Severe Typhoon Vicente

        Vicente was the third tropical cyclone that necessitated the issuance of a tropical cyclone warning signal by the Hong Kong Observatory in 2012. It also necessitated the issuance of the first No. 10 Hurricane Signal in Hong Kong since Typhoon York in September 1999. Hurricane force winds were recorded over the southwestern part of Hong Kong during the passage of Vicente. Vicente underwent rapid intensification within around 30 hours prior to its closest approach to Hong Kong, strengthening by three categories from a tropical storm to a severe typhoon. Such rapid intensification near the territory was rather rare among the tropical cyclones that had necessitated the issuance of the No. 10 Signal since 1946.

        Vicente formed as a tropical depression over the western North Pacific about 450 km northeast of Manila on 20 July. Moving west-northwestwards, it made its way over Luzon Strait that night and entered the northern part of the South China Sea on the morning of 21 July. Moving westwards, it intensified into a tropical storm that night. On 22 July, it was almost stationary over the South China Sea about 350 km south-southeast of Hong Kong. Vicente intensified into a severe tropical storm on the small hours of 23 July and gradually turned to move northwestwards in the morning. It underwent intensification into a typhoon in the afternoon, with its eye clearly discernible on the Observatory's radar. After dusk, very intense convection was observed on the eyewall of Vicente and was captured on both radar imagery and lightning location map. The corresponding cloud top overshot 15 km up to the top of the troposphere² accompanied by cloud-to-ground lightning. Such observations signified that the associated updraft turned violent. Shortly afterwards, Vicente intensified rapidly to a severe typhoon over the South China Sea to the south-southwest of Hong Kong towards mid-night, reaching its peak intensity with an estimated maximum sustained wind of 155 km/h near its centre. Vicente speeded up towards the region west of the Pearl River Estuary thereafter and made landfall near the coastal areas of Taishan, about 130 km west-southwest of Hong Kong before dawn on 24 July and subsequently weakened into a typhoon. It took up a west-northwesterly track over western Guangdong that morning and weakened into a severe tropical storm. Vicente continued to weaken into a tropical storm in the afternoon and turned to move westwards across Guangxi. It became a tropical depression that night and dissipated over the northern part of Vietnam on 25 July.

        According to press reports, Vicente brought rainstorms to Guangdong where at least five people were killed and six others missing. Over 44000 hectares of farmland were inundated, some 1 085 houses collapsed and the economic loss amounted to 845 million RMB.

        In Hong Kong, the Standby Signal No. 1 was issued at 3:40 p.m. on 21 July when Vicente was about 540 km southeast of Hong Kong. Local winds were moderate westerlies that afternoon, becoming northeasterly in the evening. Moderate to fresh northeasterlies prevailed over Hong Kong on 22 July, with occasional strong winds over offshore waters and on high ground. As Vicente started to move towards the south China coast, the Strong Wind Signal No. 3 was issued at 5:20 a.m. on 23 July, when Vicente was about 320 km south-southeast of Hong Kong. Local winds strengthened gradually during the day, becoming generally strong northeasterlies in the afternoon, reaching gale force offshore and on high ground. The No. 8 NE Gale or Storm Signal was issued at 5:40 p.m. when Vicente was about 170 km south of Hong Kong. Local winds strengthened further that night, with gales in many parts of Hong Kong, reaching storm force over the waters in the southern part of Hong Kong. The Increasing Gale or Storm Signal No. 9 was issued at 11:20 p.m. when Vicente was about 110 km south-southwest of Hong Kong.

        Vicente continued to move closer to Hong Kong and its eyewall came close to the southwestern part of Hong Kong during the small hours on 24 July. Local winds turned to the east to southeasterlies, with gale or storm force winds over Victoria Harbour, Chek Lap Kok, parts of the northeastern New Territories and the waters over the southern part of Hong Kong, reaching hurricane force over the waters in the southwestern part of Hong Kong and on high ground. The Hurricane Signal No. 10 was issued at 12:45 a.m. to replace the No. 9 Signal. The centre of Vicente was closest to Hong Kong between 1 a.m. and 2 a.m., passing about 100 km to the southwest of the Hong Kong Observatory. As Vicente started to move away and local winds gradually subsided, the No. 8 SE Gale or Storm Signal was issued at 3:35 a.m. to replace the No. 10 Signal. The No. 8 Signal was then replaced by the Strong Wind Signal No. 3 at 10:10 a.m., followed by the Standby Signal No. 1 at 2:40 p.m. Vicente moved further away and its outer circulation no longer covered Hong Kong that night and all tropical cyclone warning signals were cancelled at 11:15 p.m. Nevertheless, a ridge of high pressure along the southeastern coast of China came into play and continued to maintain strong winds over the offshore waters of Hong Kong. The Strong Monsoon Signal was issued immediately afterwards, which was cancelled at 5:20 a.m. on 25 July.

        During the passage of Vicente, a maximum hourly mean wind of 126, 135 and 153 km/h and gusts of 184, 196 and 256 km/h were recorded at Cheung Chau, Tai Mo Shan and Ngong Ping respectively. The lowest instantaneous mean sea-level pressures recorded at some selected stations are as follows:-

        During the passage of Vicente, a maximum sea level of 3.23m above chart datum was recorded at Tsim Bei Tsui. The maximum storm surge was 1.51 m also at Tsim Bei Tsui.

        The weather in Hong Kong was very hot and hazy on 21 July, but there were squally thunderstorms in the evening, bringing over 20 millimetres of rainfall to the eastern part of the territory. It was mainly cloudy with a few squally showers and thunderstorms on 22 July. The rainbands of Vicente brought heavy squally showers to Hong Kong on 23 July and on the morning of 24 July, during which more than 200 millimetres of rainfall were recorded over many parts of the territory. The showers gradually abated on the afternoon of 24 July.

        In Hong Kong, at least 138 people were injured during the passage of Vicente. The number of fallen trees amounted to about 8 800. There were two reports of landslip and 7 reports of flooding. Dangerous signboards or fallen scaffoldings were reported in many parts of the territory, resulting in closure of some roads and damage to many vehicles. A wooden board was blown up by strong winds in Connaught Road, Central, hitting a number of passers-by. During the storm, the East Rail line of the Mass Transit Railway had to halt service because of damage of overhead cables by toppling trees. As a result, hundreds of commuters were forced to spend the night in trains or at the MTR stations. Crops were damaged by flood waters in some farmlands in Sheung Shui. A small craft ran aground in Deep Water Bay and was damaged. Seven containers fell overboard from a freighter in waters nearby and about 150 tons of plastic pallets drifted over the sea or were washed ashore. At the Hong Kong International Airport, at least 90 flights were cancelled, over 446 flights delayed and 50 flights diverted on 23-24 July.

        Details on typhoons that had necessitated the issuance of the Hurricane Signal No. 10 are available in the Observatory's website: Typhoons necessitating the issuing of the Hurricane Signal No.10.

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² Based on the temperature distribution in the vertical, the atmosphere can be divided into four layers, that is, the troposphere, stratosphere, mesosphere and thermosphere. Troposphere is the lowest layer of the atmosphere.