Report on Severe Tropical Storm Prapiroon (2404)

Severe Tropical Storm Prapiroon (2404)
19 – 23 July 2024

Prapiroon was the second tropical cyclone affecting Hong Kong in 2024.

Prapiroon formed as a tropical depression over the central part of the South China Sea about 630 km east-southeast of Xisha on the afternoon of 19 July and moved west-northwestwards across the central part of the South China Sea. It intensified into a tropical storm on the morning of 21 July and turned to move north-northwestwards towards Hainan Island. Before making landfall over Hainan Island, Prapiroon further intensified into a severe tropical storm that night. Prapiroon made landfall over Wanning, Hainan in the small hours of 22 July and weakened slightly into a tropical storm as it moved across Hainan Island. Prapiroon re-intensified into a severe tropical storm as it moved across Beibu Wan. It attained its peak intensity with an estimated maximum sustained wind of 105 km/h near its centre on the evening of 22 July. Prapiroon made landfall over the northern part of Vietnam on the morning of 23 July. It then moved inland and weakened gradually. Prapiroon finally degenerated into an area of low pressure that night.

According to press reports, Prapiroon brought torrential rain and squalls to Hainan Island, resulting in fallen trees in many parts of the region and an interruption in electricity supply to over 220 000 households.

The Standby Signal No. 1 was issued at 10:40 p.m. on 20 July, when Prapiroon was about 710 km south-southwest of Hong Kong. Local winds were moderate to fresh east to southeasterlies and occasionally strong offshore and on high ground the next day. Prapiroon came closest to Hong Kong at around 2 a.m. on 22 July, skirting past about 570 km southwest of the territory. With Prapiroon departing from Hong Kong, all tropical cyclone warning signals were cancelled at 12:20 p.m. on 22 July.

Prapiroon did not cause any significant damage in Hong Kong during its passage. Under the influence of Prapiroon, a maximum sea level (above chart datum) of 3.17 m and a maximum storm surge (above astronomical tide) of 0.30 m were recorded at Tsim Bei Tsui. At the Observatory Headquarters, the lowest instantaneous mean sea-level pressure of 1005.2 hPa was recorded at 4:00 a.m. on 22 July.

The outer rainbands of Prapiroon brought a few squally showers and thunderstorms to Hong Kong on 21 July. With Prapiroon departing from Hong Kong, it was very hot with sunny periods during the day on 22 July.