Report on Tropical Storm Lupit (2109)

Lupit was the fifth tropical cyclone affecting Hong Kong in 2021.

Lupit formed as a tropical depression over the northern part of the South China Sea at about 280 km southwest of Hong Kong on the night of 2 August. It moved generally east-northeastwards across the northern part of the South China Sea and intensified gradually. Lupit slowed down on the morning of 3 August and turned to move southeastwards in the afternoon. It then turned to move northeastwards in the small hours on 4 August and intensified into a tropical storm in the morning. Lupit reached its peak intensity in the small hours on 5 August with an estimated maximum sustained wind of 85 km/h near its centre. It skirted past the coastal areas of Fujian in the afternoon and the next day, and weakened into a tropical depression. Lupit re-intensified into a tropical storm over the Taiwan Strait in the small hours on 7 August and tracked northeastwards towards Japan. It finally evolved into an extratropical cyclone over the seas north of Honshu of Japan on 9 August.

According to press reports, Lupit brought torrential rain and flooding to Taiwan and Kyushu of Japan.

The Standby Signal, No.1 was issued at 9:40 p.m. on 2 August when Lupit was about 260 km southwest of Hong Kong. Local winds were generally moderate to fresh east to southeasterlies that night. Lupit gradually edged closer to Hong Kong the next day and local winds strengthened in the afternoon. Lupit was closest to Hong Kong at around 2 p.m. on 3 August with its centre about 110 km south-southwest of the territory. As Lupit was very close to Hong Kong and local winds were expected to strengthen further at night, the Strong Wind Signal, No.3 was issued at 4:25 p.m. on 3 August when Lupit was about 120 km south-southwest of Hong Kong. Local winds were generally moderate to fresh east to northeasterlies that night and occasionally reached strong force offshore and on high ground. As Lupit moved to the southeast of Hong Kong and gradually departed from the territory, local winds turned to northerly and weakened. The Strong Wind Signal, No.3 was replaced by the Standby Signal, No.1 at 4:20 a.m. on 4 August. Local winds became moderate to fresh north to northwesterlies during the day. With Lupit further departing from Hong Kong in the afternoon, all tropical cyclone warning signals were cancelled at 6:20 p.m. on 4 August.

Under the influence of Lupit, a maximum sea level (above chart datum) of 2.33 m was recorded at Tsim Bei Tsui. A maximum storm surge of 0.30 m (above astronomical tide) was recorded at Tai Po Kau and Tai Miu Wan. At the Observatory Headquarters, the lowest instantaneous mean sea-level pressure of 993.0 hPa was recorded at 4:21 p.m. on 4 August.

There were sunny intervals and a few showers in Hong Kong on 2 August. The outer rainbands associated with Lupit brought occasional heavy showers and squally thunderstorms to Hong Kong on 3 - 5 August. More than 100 millimetres of rainfall were recorded over most parts of the territory on these three days, and rainfall even exceeded 140 millimetres over the central part of Hong Kong Island, the northern part of the New Territories and the northeastern part of Lantau Island. The Amber Rainstorm Warning and the Special Announcement on Flooding in Northern New Territories were issued on the evening of 4 August.

A number of flooding were reported in Hong Kong during the passage of Lupit. There were flooding over many places of the northern part of the New Territories on 4 August when the Amber Rainstorm Warning was in force. A person was trapped inside a vehicle and was taken to safety by rescuers.