The Weather of September 2003

    September 2003 was wetter than usual. The monthly rainfall of 394.0 millimetres was more than 30 per cent above the normal figure of 299.7 millimetres. However, the accumulated rainfall since the beginning of the year of 1 843.2 millimetres was still about 8 per cent below the normal figure of 2 007.1 millimetres for the same period.

    On the first day of the month, it was fine apart from a few isolated thunderstorms over the northwestern part of the New Territories. The Standby Signal No. 1 was issued that evening as Typhoon Dujuan approached from the east and came within 800 kilometres of Hong Kong. On the afternoon of 2 September, the local weather deteriorated rapidly with occasional heavy rain and severe squalls. Dujuan skirted the north of Hong Kong at about 30 kilometres from the Hong Kong Observatory that evening, necessitating the issuance of the Increasing Gale or Storm Signal No. 9 for the first time since 1999. Dujuan continued to move westwards across southern Guangdong and weakened into an area of low pressure on 3 September.

    With a broad area of low pressure over the northern part of the South China Sea, it remained cloudy and showery up to 8 September. As a ridge of high pressure was established over southern China, the local weather turned fine on 9 September and remained so for the next 4 days. On 14 September, unsettled weather associated with a broad area of low pressure near Hainan drifted north and brought heavy rain and thunderstorms to Hong Kong. Over 80 millimetres of rainfall was recorded at the Hong Kong Observatory Headquarters on two consecutive days.

    Rain became less frequent on 16 September and the weather was mainly fine in the next 4 days. Isolated thunderstorms returned in the evening of 20 September and affected the northwestern part of the New Territories.

    A weak surge of the northeast monsoon arrived in Hong Kong on 21 September, bringing with it some heavy showers and thunderstorms. It became cloudy and cooler in Hong Kong in the next 4 days. The minimum temperature fell to 23.6 degrees on 23 September, the lowest of the month.

    The weather turned fine on 24 September as drier continental air was established over South China. The Red Fire Danger Warning was issued on 25 September, the first time this autumn. It remained fine with long periods of sunshine for the ensuing 5 days. There were some isolated showers in the small hours of 30 September but it became fine again during the day.

    A total of 4 tropical cyclones occurred in the western North Pacific and the South China Sea in the month. 

    Details of issuance and cancellation of various warnings/signals in the month are summarized in Tables 1.1 to 1.6.  Monthly meteorological figures and departures from normal for September are tabulated in Table 2.