Report on Severe Tropical Storm Mitag (2517)

Severe Tropical Storm Mitag (2517)
16 to 20 September 2025

Mitag was the tenth tropical cyclone affecting Hong Kong in 2025.

Mitag formed as a tropical depression over the seas east of Luzon about 300 km east-northeast of Manila on the afternoon of 16 September. It moved generally northwestwards across Luzon and the northeastern part of the South China Sea in the following two days, approaching the coast of eastern Guangdong. Mitag intensified into a severe tropical storm on the morning of 19 September, attaining its peak intensity with an estimated maximum sustained wind of 90 km/h near its centre. It made landfall near Shanwei of Guangdong that afternoon, then turned west-northwestwards and moved inland, where it weakened rapidly. Mitag finally degenerated into an area of low pressure over Guangdong on the morning of 20 September.

According to press reports, Mitag brought heavy rain and caused flooding in the Philippines. Mitag and its remnant brought torrential rain and squalls to Taiwan, Fujian, Guangdong and Guangxi, with more than 130 000 people affected and over 100 000 people evacuated.

The Standby Signal No. 1 was issued at 9:20 p.m. on 17 September when Mitag was about 760 km east-southeast of Hong Kong. Local winds were moderate to fresh east to northeasterlies, occasionally strong offshore and on high ground at night. With Mitag edging closer to the coast of eastern Guangdong, the strong winds associated with Mitag were expected to affect Hong Kong gradually, the No. 3 Strong Wind Signal was issued at 9:20 a.m. on 19 September when Mitag was about 160 km east of Hong Kong. Strong north to northwesterlies were affecting many places in Hong Kong that day. Local winds became westerlies the next morning. Mitag came closest to Hong Kong at around 2 a.m. on 20 September, skirting past about 110 km north-northeast of the territory. With Mitag departing from Hong Kong and weakening, the No. 1 Standby Signal was issued at 9:20 a.m. and all tropical cyclone warning signals were cancelled at 10:40 a.m. on 20 September.

Mitag did not cause any significant damage in Hong Kong during its passage. Under the influence of Mitag, a maximum sea level of 2.79 m (above chart datum) was recorded at Tsim Bei Tsui and a maximum storm surge of 0.34 m (above astronomical tide) was recorded at Tai Po Kau. At the Observatory Headquarters, the lowest instantaneous mean sea-level pressure of 1003.7 hPa was recorded at 2:53 p.m. on 19 September.

Under the influence of an anticyclone aloft, apart from a few showers and isolated thunderstorms, the weather in Hong Kong was very hot with sunny periods on 18 September. With the approach of Mitag, the local weather turned mainly cloudy with a few squally showers on 19 September. Under the influence of the rainbands associated with Mitag and its remnant, there were heavy showers and squally thunderstorms in Hong Kong on 20 September. More than 100 millimetres of rainfall were recorded over Lantau Island, Hong Kong Island and the eastern part of the New Territories.