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  • The Weather of August 2018

  • 4 September 2018

    Affected by the outer rainbands of tropical cyclone Bebinca in mid-August and the heavy showers associated with an active trough of low pressure towards the end of the month, the weather in Hong Kong was wetter and much gloomier than usual in August 2018. The mean amount of cloud in the month was 84 percent, 15 percent above the normal of 69 percent and one of the highest on record for August. The duration of bright sunshine in the month was only 116.2 hours, about 38 percent lower than the normal figure of 188.9 hours and the lowest on record for August. The monthly rainfall was 615.1 millimetres, about 42 percent above the normal of 432.2 millimetres in August. The accumulated rainfall recorded in the first eight months of the year was 1590.0 millimetres, a deficit of 17 percent compared to the normal of 1905.5 millimetres for the same period.

    Under the influence of an anticyclone aloft southern China, the weather in Hong Kong was marked by a mixture of sunshine and showers on 1 - 9 August. With plenty of sunshine in the morning, it was very hot with the temperature at the Hong Kong Observatory soaring to 34.2 degrees around noon on 7 August, the highest in the month. The high temperatures then triggered heavy thundery showers over the western part of Hong Kong in that afternoon, bringing more than 30 millimetres of rainfall to the western part of the New Territories and over 100 millimetres to the southwestern part of Lantau Island.

    Meanwhile, a broad area of low pressure over the northern part of the South China Sea intensified into a tropical depression on 9 August and was later named as Bebinca. It moved slowly northward and made landfall near Yangjiang around noon on 11 August. Bebinca then made an anti-clockwise loop over the coastal region of western Guangdong and moved back to the coastal waters that night. After drifting southeastwards on 12 August, Bebinca intensified into a tropical storm and looped slowly in anti-clockwise direction off the coast of western Guangdong on 13 and 14 August. Bebinca picked up speed to move west-southwestwards and intensified into a severe tropical storm on 15 August. It moved across Beibu Wan the next day. Bebinca made landfall over the northern part of Vietnam and weakened into an area of low pressure inland on 17 August. The outer rainbands associated with Bebinca brought occasional heavy squally showers and thunderstorms to Hong Kong on 10 - 16 August with more than 150 millimetres of rainfall generally recorded over the territory during this period.

    Affected by a south to southwesterly airstream, the weather in Hong Kong was mainly cloudy with occasional showers and thunderstorms on 17 - 19 August. The showers were heavier on 19 August with more than 70 millimetres of rainfall recorded over Tsuen Wan, Kwai Tsing and Lantau Island. A broad trough of low pressure over the south China coast continued to bring showery weather to Hong Kong on 20 - 21 August.

    A low pressure area over the northeastern part of the South China Sea moved slowly northeastwards on 22 August. It then developed into a tropical depression on 23 August near Taiwan and edged northwards slowly along the western coast of Taiwan. The tropical depression turned west-northwest on 24 August and made landfall over Fujian on 25 August. Locally, under light wind condition, it was hot with sunny periods on 22 August. Convective activities triggered by high temperatures also brought heavy showers and thunderstorms to Hong Kong on that evening. Occasional showers and squally thunderstorms still affected the territory on 23 August, the temperature at the Hong Kong Observatory fell to the lowest in the month of 24.6 degrees in rain that night.

    Apart from one or two showers, the weather of Hong Kong was generally fine on 24 - 25 August. Under light winds condition, there were some haze during the day. Affected by a broad area of low pressure along the coast of Guangdong, local weather started to deteriorate with heavy showers in the evening of 26 August. The heavy rain around midnight of 26 August brought more than 100 millimetres of rainfall to parts of the Lantau Island and Hong Kong Island. An active trough of low pressure continued to bring occasional heavy showers and squally thunderstorms to Hong Kong for the rest of the month. Rain was particularly heavy in the New Territories on 29 August, necessitating the issuance of the Red Rainstorm Warning, Landslip Warning and Special Announcement on Flooding in the Northern New Territories. More than 100 millimetres of rainfall were recorded over most parts of the New Territories, and rainfall even exceeded 200 millimetres over Tuen Mun, Yuen Long, Tai Po and North District. There were serious flooding over many places in the New Territories and landslides in Fanling, resulting in significant disruption of traffic. A waterspout was also reported near Ting Kau on the morning of 29 August.


A waterspout reported near Ting Kau on the morning of 29 August 2018
A waterspout reported near Ting Kau on the morning of 29 August 2018


     Eleven 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 1.6.  Monthly meteorological figures and departures from normal for August are tabulated in Table 2.
 

Warnings and Signals issued in August 2018

Table 1.1   Tropical Cyclone Warning Signals
Name of
Tropical Cyclone
Signal
Number
Beginning Time Ending Time
Day/Month HKT Day/Month HKT
BEBINCA 1 9 / 8 1715 14 / 8 0520
3 14 / 8 0520 15 / 8 0220
1 15 / 8 0220 15 / 8 0520


Table 1.2   Rainstorm Warning Signals
Colour Beginning Time Ending Time
Day/Month HKT Day/Month HKT
Amber 10 / 8 1615 10 / 8 1850
Amber 11 / 8 0715 11 / 8 1205
Amber 12 / 8 0515 12 / 8 0645
Amber 17 / 8 1020 17 / 8 1125
Amber 19 / 8 0625 19 / 8 0915
Amber 20 / 8 0510 20 / 8 0745
Amber 22 / 8 1810 22 / 8 1945
Amber 26 / 8 2215 26 / 8 2305
Red 26 / 8 2305 27 / 8 0045
Amber 27 / 8 0045 27 / 8 0145
Amber 27 / 8 2110 28 / 8 0220
Amber 28 / 8 1320 28 / 8 1445
Amber 29 / 8 1410 29 / 8 1840
Red 29 / 8 1840 29 / 8 2150
Amber 29 / 8 2150 29 / 8 2230


Table 1.3   Landslip Warning
Beginning Time Ending Time
Day/Month HKT Day/Month HKT
29 / 8 1800 30 / 8 1800


Table 1.4   Thunderstorm Warning
Beginning Time Ending Time
Day/Month HKT Day/Month HKT
1 / 8 0937 1 / 8 1230
2 / 8 0500 2 / 8 0700
2 / 8 0720 2 / 8 0830
3 / 8 1025 3 / 8 1330
3 / 8 1855 3 / 8 2025
4 / 8 0620 4 / 8 0945
4 / 8 1650 4 / 8 1800
5 / 8 0625 5 / 8 0830
5 / 8 1210 5 / 8 1400
5 / 8 1446 5 / 8 1700
6 / 8 0935 6 / 8 1100
6 / 8 1235 6 / 8 1600
7 / 8 0424 7 / 8 0730
7 / 8 1045 7 / 8 1430
8 / 8 0240 8 / 8 0520
10 / 8 0410 10 / 8 0710
10 / 8 1245 10 / 8 1445
10 / 8 1530 10 / 8 2400
11 / 8 0515 11 / 8 1700
12 / 8 0140 12 / 8 1000
12 / 8 1023 12 / 8 1730
14 / 8 0145 14 / 8 0830
14 / 8 0925 14 / 8 1230
14 / 8 1345 14 / 8 1700
16 / 8 1725 16 / 8 1900
17 / 8 0045 17 / 8 0245
17 / 8 0330 17 / 8 0430
17 / 8 0720 17 / 8 1445
17 / 8 2335 18 / 8 0500
18 / 8 0515 18 / 8 0900
19 / 8 0405 19 / 8 1045
19 / 8 1745 19 / 8 2000
20 / 8 0135 20 / 8 0900
20 / 8 1710 20 / 8 2400
21 / 8 1225 21 / 8 1800
22 / 8 1230 22 / 8 1345
22 / 8 1625 22 / 8 2100
22 / 8 2210 23 / 8 0030
23 / 8 1015 23 / 8 1130
23 / 8 1915 23 / 8 2345
26 / 8 0305 26 / 8 0445
26 / 8 2018 27 / 8 0400
27 / 8 2040 28 / 8 0400
28 / 8 1145 28 / 8 1900
29 / 8 0325 29 / 8 0530
29 / 8 0805 29 / 8 1000
29 / 8 1105 30 / 8 1400
31 / 8 0315 31 / 8 1030
31 / 8 1453 31 / 8 2315


Table 1.5   Very Hot Weather Warning
Beginning Time Ending Time
Day/Month HKT Day/Month HKT
27 / 7 0645 2 / 8 1700
3 / 8 0830 9 / 8 1920
25 / 8 1145 25 / 8 1900


Table 1.6   Special Announcement on Flooding
in the Northern New Territories
Beginning Time Ending Time
Day/Month HKT Day/Month HKT
22 / 8 1845 22 / 8 2130
28 / 8 1425 28 / 8 1635
29 / 8 1600 30 / 8 0645


Table 2   Figures and Departures from Normal - August 2018
Meteorological Element Figure of the Month Departure from Normal*
Mean Daily Maximum Air Temperature 31.0 degrees C 0.1 degree below normal
Mean Air Temperature 28.6 degrees C normal
Mean Daily Minimum Air Temperature 26.7 degrees C 0.1 degree above normal
Mean Dew Point Temperature 25.5 degrees C 0.5 degree above normal
Mean Relative Humidity 84 % 3 % above normal
Mean Cloud Amount 84 % 15 % above normal
Total Rainfall 615.1 mm 182.9 mm above normal
Number of hours of Reduced VisibilityΔ 35 hours 11.5 hours below normal§
Total Bright Sunshine Duration 116.2 hours 72.7 hours below normal
Mean Daily Global Solar Radiation 13.03 Megajoule / square metre 2.6 Megajoule below normal
Total Evaporation 99.1 mm 35.8 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 2017

daily values of selected meteorological elements for HK for August 2018

The percentile map of mean temperature of August 2018

  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 August 2018 (isohyets are in millimetres)