The Weather of April 2007

    April 2007 was drier and cooler than usual. The mean temperature of 21.8 degrees was 0.4 degree below normal. The monthly rainfall of 125.5 millimetres was about 22 percent below normal. The accumulated rainfall in the first four months of the year amounted to 189.6 millimetres, about 37 percent below the normal figure of 299.8 millimetres for the same period.

    Under the influence of a maritime airstream, it was warm with sunny periods on the first day of April 2007. A cold front moved across the coast of Guangdong on 2 April, bringing squally showers and thunderstorms to the territory. It was rather cool with rain on 3 April. Temperature dropped further to 12.3 degrees on the morning of 4 April, the lowest in the month. The weather stayed cloudy with a few rain patches in the following four days.

    The weather improved with plenty of sunshine on 9 April. It turned rainy again the next day when a broad band of cloud covered southern China. With a ridge of high pressure establishing over southeastern China, it became mainly fine on 11 April and the following two days. A maritime airstream set in on 14 April and brought a few light rain patches in the morning. It was warm and sunny on the next two days. The temperature rose to 29.4 degrees on 16 April, the highest in the month. The weather became unstable on 17 April when a cold front reached the south China coast. A squall line swept across Hong Kong that night, bringing severe gusts and heavy showers. Peak gusts of over 100 kilometres per hour were recorded at some places of the territory. In Admiralty, three persons were injured when a sign board collapsed in gusty winds.

    Hong Kong came under the influence of dry northerlies on 18 April. It was fine, clear and very dry with relative humidity dropping below 30 percent. The weather remained generally fine in the ensuing two days.

    A moist maritime airstream brought misty weather to Hong Kong on 21 April, and visibility in the Hong Kong International Airport fell below 3000 metres. It was cloudy with a few showers on 22 April.

    Under the influence of a trough of low pressure over southern China, there were heavy rain and squally thunderstorms on 23 and 24 April. The Red Rainstorm Warning Signal was issued for the first time this year on 24 April. More than 70 millimetres of rainfall were recorded over Hong Kong Island, Tseung Kwan O, Sha Tin and the northern part of the New Territories. The weather remained cloudy with some rain patches on 25 April.

    Clouds thinned out with plenty of sunshine during the day on 26 April. Mainly fine weather continued in the next two days. The weather became cloudy with rain patches on the last two days of the month when local winds freshening from the east.

    Only one tropical cyclone 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 April are tabulated in Table 2.