The Weather of August 2018

    Affected by the outer rainbands of tropical cyclone Bebinca in mid-August and the heavy showers associated with an active trough of low pressure towards the end of the month, the weather in Hong Kong was wetter and much gloomier than usual in August 2018. The mean amount of cloud in the month was 84 percent, 15 percent above the normal of 69 percent and one of the highest on record for August. The duration of bright sunshine in the month was only 116.2 hours, about 38 percent lower than the normal figure of 188.9 hours and the lowest on record for August. The monthly rainfall was 615.1 millimetres, about 42 percent above the normal of 432.2 millimetres in August. The accumulated rainfall recorded in the first eight months of the year was 1590.0 millimetres, a deficit of 17 percent compared to the normal of 1905.5 millimetres for the same period.

    Under the influence of an anticyclone aloft southern China, the weather in Hong Kong was marked by a mixture of sunshine and showers on 1 - 9 August. With plenty of sunshine in the morning, it was very hot with the temperature at the Hong Kong Observatory soaring to 34.2 degrees around noon on 7 August, the highest in the month. The high temperatures then triggered heavy thundery showers over the western part of Hong Kong in that afternoon, bringing more than 30 millimetres of rainfall to the western part of the New Territories and over 100 millimetres to the southwestern part of Lantau Island.

    Meanwhile, a broad area of low pressure over the northern part of the South China Sea intensified into a tropical depression on 9 August and was later named as Bebinca. It moved slowly northward and made landfall near Yangjiang around noon on 11 August. Bebinca then made an anti-clockwise loop over the coastal region of western Guangdong and moved back to the coastal waters that night. After drifting southeastwards on 12 August, Bebinca intensified into a tropical storm and looped slowly in anti-clockwise direction off the coast of western Guangdong on 13 and 14 August. Bebinca picked up speed to move west-southwestwards and intensified into a severe tropical storm on 15 August. It moved across Beibu Wan the next day. Bebinca made landfall over the northern part of Vietnam and weakened into an area of low pressure inland on 17 August. The outer rainbands associated with Bebinca brought occasional heavy squally showers and thunderstorms to Hong Kong on 10 - 16 August with more than 150 millimetres of rainfall generally recorded over the territory during this period.

    Affected by a south to southwesterly airstream, the weather in Hong Kong was mainly cloudy with occasional showers and thunderstorms on 17 - 19 August. The showers were heavier on 19 August with more than 70 millimetres of rainfall recorded over Tsuen Wan, Kwai Tsing and Lantau Island. A broad trough of low pressure over the south China coast continued to bring showery weather to Hong Kong on 20 - 21 August.

    A low pressure area over the northeastern part of the South China Sea moved slowly northeastwards on 22 August. It then developed into a tropical depression on 23 August near Taiwan and edged northwards slowly along the western coast of Taiwan. The tropical depression turned west-northwest on 24 August and made landfall over Fujian on 25 August. Locally, under light wind condition, it was hot with sunny periods on 22 August. Convective activities triggered by high temperatures also brought heavy showers and thunderstorms to Hong Kong on that evening. Occasional showers and squally thunderstorms still affected the territory on 23 August, the temperature at the Hong Kong Observatory fell to the lowest in the month of 24.6 degrees in rain that night.

    Apart from one or two showers, the weather of Hong Kong was generally fine on 24 - 25 August. Under light winds condition, there were some haze during the day. Affected by a broad area of low pressure along the coast of Guangdong, local weather started to deteriorate with heavy showers in the evening of 26 August. The heavy rain around midnight of 26 August brought more than 100 millimetres of rainfall to parts of the Lantau Island and Hong Kong Island. An active trough of low pressure continued to bring occasional heavy showers and squally thunderstorms to Hong Kong for the rest of the month. Rain was particularly heavy in the New Territories on 29 August, necessitating the issuance of the Red Rainstorm Warning, Landslip Warning and Special Announcement on Flooding in the Northern New Territories. More than 100 millimetres of rainfall were recorded over most parts of the New Territories, and rainfall even exceeded 200 millimetres over Tuen Mun, Yuen Long, Tai Po and North District. There were serious flooding over many places in the New Territories and landslides in Fanling, resulting in significant disruption of traffic. A waterspout was also reported near Ting Kau on the morning of 29 August.