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The Weather of August 2007

    August 2007 was cloudier and wetter than usual. The monthly mean cloud amount of 74 percent was 8 percent higher than the normal figure. The total bright sunshine duration was only 134.3 hours, the second lowest for August. The monthly rainfall of 488.4 millimetres was about 25 percent above the normal figure of 391.4 millimetres. The accumulated rainfall since the beginning of the year was 1533.3 millimetres, about 10 percent below the normal of 1707.4 millimetres for the same period.

    It was fine and very hot on the first four days of the month. With plenty of sunshine, temperature rose to 35.3 degrees on 3 August, the highest of the month.

    The outer rainband of the tropical storm over the central part of the South China Sea brought scattered showers and thunderstorms to the territory on 5 and 6 August. There were heavy showers on 6 August. Over 70 millimetres of rainfall was generally recorded in Kowloon and the Hong Kong Island. It was partly sunny with showers on 7 August.

    With the approach of Severe Tropical Storm Pabuk from the east, local weather turned cloudy with rain later on 8 August. While weakened into a tropical depression, Pabuk skirted the seas south of Hong Kong on the morning of 9 August, bringing strong winds and heavy showers to the territory. Local winds subsided that afternoon when Pabuk moved west away from Hong Kong. After changing its course, Pabuk accelerated towards Hong Kong and intensified into a tropical storm on the morning of 10 August. In that afternoon, Pabuk moved across the western part of Hong Kong. Locally, it was overcast with squally heavy showers on 10 August. Gale winds affected the western part of Hong Kong and offshore waters during the afternoon and evening.

    An active southwest monsoon set in after the dissipation of Pabuk on the morning of 11 August. It was showery on 11 August and the next two days. A trough of low pressure over the south China coast brought occasional heavy rain to Hong Kong between 14 and 16 August. The weather improved gradually on 17 August when the trough of low pressure dissipated. Apart from a few isolated showers, it was mainly fine but hazy on 18 and 19 August.

    Showery weather returned on 20 August when the south China coast came under the influence of a fresh southwesterly airstream. The weather stayed cloudy with some showers in the ensuing three days. The southwesterly airstream gave way to an easterly airstream on 24 August. There were sunny periods and a few showers from 25 to 28 August. A weak ridge of high pressure over southeastern China brought fine and clear weather to Hong Kong between 29 and 31 August.

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


 

Warnings and Signals issued in August 2007


Table 1.1   Tropical Cyclone Warning Signals

Name of
Tropical Cyclone		 Signal
Number		 Beginning Time Ending Time
Day/Month HKT Day/Month HKT
PABUK 1 8 / 8 0540 9 / 8 0240
3 9 / 8 0240 9 / 8 1115
1 10 / 8 0750 10 / 8 1240
3 10 / 8 1240 10 / 8 1430
8 SW 10 / 8 1430 10 / 8 2140
3 10 / 8 2140 11 / 8 0140
1 11 / 8 0140 11 / 8 0830


Table 1.2   Strong Monsoon Signal

Beginning Time Ending Time
Day/Month HKT Day/Month HKT
17 / 8 0515 17 / 8 0845
20 / 8 0415 20 / 8 1030


Table 1.3   Rainstorm Warning Signals

Colour Beginning Time Ending Time
Day/Month HKT Day/Month HKT
Amber 6 / 8 0355 6 / 8 0530
Amber 22 / 8 1000 22 / 8 1100


Table 1.4   Thunderstorm Warning

Beginning Time Ending Time
Day/Month HKT Day/Month HKT
1 / 8 1235 1 / 8 1545
4 / 8 1320 4 / 8 1430
5 / 8 1015 5 / 8 1615
5 / 8 1730 5 / 8 1930
6 / 8 0220 6 / 8 0600
6 / 8 0710 6 / 8 2330
7 / 8 0830 7 / 8 1130
8 / 8 1630 8 / 8 1850
12 / 8 1040 12 / 8 1130
13 / 8 1120 13 / 8 1300
14 / 8 1145 14 / 8 1600
14 / 8 1910 14 / 8 2115
14 / 8 2210 15 / 8 0130
15 / 8 1615 15 / 8 2115
18 / 8 1930 18 / 8 2130
20 / 8 0500 20 / 8 1030
20 / 8 1800 20 / 8 2100
22 / 8 0220 22 / 8 1200
22 / 8 1525 22 / 8 1800
22 / 8 1930 22 / 8 2130
23 / 8 0805 23 / 8 0930
23 / 8 1130 23 / 8 1330
24 / 8 0215 24 / 8 0615
25 / 8 1312 25 / 8 1715
25 / 8 1830 25 / 8 2030
25 / 8 2050 25 / 8 2300
26 / 8 1515 26 / 8 1715
27 / 8 0730 27 / 8 0830
27 / 8 1845 27 / 8 2145
28 / 8 2122 29 / 8 0330
29 / 8 1250 29 / 8 1600
30 / 8 1135 30 / 8 1345
30 / 8 1500 30 / 8 1800
31 / 8 1333 31 / 8 1545


Table 1.5   Very Hot Weather Warning

Beginning Time Ending Time
Day/Month HKT Day/Month HKT
24 / 7 1420 5 / 8 1230
18 / 8 1530 18 / 8 2145


Table 2   Figures and Departures from Normal - August 2007

Meteorological Element Figure of the Month Departure from Normal*
Mean Daily Maximum Air Temperature 30.7 degrees C 0.6 degree below normal
Mean Air Temperature 28.0 degrees C 0.4 degree below normal
Mean Daily Minimum Air Temperature 26.1 degrees C 0.2 degree below normal
Mean Dew Point Temperature 24.9 degrees C 0.1 degree above normal
Mean Relative Humidity 84 % 3 % above normal
Mean Cloud Amount 74 % 8 % above normal
Total Rainfall 488.4 mm 97.0 mm above normal
Number of hours of Reduced VisibilityΔ 81 hours 19.4 hours above normal§
Total Bright Sunshine Duration 134.3 hours 72.7 hours below normal
Mean Daily Global Solar Radiation 13.51 Megajoule / square metre 4.10 Megajoule below normal
Total Evaporation 107.9 mm 49.0 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.


 

The calibration factors of the pyranometer at King's Park in 2006 and 2007 have been re-computed based on the results of a regional instrument comparison in Asia in 2007. The readings of total global solar radiation at King's Park in 2006 and 2007 displayed in this web page before 13 June 2008 have been revised on 13 June 2008 using the new calibration factors.

  *   Departure from 1961-1990 climatological normal, except for number of hours of reduced visibility.
  §   Departure from mean value between 1997 and 2006.


daily values of selected meteorological elements for HK for August 2007

Extract of Meteorological Observations in Hong Kong for August 2007