Tropical Cyclones in 2017 > Report on Tropical Storm Roke (1707)

3.2 Tropical Storm Roke (1707): 21 – 23 July 2017

Roke was the second tropical cyclone affecting Hong Kong in 2017 and necessitating issuance of the No. 8 Gale or Storm Signal by the Hong Kong Observatory.

Roke originated from a tropical depression that developed over the sea areas east of northern Luzon on the afternoon of 21 July. It moved across the Luzon Strait on 22 July and after entering the northeastern part of the South China Sea, took on a west-northwestward course and headed steadily towards the Pearl River Delta. It intensified into a tropical storm that evening, reaching its peak intensity with an estimated sustained wind of 65 km/h near its centre. Roke swept past the northeastern part of Hong Kong on the morning of 23 July and weakened into a tropical depression during the day. It finally degenerated into an area of low pressure over inland Guangdong in the evening.

According to press reports, Roke brought squally showers to Guangdong during its passage. A vessel sunk over the seas about 70 km east of Hong Kong and all 12 crew members on board were rescued.

In Hong Kong, the No. 1 Standby Signal was issued at 3:40 p.m. on 22 July when Roke was about 460 km east-southeast of the territory. As Roke moved rapidly towards the Pearl River Delta, the No. 3 Strong Wind Signal was issued at 3:40 a.m. on 23 July when Roke was about 150 km east-southeast of Hong Kong. Local wind strengthened gradually, becoming moderate to fresh northerlies and occasionally reaching strong force on high ground. As Roke approached Hong Kong, gale winds were recorded near its centre from oil rig and on the right side along its path from weather buoy, ship, as well as weather stations at the Dapeng Peninsula. With Roke coming very close to Hong Kong in the morning and posing a threat to the territory, the Observatory issued the No. 8 Northwest Gale or Storm Signal at 9:20 a.m. on 23 July when it was about 35 km east-northeast of the Hong Kong Observatory.

Roke turned slightly more to the northwest as it made landfall near Sai Kung around 9:40 a.m. and as a result, Hong Kong for the most part was not exposed to the gale on the right side of its circulation. Only Tap Mun and some places on high ground reported gust reaching gale force during its passage. Roke came closest to the Hong Kong Observatory Headquarters around 10 a.m. that morning with its centre located about 25 km to the northeast. With Roke moving away and weakening, the No. 3 Strong Wind Signal was issued at 1:20 p.m. on 23 July, followed by the No. 1 Standby Signal at 3:10 p.m. All tropical cyclone warning signals were cancelled at 7:40 p.m. that evening. Sustained wind speed of all eight reference anemometers did not reach strong force when the tropical cyclone warning signals for Roke were in force.

Under the influence of Roke, a maximum sea level (above chart datum) of 3.18 m and a maximum storm surge (above astronomical tide) of 0.28 m were recorded at Tsim Bei Tsui. The lowest instantaneous mean sea-level pressures recorded at some selected stations are as follows:

Locally, it was very hot with sunny periods during the day on 22 July. The rainbands associated with Roke brought occasional heavy squally showers and thunderstorms to Hong Kong on 23 July that lasted till the small hours of 24 July. Amber Rainstorm Warning was issued on the night of 23 July. The weather improved during the day on 24 July with sunny periods. More than 40 millimetres of rainfall were recorded over most parts of Hong Kong during these three days.

Roke did not cause any significant damage in Hong Kong. More than 550 flights were cancelled or delayed at the Hong Kong International Airport.