The Weather of April 2016

    With a maritime airstream trying to exert control over the coastal areas of Guangdong in a change of seasons, the weather of April 2016 was exceptionally humid and gloomy. The monthly mean relative humidity was 89 percent, six percent higher than normal and also the most humid for April since 1961. Under long spells of clouds, fog or mist, the sunshine duration of 6.9 hours on 6 April already made it the sunniest day in the month. The total duration of bright sunshine recorded in the month was only 55.4 hours, around 54 percent of normal and the sixth lowest for April on record. The month was also warmer and rainier than usual. The monthly mean temperature was 23.6 degrees, 1.0 degrees above the normal figure of 22.6 degrees. The monthly total rainfall was 211.4 millimetres, about 21 percent more than the normal figure of 174.7 millimetres. The accumulated rainfall of 651.8 millimetres in the first four months of the year was nearly double the normal figure of 336.1 millimetres for the same period.

    Apart from a relatively sunny day on 6 April, the weather in Hong Kong was warm, humid and foggy on the first nine days of the month, with the visibility in the harbour and over the coastal waters occasionally falling to around 100 metres under the influence of a humid maritime airstream. There were also some heavy showers and squally thunderstorms on 4 April, particularly over Lantau Island and the northern part of the New Territories.

    With a trough of low pressure edging southwards and crossing the south China coastal areas, local weather became unsettled with outbreak of heavy rain and squally thunderstorms from 10 till 15 April. Again, rain was heaviest over Lantau Island and the northern part of the New Territories on 10 April. Easterly winds then freshened on 11 and 12 April and more widespread heavy rain occurred on the morning of 13 April as an area of intense thunderstorms swept across the coast of Guangdong. More than 50 millimetres of rainfall were generally recorded over Hong Kong that day and severe gusts reaching 113 kilometres per hour were reported at Lau Fau Shan.

    As the trough weakened and the rain eased off, some sunny intervals appeared on 16 April. Meanwhile, the setting in of a maritime airstream also brought humid and foggy weather to the territory. With another trough of low pressure crossing the coast of Guangdong on 18 April, the weather turned unsettled again with rain and squally thunderstorms. This was followed by a fresh to strong easterly airstream that brought cooler weather with rain patches to Hong Kong on 19 - 20 April.

    After some sunny intervals and fog patches on 21 April, an upper-air disturbance brought thundery showers to Hong Kong on 22 April, with the heaviest rain falling over the northern part of the New Territories. Affected by a trough of low pressure, local weather deteriorated further with scattered heavy showers and squally thunderstorms in the next three days. While the showery conditions persisted in the presence of a lingering trough, the increasing influence of a warm maritime airstream caused temperatures at the Hong Kong Observatory to climb to a maximum of 29.1 degrees on the afternoon of 27 April, the highest of the month. The arrival of an easterly airstream brought slightly cooler weather and a mixture of sunshine and showers towards the end of the month.