Merbok was the first tropical cyclone affecting Hong Kong in 2017 and the No. 8 Gale or Storm Signal was issued by the Hong Kong Observatory during its passage. The centre of Merbok moved across the eastern part of Hong Kong waters on the night of 12 June, the first time the centre of a tropical cyclone entered the territory of Hong Kong since Typhoon Nuri in August 2008.
Merbok formed as a tropical depression over the central part of the South China Sea about 580 km south of Dongsha in the small hours of 11 June. Moving north-northwestwards, it intensified into a tropical storm that afternoon. Merbok continued to move closer to the coastal areas of Guangdong on 12 June and intensified into a severe tropical storm that night, reaching its peak intensity with an estimated sustained wind of 90 km/h near its centre. It made landfall over the Dapeng Peninsula before midnight and weakened into a tropical storm. Taking on a north-northeasterly track, Merbok moved across Guangdong on the morning of 13 June and dissipated over Jiangxi in the afternoon.
According to press reports, Merbok brought heavy rain and squalls to Guangdong with extensive flooding. At least 120 000 people were affected with a direct economic loss reaching 260 million RMB. Electricity supply to more than 45 000 households was interrupted in Shanwei.
In Hong Kong, the No. 1 Standby Signal was issued at 7:40 p.m. on 11 June when Merbok was about 530 km south-southeast of the territory. Local winds were moderate easterlies during the night. As Merbok edged closer to the coast of Guangdong, the No. 3 Strong Wind Signal was issued at 10:40 a.m. on 12 June when Merbok was about 210 km south-southeast of Hong Kong. Local winds gradually became fresh to strong east to northeasterlies in the afternoon and occasionally reaching gale force offshore. The No. 8 Northeast Gale or Storm Signal was issued at 5:20 p.m. on 12 June when Merbok was about 90 km south-southeast of the Hong Kong Observatory. Local winds strengthened significantly, becoming generally strong to gales force from north to northeast, with winds reaching storm force occasionally offshore and on high ground.
With Merbok taking on a more northerly track on its approach, winds started to turn northwesterly and the No. 8 Northwest Gale or Storm Signal was issued at 8:20 p.m. Merbok traversed the eastern part of Hong Kong waters and came closest to the Observatory Headquarters around 9:30 p.m. that evening with its centre located about 25 km to the east. Merbok made landfall over the Dapeng Peninsula before midnight and local winds gradually turned southwesterly. The No. 8 Southwest Gale or Storm Signal was issued at 12:10 a.m. on 13 June. With Merbok moving inland and weakening, local winds soon subsided. The No. 8 Southwest Gale or Storm Signal was replaced by the No. 3 Strong Wind Signal at 4:40 a.m. on 13 June, and all tropical cyclone warning signals were cancelled at 11:10 a.m. later that morning.
Under the influence of Merbok, maximum hourly mean winds of 59, 87 and 85 km/h and gusts of 77, 113 and 131 km/h were recorded at Star Ferry (Kowloon), Waglan Island and Tate’s Cairn respectively. A maximum sea level (above chart datum) of 2.86 m was recorded at Tsim Bei Tsui, and a maximum storm surge (above astronomical tide) of 0.55 m was recorded at Tai Po Kau. The lowest instantaneous mean sea-level pressures recorded at some selected stations are as follows:
Locally, it was mainly fine and very hot during the day on 11 June. The rainbands associated with Merbok brought heavy squally showers and thunderstorms to Hong Kong on 12 and 13 June. The rain was most intense on the morning of 13 June. Red Rainstorm Warning, Landslip Warning, Special Announcement on Flooding in the Northern New Territories and Thunderstorm Warning were issued by the Observatory that morning. More than 150 millimetres of rainfall were generally recorded over the territory during these two days, with rainfall in the urban areas exceeding 250 millimetres.
In Hong Kong, at least 10 people were injured during the passage of Merbok. There were more than 600 reports of fallen trees, 20 reports of flooding and two reports of landslide. The glass curtain wall of a commercial building in Sheung Wan cracked, and an aluminum window fell down from a building in To Kwa Wan, damaging two private cars. Traffic was seriously disrupted as many roads were flooded during the rainstorm on the morning of 13 June. A retaining wall at Tai Tam Road in Stanley collapsed under the heavy rain. About 300 hectares of farmland in the New Territories were affected. More than 500 flights were cancelled or delayed at the Hong Kong International Airport.