The Weather of July 2006

    The weather of July 2006 was marked by heavy rain and severe thunderstorms associated with an active southwest monsoon that affected the south China coast. The total rainfall of 569.2 millimetres in the month was 245.7 millimetres above the normal figure. The accumulated rainfall since 1 January amounted to 1771.5 millimetres, 35 percent more than the normal of 1316 millimetres for the same period.

    Apart from some isolated showers, it was fine and hot in the first four days of the month. Under the influence of the southwest monsoon, the weather was characterized by periods of sunshine and some showers from 5 to 10 July.

    Affected by a weak trough of low pressure along the south China coast, there were scattered showers and squally thunderstorms on 11 July. The weather turned fine the following day. When Severe Tropical Storm Bilis moved near Taiwan on 13 July, it was very hot in Hong Kong and the maximum temperature shot up to 34.0 degrees, the highest in the month. The outer rainbands of Bilis brought scattered squally showers to Hong Kong on 14 July. Showery weather continued on 15 July as an active southwest monsoon set in. On the early morning of 16 July, the weather deteriorated further with heavy downpour and squally thunderstorms. During the torrential rain, more than 150 millimetres of rainfall was recorded in Hong Kong Island, Kowloon, Cheung Chau and Tseung Kwan O, necessitating the issuance of the Black Rainstorm Warning. Between 2 a.m. and 3 a.m., a record-breaking 115.1 millimetres of rainfall was registered at the Hong Kong Observatory Headquarters, breaking the pervious record of hourly rainfall of 109.9 millimetres recorded from 6 a.m. to 7 a.m. on 8 May 1992. The weather stayed cloudy with a few showers on 17 July.

    Sunny weather returned on 18 July when a ridge of high pressure dominated over southeastern China. Apart from a few isolated showers, fine and hot weather prevailed in the next five days. Under the influence of the subsiding air ahead of Typhoon Kaemi, it was very hot and hazy on 24 and 25 July. The high daytime temperatures also led to development of severe squally thunderstorms in the afternoon of 24 July. Hails were reported at Sai Kung in the thunderstorms.

    The weather became cloudy with some showers on 26 July as affected by the rainbands of Kaemi. Hong Kong came under the influence of an active southwesterly airstream on 27 July. It was rainy with scattered squally thunderstorms. Unsettled weather persisted in the following two days.

    Local weather improved on 30 July under the influence of a ridge of high pressure over southeastern China. It was sunny on the last day of the month.

    Four 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 1.4.  Monthly meteorological figures and departures from normal for July are tabulated in Table 2.