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The Weather of April 2014

    The weather of April 2014 was drier and sunnier than usual.  The total rainfall of the month was 132.4 millimetres, about 24 percent below the normal figure of 174.7 millimetres.  However, the accumulated rainfall since 1 January of 379.5 millimetres was about 13 percent above the normal figure of 336.1 millimetres for the same period.  The total duration of bright sunshine of the month was 119.4 hours, about 17 percent above the normal figure of 101.7 hours.  The mean temperature of 22.6 degrees for the month was on par with normal.  

    Under the influence of a trough of low pressure, the weather was cloudy with showers and a few squally thunderstorms in Hong Kong for the first three days of the month.  Rainfall was heavy at times, exceeding 50 millimetres at some places in the territory.  Hail was reported at Yuen Long, Sheung Shui and Fanling during the passage of thunderstorms on the night of 2 April. 

    With the setting in of a relative dry northeast monsoon, it became mainly fine on 4 and 5 April.  A fresh to strong easterly airstream brought windy, rainy and appreciably cooler weather to Hong Kong for the next two days, with temperatures at the Observatory falling to 17.5 degrees on 6 April, the lowest of the month.  Despite the moderation of the easterlies on 8 April, local weather remained cloudy with isolated heavy showers.  While the weather became brighter on 9 and 10 April, there were mist patches and coastal fog in the morning under the influence of a moist easterly airstream. 

   The weather then stayed mostly sunny and warm up to 19 April.  Under light wind condition, fog returned in the morning on 13 April.  A fresh to strong easterly airstream brought cloudier and slightly cooler weather over the next three days, as well as some rain patches on 14 April.  But as the easterlies moderated, the weather again became warm with mist and coastal fog from 17 to 19 April.  

   Under the influence of a maritime airstream over the coast of Guangdong, the weather turned mainly cloudy with rain patches and coastal fog from 20 to 22 April.  The easterlies strengthened again and brought clouds with rain as well as fog over the next few days.  Visibility fell below 1,000 metres in the harbour on the morning of 25 April.  After the passage of a trough of low pressure that brought more rain, the weather turned sunny on 27 April with temperatures at the Observatory rising to a maximum of 29.0 degrees, the highest of the month.  Affected by a dry continental airstream, the weather was mainly fine over the next couple of days.  The month ended with cloudy weather and some showers as easterly winds became established again. 

 

Radar image showing thunderstorms crossing the northern part of the New Territories at 9:30 p.m. on 2 April 2014 
Radar image showing thunderstorms crossing the northern part of the New Territories at 9:30 p.m. on 2 April 2014


Hails found in Yuen Long at around 9:35 p.m. on 2 April 2014 
Hail found in Yuen Long at around 9:35 p.m. on 2 April 2014 (Courtesy of Ms. Clara Ng)

 

    Two tropical cyclones occurred 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 1.4.  Monthly meteorological figures and departures from normal for April are tabulated in Table 2.



 

Warnings and Signals issued in April 2014


Table 1.1   Strong Monsoon Signal

Beginning Time Ending Time
Day/Month HKT Day/Month HKT
6 / 4 1500 7 / 4 1415


Table 1.2   Rainstorm Warning Signals

Colour Beginning Time Ending Time
Day/Month HKT Day/Month HKT
Amber 3 / 4 0445 3 / 4 0600


Table 1.3   Thunderstorm Warning

Beginning Time Ending Time
Day/Month HKT Day/Month HKT
31 / 3 1450 1 / 4 0200
1 / 4 0634 1 / 4 1245
1 / 4 1815 1 / 4 1945
1 / 4 2345 2 / 4 0045
2 / 4 0430 2 / 4 0930
2 / 4 1025 2 / 4 1530
2 / 4 1715 2 / 4 2235
3 / 4 0325 3 / 4 0700
3 / 4 0945 3 / 4 1415
8 / 4 1245 8 / 4 1430


Table 1.4   Fire Danger Warnings

Colour Beginning Time Ending Time
Day/Month HKT Day/Month HKT
Yellow 5 / 4 0600 5 / 4 1145
Red 5 / 4 1145 6 / 4 0600
Yellow 6 / 4 0600 6 / 4 1115
Yellow 13 / 4 0600 13 / 4 2030
Yellow 19 / 4 1130 19 / 4 2030
Yellow 20 / 4 0600 20 / 4 2000


Table 2   Figures and Departures from Normal - April 2014

Meteorological Element Figure of the Month Departure from Normal*
Mean Daily Maximum Air Temperature 24.9 degrees C 0.1 degree below normal
Mean Air Temperature 22.6 degrees C normal
Mean Daily Minimum Air Temperature 21.0 degrees C 0.2 degree above normal
Mean Dew Point Temperature 20.0 degrees C 0.6 degree above normal
Mean Relative Humidity 86 % 3 % above normal
Mean Cloud Amount 72 % 9 % below normal
Total Rainfall 132.4 mm 42.3 mm below normal
Number of hours of Reduced VisibilityΔ 75 hours 20.9 hours below normal§
Total Bright Sunshine Duration 119.4 hours 17.7 hours above normal
Mean Daily Global Solar Radiation 12.95 Megajoule / square metre 1.35 Megajoule above normal
Total Evaporation 82.3 mm^ 1.5 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 2013

  ^   Total for 29 days

daily values of selected meteorological elements for HK for April 2014

The percentile map of mean temperature of April 2014

  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



Rainfall Map For April 2014 (isohyets are in millimetres)

Extract of Meteorological Observations in Hong Kong for April 2014