***************************************
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 per cent, 6 per cent higher than normal and the most humid for April since 1961. Under long spells of clouds with fog or mist, the bright sunshine duration of only 6.9 hours on April 6 was the longest in the month. The total duration of bright sunshine recorded in the month was only 55.4 hours, around 54 per cent of the normal amount and the sixth lowest for April on record. The month was also warmer with more rain 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 per cent 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.
Under the influence of a humid maritime airstream, apart from a relatively sunny day on April 6, the weather in Hong Kong was warm, humid and foggy on the first nine days of the month. The visibility in the harbour and over the coastal waters occasionally fell to around 100 metres. There were some heavy showers and squally thunderstorms on April 4, 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 outbreaks of heavy rain and squally thunderstorms from April 10 to 15. Rainfall over Lantau Island and the northern part of the New Territories was the heaviest on April 10. Easterly winds then freshened on April 11 and 12, and more widespread heavy rain occurred in the morning on April 13 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 April 16. Meanwhile, the setting in of a maritime airstream brought humid and foggy weather to the territory. With another trough of low pressure crossing the coast of Guangdong on April 18, the weather became 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 April 19 and 20.
After some sunny intervals and fog patches on April 21, an upper-air disturbance brought thundery showers to Hong Kong on April 22, with the heaviest rain recorded in the northern part of the New Territories. Affected by a trough of low pressure, local weather further deteriorated in the next three days with scattered heavy showers and squally thunderstorms. While the showery conditions persisted in the presence of a lingering trough, the influence of a warm maritime airstream became increasingly apparent. Temperatures at the Hong Kong Observatory climbed to a maximum of 29.1 degrees in the afternoon on April 27, 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.
There was no tropical cyclone over the South China Sea and the western North Pacific in the month.
Details of issuance and cancellation of various warnings/signals in the month are summarised in Table 1. Monthly meteorological figures and departures from normal for April are tabulated in Table 2.
Ends/Wednesday, May 4, 2016
Issued at HKT 18:10
NNNN
