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Section 2 TROPICAL CYCLONE OVERVIEW FOR 2023
2.1 Review of tropical cyclones in 2023
2.1.1 Tropical cyclones over the western North Pacific (including the South China Sea)
In 2023, a total of 19 tropical cyclones occurred over the western North Pacific (WNP) and the South China Sea (SCS) bounded by the Equator, 45°N, 100°E and 180°, considerably less than the long-term (1961 - 2020) average figure of around 30. During the year, 11 of the tropical cyclones attained typhoon intensity or above, less than the long-term average (1961 - 2020) of about 15, with five of them reaching super typhoon intensity (maximum 10-minute wind speed of 185 km/h or above near the centre).
Figure 2.1 shows the monthly frequencies of the occurrence of tropical cyclones in WNP and SCS in 2023.
During the year, six tropical cyclones made landfall over China, with one of them crossing the coast of southern China within 300 km of Hong Kong and two crossed Taiwan. Two made landfall over the Philippines and one made landfall over Vietnam. With an estimated maximum sustained wind speed of 250 km/h and a minimum sea-level pressure of 900 hPa near the centre (Table 4.1), Super Typhoon Mawar (2302) in May to June (Figure 2.3) was the most intense tropical cyclone over the WNP and the SCS in 2023.
2.1.2 Tropical cyclones in Hong Kong’s area of responsibility
Amongst the 19 tropical cyclones in 2023, 10 of them occurred inside Hong Kong’s area of responsibility (i.e. the area bounded by 10°N, 30°N, 105°E and 125°E), less than the long-term annual average (1961-2020) figure of around 16 (Table 2.1). Three of them developed within Hong Kong’s area of responsibility. Altogether, 314 tropical cyclone warnings to ships and vessels were issued by the Hong Kong Observatory this year (Table 4.2).
2.1.3 Tropical cyclones over the South China Sea
Seven tropical cyclones affected SCS bounded by 10°N, 25°N, 105°E and 120°E in 2023, less than the long-term annual average (1961-2020) of around 12. Two of them formed over the region.
2.1.4 Tropical cyclones affecting Hong Kong
In 2023, the typhoon season in Hong Kong started on 15 July. Tropical Depression Talim (2304) moved towards the northern part of the SCS in that morning, necessitating the issuance of the Standby Signal No. 1. The typhoon season ended with the cancellation of all tropical cyclone warning signals on 9 October when Tropical Depression Koinu (2314) further departed from Hong Kong and weakened in that afternoon.
Five tropical cyclones affected Hong Kong during 2023 (Figure 2.2), slightly less than the long-term (1961-2020) average of about six in a year (Table 2.2). They were Typhoon Talim (2304) and Super Typhoon Doksuri (2305) in July, Super Typhoon Saola (2309) and Severe Typhoon Haikui (2311) in August to September and Severe Typhoon Koinu (2314) in September to October. The No. 10 Hurricane Signal was issued during the passage of Saola on 1 September, the highest tropical cyclone warning signal issued in 2023 and the first No. 10 Hurricane Signal since Mangkhut in 2018. The Increasing Gale or Storm Signal No. 9 and the No. 8 Gale or Storm Signal were issued during the passages of Koinu and Talim respectively. Doksuri and Haikui necessitated the issuance of the Standby Signal No. 1 in Hong Kong.
2.1.5 Tropical cyclone rainfall
Tropical cyclone rainfall for Hong Kong (total rainfall recorded at the Hong Kong Observatory Headquarters from the time when a tropical cyclone comes within 600 km of Hong Kong to 72 hours after it has dissipated or moved more than 600 km away from Hong Kong) in 2023 was 1427.8 mm (Table 4.8.1), which accounted for approximately 51.5% of the year’s total rainfall of 2774.5 mm and more than double of the 1961-2020 long-term average of 704.2 mm.
According to the above definition, Severe Typhoon Haikui (2311) brought 641.1 mm of rainfall to Hong Kong (Table 4.8.1) and was the wettest tropical cyclone in 2023, breaking the previous record of 616.5 mm set by Typhoon Sam in 1999, and making it the wettest tropical cyclone ever to affect Hong Kong since records began in 1884.