Sept hit with extreme weather

October 4, 2023

In terms of extreme weather, September was an eventful month in Hong Kong with an all-time high rainfall of 1,067.1mm - more than three times the September norm, the Hong Kong Observatory said today.


Hong Kong saw a ferocious strike by Super Typhoon Saola on the first two days of September, the second most intense tropical cyclone affecting the South China Sea since 1950. Hurricane Signal No. 10 was issued during its passage, the first time since Super Typhoon Mangkhut hit the city in September 2018.


On September 7 and 8, a trough of low pressure associated with remnants of Tropical Cyclone Haikui brought prolonged torrential rain to Hong Kong, necessitating the issuance of the Black Rainstorm Warning for 16 hours and 35 minutes, the longest duration since the introduction of the rainstorm warning system in 1992.


The record rainfall of 1,067.1mm registered in September was mainly attributed to the heavy rain associated with Saola and troughs of low pressure in the first half of the month. The record-breaking rainfall mostly compensated for the rainfall deficit in the first eight months of this year.


Despite the stormy weather in the first part of the month, there was a long spell of sunny and very hot weather from September 21 to 30, setting another record for consecutive very hot days for September.


The month as a whole remained hotter than usual with a mean temperature of 28.5 degrees Celsius, 0.6 degrees above normal.


Hong Kong was also affected by Tropical Cyclone Haikui, resulting in mainly cloudy weather with a few showers on September 5 and 6.


Under the influence of a trough of low pressure associated with remnants of Haikui over the coast of Guangdong, the weather started to deteriorate with heavy rain and squally thunderstorms on the evening of September 7.


The incessant downpours continued to affect the city till the following day. During the torrential rain, the Hong Kong Observatory registered a record-breaking hourly rainfall of 158.1mm from 11pm to midnight on September 7, the highest since records began in 1884.


With a trough of low pressure lingering over the coastal areas of Guangdong, Hong Kong's weather remained unsettled with outbreaks of heavy showers and thunderstorms from September 9 to 16. The showers eased off with sunny periods the following day as the trough of low pressure weakened.


From September 18 to the end of month, under the influence an anticyclone aloft, the weather was generally fine and very hot apart from isolated showers.


Six tropical cyclones occurred over the South China Sea and the western North Pacific in the month.

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