Overview of Tropical Cyclones

Overview of Tropical Cyclones in August 2017

Wednesday, 25th October 2017

 

        Seven tropical cyclones occurred over the western North Pacific and the South China Sea in August 2017. The successive passages of Hato and Pakhar within five days in late August necessitated respectively the issuance of No.8 Gale or Storm Signals by the Hong Kong Observatory for the third and fourth time this year. The issuance of No.10 Hurricane Signal during the passage of Hato on 23 August was the first time since Severe Typhoon Vicente hitting Hong Kong in July 2012.

        Noru formed as a tropical depression over the western North Pacific about 1140 km northwest of Wake Island in the early hours of 21 July. It developed into a super typhoon by 31 July (for details of the process, please refer to Overview of Tropical Cyclones in July 2017), reaching its peak intensity with an estimated sustained wind of 185 km/h near its centre. Noru moved generally northwestwards on 1 - 4 August and gradually weakened. It started to turn northeast towards Japan on 5 August and accelerated across Shikoku and Honshu over the next couple of days. Noru finally degenerated into an area of low pressure over the sea areas north of Honshu on 8 August. Noru’s life span reached 19 days, making it the third longest-living tropical cyclone over the western North Pacific and the South China Sea since 1961, after Rita in 1972 and Wayne in 1986.

        According to press reports, at least two persons were killed, 36 injured and nine reported missing in Japan during the passage of Noru. Tens of thousands people had to be evacuated, and transportation services were seriously disrupted. Electricity supply to near 200 000 households was affected.

        Nalgae formed as a tropical depression over the western North Pacific about 920 km north-northwest of Wake Island on 1 August and drifted east-southeastwards initially. It intensified into a tropical storm the next day and turned northwestwards, reaching its peak intensity with an estimated sustained wind of 75 km/h near its centre on 3 August. Nalgae accelerated northwards on 4 August and evolved into an extratropical cyclone over the western North Pacific east of Japan the next day.

        Banyan formed as a tropical depression over the western North Pacific about 490 km southeast of Wake Island on 11 August. Moving northwestwards at first, it took on a more northerly course over the next few days and intensified gradually, developing into a typhoon on 13 August with an estimated sustained wind of 145 km/h near its centre at peak intensity. Banyan started to turn northeastwards and weakened gradually on 16 August, evolving into an extratropical cyclone the next day over the sea areas west of the International Date Line.

        Hato formed as a tropical depression over the western North Pacific about 740 km east-southeast of Gaoxiong on the night of 20 August. It moved generally westwards across the Luzon Strait and entered the northeastern part of the South China Sea on 22 August, intensifying into a typhoon and tracking west-northwest towards the coast of Guangdong. During its approach towards the Pearl River estuary on 23 August, Hato intensified further and became a super typhoon that morning over the sea areas south of Hong Kong, reaching its peak intensity with an estimated sustained wind of 185 km/h near its centre. After making landfall over the coast near Macao and Zhuhai shortly after noon time, Hato entered western Guangdong and gradually weakened. It moved across Guangxi the next day and degenerated into an area of low pressure over Yunnan at night.

        Hato brought severe storm surge to the coast of Pearl River estuary. Record-high sea levels were recorded at many places. A maximum storm surge of 2.79 m and a maximum sea level of 6.14 m were recorded at Zhuhai station. The coastal areas in Zhuhai including some underground carparks were flooded by sea water. Electricity and water supply in the city became unstable. A number of vessels ran aground about 30 km southwest of Hong Kong and 39 crew members were rescued. Hato brought damaging winds and storm surge to Macao. Extensive areas of Macao suffered damage and were seriously flooded, resulting in at least ten deaths and more than 240 injuries. The direct economic loss exceeded 8.3 billion MOP. A maximum sea level of 5.58 metres was recorded in A-Ma station, a record high in Macao since records began in 1925. Electricity and water supplies were also affected. In Guangdong, Guangxi, Fujian, Guizhou and Yannan, there were at least 15 deaths and one missing during the passage of Hato. Around 740 000 people were affected and over 6 500 houses collapsed, with direct economic loss exceeding 27.2 billion RMB. For detailed information of Hato including the damage caused in Hong Kong, please refer to the Tropical Cyclone Report of Hato.

        Pakhar formed as a tropical depression over the western North Pacific about 570 km east of Manila on the night of 24 August. Moving generally westwards at first, it developed into a tropical storm the next day and moved northwestwards across Luzon. After entering the South China Sea on the morning of 26 August, Pakhar maintained a northwestward track and accelerated towards the coast of Guangdong. It intensified into a severe tropical storm during the night, reaching its peak intensity with an estimated sustained wind of 110 km/h near its centre. After making landfall over the coast of western Guangdong in the vicinity of Zhuhai and Taishan on the morning of 27 August, Pakhar weakened gradually and dissipated over Guangxi that night.

        According to press reports, Pakhar and its remnant brought heavy rain and squalls to Guangdong, Guangxi, Guizhou and Yunnan, resulting in at least 12 deaths. Around 100 000 people were affected with direct economic loss around 370 million RMB. Eight people were injured and many places were flooded in Macao during the passage of Pakhar. A cargo vessel sunk about 120 km east of Hong Kong and 11 crew members on board were rescued. For detailed information of Pakhar including the damage caused in Hong Kong, please refer to the Tropical Cyclone Report of Pakhar.

        Sanvu formed as a tropical depression over the western North Pacific about 880 km southeast of Iwo Jima on 28 August and, moving northwards, intensified into a tropical storm the next day. Turning gradually westwards and intensifying further, Sanvu developed into a typhoon on 31 August and lingered over the sea areas north of Iwo Jima. Meanwhile, Mawar formed as a tropical depression over the northern part of the South China Sea about 270 km east-southeast of Dongsha on the afternoon of 31 August. The further development of Sanvu and Mawar will be described in the Overview of Tropical Cyclones in September 2017.