Overview of Tropical Cyclone in September 2023

Six tropical cyclones occurred over the western North Pacific and the South China Sea in September 2023. Among them, Saola, Haikui and Koinu necessitated the issuance of the tropical cyclone warning signals by the Observatory.

Saola formed as a tropical depression over the western North Pacific about 670 km southeast of Gaoxiong on the night of 23 August and moved slowly at first. It then made an anti-clockwise loop over the seas east of Luzon and intensified rapidly in the following five days. Saola intensified into a super typhoon on the night of 26 August. Saola weakened from super typhoon into a severe typhoon twice in the following three days, but intensified into a super typhoon again on the evening of 29 August and tracked west-northwestwards across Luzon Strait. Saola attained its peak intensity with an estimated maximum sustained wind of 230 km/h near its centre in the small hours of 30 August. Saola maintained this intensity and entered the South China Sea later that day, making it the second strongest tropical cyclone in the South China Sea since the Observatory’s records began in 1950, just after Super Typhoon Rammasun in 2014. It edged closer to the coast of Guangdong gradually while maintaining super typhoon intensity on the next day. Saola turned to move westwards across the coastal waters of Guangdong on 1 September. It weakened rapidly on 2 September and made landfall near Yangjiang of Guangdong in the afternoon. Saola continued to move across the coast of western Guangdong afterwards and weakened into a tropical depression progressively. Saola entered Beibu Wan on the morning of 3 September and finally weakened into an area of low pressure that night.

According to press reports, Saola brought torrential rain and squalls to the northern part of the Philippines, causing 2 deaths, 3 injures and 2 missing. More than 1.16 million people were affected, more than 7 800 houses were damaged and economic loss exceeded PHP 2.4 billion. Under the influence of the outer rainbands of Saola, there were 60 reports of flooding in Taiwan. Around 200 people were displaced and electricity supply to more than 10 000 households was disrupted; whereas in Fujian, about 450 000 people were affected, 170 000 people were displaced, more than 140 houses were damaged and economic loss exceeded RMB 870 million. There were over 16 000 reports of fallen trees in Zhuhai. About 70 vehicles were damaged and economic loss was around RMB 60 million. In Shenzhen, a large tree fell under strong winds and hit a passing vehicle, killing one person and injuring two people. For detailed information of Saola including its impact to Hong Kong, please refer to the Tropical Cyclone Report of Saola.

Haikui formed as a tropical depression over the western North Pacific about 760 km south-southeast of Iwo Jima on the night of 27 August. It moved westwards or west-northwestwards towards the southern part of Taiwan and intensified gradually in the following six days. Haikui intensified into a severe typhoon in the small hours on 3 September and attained its peak intensity over the seas east of Taiwan, with an estimated maximum sustained wind of 175 km/h near its centre before noon on that day. It then moved across the southern part of Taiwan and weakened gradually. Haikui weakened into a tropical storm when it moved across the Taiwan Strait on 4 September. Haikui made landfall near Dongshan in Fujian on the morning of 5 September. It then moved into inland eastern Guangdong and finally degenerated into an area of low pressure that night.

According to press reports, at least 143 people were injured when Haikui affected Taiwan. Water and electricity supply to more than 20 000 and 270 000 households were disrupted respectively. Around 8 000 people were displaced. Economic loss exceeded USD 43 million. In Fujian province, more than 1.59 million people were affected, more than 2 500 houses were damaged and economic loss exceeded RMB 5 billion. Besides, after Haikui has weakened into an area of low pressure over inland eastern Guangdong, its remnant continued to move westwards slowly and wreaked havoc the coastal areas with torrential rain affecting many places in Guangdong and Guangxi provinces during 5 – 11 September. In Shenzhen, from the night of 7 September to the morning of 8 September, maximum 2-hour rainfall of 195.8 millimetres, 3-hour rainfall of 246.8 millimetres, 6-hour rainfall of 349.7 millimetres and 12-hour rainfall of 465.5 millimetres were recorded, all breaking their respective records since Shenzhen’s meteorological records began in 1952. Many metro stations were flooded and some of the lines were suspended in Shenzhen. Some flights at Shenzhen Airport were delayed. Water was discharged from Shenzhen Reservoir in the small hours on 8 September. For detailed information of Haikui including its impact to Hong Kong, please refer to the Tropical Cyclone Report of Haikui.

Kirogi formed as a tropical depression over the western North Pacific about 1 110 km east of Guam in the small hours on 30 August. It moved northwards and intensified gradually. Kirogi turned to move north-northwestwards, intensified into a severe tropical storm and attained its peak intensity with an estimated maximum sustained wind of 90 km/h near its centre the next afternoon. It tracked northwestwards or west-northwestwards towards the seas south of Japan and weakened gradually in the following three days. Kirogi finally degenerated into an area of low pressure over the seas south of Japan on the afternoon of 4 September.

Yun-yeung formed as a tropical depression over the western North Pacific about 710 km south-southeast of Okinawa on the afternoon of 4 September. It moved northeastwards or north-northeastwards towards Honshu, Japan and intensified gradually. Yun-yeung intensified into a tropical storm the next night and attained its peak intensity with an estimated maximum sustained wind of 75 km/h near its centre on the morning of 6 September. It weakened gradually on 8 September and finally evolved into an extratropical cyclone in the vicinity of Honshu, Japan in the small hours of the next day.

According to press reports, Yun-yeung left 3 deaths and 21 injures in Japan during its passage. More than 2 600 houses were damaged. Water and electricity supply to more than 170 and 20 000 households were disrupted respectively.

A tropical depression formed over the central part of the South China Sea about 320 km east-southeast of Da Nang in the small hours on 25 September, with an estimated maximum sustained wind of 45 km/h near its centre. It moved northwestwards or west-northwestwards that day and finally degenerated into an area of low pressure over the central part of Vietnam the next morning.

Koinu formed as a tropical depression over the western North Pacific about 1 920 km east of Manila on the night of 28 September. It then moved westwards and intensified gradually. Koinu turned to move northwestwards across the seas east of the Philippines on the afternoon of 30 September.