TROPICAL CYCLONES IN 2010

Chanthu was the second tropical cyclone that necessitated the issuance of a tropical cyclone warning signal by the Hong Kong Observatory in 2010.

A tropical depression formed over the central part of the South China Sea about 900 km south-southeast of Hong Kong on 19 July and moved generally northwestwards. It intensified into a tropical storm on 20 July and was named Chanthu, turning to move westwards for a while that evening. Chanthu intensified into a severe tropical storm and resumed a northwesterly track on 21 July across the northern part of the South China Sea. Chanthu intensified into a typhoon to the east of Hainan Island in the early hours of 22 July, reaching its peak intensity with estimated maximum sustained winds of 120 km/h near its centre. It made landfall near Zhanjiang that afternoon and weakened into a severe tropical storm that evening. Chanthu moved across Guangxi on 23 July. It weakened into a tropical storm that morning and a tropical depression in the evening. Chanthu eventually dissipated inland that night. According to press reports, Chanthu brought rainstorms to Guangdong where at least two people were killed and over 2 900 houses collapsed. The total economic losses amounted to 2.21 billion RMB.

In Hong Kong, the Standby Signal No. 1 was issued at 12:15 p.m. on 20 July when Chanthu was about 540 km south-southeast of Hong Kong. Local winds were moderate easterlies that afternoon, occasionally strong on high ground that night. As Chanthu moved closer and intensified, winds freshened from the east on 21 July and became strong on high grounds. The Strong Wind Signal No. 3 was issued at 4:40 p.m. when Chanthu was centred about 400 km to the south-southwest. Chanthu was closest to Hong Kong at about 5 a.m. on 22 July passing about 330 km to the southwest. At the Hong Kong Observatory Headquarters, the lowest instantaneous mean sea-level pressure of 1005.2 hPa was recorded at 5:06 a.m. that day. Local winds were strong offshore and on high ground in the morning on 22 July and turned to southeasterlies during the day. As Chanthu moved gradually away from Hong Kong, the No. 3 Signal was replaced by the Standby Signal No. 1 at 11:40 a.m. All tropical cyclone warning signals were cancelled at 2:40 p.m. as local winds subsided further that afternoon. The maximum winds recorded at various stations and the periods of strong winds during the passage of Chanthu are given in Tables 3.2.1 and 3.2.2 respectively.

Affected by the subsidence zone ahead of Chanthu, the weather in Hong Kong was fine and very hot on 20 July. Under the influence of the outer rainbands of Chanthu, there were squally showers and thunderstorms in the following two days. Heavy rain affected Hong Kong in the afternoon on 22 July and the Amber, Red and the first Black Rainstorm Warning Signal this year were issued at 4:35 p.m., 5:20 p.m. and 5:30 p.m. respectively. The Special Announcement on Flooding in the northern New Territories and the Landslip Warning were also issued at 5:40 p.m. and 6:10 p.m. respectively.

In Hong Kong, a passer-by was injured by fallen objects blown off by winds in Sham Shui Po. A section of a 20-metre tall tree fell in Tsuen Wan on 21 July, fortunately no one was injured. The heavy rain during the afternoon on 22 July resulted in at least 42 reports of flooding and seven reports of landslips. During the period when the rainstorm warnings were in force, there were widespread flooding in Hong Kong Island, Kowloon and the New Territories and the flooding was most severe in the northern part of the New Territories. Four people were killed by the flood water in Sheung Shui, Tai Po and Sha Tin and tens of people were injured. At the Hong Kong International Airport, two flights were diverted due to adverse weather.

Information on the daily rainfall and maximum sea level in Hong Kong during the passage of Chanthu is given in Tables 3.2.3 and 3.2.4 respectively. Figures 3.2.1 - 3.2.6 show respectively the track of Chanthu, the rainfall distribution for Hong Kong, hourly rainfall recorded at the Hong Kong Observatory, time series of the wind speed recorded at Cheung Chau, a satellite imagery of Chanthu and a related radar imagery.

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