TROPICAL CYCLONES IN 2010

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

Lionrock formed as a tropical depression over the northern part of the South China Sea about 600 km south-southeast of Hong Kong on 28 August and moved northwestwards. It intensified into a tropical storm the next day and then took a north to northeasterly track. Lionrock slowed down and drifted east to east-southeastwards on 30 August. It intensified into a severe tropical storm that evening, reaching its peak intensity with estimated maximum sustained winds of 90 km/h near its centre. On 31 August, Lionrock speeded up and gradually changed its course to the north-northeast. It adopted a northwesterly course the following day and traversed the northeastern part of the South China Sea. After making landfall over the coast of southern Fujian on 2 September morning, Lionrock weakened into a tropical storm. It then moved generally westwards and subsequently dissipated over Guangdong on 3 September afternoon. According to press reports, Lionrock brought rainstorms to Guangdong where at least 165 houses collapsed and more than 10 000 hectares of farmland inundated.

In Hong Kong, the Standby Signal No. 1 was issued at 10:35 a.m. on 29 August when Lionrock was about 340 km southeast of Hong Kong. Local winds were moderate northerlies that day and became occasionally strong on high ground the next day. All signals were cancelled at 7:10 p.m. on 30 August as Lionrock moved away and did not pose a threat to Hong Kong. Light to moderate northerlies generally prevailed for the next two days. The winds turned to moderate westerlies on 2 September. The Standby Signal No. 1 was issued again at 8:40 p.m. on 2 September when Lionrock moved across southern China, edging closer to Hong Kong once more. Local winds turned to the south on 3 September and were occasionally fresh offshore. All tropical cyclone warning signals were cancelled at 4:40 p.m. on 3 September as Lionrock dissipated over Guangdong. Lionrock was closest to Hong Kong at about 2:00 p.m. on 3 September passing about 150 km to the north-northwest. At the Hong Kong Observatory Headquarters, the lowest instantaneous mean sea-level pressure of 1001.6 hPa was recorded at 4:57 p.m. on 30 August when Lionrock was located about 340 km to the east-southeast. The maximum winds recorded at various stations during the passage of Lionrock are given in Table 3.3.1.

Under the influence of the outer rainbands of Lionrock, there were isolated squally thunderstorms on 29 August and 30 August. Under the subsidence ahead of Lionrock, it was very hot with sunny periods in the following two days. The weather turned cloudy with a few showers on 2 September. Rain became heavy at times with a few squally thunderstorms the following day.

No significant damage was reported in Hong Kong during the passage of Lionrock.

Information on the daily rainfall and maximum sea level in Hong Kong during the passage of Lionrock is given in Tables 3.3.2 and 3.3.3 respectively. Figures 3.3.1 - 3.3.4 show respectively the track of Lionrock, the rainfall distribution for Hong Kong, a satellite imagery of Lionrock and a related radar imagery.

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