The Weather of August 2004

    August 2004 had more than its fair share of thunderstorms. Thunderstorm warnings were issued in 18 days in the month. It was also wetter than usual. The monthly rainfall of 488.5 millimetres was about 25 percent above the normal figure of 391.4 millimetres. However, the accumulated rainfall since the beginning of the year was 1568.6 millimetres, about eight percent below the normal of 1707.4 millimetres for the same period. The total bright sunshine duration of 165.9 hours was about 20 percent below normal.

    It was sunny and hot on the first three days of August 2004. Showers and thunderstorms associated with a broad trough of low pressure which developed over South China started to affect Hong Kong on 4 August. The unstable weather persisted on 5 and 6 August. The heavy showers on 6 August brought over 150 millimetres of rainfall to Sai Kung and the eastern part of Hong Kong Island.

    Under the influence of a ridge of high pressure, the weather in Hong Kong became fine on 7 August. The fine and hot weather prevailed in the next three days. The temperature on 10 August rose to a maximum of 33.9 degree, the highest in the month.

    The weather turned cloudy with some thundery showers on 11 and 12 August. The weather in Hong Kong improved on 13 August as the showery activity shifted south into the South China Sea. Apart from some showers on 14 August, it was mainly fine and hot in the following four days.

    With light winds on 18 and 19 August, it was hot and hazy. The visibility dropped to below 1000 metres in parts of the territory. Showers associated with a trough of low pressure cleared the haze on 20 August. In the ensuing three days, the weather remained unsettled with heavy showers and thunderstorms.

    After skirting the northern part of Taiwan on 24 and 25 August, Typhoon Aere made landfall near Xiamen the following day. With Aere moving west-southwest towards Guangdong, the Standby Signal No. 1 was issued by the Hong Kong Observatory on 26 August. Aere eventually weakened into an area of low pressure over central Guangdong on 27 August. Locally, apart from a few isolated showers and thunderstorms, it was hot and hazy on 24 and 25 August. The outer rain bands of Aere brought rainy weather to Hong Kong on 26 and 27 August.

    A broad area of low pressure associated with the remnant of Aere continued to affect the south China coast for the rest of the month, bringing overcast and rainy weather to Hong Kong. The rain was particularly heavy on 29 August. About 200 millimetres of rainfall was recorded in Lantau Island and Tsuen Wan that day.

    A total of nine 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 August are tabulated in Table 2.