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  • The Weather of August 2019

  • 3 September 2019

    August 2019 was hotter than usual in Hong Kong, mainly attributing to the warmer than normal sea surface temperature over the northern part of the South China Sea. The monthly mean temperature of 29.0 degrees was 0.4 degree above the normal figure of 28.6 degrees. Moreover, the summer of this year from June to August was exceptionally hot. The mean minimum temperature of 27.2 degrees, mean temperature of 29.2 degrees and mean maximum temperature of 31.8 degrees were respectively the second, third and fourth highest on record for the same period. Due to the heavy rain brought by tropical cyclones Wipha and Bailu, the month was wetter than normal with the monthly total rainfall amounting to 596.4 millimetres, about 38 percent above the normal figure of 432.2 millimetres. The accumulated rainfall recorded in the first eight months of the year was 2034.3 millimetres, a surplus of 7 percent compared to the normal of 1905.5 millimetres for the same period.

    After making an anti-clockwise loop around the northeastern coast of Hainan Island on the early morning of 1 August, Tropical Storm Wipha tracked northwards in the morning and then moved westwards across the Leizhou Peninsula that night. Wipha moved across the coast of Guangxi and the vicinity of Beibu Wan on 2 August and weakened gradually. It made landfall over the coast of Guangxi and further weakened into an area of low pressure over the northern part of Vietnam on 3 August.

    Under the influence of Wipha, it was windy with occasional gale force winds offshore and on high ground at first on 1 August in Hong Kong. Heavy squally showers and thunderstorms associated with the rainbands of Wipha also brought more than 100 millimetres of rainfall to most parts of the territory on 1 - 2 August and rainfall even exceeded 150 millimetres over parts of Lantau Island in these two days.

    Affected by upper-air disturbances, the weather of Hong Kong remained showery on 3 August. With the departure of the upper-air disturbances, showers abated gradually with sunny intervals on the next day. Dominated by an anticyclone aloft, the weather became generally fine and very hot on 5 August. A broad area of low pressure over the central part of the South China Sea brought some showers and isolated thunderstorms to the territory on 6 August.

    Over the western North Pacific, Super Typhoon Lekima moved northwestward across the sea areas to the east of Taiwan on 7 - 9 August and made landfall over eastern China on 10 August. Under the influence of the outer subsiding air of Lekima, the weather of Hong Kong was very hot with haze on 7 - 9 August. The high temperature also triggered thundery showers on the night of 8 August. With plenty of sunshine, the maximum temperature at the Observatory soared to 35.1 degrees on 9 August, the highest of the month.

    With the prevalence of a southwesterly airstream, it was hot with a mixture of sunshine and thundery showers in Hong Kong on 10 - 18 August. The showers were particularly heavy on 14 August and 17 August with more than 30 millimetres of rainfall generally recorded over Hong Kong on both of these two days. Under the influence of a trough of low pressure lingering over the northern part of the South China Sea, there were sunny periods and some showers in Hong Kong on 19 - 20 August. With the departure and weakening of the trough of low pressure, local weather became generally fine and very hot apart from isolated showers on 21 - 22 August. Under light wind conditions, it was mainly cloudy with isolated heavy showers and thunderstorms on 23 August.

    Meanwhile, an area of low pressure to the east of the Philippines intensified into a tropical depression and was named Bailu on 21 August. Bailu further intensified in and severe tropical storm on 22 August and moved generally northwestward across the western North Pacific. It skirted past the southern tip of Taiwan and entered the Taiwan Strait on 24 August. Bailu made landfall over the coast of southeastern China on 25 August and weakened progressively into an area of low pressure over inland Guangdong.

    Affected by the outer subsiding air of Bailu, it was generally fine and very hot with haze in Hong Kong on 24 August. Lashed by the outer rainbands associated with Bailu, there were occasional heavy squally showers and thunderstorms in Hong Kong on 25 – 26 August. More than 150 millimetres of rainfall were recorded over many places, and rainfall even exceeded 200 millimetres in the urban areas and parts of New Territories in these two days. During the incessant downpour on the early morning of 26 August, the temperature at the Observatory dropped to a minimum of 22.9 degrees, the lowest of the month.

    With the strengthening of an anticyclone aloft southeastern China, the showers eased off gradually on 27 August and the weather became mainly fine and very hot on 28 August. Meanwhile, an area of low pressure developed into a tropical cyclone over the seas east to the Philippines on 27 August and was named Podul. It moved generally westward and entered the South China Sea on 28 August. With Podul moving across the central part of the South China Sea towards the vicinity of the southern part of Hainan Island, local weather turned mainly cloudy and windier with a few showers and thunderstorms on 29 August. Under the influence of the outer rainbands associated with Podul, local weather was unsettled with occasional showers and thunderstorms on 30 August. A broad trough of low pressure over the south China coast continued to bring thundery showers to the territory on the last day of the month. Heavy showers in the morning brought more than 50 millimetres of rainfall to Sha Tin, Sai Kung and Tseung Kwan O.


     Six 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 1.5.  Monthly meteorological figures and departures from normal for August are tabulated in Table 2.
 

Warnings and Signals issued in August 2019

Table 1.1   Tropical Cyclone Warning Signals
Name of
Tropical Cyclone
Signal
Number
Beginning Time Ending Time
Day/Month HKT Day/Month HKT
WIPHA 3 31 / 7 2340 1 / 8 1920
1 1 / 8 1920 2 / 8 0840
BAILU 1 24 / 8 1440 25 / 8 1920
PODUL 1 28 / 8 1440 29 / 8 1220


Table 1.2   Rainstorm Warning Signals
Colour Beginning Time Ending Time
Day/Month HKT Day/Month HKT
Amber 1 / 8 0725 1 / 8 2100
Amber 2 / 8 0325 2 / 8 0440
Amber 14 / 8 0445 14 / 8 0610
Amber 17 / 8 1115 17 / 8 1230
Amber 25 / 8 0050 25 / 8 0240
Amber 25 / 8 1130 25 / 8 1445
Amber 25 / 8 2355 26 / 8 0040
Red 26 / 8 0040 26 / 8 0325
Amber 26 / 8 0325 26 / 8 0500


Table 1.3   Landslip Warning
Beginning Time Ending Time
Day/Month HKT Day/Month HKT
31 / 7 2040 2 / 8 0915
26 / 8 0250 26 / 8 2155


Table 1.4   Thunderstorm Warning
Beginning Time Ending Time
Day/Month HKT Day/Month HKT
1 / 8 0615 2 / 8 0530
2 / 8 0625 2 / 8 0930
3 / 8 0630 3 / 8 0945
6 / 8 1245 6 / 8 1445
8 / 8 2050 8 / 8 2300
10 / 8 0155 10 / 8 0500
10 / 8 1645 10 / 8 1825
11 / 8 0310 11 / 8 0515
12 / 8 0420 12 / 8 0630
12 / 8 1315 12 / 8 1430
12 / 8 1550 12 / 8 1900
14 / 8 0415 14 / 8 0615
14 / 8 1800 14 / 8 1915
15 / 8 0638 15 / 8 0730
15 / 8 1430 15 / 8 1550
16 / 8 0325 16 / 8 0645
16 / 8 1125 16 / 8 1730
16 / 8 1910 16 / 8 2015
16 / 8 2110 17 / 8 0100
17 / 8 0535 17 / 8 1400
17 / 8 1450 17 / 8 1700
18 / 8 1105 18 / 8 1830
19 / 8 1245 19 / 8 1345
19 / 8 1645 19 / 8 1945
23 / 8 0700 23 / 8 1430
23 / 8 1520 23 / 8 1700
24 / 8 2355 25 / 8 0245
25 / 8 1055 25 / 8 1500
25 / 8 2140 26 / 8 1530
27 / 8 0050 27 / 8 0200
29 / 8 0315 29 / 8 0730
29 / 8 1055 29 / 8 1630
30 / 8 0535 30 / 8 1030
31 / 8 0130 31 / 8 0600
31 / 8 1455 31 / 8 1945


Table 1.5   Very Hot Weather Warning
Beginning Time Ending Time
Day/Month HKT Day/Month HKT
5 / 8 1230 6 / 8 1325
7 / 8 1240 10 / 8 1620
11 / 8 0945 11 / 8 1800
12 / 8 0945 12 / 8 1800
13 / 8 0845 14 / 8 0440
14 / 8 1115 14 / 8 1800
15 / 8 1115 15 / 8 1800
16 / 8 0845 16 / 8 1620
21 / 8 1220 21 / 8 1800
22 / 8 0945 25 / 8 0040
28 / 8 0645 28 / 8 1900


Table 2   Figures and Departures from Normal - August 2019
Meteorological Element Figure of the Month Departure from Normal*
Mean Daily Maximum Air Temperature 31.9 degrees C 0.8 degree above normal
Mean Air Temperature 29.0 degrees C 0.4 degree above normal
Mean Daily Minimum Air Temperature 26.9 degrees C 0.3 degree above normal
Mean Dew Point Temperature 25.6 degrees C 0.6 degree above normal
Mean Relative Humidity 82 % 1 % above normal
Mean Cloud Amount 73 % 4 % above normal
Total Rainfall 596.4 mm 164.2 mm above normal
Number of hours of Reduced VisibilityΔ 10 hours 36.0 hours below normal§
Total Bright Sunshine Duration 178.6 hours 10.3 hours below normal
Mean Daily Global Solar Radiation 16.22 Megajoule / square metre 0.59 Megajoule above normal
Total Evaporation 109.5 mm 25.4 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 2018

daily values of selected meteorological elements for HK for August 2019

The percentile map of mean temperature of August 2019

  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


Extract of Meteorological Observations in Hong Kong for August 2019