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The Weather of December 2008

    December 2008 was warmer and drier than usual. The monthly mean temperature of 18.4 degrees was 0.6 degrees above normal. The monthly total rainfall of 9.0 millimetres was 25.5 millimetres below normal. The annual rainfall for 2008 was 3066.2 millimetres, about 29 percent above the normal figure of 2382.7 millimetres.

    Under the influence of a ridge of high pressure over southern China, the weather in Hong Kong was fine and dry for the first two days of the month. An easterly airstream brought a few rain patches to the territory on 3 December.

    It was cloudy with some sunny intervals during the day on 4 December. A cold front moved across the south China coastal areas that evening, bringing a few rain patches to Hong Kong at night. The winter monsoon behind the cold front brought rather cool and very dry weather to Hong Kong for the ensuing seven days. Affected by an easterly airstream, it was mainly cloudy with low visibility on 12 December. It was warm with some sunny intervals on 13 December.

    A dry northeast monsoon reached the south China coastal areas on the morning of 14 December and brought fine and dry conditions to the territory from 14 to 21 December. Under the influence of an intense winter monsoon, the weather became cold on 22 and 23 December. The temperature recorded at the Hong Kong Observatory fell to 11.5 degrees on the morning of 23 December, the lowest of the month. It was mainly fine and dry on 24 and 25 December.

    Affected by a broad cloud band over southern China, the weather became cloudy on 26 December. There were a few rain patches from 27 to 29 December. A cold front crossed the coastal areas of Guangdong in the afternoon of 29 December. The weather in Hong Kong turned cool and rainy for the rest of the month.

    One tropical cyclone 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 1.3.  Monthly meteorological figures and departures from normal for December are tabulated in Table 2.


 

Warnings and Signals issued in December 2008


Table 1.1   Strong Monsoon Signal

Beginning Time Ending Time
Day/Month HKT Day/Month HKT
5 / 12 0215 5 / 12 1030
26 / 12 0445 26 / 12 1345


Table 1.2   Fire Danger Warnings

Colour Beginning Time Ending Time
Day/Month HKT Day/Month HKT
Red 24 / 11 0600 3 / 12 0600
Red 5 / 12 0600 12 / 12 0600
Yellow 12 / 12 0600 12 / 12 1800
Yellow 13 / 12 0600 13 / 12 1215
Red 13 / 12 1215 16 / 12 0600
Yellow 16 / 12 0600 16 / 12 1245
Red 16 / 12 1245 17 / 12 0600
Yellow 17 / 12 0600 18 / 12 1140
Red 18 / 12 1140 18 / 12 1800
Yellow 18 / 12 1800 21 / 12 0600
Red 21 / 12 0600 25 / 12 1800
Yellow 25 / 12 1800 27 / 12 0600
Yellow 28 / 12 0600 28 / 12 1345
Yellow 31 / 12 1800 1 / 1 0600


Table 1.3   Cold Weather Warning

Beginning Time Ending Time
Day/Month HKT Day/Month HKT
5 / 12 1620 6 / 12 0800
22 / 12 1620 24 / 12 0600
30 / 12 1620 3 / 1 1045


Table 2   Figures and Departures from Normal - December 2008

Meteorological Element Figure of the Month Departure from Normal*
Mean Daily Maximum Air Temperature 21.0 degrees C 0.7 degree above normal
Mean Air Temperature 18.4 degrees C 0.6 degree above normal
Mean Daily Minimum Air Temperature 16.2 degrees C 0.5 degree above normal
Mean Dew Point Temperature 11.1 degrees C 0.5 degree below normal
Mean Relative Humidity 63 % 6 % below normal
Mean Cloud Amount 50 % 1 % below normal
Total Rainfall 9.0 mm 25.5 mm below normal
Number of hours of Reduced VisibilityΔ 283 hours 35.4 hours above normal§
Total Bright Sunshine Duration 188.5 hours 15.2 hours above normal
Mean Daily Global Solar Radiation 12.22 Megajoule / square metre 1.09 Megajoule above normal
Total Evaporation 89.5 mm 5.0 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.


  *   Departure from 1971 - 2000 climatological normal, except for number of hours of reduced visibility

  §   Departure from mean value between 1997 and 2007
daily values of selected meteorological elements for HK for December 2008

Extract of Meteorological Observations in Hong Kong for December 2008