The Weather of April 2001

    April 2001 was warmer and drier than usual. The mean temperature of 22.4 degrees was 0.2 degrees above normal and the monthly maximum temperature of 31.8 degrees was the fourth highest for April. The monthly rainfall of 133.0 millimetres was 18 per cent below normal. The accumulated rainfall in the first four months of the year amounted to 248.0 millimetres, 17 per cent below the normal figure of 299.8 millimetres for the same period. Hail fell on 9 April during the passage of a thunderstorm.

    A surge of the northeast monsoon affected the south China coastal areas on 1 April and brought cloudy weather to Hong Kong with some light rain at first. Clouds dissipated in the next afternoon and there were sunny periods. Sunny weather continued on 3 April.

    A trough of low pressure crossed the coast and moved to the northern part of the South China Sea on 4 April. The weather of Hong Kong became overcast with thunderstorms, and easterly winds strengthened during the afternoon. Rainy weather continued the following three days.

    Under the influence of a warm and humid maritime airstream, it was foggy on the morning of 8 April with visibility inside the harbour falling to 400 metres. Fog dispersed during the day as temperature rose.

    Fog patches returned on the morning of 9 April. As the maritime airstream converged with an easterly airstream which arrived later during the day, an area of active thunderstorms developed rapidly in the vicinity of the Pearl River Estuary. The sky became almost dark in the afternoon. Squally thunderstorms and heavy rain brought over 50 millimetres of rainfall to Kowloon and the New Territories. Hail fell at the Hong Kong Observatory Headquarters between 5:35 and 5:50 p.m. The largest hailstone measured about 2.5 centimetres in diameter. Hail was also reported in Tsing Yi, most districts of Kowloon and the northern part of Hong Kong Island. Lightning struck an overhead power cable in Ma On Shan. Electricity was cut off to 13 village houses in Ma On Shan and 16 village houses in Sai Kung. Thunderstorms also caused disruptions to mobile and residential phone services. The weather remained overcast with a few rain patches the next day.

    A cold front crossed the south China coast on 11 April. Northerly winds strengthened and brought cool and rainy weather to the territory. Winds moderated the next morning but the weather remained cool with a minimum temperature of 15.0 degrees, the lowest in the month. The weather became fine and dry during the day.

    A broad band of cloud over the northern part of the South China Sea drifted northwards and brought cloudy weather to Hong Kong on 13 April. Cloudy conditions prevailed the next day while mist and haze occurred over parts of the territory.

    A dry easterly airstream affected the coastal areas on 15 April and the weather turned mainly fine. The weather remained sunny the next day apart from some mist patches in the morning.

    A moist maritime airstream brought misty weather to Hong Kong on the morning of 17 April. Besides morning mist and some showers, there were isolated thunderstorms in the northern New Territories on 18 April. Southeasterly winds became strong briefly in the late evening. Mist and rain continued the next day.

    Under the influence of a warm maritime airstream, it was hot on 20 April. A trough of low pressure crossed the coastal areas of Guangdong and brought some rain and isolated thunderstorms to Hong Kong on 21 April. Winds strengthened from the northeast the next morning and the weather became cooler. Winds moderated on 23 April but the weather remained cloudy with light rain.

    Mist occurred on 24 April and visibility fell to around 1 000 metres inside the harbour. There were isolated thunderstorms in the northern part of the New Territories. The weather was cloudy with rain on 25 April. It became mainly fine the next two days.

    Under the influence of a warm and moist maritime airstream, it was misty on 28 April. Fog formed over the eastern part of the territory the next morning. A vessel sank off Shau Kei Wan typhoon shelter after collision with another cargo boat and one man was slightly injured. It remained mainly cloudy with a few rain patches during the day.

    Apart from some fog patches in the morning, it was sunny and hot on 30 April with temperatures rising to a maximum of 31.8 degrees, the highest in the month. A few isolated thunderstorms affected Hong Kong in the late evening as a trough of low pressure edged closer from the north.

    There was no tropical cyclone over the South China Sea and the western North Pacific in the month.