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.
|Beginning Time||Ending Time|
|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|
|Colour||Beginning Time||Ending Time|
|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|
|Beginning Time||Ending Time|
|31 / 7||2040||2 / 8||0915|
|26 / 8||0250||26 / 8||2155|
|Beginning Time||Ending Time|
|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|
|Beginning Time||Ending Time|
|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|
|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.
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.
* Departure from 1981 - 2010 climatological normal, except for number of hours of reduced visibility
§ Departure from mean value between 1997 and 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