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The Weather of January 2010

     On the whole, the first month of 2010 was milder than usual.  The first half of January was cooler than normal while the weather became significantly milder than usual in the second half, resulting in a mean temperature of 16.8 degrees for the whole month which was 0.7 degrees above normal.  There were only four cold days (daily minimum temperature at 12.0 degrees or below) in the month, the least for January since 2001.  The month was also cloudier than normal.  The mean cloud amount for the month was 73 percent, about 13 percent above normal.  The total bright sunshine duration was 108.7 hours, about 23 percent below the normal figure of 141.7 hours.  

     Under the influence of an easterly airstream, it was generally cloudy with a few light rain patches for the first three days of the month.  A ridge of high pressure established over southeastern China and brought sunny periods to Hong Kong on 4 January. 

     An easterly airstream affected the coast of Guangdong and brought cloudy and cooler conditions to the territory on 5 January.  A cold front crossed the coastal areas of Guangdong on 6 January, bringing a few rain patches and a significant drop in temperature during the day over the territory.  The weather remained cloudy and cold for the next two days.  With moderation of the winter monsoon, the temperatures rose gradually and there were sunny periods on 9 and 10 January. 

     The winter monsoon over the south China coastal areas strengthened on 11 January.  Local weather turned overcast with rain and temperatures dropped gradually that day.  Clouds started to thin the next morning but cold weather persisted over the territory on 12 and 13 January.  The temperatures recorded at the Hong Kong Observatory fell to a minimum of 9.8 degrees on 13 January, the lowest of the month.  The weather remained fine and dry for the ensuing five days.

     A mild easterly airstream affecting the coastal areas of Guangdong brought mild weather with some sunny periods for Hong Kong from 19 to 21 January. Meanwhile, a cold front over southern China moved southward gradually on 21 January and crossed the coastal areas of Guangdong the next morning.  The northeast monsoon behind the cold front brought cooler weather with some light rain patches to Hong Kong from 22 to 24 January.  Weather improved the next day with some sunny intervals. 

     A humid maritime airstream over the coastal areas of Guangdong brought cloudy and misty weather with some light rain patches to the territory from 26 to 28 January.  Affected by a fresh easterly airstream, it was slightly cooler on 29 January.  With moderation of the easterly winds, local weather became mainly fine apart from some mist patches on 30 January.  With abundant sunshine, the temperature rose to 24.5 degrees on the last day of the month, the highest of the month.

     There was no tropical cyclone 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 1.3.  Monthly meteorological figures and departures from normal for January are tabulated in Table 2.

Warnings and Signals issued in January 2010


Table 1.1   Strong Monsoon Signal

Beginning Time Ending Time
Day/Month HKT Day/Month HKT
5 / 1 0845 6 / 1 0745
12 / 1 0610 12 / 1 1130


Table 1.2   Fire Danger Warnings

Colour Beginning Time Ending Time
Day/Month HKT Day/Month HKT
Yellow 1 / 1 0600 1 / 1 2315
Yellow 10 / 1 0600 10 / 1 1800
Yellow 12 / 1 0600 13 / 1 0600
Red 13 / 1 0600 14 / 1 0600
Yellow 14 / 1 0600 15 / 1 0600
Red 15 / 1 1245 17 / 1 0600
Yellow 17 / 1 0600 17 / 1 1800


Table 1.3   Cold Weather Warning

Beginning Time Ending Time
Day/Month HKT Day/Month HKT
6 / 1 1620 8 / 1 1200
11 / 1 1145 14 / 1 0920


Table 2   Figures and Departures from Normal - January 2010

Meteorological Element Figure of the Month Departure from Normal*
Mean Daily Maximum Air Temperature 19.0 degrees C 0.4 degree above normal
Mean Air Temperature 16.8 degrees C 0.7 degree above normal
Mean Daily Minimum Air Temperature 15.2 degrees C 1.1 degrees above normal
Mean Dew Point Temperature 13.3 degrees C 2.3 degrees above normal
Mean Relative Humidity 80 % 7 % above normal
Mean Cloud Amount 73 % 13 % above normal
Total Rainfall 24.6 mm 0.3 mm below normal
Number of hours of Reduced VisibilityΔ 239 hours 0.1 hour above normal§
Total Bright Sunshine Duration 108.7 hours 33.0 hours below normal
Mean Daily Global Solar Radiation 9.25 Megajoule / square metre 1.30 Megajoule below normal
Total Evaporation 58.2 mm 22.5 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 2009

daily values of selected meteorological elements for HK for January 2010

Extract of Meteorological Observations in Hong Kong for January 2010