The Weather of September 2004

    All tropical cyclones originating from the western Pacific did not come close to Hong Kong during the month. As a result, September 2004 was drier than usual. The monthly rainfall of 167.3 millimetres was about 44 percent below the normal figure of 299.7 millimetres. The accumulated rainfall since the beginning of the year was 1735.9 millimetres, about 14 percent below the normal of 2007.1 for the same period.

    It was mainly fine with long hours of sunshine in the first five days of the month apart from some showers on 3 September.

    Associated with Typhoon Songda in the East China Sea, a trough of low pressure formed over the coast of Guangdong and brought thundery showers to the territory on 6 September. A tornado developed amidst the thunderstorms and struck the Hong Kong International Airport at Chek Lap Kok. In a span of just a few minutes, gusts in excess of 60 kilometres overturned a van, injuring one person. Some cargoes were tossed towards a cargo plane while it was being refueled, damaging a fuel pipe and causing oil spill. In the ensuing three days, unsettled weather persisted as the trough of low pressure continued to linger along the coast. A heavy downpour on 8 September brought over 100 millimetres of rainfall to Ho Man Tin and Kwun Tong.

    The rain eased off on 10 September when a dry continental airstream arrived at the coast. While it remained cloudy in the next two days, the weather became sunny and dry on 13 September. Generally fine weather continued in the next five days. Under light wind conditions, it was hazy on 15 and 16 September with the visibility falling to below 2000 metres in some parts of the territory.

    Showers and thunderstorms returned on 19 September and resulted in over 70 millimetres of rainfall in parts of the Kowloon and Hong Kong Island.

    The weather improved with plenty of sunshine on 20 September. Although it remained sunny during the day on 21 September, the weather deteriorated with frequent thunderstorms that night when a cold front moved across the south China coast. The clouds dispersed gradually the next day as the continental airstream behind the cold front dominated over southern China. Apart from a few showers on 25 and 30 September, the weather remained generally fine for the rest of the month.

    A total of four tropical cyclones occurred in the western North Pacific in the month. 

    Details of issuance and cancellation of various warnings/signals in the month are summarized in Tables 1.1 to 1.4.  Monthly meteorological figures and departures from normal for September are tabulated in Table 2.