Report on Severe Typhoon Haikui (2311)

Severe Typhoon Haikui (2311)
27 August - 5 September 2023

Haikui was the fourth tropical cyclone affecting Hong Kong in 2023. While only the Standby Signal No. 1 was issued during the approach of Haikui, the trough of low pressure associated with the remnant of Haikui brought incessant downpour to Hong Kong from the night of 7 September to the morning of 8 September, breaking a number of rainfall records and triggering severe flooding in many parts of Hong Kong. Overall, Haikui and its remnant brought 641.1 millimetres of rainfall² to Hong Kong, breaking the previous record of 616.5 millimetres set by Typhoon Sam in 1999, and making it the wettest tropical cyclone ever to affect Hong Kong since records began in 1884.

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.

In Hong Kong, the Standby Signal No. 1 was issued at 4:40 a.m. on 4 September, when Haikui was about 610 km east of Hong Kong. Local winds were generally moderate west to northwesterlies, occasionally fresh offshore and on high ground on that day and during the day next day. The lowest instantaneous mean sea-level pressure of 1000.7 hPa was recorded at the Observatory Headquarters at 3:24 p.m. on that day. Haikui came closest to the territory at around 8 p.m. on 5 September, when it was about 250 km northeast of Hong Kong. As Haikui weakened into an area of low pressure over inland eastern Guangdong, all tropical cyclone warning signals were cancelled at 9:40 p.m. on 5 September.

During the passage of Haikui, a maximum sea level (above chart datum) of 2.53 m was recorded at Tsim Bei Tsui, while a maximum storm surge of 0.39 m (above astronomical tide) was recorded at Tai Po Kau.

Under the influence of the outer subsiding air of Haikui, apart from isolated showers and squally thunderstorms, it was generally fine and very hot during the day in Hong Kong on 3 – 4 September. Affected by the remnant of Haikui, it was mainly cloudy with a few showers on 5 – 6 September. The trough of low pressure associated with the remnant of Haikui over the coast of Guangdong started to bring heavy rain and squally thunderstorms to Hong Kong on the night of 7 September. The heavy downpour continued to affect the territory till the next day. During the torrential rain, the Hong Kong Observatory Headquarters registered a record-breaking hourly rainfall of 158.1 millimetres from 11 p.m. to midnight on 7 September, the highest since records began in 1884. The 2-hour total rainfall of 201.0 millimetres and 12-hour total rainfall of 605.8 millimetres recorded at the Observatory Headquarters during this phenomenal rainstorm also broke their respective records. Moreover, the 24-hour rainfall from 4 p.m. on 7 September to 4 p.m. next day reached 638.5 millimetres, about a quarter of the normal annual total rainfall of Hong Kong and just next to the highest records kept by the historical rainstorm on 30 May 1889. More than 400 millimetres of rainfall were recorded over many parts of the territory and rainfall even exceeded 800 millimetres over the Eastern District and Southern District of Hong Kong Island on 7 – 8 September. The prolonged heavy rain necessitated the issuance of the Black Rainstorm Warning for 16 hours and 35 minutes, setting the longest record since the introduction of the rainstorm warning system in 1992.

The unrelenting heavy rain triggered flash floods and landslides in many parts of Hong Kong, resulting in widespread traffic disruption and damage to infrastructures. Locally, there were 60 reports of flooding and over 200 reports of landslides. Power and water supply were temporarily interrupted in some places. At least two people were killed and more than 140 were injured during the rainstorm. Wong Tin Sin was swamped by severe flooding. At Wong Tai Sin Mass Transit Railway Station, rainwater poured into the station platform and tunnel along the elevators and stairs. Parts of the Kwun Tong Line were suspended. The entire underground floor of the nearby Temple Mall North was submerged. The Lung Cheung Road in front of the mall was also flooded with many vehicles trapped. A house collapsed at Lei Uk Tsuen in Sha Tin. A landslide occurred on a mountain slope near Yiu Hing Road in Shau Kei Wan with many boulders falling and blocking the road. A vehicle was hit by the rocks. Water pipes were damaged and water supply to nearby residences was suspended. The car park at Wan Tsui Estate in Chai Wan was flooded with the water depth reaching half a vehicle. There were road subsidence in different places of Hong Kong Island, including Repulse Bay, Shek O, and Chai Wan. A passing vehicle fell into a subsided hole at the intersection of Island Road and Repulse Bay Road. Shek O Road was once closed due to landslides and road subsidence.

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²  defined as the total rainfall recorded at the Hong Kong Observatory Headquarters from the time when a tropical cyclone was centred within 600 km of Hong Kong to 72 hours after the tropical cyclone has dissipated or moved outside 600 km of Hong Kong.