TROPICAL CYCLONES IN 2011
Nalgae was the fifth tropical cyclone that necessitated the issuance of a tropical cyclone warning signal by the Hong Kong Observatory in 2011. Nalgae formed as tropical depression over the western North Pacific about 1 850 km east-northeast of Manila on 27 September and moved generally westwards. It intensified into a tropical storm on the following day and moved west to west-southwestwards. Nalgae intensified further into a severe tropical storm on 29 September and became a typhoon over the western North Pacific to the east-northeast of Manila during the early hours on 30 September. It further strengthened into a severe typhoon that evening, attaining its peak intensity with an estimated maximum sustained wind of 175 km/h near its centre over the seas about 300 km northeast of Manila on the morning of 1 October. Nalgae then crossed Luzon and entered the South China Sea in the late afternoon. It moved west to west-northwestwards across the northern part of the South China Sea at about 14 km/h for the following two days. Nalgae weakened into a typhoon in the early hours on 2 October and a severe tropical storm that afternoon. It weakened further into a tropical storm on 4 October and crossed the southern part of Hainan Island that afternoon, entering Beibu Wan and weakening further into a tropical depression at night. Nalgae moved southwestwards across the southern part of Beibu Wan on 5 October and dissipated over the seas near Hainan that day. According to press reports, at least three people were killed in the Philippines during the passage of Nalgae. In Hainan Island, at least five houses collapsed and direct economic loss exceeded 260 million RMB. In Hong Kong, the Standby Signal No. 1 was issued at 10:40 a.m. on 2 October when Nalgae was about 740 km south-southeast of Hong Kong. Local winds were moderate to fresh northeasterlies that day, strong on high ground during the afternoon and evening. At the Hong Kong Observatory Headquarters, the lowest instantaneous mean sea-level pressure of 1007.6 hPa was recorded at 4:41 p.m. that day when Nalgae was about 660 km south-southeast of Hong Kong. Under the combined effect of the northeast monsoon and Nalgae, local winds strengthened on the morning of 3 October and were strong at times offshore, occasionally reaching gale force on high ground. The Strong Wind Signal No. 3 was issued at 6:40 a.m. when Nalgae was about 530 km south of Hong Kong. Nalgae was closest to Hong Kong between about 10 a.m. to 5 p.m. that day passing about 510 km to the south. As Nalgae weakened slightly and moved gradually away, Hong Kong came increasingly under the influence of the northeast monsoon. The Observatory cancelled all tropical cyclone warning signals at 7:10 p.m. and issued the Strong Monsoon Signal at the same time. Gusts of over 80 km/h were recorded at Ngong Ping, Tai Mo Shan and Tates Cairn during the period when the tropical cyclone warning signals were in force. Under the influence of the outer rainbands of Nalgae, the weather in Hong Kong was cloudy with some rain on 2 and 3 October. Several millimetres of rainfall were generally recorded over the territory. In Hong Kong, a fishing boat collided with a tugboat off Ap Chau in Mirs Bay and a fisherman was injured during the passage of Nalgae. Under the combined influence of the northeast monsoon and Nalgae, there were reports of sea water backflow in low-lying areas such as Tai O, Sha Tin and Tai Po during the early hours of 2 October and 3 October, resulting in minor flooding in the areas. A person was reported to have been trapped in a beach at Cheung Sha, Lantau Island during high tide. No one was injured during the incident. Information on maximum wind, period of strong winds, daily rainfall and maximum sea level in Hong Kong during the passage of Nalgae is given in Tables 3.5.1- 3.5.4 respectively. Figures 3.5.1 - 3.5.4 show respectively the track of Nalgae, the rainfall distribution for Hong Kong, a satellite and a related radar imagery of Nalgae. -Index - |