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 gloomier and wetter than usual in August 2018. The mean amount of cloud in the month was 84 per cent, 15 per cent above the normal figure of 69 per cent and one of the highest on record for August. The duration of bright sunshine in the month was only 116.2 hours, about 38 per cent 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 per cent above the normal figure 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 per cent compared to the normal figure of 1905.5 millimetres for the same period.
Under the influence of an anticyclone over southern China, the weather in Hong Kong was marked by a mixture of sunshine and showers from August 1 to 9. With plenty of sunshine in the morning on August 7, the weather was very hot and the temperature at the Hong Kong Observatory soared to 34.2 degrees around noon, the highest of the month. The high temperature triggered heavy thundery showers over the western part of Hong Kong that afternoon, bringing more than 30 millimetres of rainfall to the western part of the New Territories and over 100 millimetres of rainfall to the southwestern part of Lantau Island.
A broad area of low pressure over the northern part of the South China Sea intensified into a tropical depression on August 9 and was later named as Bebinca. It moved slowly northwards and made landfall near Yangjiang around noon on August 11. 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 August 12, Bebinca intensified into a tropical storm and looped slowly in an anti-clockwise direction off the coast of western Guangdong on August 13 and 14. Bebinca picked up speed to move west-southwestwards and intensified into a severe tropical storm on August 15. 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 August 17. The outer rainbands associated with Bebinca brought occasional heavy squally showers and thunderstorms to Hong Kong from August 10 to 16 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 from August 17 to 19. The showers were heavier on August 19, 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 August 20 and 21.
A low pressure area over the northeastern part of the South China Sea moved slowly northeastwards on August 22. It then developed into a tropical depression on August 23 near Taiwan and edged northwards slowly along the western coast of Taiwan. The tropical depression turned west-northwest on August 24 and made landfall over Fujian on August 25. Locally, under light wind conditions, the weather was hot with sunny periods on August 22. Convective activities triggered by high temperatures also brought heavy showers and thunderstorms to Hong Kong that evening. Occasional showers and squally thunderstorms still affected the territory on August 23, and the temperature at the Hong Kong Observatory fell to 24.6 degrees during rainfall that night, the lowest of the month.
Apart from one or two showers, the weather in Hong Kong was generally fine on August 24 and 25. Under light wind conditions, 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 on August 26. Heavy rain around midnight on August 26 brought more than 100 millimetres of rainfall to parts of 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 August 29, necessitating the issuance of a Red Rainstorm Warning Signal, a Landslip Warning and a 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 exceeded 200 millimetres over Tuen Mun, Yuen Long, Tai Po and North District. There was serious flooding in many parts of the New Territories and landslides in Fanling, resulting in significant disruption to traffic. A waterspout was also reported near Ting Kau on the morning of August 29.
Eleven tropical cyclones occurred over the South China Sea and the western North Pacific in August 2018.
Details of issuance and cancellation of various warnings/signals in August are summarised in Table 1. Monthly meteorological figures and departures from normal for August are tabulated in Table 2.
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