Typhoons and Rainstorms Affecting Hong Kong in September and October 2023

Typhoons and Rainstorms Affecting Hong Kong in September and October 2023

Lui Yuk-sing

Hong Kong experienced a windy and rainy autumn 2023. From September to October, Hong Kong was affected by a succession of extreme weather including tropical cyclones and rainstorms, and many records were broken.

Super Typhoon Saola hit Hong Kong directly over 1 to 2 September, leading to Hurricane Signal No.10 being issued for the first time since Mangkhut in 2018. Saola brought hurricane-force winds to many parts of Hong Kong, and storm surges caused flooding in some low-lying coastal areas. A few days later, the low-pressure trough associated with the remnants of tropical cyclone Haikui brought record breaking rainstorms to Hong Kong over 7 to 8 September, resulting in flooding and landslides in many places. During the rainstorms, the Hong Kong Observatory Headquarters recorded 158.1 mm of rainfall between 11 pm and midnight on 7 September – the highest hourly rainfall since records began in 1884.

Severe Typhoon Koinu hit Hong Kong over 8 to 9 October, and the area of its hurricane -force winds passed very close to Hong Kong. The Observatory needed to issue the Increasing Gale or Storm Signal No. 9 for the first time in October since 1975. The intense outer rainbands associated with Koinu brought strong winds and heavy showers to Hong Kong. The Observatory’s Headquarters recorded 369.7 mm of rainfall on 9 October, setting a new record for the highest daily rainfall in October. In addition, the 24-hour rainfall from 3 pm on 8 October to 3 pm the following day reached 439.8mm, again setting a new record high for October.

Provisional tracks of tropical cyclones Saola, Haikui, and Koinu

24-hour rainfall distribution map (3 p.m. on 8 October 2023 to 3 p.m. on 9 October 2023)