TROPICAL CYCLONES IN 2011

        Nock-ten was the third tropical cyclone that necessitated the issuance of a tropical cyclone warning signal by the Hong Kong Observatory in 2011. 

        Nock-ten formed as a tropical depression over the western North Pacific about 790 km east-southeast of Manila on 25 July and moved generally west-northwestwards.  Nock-ten intensified into a tropical storm and turned to move northwestwards on 26 July. It intensified further into a severe tropical storm on the morning of 27 July, crossed Luzon in the afternoon and entered the South China Sea that evening. Nock-ten moved generally west to west-northwestwards at about 22 km/h across the northern part of the South China Sea for the following two days, reaching its peak intensity with an estimated maximum sustained wind of 105 km/h near its centre. It made landfall near Wenchang, Hainan Island about 450 km southwest of Hong Kong on 29 July. Moving westwards across Beibu Wan on 30 July, Nock-ten weakened into a tropical storm. It made landfall again over the coast of northern Vietnam that evening and subsequently dissipated inland over Laos on 31 July. According to press reports, 50 people were killed in the Philippines with a direct economic loss amounted to 1 460 million peso (around HK$270 million) during the passage of Nock-ten. It also brought about two deaths in Hainan Island. The direct economic loss there was reported to be 377 million RMB.

        In Hong Kong, the Standby Signal No. 1 was issued at 8:40 a.m. on 28 July when Nock-ten was about 530 km southeast of Hong Kong. As Nock-ten moved gradually closer to Hong Kong, the Strong Wind Signal No. 3 was issued at 6:45 p.m. when Nock-ten was about 460 km south of Hong Kong. Winds in Hong Kong were generally moderate east to northeasterlies that day, becoming strong over offshore waters, occasionally reaching gale force on high ground that evening. At the Hong Kong Observatory Headquarters, the lowest instantaneous mean sea-level pressure of 1000.8 hPa was recorded at 6:26 a.m. on 29 July when Nock-ten was about 460 km south-southwest of Hong Kong. Generally strong easterlies affected the territory that morning, with occasional gales observed on high ground.  Gusts of over 90 km/h were recorded at Green Island, Ngong Ping, Tai Mo Shan, Tates Cairn and Waglan Island in the morning. Nock-ten was closest to Hong Kong at around 2 p.m. that day passing about 440 km to the southwest. Local winds moderated gradually and became east to southeasterlies that afternoon. The Standby Signal No. 1 was issued at 2:10 p.m. to replace the Strong Wind Signal No. 3. All signals were cancelled at 4:40 p.m. on the same day as local winds subsided further.

        On 28 July, the weather in Hong Kong was fine and very hot apart from a few squally showers and thunderstorms in the afternoon. The maximum temperature recorded at the Hong Kong Observatory Headquarters was 33.7 degrees. It became cloudy on 29 July. The outer rainbands of Nock-ten also brought squally showers and thunderstorms to the territory that day.

        During the passage of Nock-ten, there were at least 11 reports of fallen trees and two reports of collapsed scaffoldings in Hong Kong. Three people were injured due to fallen objects in Sham Shui Po and Ap Lei Chau. Broken tree branches resulted in a traffic accident in Shek Kip Mei, injuring another person. At the Hong Kong International Airport, four aircraft were diverted due to adverse weather on 29 July.

        Information on maximum wind, period of strong winds, daily rainfall and maximum sea level in Hong Kong during the passage of Nock-ten is given in Tables 3.3.1-3.3.4 respectively. Figures 3.3.1 - 3.3.4 show respectively the track of Nock-ten, the rainfall distribution for Hong Kong, a satellite imagery of Nock-ten and a related radar imagery.

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