Report on Typhoon Kompasu (2118)

Typhoon Kompasu (2118)
8 - 14 October 2021

Kompasu was the seventh tropical cyclone affecting Hong Kong in 2021. Tropical Cyclones Lionrock and Kompasu successively hit Hong Kong within four days between 9 – 12 October and both necessitated the issuance of No. 8 Gale or Storm Signal. The time separation between the cancellation of the No. 8 signal for Lionrock and the issuance of the No. 8 signal for Kompasu was only 60 hours 40 minutes, the shortest record of break time between two No. 8 signals for two tropical cyclones since 1946.

Kompasu developed as a tropical depression over the western North Pacific about 1 020 km east of Manila on the night of 8 October. It moved northwards at first and intensified gradually. Kompasu picked up speed towards the west on 10 October. It developed into a severe tropical storm while moving across the Luzon Strait on 11 October. Kompasu moved westwards across the northern part of the South China Sea on 12 October. It further developed into a typhoon on the morning of next day, reaching its peak intensity with an estimated sustained wind of 120 km/h near its centre. Kompasu moved across Hainan Island on 13 October and weakened rapidly. It degenerated into an area of low pressure over Beibu Wan on 14 October.

According to press reports, Kompasu left 40 deaths, 5 injuries, 17 missing and over 500 000 people evacuated in the Philippines during its passage. Besides, the Yantian Port in Guangdong and 3 ports in Hainan Island were closed and the marine transportation services were suspended owing to the torrential rain brought by Kompasu.

The Strong Monsoon Signal was issued at 4:00 p.m. on 11 October. Under the combined effect of the northeast monsoon and the outer circulation of Kompasu, local winds were fresh north to northeasterlies, reaching strong force offshore. With Kompasu entering the northeastern part of the South China Sea, the No. 3 Strong Wind Signal was issued to replace the Strong Monsoon Signal at 12:40 a.m. on 12 October when Kompasu was about 770 km east-southeast of Hong Kong. Local winds were generally fresh to strong north to northeasterlies, occasionally reaching gale force offshore and on high ground that morning. Since Kompasu gradually edged closer to the coast of Guangdong, local winds were expected to strengthen further at night and the No. 8 Northeast Gale or Storm Signal was issued at 5:20 p.m. on 12 October when Kompasu was about 480 km southeast of Hong Kong. Local winds were strong to gale force east to northeasterlies, occasionally reaching storm force offshore and even hurricane force on high ground on the morning of 13 October. Kompasu came closest to Hong Kong at around 4 a.m. on 13 October when it skirted past about 360 km south of Hong Kong. With Kompasu making landfall over Hainan Island and gradually departing from Hong Kong, local winds moderated in the afternoon. The No. 3 Strong Wind Signal was issued to replace the No. 8 Northeast Gale or Storm Signal at 4:40 p.m. on 13 October. As Kompasu continued to weaken and further departed from Hong Kong in the next early morning, the No. 1 Standby Signal was issued to replace the No. 3 Strong Wind Signal at 4:40 a.m. on 14 October and all tropical cyclone warning signals were cancelled at 6:20 a.m. on that day.

Under the influence of Kompasu, maximum hourly mean winds of 111, 85 and 76 km/h and maximum gusts of 153, 110 and 119 km/h were recorded at Tate’s Cairn, Waglan Island and Cheung Chau Beach respectively. A maximum sea level of 3.53 m (above chart datum) was recorded at Tai Po Kau and a maximum storm surge of 1.36 m (above astronomical tide) was recorded at Shek Pik. The lowest instantaneous mean sea-level pressures recorded at some selected stations are as follows:

Affected by the dry northeast monsoon, local weather was mainly fine on 11 October. The outer rainbands of Kompasu brought heavy showers to Hong Kong on 12–13 October. With Kompasu weakening and moving away from Hong Kong, rain eased off locally and there were sunny internals on 14 October. Over 100 millimetres of rainfall was recorded over most parts of the territory during 12–14 October.

In Hong Kong, at least 20 persons were injured during the passage of Kompasu. There were 877 reports of fallen trees and 10 reports of flooding. The fallen trees in Wong Tai Sin and Wan Chai damaged five vehicles. The storm surge brought by Kompasu raised the water level in Hong Kong generally by more than one metre. Coinciding with the astronomical high tide, the aggregated effect resulted in the inundation of some low-lying areas in Hong Kong. The cycle tracks and subways near Shing Mun River in Sha Tin were flooded. Minor flooding was also reported in the promenade of Heng Fa Chuen and Island Resort in Siu Sai Wan. With sea water flowing into the carpark of an industrial building in Chai Wan, a security guard post and water-filled barriers were washed away. Some village houses of Sam Ka Tsuen in Lei Yue Man were inundated. A resident in Tai O was trapped by flooding and needed to be rescued.