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Under the dominance of a subtropical ridge over southern China, September 2014 was the hottest September on record. The monthly mean minimum temperature of 27.0 degrees and mean temperature of 29.0 degrees were respectively the highest and one of the highest for September since records began in 1884. The month was also drier than usual with a monthly total rainfall amount of 140.6 millimetres, only about 43 per cent of the September normal of 327.6 millimetres. The accumulated rainfall since January 1 was 2452.7 millimetres, about 10 per cent above the normal of 2233.1 millimetres for the same period.
The weather was sunny and very hot apart from a few isolated showers for the first three days of the month. With an easterly airstream setting in, it became cloudier with a few showers and thunderstorms on September 4 and 5. As the easterly airstream weakened, the weather turned mainly fine and very hot in Hong Kong on September 6.
An area of low pressure over the northern part of the South China Sea intensified into a tropical depression on September 7 and brought cloudy and showery weather with isolated squally thunderstorms to the territory that day. The tropical depression moved gradually away from Hong Kong and made landfall near Zhanjiang the next day. Under the influence of its rainbands, showers continued to affect Hong Kong.
Generally fine and very hot conditions returned from September 9 to 11. Under light wind conditions, temperatures at the Hong Kong Observatory rose to a maximum of 34.1 degrees on September 11, the highest of the month. High temperatures also triggered isolated showers during the day. As another area of low pressure approached the coast of western Guangdong, local weather turned mainly cloudy with showers on September 12. Showers then eased off over the next two days as generally fine weather returned.
Meanwhile, tropical cyclone Kalmaegi intensified into a typhoon east of the Philippines on September 14. It moved across Luzon and tracked generally west-northwestwards across the South China Sea on September 15. Local weather was very hot with sunny periods at first. It became cloudy to overcast as winds strengthened gradually with a few squally showers and thunderstorms later that day. Kalmaegi passed to the south-southwest of Hong Kong and brought gale force winds to the territory with heavy squally showers during the night. Under the combined effect of Kalmaegi and a ridge of high pressure along the southeastern coast of China, local weather remained showery and rather windy over the next couple of days.
With the establishment of a continental anticyclone over China, the weather in Hong Kong became generally fine and hot on September 18. Dominated by a dry continental airstream, the weather remained dry with sunny periods for the next five days. Under light winds, hazy conditions affected the territory on September 24 and 25. Apart from some isolated showers on September 26, generally fine and hot weather prevailed till the end of the month. High temperatures on September 30 also triggered some thundery showers that evening.
Six tropical cyclones occurred over the South China Sea and the western North Pacific in the month.
Details of the issuance and cancellation of various warnings/signals during the month are summarised in Table 1. Monthly meteorological figures and departures from the normal for September are tabulated in Table 2.
Ends/Monday, October 6, 2014
Issued at HKT 18:30
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