Mainly attributing to the heavy rain associated with an active southwest monsoon and upper-air disturbances in early August, and a number of tropical cyclones in mid-August, the month was much wetter than usual. The monthly rainfall recorded at the Hong Kong Observatory was 939.2 millimetres, more than double the August normal of 453.2 millimetres, and the third highest on record for August. Although the first half of the year was much drier than usual, with outbreaks of heavy rain in July and August, the accumulated rainfall in the first eight months of the year was 1985.3 millimetres, catching up the normal value of 1921.5 millimetres for the same period. The month was also much cloudier than usual. The mean amount of cloud in the month was 81 percent, 11 percent above the normal of 70 percent, one of the fourth highest on record for August. While the monthly mean temperature of 29.0 degrees was only 0.3 degrees above the normal, together with the higher than normal temperatures in June and July, the summer of this year from June to August was hotter than normal. The mean minimum temperature of 27.2 degrees, the mean maximum temperature of 31.9 degrees and the mean temperature of 29.1 degrees were respectively one of the sixth, one of the seventh and one of the ninth highest on record for the same period.

Under the influence of a southwesterly airstream, the weather of Hong Kong was very hot with sunny periods on the first day of the month. There were also heavy showers and thunderstorms in some areas in the afternoon with more than 70 millimetres of rainfall recorded over the North District. An active southwest monsoon and upper-air disturbances brought heavy showers and squally thunderstorms to the coast of Guangdong on 2 – 5 August. The outbreaks of heavy showers necessitated the issuance of the Black Rainstorm Warnings for three times in just four days. The Hong Kong Observatory Headquarters registered a record-breaking daily rainfall of 368.9 millimetres on 5 August, the highest daily rainfall in August since records began in 1884. This daily rainfall amount was already more than 80 percent of the August normal rainfall. The accumulated rainfall recorded at the Observatory during these four days was near 600 millimetres and rainfall even exceeded 800 millimetres over Tseung Kwan O and Tsz Wan Shan. In the midst of incessant downpour, the temperature at the Observatory dropped to the month’s lowest of 24.0 degrees on the morning of 5 August. 

While showery conditions persisted on 6 August, with the establishment of an anticyclone aloft, apart from a few showers, it was generally fine with prolonged heat on 7 – 12 August. The maximum temperature at the Observatory rose to 34.4 degrees on the afternoon of 10 August, the highest of the month. Meanwhile, Typhoon Podul over the western North Pacific moved west-northwestwards towards Taiwan on 12 August. It further intensified into a severe typhoon before making landfall over the southeastern part of Taiwan the next day. Under the influence of its outer subsiding air, the weather in Hong Kong was mainly fine apart from isolated showers on 13 August. It was also extremely hot in the afternoon. Podul rapidly weakened into a tropical depression as it moved into inland Guangdong on 14 August. Under the influence of its outer band of intense thundery showers, it was overcast with heavy showers and severe squally thunderstorms in Hong Kong. More than 100 millimetres of rainfall were recorded over many places, and rainfall even exceeded 200 millimetres over Lantau Island, Tuen Mun and parts of Hong Kong Island. The incessant downpour necessitated the issuance of the Black Rainstorm Warning for the fifth time this year, breaking the previous record of three times set in 2000 and 2006 since the commencement of rainstorm system operation in 1992. While there were still a few showers on 15 August, with the dissipation of Podul and the establishment of the ridge of high pressure over southeastern China, local weather turned mainly fine on 16 August.

Meanwhile, the broad area of low pressure over the central part of the South China Sea intensified into a tropical depression on 16 August. It moved west-northwestwards towards the seas south of Hainan Island on 17 August and skirted across Beibu Wan the next day. Under the combined effect of the tropical depression and the ridge of high pressure over southeastern China, it was windy with squally showers and thunderstorms on 17 August. The heavy showery weather continued on 18 August with more than 100 millimetres of rainfall recorded over many places in Hong Kong.

The weather remained unsettled on 19 August under the influence of an active southerly airstream. More than 30 millimetres of rainfall were recorded over most parts of the territory, and rainfall even exceeded 100 millimetres over parts of Kowloon and the New Territories. With the strengthening of an anticyclone aloft, local weather was generally fine and very hot on 20 – 22 August. 

The area of low pressure over the seas west of Luzon intensified into a tropical depression on the night of 22 August and was later named Kajiki. Kajiki moved westwards across the central part of the South China Sea and intensified progressively into a severe tropical storm the next day. It rapidly intensified into a severe typhoon over the seas south of Hainan Island on 24 August and made landfall over the northern part of Vietnam the next night. Locally, it was mainly fine on 23 August apart from a few showers and squally thunderstorms at night. There were sunny periods in the following two days. Under the influence of a ridge of high pressure over southeastern China, apart from isolated showers and thunderstorms over the western part of the New Territories in the afternoon, local weather was mainly fine and very hot on 26 – 27 August. Affected by upper-air disturbances, it was mainly cloudy with a few showers and squally thunderstorms locally on 28 August. Besides, Nongfa formed as a tropical depression over the central part of the South China Sea that afternoon and moved northwestwards towards the seas south of Hainan Island. The Standby Signal, No. 1 was issued that night, the eighth time this year and breaking the highest record between January and August since 1946. Nongfa intensified into a tropical storm and tracked across the seas south of Hainan Island on 30 August. It made landfall over central and northern Vietnam that afternoon and then weakened into a tropical depression at night. Locally, it was very hot with sunny periods on 29 August. It was also windy under the combined effect of the ridge of high pressure over southeastern China and Nongfa. An easterly airstream affected the coast of Guangdong on 30 August and the weather of Hong Kong was mainly cloudy with a few showers. The weather turned generally fine and very hot on the last day of the month.

Eleven tropical cyclones occurred over the South China Sea and the western North Pacific in August 2025.

Rainfall distribution map on 5 August 2025

A carpark in Tseung Kwan O was flooded on the night of 4 August 2025 (Courtesy of HK01 / Photo by 李家傑)