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September 2007 was drier than usual. The monthly rainfall was 102.3 millimetres, about one third of the normal figure of 299.7 millimetres. The accumulated rainfall since the beginning of the year was 1635.6 millimetres, about 19% below the normal figure of 2007.1 millimetres for the same period.
It was sunny on the first day of the month. A trough of low pressure over the South China coast brought showery weather to the territory on September 2 and the next three days. With the trough of low pressure moving south to the northern part of the south China Sea, there were sunny intervals during the day on September 6. The weather stayed mainly cloudy with isolated showers in the following four days.
Under the influence of a continental airstream, the weather turned fine on September 11 and remained so in the ensuing two days. With light wind conditions, it was hazy from September 14 to 17 with visibility dropping below 3000 metres in some places. With winds strengthening from the north, it was mainly fine and dry on September 18 and the next four days. The relative humidity dropped to about 40% over most parts of the territory during the day on September 18 and 19.
The combined effect of the northeast monsoon and the tropical storm Francisco over the northern part of the South China Sea brought windy and rainy weather to Hong Kong from September 23 to 25.
Under the influence of a ridge of high pressure over southeastern China, it was mainly fine from September 26 to 30.
Six tropical cyclones occurred in the western North Pacific and the South China Sea in the month.
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/Wednesday, October 3, 2007
Issued at HKT 15:01
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