The Weather of July 2004

    July 2004 was wetter than normal, with a monthly rainfall of 386.7 millimetres against the normal of 323.5 millimetres for July. However, the accumulated rainfall since 1 January, at 1080.1 millimetres, was about 18 percent below the normal of 1316.0 millimetres for the same period.

    It was very hot and hazy in Hong Kong in the first two days of July 2004. On 1 July, the maximum temperature at the Hong Kong Observatory rose to 34.6 degrees, the highest so far this year. Some parts of the New Territories recorded temperatures as high as 37 degrees.

    With the establishment of an active southwest monsoon over South China on 3 July, it was overcast with scattered showers and thunderstorms in Hong Kong. The monsoon prevailed in the next 10 days. The weather was characterized by periods of sunshine and interludes of showers and thunderstorms. As a ridge of high pressure over the western North Pacific extended westward to cover southeastern China, it became fine and hot in Hong Kong on 14 and 15 July.

    Meanwhile, Tropical Storm Kompasu came within 800 kilometres of Hong Kong on 14 July and the Standby Signal Number 1 was issued that evening. Kompasu continued to edge towards Hong Kong on 15 July. On 16 July, squally heavy showers began to affect Hong Kong. Gales were experienced in parts of the territory. The first Number 3 and later the first Number 8 Tropical Cyclone Signal of the year were issued on that day. Kompasu finally made landfall over Sai Kung on the afternoon of 16 July. The rain bands associated with the remnant of Kompasu continued to affect Hong Kong the next day, bringing over 100 millimetres of rainfall to Tsuen Wan and the northeastern part of Lantau Island. It became fine on 18 July.

    The weather deteriorated again when an unstable maritime airstream affected South China on 19 July. It became cloudy to overcast with heavy showers in the ensuing three days.

    With the establishment of a ridge of high pressure over southern China, the weather turned fine and hot on 23 July and the following three days.

    An area of low pressure over the northern part of the South China Sea intensified into a tropical depression on the early morning of 27 July. It moved north-northwest and made landfall near Shantou shortly afterwards. Locally, the weather was mainly fine in the morning, but became cloudy with some showers in the afternoon.

    The return of an unstable maritime airstream gave rise to heavy showers and thunderstorms in Hong Kong on 28 and 29 July. The heavy downpour on 29 July resulted in over 100 millimetres of rainfall in Sha Tin, Sai Kung and the eastern part of Kowloon. The weather remained cloudy with some showers on 30 July.

    The weather turned fine on the last day of the month as a ridge of high pressure established over the southeastern China.

    A total of five 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 1.7. Monthly meteorological figures and departures from normal of July are tabulated in Table 2.