The Weather of April 2000

    April 2000 was marked by unsettled weather and heavy rain due to the frequent passages of troughs of low pressure and a very active southwest monsoon. The total rainfall of 547.7 millimetres, more than three times the normal figure of 161.5 millimetres, was the highest for April since records began in 1884. The daily rainfall of 172.5 millimetres on 23 April was the second highest for April. The accumulated rainfall in the first four months of the year amounted to 686.5 millimetres, more than double the normal figure of 299.8 millimetres and ranking the third highest for the same period.

    The Observatory issued four Red and one Black Rainstorm Warning Signals this month, the highest on record for April. The Red and Black Rainstorm Warning Signals on 3 April and 23 April respectively were also the earliest for the two Signals in a year since the introduction of the Rainstorm Warning System in 1992.

    This April was warmer than usual with the monthly mean temperature of 23.1 degrees, 0.9 degrees higher than normal. The monthly mean pressure of 1 011.1 hectoPascals was the third lowest for April.

    An extensive rainband brought thunderstorms to Hong Kong on the morning of 1 April. Clouds thinned out in the afternoon and there were sunny intervals.

    Under the influence of a trough of low pressure over southern China, there were squally thunderstorms and heavy rain on the late evening of 2 April. More than 50 millimetres of rainfall were recorded over the northern part of the New Territories. There were 38 reports of flooding and a stranded family in Yuen Long had to be rescued by firemen.

    Unsettled weather persisted the next day. Thundery showers brought more than 100 millimetres of rainfall to urban areas. Two men working at a pier in Central were struck by lightning and injured. A retaining wall in Kowloon City collapsed and 15 people had to be evacuated though no one was hurt. A road in Lam Tin also subsided in heavy rain.

    As the trough of low pressure moved into the northern part of the South China Sea and dissipated, the weather became foggy with drizzle on 4 April. Visibility inside the harbour fell to around 300 metres in the morning.

    A weak surge of the northeast monsoon reached the coastal areas the next day. There were sunny intervals as well as a few rain patches.

    A ridge of high pressure over southeastern China brought fresh easterly winds to the coast of Guangdong on 6 April. Under its influence, the weather remained cloudy with a few light rain patches. These conditions persisted for the next few days.

    Winds became light variable on 10 April. There were drizzle and mist with visibility falling to 1 100 metres over the western part of the territory. Visibility improved as winds strengthened from the east in the evening. Winds then moderated gradually and there were sunny intervals in the next couple of days.

    Another extensive rainband affected the coastal areas of Guangdong and it became cloudy with rain on 13 April.

    Under the influence of strong southwesterly winds, heavy rain and thunderstorms affected Hong Kong on 14 April. Over 500 millimetres of rainfall were recorded in the western part of the New Territories. Villages were half-submerged in flash floods and water was about a metre deep. There were 128 reports of flooding and 28 landslides. About 160 villagers were rescued by helicopter crews and firemen in dinghies with 7 of them taken to hospitals. More than 200 hectares of farmland and 35 hectares of fish pond were inundated. The Light Rail services were disrupted for about 5 hours.

    A cold front crossed the coast of Guangdong on the morning of 15 April and the associated northerly winds were strong at first. The weather improved gradually in the afternoon and it turned mainly fine the next day. It was slightly cooler with a minimum temperature of 19.0 degrees on the morning of 16 April, the lowest in the month. Generally fine weather prevailed for the next few days.

    A trough of low pressure brought showers and isolated squally thunderstorms to the territory on 21 April. Weather remained unsettled for the next couple of days. Heavy rain and thunderstorms brought more than 100 millimetres of rainfall to many areas on 23 April, with Peng Chau and parts of Lantau Island recording over 200 millimetres. There were altogether 64 reports of flooding and two reports of landslide.

    As the trough of low pressure dissipated, rain eased off during the day of 24 April though cloudy to overcast conditions continued.

    Under the influence of a southerly airstream, it was hot on 25 April with sunny periods in the afternoon apart from a few showers. Temperatures rose to a maximum of 30.2 degrees in the afternoon, the highest in the month.

    Another trough of low pressure crossed the coast of Guangdong on 26 April and again brought thundery showers to Hong Kong in the evening. Rain eased off overnight as the trough moved further southwards. However, heavy showers returned on 28 April. In a landslide, a 2-ton rock fell from a retaining wall in Sham Tseng and blocked a road. Weather remained cloudy with some showers till the end of the month.

    No tropical cyclone occurred in the South China Sea and the western North Pacific in the month.

    During the month, a total of 13 aircraft was diverted due to adverse weather.