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TROPICAL CYCLONE OVERVIEW FOR 2020
2.1 Review of tropical cyclones in 2020
2.1.1 Tropical cyclones over the western North Pacific (including the South China Sea)
In 2020, a total of 25 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°, less than the long-term (1961 - 2010) average figure of around 30. During the year, 12 of the tropical cyclones attained typhoon intensity or above, less than the long-term average (1961 - 2010) of about 15, with three 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 2020. During the year, six tropical cyclones made landfall over China, with two of them crossing the south China coast within 300 km of Hong Kong. Four tropical cyclones made landfall over the Korean Peninsula, six traversed the Philippines and seven made landfall over Vietnam. With an estimated maximum sustained wind speed of 275 km/h and a minimum sea-level pressure of 895 hPa near the centre (Table 4.1), Super Typhoon Goni (2019) in October (Figure 2.3) is the most intense tropical cyclone over the WNP and the SCS in 2020. It is also the most intense tropical cyclone in the region since Super Typhoon Haiyan in November 2013.
2.1.2 Tropical cyclones in Hong Kong’s area of responsibility
Amongst the 25 tropical cyclones in 2020, 18 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), more than the long-term annual average (1961-2010) figure of around 16 (Table 2.1). Ten of them developed within Hong Kong’s area of responsibility. Altogether, 405 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
14 tropical cyclones affected SCS bounded by 10°N, 25°N, 105°E and 120°E in 2020, more than the long-term annual average (1961-2010) of around 12. Eight of them formed within SCS.
2.1.4 Tropical cyclones affecting Hong Kong
In 2020, the typhoon season in Hong Kong started on 12 June when Tropical Depression Nuri (2002) formed over the Philippines and entered the SCS, necessitating the issuance of the Standby Signal No. 1. The typhoon season ended with the cancellation of all tropical cyclone warning signals on 24 October when Severe Tropical Storm Saudel (2017) moved away from Hong Kong and weakened that day.
Five tropical cyclones affected Hong Kong during 2020 (Figure 2.2), slightly less than the long-term (1961-2010) average of about six in a year (Table 2.2). They were Tropical Storm Nuri (2002) in June, Tropical Storm Sinlaku (2003) in July to August, Typhoon Higos (2007) in August, Tropical Storm Nangka (2016) and Typhoon Saudel (2017) in October. The No. 9 Increasing Gale or Storm Signal was issued by the Hong Kong Observatory during the passage of Higos on 19 August. It was the highest tropical cyclone warning signal issued in 2020 and for the first time since Super Typhoon Mangkhut hitting Hong Kong in 2018. The No. 8 Gale or Storm Signal was issued during the passage of Nangka. The rest of the three tropical cyclones all necessitated the issuance of the Strong Wind Signal No. 3 in Hong Kong.
2.1.5 Tropical cyclone rainfall
Tropical cyclone rainfall (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 2020 was 421.7 mm (Table 4.8.1). This accounted for approximately 17.6 % of the year’s total rainfall of 2395.0 mm and was about 42.1 % below the 1961-2010 long-term average of 728.8 mm.
Typhoon Higos (2007) brought 172.2 mm of rainfall to the Hong Kong Observatory Headquarters (Table 4.8.1) and was the wettest tropical cyclone in 2020.