 26 were missing, about 30 were injured and over
100 000 people had to be evacuated.
Vamco (1519) formed as a tropical depression over the central part of the South China Sea about 120 km south of Xisha on the afternoon of 13 September and tracked generally westwards. It reached its peak intensity on the morning of 14 September with an estimated sustained wind of 55 km/h near its centre. Vamco made landfall over the coast of central Vietnam that night and degenerated into an area of low pressure over Lao PDR early next morning.
Krovanh (1520) formed as a tropical depression over the western North Pacific about 1 390 km north-northwest of Iwo Jima in the early hours of 15 September. It tracked northwestwards and intensified gradually, becoming a severe typhoon and reaching its peak intensity on the night of 17 September with an estimated sustained wind of 155 km/h near its centre. Krovanh moved northwards and skirted past the sea areas east of Iwo Jima on 18 September. It then turned further to the northeast and weakened gradually, before finally evolving into an extratropical cyclone over the western North Pacific east of Japan in the early morning on 21 September.
Dujuan (1521) formed as a tropical depression over the western North Pacific about 2 080 km east-southeast of Taibei on the night of 22 September. It moved generally to the northwest or west-northwest towards Taiwan and intensified gradually. Dujuan developed into a super typhoon on 27 September, reaching its peak intensity with an estimated sustained wind of 210 km/h near its centre. It moved across Taiwan on the night of 28 September and weakened into a typhoon before making landfall over the coast of Fujian the next morning. Dujuan finally degenerated into an area of low pressure over Jiangxi on the night of 29 September.
According to press reports, Dujuan caused extensive damage in Taiwan, resulting in at least three deaths, over 300 injuries and more than 2.2 million households without electricity supply. There was widespread backflow of sea water along the coast of Xiamen. More than 400 000 people had to be evacuated in Fujian and Zhejiang during the passage of Dujuan.
OCTOBER
Mujigae (1522) formed as a tropical depression over the sea areas east of the Philippines about 290 km east of Manila on the afternoon of 1 October and tracked west-northwestwards in the direction of Luzon. Mujigae entered the South China Sea the next morning and intensified into a tropical storm. Moving west-northwestwards steadily, it edged closer to western Guangdong and continued to intensify in the next two days. Mujigae developed into a severe typhoon in the small hours of 4 October, reaching its peak intensity before noon with an estimated sustained wind of 175 km/h near its centre. It made landfall near Zhanjiang in Guangdong that afternoon and weakened gradually. Mujigae finally degenerated into an area of low pressure on the afternoon of 5 October over Guangxi.
According to press reports, at least 4.6 million people were affected and 8 500 houses were damaged in Guangdong and Guangxi during the passage of Mujigae, with direct economic loss amounting to over 12 billion RMB. Under the influence of the circulation of Mujigae, Shunde district in Foshan and Panyu district in Guangzhou were affected by tornadoes, resulting in at least six deaths and over 200 injuries. Houses were damaged and vehicles were overturned.
Choi-wan (1523) formed as a tropical depression over the western North Pacific about
2 690 km east of Iwo Jima on the night of 2 October. It moved west-northwestwards and intensified gradually. Choi-wan developed into a severe tropical storm on the afternoon of 5 October. Turning northwards the next day, it reached its peak intensity with an estimated sustained wind of 110 km/h near its centre. Choi-wan finally evolved into an extratropical cyclone over the western North Pacific east of Japan on the early morning of 8 October.
Koppu (1524) formed as a tropical depression over the western North Pacific about 2 320 km east of Manila on the morning of 13 October. It moved westwards and intensified gradually. Koppu developed into a super typhoon on the afternoon of 17 October and reached its peak intensity that night with an estimated sustained wind of 205 km/h near its centre. Koppu moved across Luzon on 18 October and weakened into a typhoon. It moved slowly northwards along the western coast of Luzon in the next two days and continued to weaken. Koppu finally degenerated into an area of low pressure near the Luzon Strait on 21 October.
According to press reports, Koppu brought torrential rain and flood to the northern part of the Philippines during its passage. At least 16 people were killed and more than 180 000 people had to be evacuated.
Champi (1525) formed as a tropical depression over the western North Pacific about 1 660 km east of Guam on the afternoon of 13 October. It moved generally west-northwestwards and intensified gradually. Champi developed into a typhoon in the early hours of 17 October and gradually took on a northward course towards the vicinity of Iwo Jima. It further intensified into a super typhoon on the night of 18 October, reaching its peak intensity with an estimated sustained wind of 195 km/h near its centre. Champi slightly weakened into a typhoon in the next three days and started to turn east-northeastwards. It intensified again into a severe typhoon and skirted past the seas south of Iwo Jima on 22 October. Champi then speeded up on an east-northeasterly track and weakened gradually, before finally evolved into an extratropical cyclone over the western North Pacific east-northeast of Iwo Jima on the morning of 25 October.
NOVEMBER
In-fa (1526) formed as a tropical depression over the western North Pacific about 2 240 km east-southeast of Guam on the morning of 17 November. It generally moved west-northwestwards and intensified gradually. In-fa developed into a super typhoon over the sea areas about 340 km southwest of Guam on the morning of 21 November, reaching its peak intensity with an estimated sustained wind of 185 km/h near its centre. It became slow-moving two days later and started to recurve. In-fa subsequently moved to the northeast and weakened, before finally evolving into an extratropical cyclone over the western North Pacific southwest of Iwo Jima on 26 November.
DECEMBER
Melor (1527) formed as a tropical depression over the western North Pacific about 70 km south of Yap on the afternoon of 11 December. Moving west-northwestwards, it became a tropical storm the next morning and continued to intensify, developing into a severe typhoon on the night of 13 December and reaching its peak intensity the following morning with an estimated sustained wind of 175 km/h near its centre. It then moved across the central part of the Philippines and entered the South China Sea in the next couple of days, decelerating and weakening in the process. It finally dissipated over the South China Sea in the early hours of 17 December.
According to press reports, Melor brought heavy rain and flooding to the Philippines during its passage. At least 11 persons were killed and over 700 000 people had to be evacuated.
Note: Casualties and damage figures were compiled from press reports.
