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  • The Weather of May 2016

  • 2 June 2016

    The weather for May 2016 was warmer and drier than usual. The monthly mean temperature was 26.7 degrees, 0.8 degree above the normal figure of 25.9 degrees. Despite several rainstorms in the month, the monthly total rainfall was only 233.6 millimetres, about 23 percent below the normal figure of 304.7 millimetres. However, the accumulated rainfall of 885.4 millimetres in the first five months of the year was still about 38 percent more than the normal figure of 640.8 millimetres for the same period.

    Under the influence of an easterly airstream, the weather in Hong Kong was slightly cooler with a few showers on 1 May. The minimum temperature of 20.4 degrees recorded at the Hong Kong Observatory that morning was the lowest of the month. With the easterly airstream gradually replaced by a warm and humid maritime airstream, local weather became warm and foggy with a few showers on 2 May. Affected by a trough of low pressure over the coastal areas of Guangdong, there were showers and thunderstorms in the next couple of days. The showers were particularly heavy on the evening of 3 May with more than 30 millimetres of rainfall recorded over many places of the territory.

    Dominated by a southerly airstream, it was hot with sunny periods in Hong Kong from 5 to 9 May. An area of intense rain and thunderstorms associated with a trough of low pressure swept across the Pearl River estuary on 10 May. More than 70 millimetres of rainfall were generally recorded in Hong Kong, and rainfall over Sha Tin and Sai Kung even exceeded 150 millimetres. Red Rainstorm Warning Signal was twice issued that morning.

    After a mainly fine and relatively dry day on 11 May, the weather became generally cloudy with isolated showers over the next three days as a fresh easterly airstream prevailed over the coast of Guangdong. With the moderation of the easterly airstream, the weather turned mostly fine on 15 May. Despite some light rain during the passage of a cold front that night, the weather remained fine the next day with slightly cooler temperatures as a relatively dry northerly airstream reached the coast of Guangdong. The freshening of easterly winds once again brought cloudy weather and some rain patches to Hong Kong on 17 – 19 May.

    Affected by a trough of low pressure over the coast of Guangdong, local weather deteriorated with heavy showers and squally thunderstorms on 20 and 21 May. The rainstorm episode in the early morning on 21 May brought more than 70 millimetres of rainfall to many places, with rainfall exceeding 200 millimetres in Sai Kung where a few landslides were reported. With the weakening of the trough, local weather improved and it was generally fine and hot on 22 – 25 May.

    The weather became windy and showery in Hong Kong as a monsoon depression over the northern part of the South China Sea developed into a tropical depression on the night of 26 May and Tropical Cyclone Warning Signal was issued for the first time this year. The tropical depression made landfall near Yangjiang over the coast of western Guangdong the next day as strong winds affected the territory. Under the influence of an active southwest monsoon in the wake of the tropical depression, local weather became even more unsettled with heavy showers and thunderstorms on 28 May. More than 40 millimetres of rainfall were generally recorded over the territory, and rainfall even exceeded 100 millimetres in Kwai Tsing and Tsuen Wan. During the heavy downpour, 16 hikers were stranded in Fanling due to flash flood and had to be led to safety by rescue workers.

    With the moderation of the southwest monsoon, the weather became hot with sunny periods and a few showers towards the end of the month. Daytime temperature at the Hong Kong Observatory soared to 32.1 degrees on 30 May, the highest of the month.

Radar echoes during rainstorm episodes affecting Hong Kong in May 2016
Radar echoes during rainstorm episodes affecting Hong Kong in May 2016


Rainfall Map For 10 May 2016
Rainfall Map for 10 May 2016 (isohyets are in millimetres)

    One tropical cyclone 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 1.5.  Monthly meteorological figures and departures from normal for May are tabulated in Table 2.
 

Warnings and Signals issued in May 2016

Table 1.1   Tropical Cyclone Warning Signals
Name of
Tropical Cyclone
Signal
Number
Beginning Time Ending Time
Day/Month HKT Day/Month HKT
no name 1 26 / 5 2140 27 / 5 0540
3 27 / 5 0540 27 / 5 1340
1 27 / 5 1340 27 / 5 2250


Table 1.2   Rainstorm Warning Signals
Colour Beginning Time Ending Time
Day/Month HKT Day/Month HKT
Amber 3 / 5 1810 3 / 5 2055
Amber 10 / 5 0600 10 / 5 0735
Red 10 / 5 0735 10 / 5 0935
Amber 10 / 5 0935 10 / 5 1120
Red 10 / 5 1120 10 / 5 1345
Amber 10 / 5 1345 10 / 5 1445
Amber 21 / 5 0155 21 / 5 0615
Amber 28 / 5 1635 28 / 5 1840


Table 1.3   Thunderstorm Warning
Beginning Time Ending Time
Day/Month HKT Day/Month HKT
3 / 5 1505 3 / 5 2200
4 / 5 1210 4 / 5 1330
6 / 5 2107 6 / 5 2230
10 / 5 0540 10 / 5 1345
12 / 5 1710 12 / 5 1815
15 / 5 1820 15 / 5 2200
20 / 5 1130 21 / 5 0700
28 / 5 1315 28 / 5 1930
29 / 5 0230 29 / 5 0330
30 / 5 1000 30 / 5 1100


Table 1.4   Very Hot Weather Warning
Beginning Time Ending Time
Day/Month HKT Day/Month HKT
31 / 5 1145 4 / 6 1450


Table 1.5   Special Announcement on Flooding
in the Northern New Territories
Beginning Time Ending Time
Day/Month HKT Day/Month HKT
10 / 5 0705 10 / 5 1300
21 / 5 0510 21 / 5 0740


Table 2   Figures and Departures from Normal - May 2016
Meteorological Element Figure of the Month Departure from Normal*
Mean Daily Maximum Air Temperature 29.1 degrees C 0.7 degree above normal
Mean Air Temperature 26.7 degrees C 0.8 degree above normal
Mean Daily Minimum Air Temperature 24.9 degrees C 0.8 degree above normal
Mean Dew Point Temperature 23.6 degrees C 1.0 degree above normal
Mean Relative Humidity 83 % normal
Mean Cloud Amount 78 % 2 % above normal
Total Rainfall 233.6 mm 71.1 mm below normal
Number of hours of Reduced VisibilityΔ 10 hours 37.3 hours below normal§
Total Bright Sunshine Duration 122.2 hours 18.2 hours below normal
Mean Daily Global Solar Radiation 14.78 Megajoule / square metre 0.59 Megajoule above normal
Total Evaporation 105.0& mm 5.7 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 May 2016

The percentile map of mean temperature of May 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