TROPICAL CYCLONES IN 2013

Jebi was the fourth tropical cyclone necessitating the issuance of tropical cyclone warning signals by the Hong Kong Observatory in 2013.

Jebi formed as a tropical depression over the central part of the South China Sea about 450 km east-southeast of Xisha on 31 July. Moving west-northwestwards, Jebi intensified into a tropical storm that afternoon. It took on a northwesterly track at a speed of about 11 km/h the next day across the seas near Xisha. Jebi intensified into a severe tropical storm in the morning on 2 August about 70 km to the north-northeast of Xisha, reaching its peak intensity with estimated sustained winds of 105 km/h near its centre that afternoon. It also speeded up to about 28 km/h, making landfall near Wenchang over the northeastern tip of Hainan Island that evening and turning west-northwestwards across the island that night. At 11 p.m., the mean sea-level pressure at Haikou fell to 987.4 hPa. Jebi moved across Beibu Wan in the early hours on 3 August and made landfall over the coast of northern Vietnam that morning. It weakened into a tropical storm in the afternoon and subsequently dissipated over the northern part of Vietnam during the night. According to press reports, Jebi severely disrupted the traffic in Hainan Island. In Vietnam, seven people were killed, and many telecommunication towers and power lines were blown down during the passage of Jebi.

The Standby Signal No. 1 was issued by the Hong Kong Observatory at 9:40 a.m. on 1 August when Jebi was about 740 km south of the territory. Under the combined effect of Jebi and the ridge of high pressure over the coast of southeastern China, local winds were moderate to fresh easterlies, occasionally strong on high ground and strengthening during the day. The Strong Wind Signal No. 3 was issued at 4:10 p.m. when Jebi was about 660 km south of Hong Kong. Jebi continued to move closer to the south China coast on 2 August. At the Hong Kong Observatory Headquarters, the lowest instantaneous mean sea-level pressure of 1002.0 hPa was recorded at 3:08 a.m., when Jebi was about 600 km to the south-southwest. Local winds were fresh to strong east to southeasterlies that day, occasionally reaching gale force on high ground. Jebi was closest to Hong Kong around 7 p.m. as it passed by about 430 km to the southwest. All tropical cyclone warning signals were cancelled at 10:15 p.m. as Jebi moved across Hainan Island away from Hong Kong and local winds subsided.

During the passage of Jebi, the maximum hourly mean wind recorded near sea level was 51 km/h at Waglan Island, while maximum gusts of 87 km/h were recorded at Cheung Chau. A maximum sea level of 2.41 m (above chart datum) was recorded at Tsim Bei Tsui, while a maximum storm surge of 0.40 m (above astronomical tide) was recorded at Tai Po Kau.

There were sunny intervals in Hong Kong during the morning of 1 August. Under the influence of the outer rainbands associated with Jebi, the weather became cloudy with scattered squally showers and thunderstorms that afternoon. The weather remained cloudy with scattered heavy showers and thunderstorms the next day. More than 100 millimetres of rainfall were recorded over the western part of Hong Kong Island and parts of the New Territories during these two days.

During the passage of Jebi, three aircraft were diverted at the Hong Kong International Airport. There were reports of glass panels suspected to be blown off by the winds in Tsim Sha Tsui and To Kwa Wan. The roof of a motor vehicle was damaged in the former incident.

Information on the maximum wind, period of strong and gale force winds, daily rainfall and maximum sea level reached in Hong Kong during the passage of Jebi is given in Tables 3.4.1 - 3.4.4 respectively. Figures 3.4.1 - 3.4.4 show respectively the track of Jebi, the rainfall distribution for Hong Kong, a satellite imagery of Jebi and radar imagery of Jebi near its closest approach to Hong Kong.