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The Weather of August 2008

    Despite being affected by two tropical cyclones, August 2008 was drier than usual. The total rainfall of the month was 317.0 millimetres, 127.6 millimetres below normal. The accumulated rainfall since 1 January was 2699.1 millimetres, about 44 percent above the normal figure of 1873.7 millimetres for the same period. It was also sunny in August with 215.5 hours of sunshine, some 14 percent longer than normal. With long periods of sunshine, the monthly total global solar radiation in August was 564.48 megajoules per square meter, the second highest for August since record began.

    Under the influence of a ridge of high pressure over southeastern China, local weather was fine and hot for the first four days of the month. Severe Tropical Storm Kammuri formed over the northeastern part of the South China Sea on 4 August. With Kammuri edging west-northwestwards towards the coast of Guangdong, local weather started to deteriorate on the next day. Kammuri passed to the southwest of Hong Kong and made landfall over Yangxi County in western Guangdong on 6 August. Under the influence of Kammuri, the weather became windy and rainy on 6 August. Local winds generally reached strong to gale force and 74.1 millimetres of rainfall were recorded at the Hong Kong Observatory on that day. The remnant of Kammuri continued to bring rainy and thundery weather to the territory on 7 and 8 August.

    Local weather improved on 9 and 10 August with sunny periods during the day. A trough of low pressure over the northern part of the South China Sea brought scattered showers to Hong Kong on 11 August. The trough of low pressure dissipated and local weather turned mainly fine the next day. A ridge of high pressure over southern China brought sunny and hot weather to Hong Kong from 13 to 21 August. The temperature recorded at the Hong Kong Observatory rose to a maximum of 34.3 degree on 21 August, the highest of the month.

    Typhoon Nuri formed over the western North Pacific on 17 August and tracked west-northwestwards. Nuri entered the South China Sea on 21 August and moved northwestwards in the general direction of Hong Kong. It passed Hong Kong on 22 August and moved further inland Guangdong on 23 August. Under the influence of Nuri, the weather became windy and rainy on 22 August. Local winds generally reached strong to gale force and a total of 61.6 millimetres of rainfall were recorded at the Hong Kong Observatory on that day. The outer rainbands southeast of Nuri continued to bring showery weather to the territory on 23 August.

    A ridge of high pressure over southern China brought generally fine and hot weather to Hong Kong from 24 to 30 August. A southwesterly airstream brought cloudier weather on the last day of the month.

    Five tropical cyclones occurred in the western North Pacific and the South China Sea 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 August are tabulated in Table 2.


 

Warnings and Signals issued in August 2008


Table 1.1   Tropical Cyclone Warning Signals

Name of
Tropical Cyclone		 Signal
Number		 Beginning Time Ending Time
Day/Month HKT Day/Month HKT
KAMMURI 1 4 / 8 1015 5 / 8 1915
3 5 / 8 1915 6 / 8 0540
8 NE 6 / 8 0540 6 / 8 0840
8 SE 6 / 8 0840 6 / 8 1715
3 6 / 8 1715 7 / 8 0415
1 7 / 8 0415 7 / 8 0715
NURI 1 20 / 8 1815 21 / 8 2040
3 21 / 8 2040 22 / 8 0740
8 NW 22 / 8 0740 22 / 8 1340
9 22 / 8 1340 23 / 8 0040
8 SW 23 / 8 0040 23 / 8 0240
3 23 / 8 0240 23 / 8 0940
1 23 / 8 0940 23 / 8 1115


Table 1.2   Rainstorm Warning Signals

Colour Beginning Time Ending Time
Day/Month HKT Day/Month HKT
Amber 8 / 8 0715 8 / 8 0905


Table 1.3   Thunderstorm Warning

Beginning Time Ending Time
Day/Month HKT Day/Month HKT
4 / 8 1650 4 / 8 1900
6 / 8 1230 6 / 8 1530
7 / 8 2325 8 / 8 1000
8 / 8 1005 8 / 8 1130
12 / 8 1455 12 / 8 1530
21 / 8 1340 21 / 8 1545
21 / 8 1715 21 / 8 1815


Table 1.4   Very Hot Weather Warning

Beginning Time Ending Time
Day/Month HKT Day/Month HKT
3 / 8 1430 4 / 8 1800
18 / 8 1400 21 / 8 0745
21 / 8 1435 21 / 8 2015


Table 2   Figures and Departures from Normal - August 2008

Meteorological Element Figure of the Month Departure from Normal*
Mean Daily Maximum Air Temperature 31.3 degrees C 0.2 degree above normal
Mean Air Temperature 28.4 degrees C normal
Mean Daily Minimum Air Temperature 26.5 degrees C 0.1 degree above normal
Mean Dew Point Temperature 24.3 degrees C 0.6 degree below normal
Mean Relative Humidity 79 % 3 % below normal
Mean Cloud Amount 66 % 3 % below normal
Total Rainfall 317.0 mm 127.6 mm below normal
Number of hours of Reduced VisibilityΔ 6 hours 57.4 hours below normal§
Total Bright Sunshine Duration 215.5 hours 25.8 hours above normal
Mean Daily Global Solar Radiation 18.21 Megajoule / square metre 2.14 Megajoule above normal
Total Evaporation 140.7^ mm 2.5 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 1971 - 2000 climatological normal, except for number of hours of reduced visibility

  §   Departure from mean value between 1997 and 2007

  ^  Total for 30 days
daily values of selected meteorological elements for HK for August 2008

Extract of Meteorological Observations in Hong Kong for August 2008