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  • The Weather of April 2016

  • 4 May 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.

Foggy weather over Hong Kong as seen from the Peak on the night of 6 April 2016
Foggy weather over Hong Kong as seen from the Peak on the night of 6 April 2016
(courtesy of Ms Debby Tam)


    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 summarized in Tables 1.1 to 1.2.  Monthly meteorological figures and departures from normal for April are tabulated in Table 2.
 

Warnings and Signals issued in April 2016

Table 1.1   Rainstorm Warning Signals
Colour Beginning Time Ending Time
Day/Month HKT Day/Month HKT
Amber 4 / 4 1635 4 / 4 1925
Amber 10 / 4 0930 10 / 4 1140
Amber 13 / 4 0630 13 / 4 1200
Amber 22 / 4 0820 22 / 4 0945


Table 1.2   Thunderstorm Warning
Beginning Time Ending Time
Day/Month HKT Day/Month HKT
4 / 4 1615 4 / 4 2215
10 / 4 0815 10 / 4 1530
11 / 4 0650 11 / 4 1035
12 / 4 1150 12 / 4 1300
12 / 4 1415 12 / 4 1630
12 / 4 1745 12 / 4 2000
13 / 4 0600 13 / 4 1300
18 / 4 0620 18 / 4 1030
22 / 4 0740 22 / 4 1045
22 / 4 1300 22 / 4 1530
23 / 4 1330 23 / 4 1600
24 / 4 0820 24 / 4 1130
24 / 4 1255 24 / 4 1535
24 / 4 1615 24 / 4 2015
25 / 4 1400 25 / 4 1730
26 / 4 0125 26 / 4 0230
26 / 4 1920 26 / 4 2030
27 / 4 0045 27 / 4 0215
27 / 4 0335 27 / 4 0730
27 / 4 0900 27 / 4 1000


Table 2   Figures and Departures from Normal - April 2016
Meteorological Element Figure of the Month Departure from Normal*
Mean Daily Maximum Air Temperature 26.0 degrees C 1.0 degree above normal
Mean Air Temperature 23.6 degrees C 1.0 degree above normal
Mean Daily Minimum Air Temperature 21.9 degrees C 1.1 degrees above normal
Mean Dew Point Temperature 21.6 degrees C 2.2 degrees above normal
Mean Relative Humidity 89 % 6 % above normal
Mean Cloud Amount 84 % 3 % above normal
Total Rainfall 211.4 mm 36.7 mm above normal
Number of hours of Reduced VisibilityΔ 16 hours 74.6 hours below normal§
Total Bright Sunshine Duration 55.4 hours 46.3 hours below normal
Mean Daily Global Solar Radiation 9.39 Megajoule / square metre 2.21 Megajoule below normal
Total Evaporation 67.5& mm 16.3 mm below normal


  Remarks : All measurements were made at the Hong Kong Observatory except sunshine, solar radiation and evaporation which were recorded at King's Park Meteorological Station and visibility which was observed at the Hong Kong International Airport.

  Δ

The visibility readings at the Hong Kong International Airport are based on hourly observations by professional meteorological observers in 2004 and before, and average readings over the 10-minute period before the clock hour of the visibility meter near the middle of the south runway from 2005 onwards. The change of the data source in 2005 is an improvement of the visibility assessment using instrumented observations following the international trend.
Before 10 October 2007, the number of hours of reduced visibility at the Hong Kong International Airport in 2005 and thereafter displayed in this web page was based on hourly visibility observations by professional meteorological observers. Since 10 October 2007, the data have been revised using the average visibility readings over the 10-minute period before the clock hour, as recorded by the visibility meter near the middle of the south runway.


  *   Departure from 1981 - 2010 climatological normal, except for number of hours of reduced visibility

  §   Departure from mean value between 1997 and 2015

  &   Data incomplete

daily values of selected meteorological elements for HK for April 2016

The percentile map of mean temperature of April 2016

  Remarks : Extremely high: above 95th percentile
Above normal: between 75th and 95th percentile
Normal: between 25th and 75th percentile
Below normal: between 5th and 25th percentile
Extremely low: below 5th percentile
Percentile and 5-day running average values are
computed based on the data from 1981 to 2010