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September 2008 was hotter and drier than usual with the monthly mean temperature of 29.0 degrees equalling the record set in 1969. The total rainfall of the month was 159.2 millimetres, which was 128.3 millimetres below normal. The accumulated rainfall since January 1 was 2858.3 millimetres, about 32% above the normal figure of 2161.2 millimetres for the same period.
The weather was mainly fine and hot on the first day of the month. Affected by a trough of low pressure over the south China coastal areas, it was cloudy with showers from September 2-4. A moist easterly airstream brought showery weather to Hong Kong in the next two days. A weak ridge of high pressure over southern China brought mainly fine weather to the territory from September 7-9.
Under the influence of a dry continental airstream over southern China, local weather remained sunny and dry from September 10-17. A trough of low pressure developed over the northern part of the South China Sea and brought showery conditions to Hong Kong on September 18 and 19.
Typhoon Hagupit formed over the western North Pacific on September 19. It moved first west-southwestwards and then northwestwards in the next two days. Affected by the hot subsiding air ahead of Hagupit, local weather became sunny and very hot from September 20-22. The daily mean air temperature of 31.2 degrees recorded at the Hong Kong Observatory on September 22 was the highest in September on record.
Hagupit entered the South China Sea in the evening of September 22 and approached the south China coast at a high speed of some 30 kilometres per hour on September 23. It made landfall over the western coast of Guangdong the next morning. Under the influence of Hagupit, local weather was windy and rainy on September 23 and 24. Local winds generally reached gale to storm force and a total of 77.8 millimetres of rainfall was recorded at the Hong Kong Observatory in these two days.
Local weather stayed cloudy with some isolated showers and thunderstorms on September 25 and 26. Under the influence of a fresh easterly airstream over the coast of Guangdong, the weather remained showery on September 27. A dry northerly airstream brought mainly fine and dry conditions to the territory on the last three days of the month.
Five tropical cyclones occurred in the western North Pacific and the South China Sea in September.
Details of the issuance and cancellation of various warnings/signals in the month are summarised in Table 1.1. Monthly meteorological figures and departures from normal of September are tabulated in Table 1.2.
Ends/Friday, October 3, 2008
Issued at HKT 15:19
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