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The Weather of November 2009

    November 2009 was cooler than usual.  The mean temperature of the month was 20.5 degrees, 0.9 degrees below the normal of 21.4 degrees.  The first cold day with daily minimum temperature of 12.0 degrees or below occurred on 17 November and was the earliest for winter since 1981.  The total rainfall of 60.4 millimetres in the month was about 72 percent above the normal of 35.1 millimetres.  The accumulated rainfall since 1 January was 2132.1 millimetres, about 9 percent below the normal figure of 2348.2 millimetres for the same period. 

    The month started with a fine and hot day.  A cold front over northern Guangdong moved across the south China coastal areas in that evening.  Under the influence of an intense northeast monsoon behind the cold front, local weather was windy, dry and cooler with minimum temperatures falling below 20 degrees from 2 to 4 November.  As the northeast monsoon weakened, it became warmer with sunny periods for the ensuing three days.  

    With a warm maritime airstream dominating over the south China coastal areas, local weather turned mainly cloudy with a few light rain patches from 8 to 11 November.  Meanwhile, another cold front had formed over southern China and moved across Hong Kong late on 12 November, bringing occasional rain.  The northeast monsoon behind the cold front brought noticeably cooler weather with some rain to the territory for the next three days.  

    An intense surge of northeast monsoon reached the south China coastal areas on 16 November.  Locally, it was rainy in the morning and the temperature started to fall significantly during the day.  Winds strengthened on 17 November and the weather became cold.  The temperature recorded at the Hong Kong Observatory fell to a minimum of 9.7 degrees on 18 November, the lowest of the month.    With the northeast monsoon persisting over the south China coast, local weather remained rather cold and dry for the following three days.  

   With moderation of the northeast monsoon, temperatures started to rise gradually on 22 November.  It remained mainly fine from 23 to 28 November.  A weak replenishment of the northeast monsoon reached the south China Coastal areas on 29 November and brought slightly cooler weather to Hong Kong for the last two days of the month.

    Six tropical cyclones occurred over 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 November are tabulated in Table 2.

 

Warnings and Signals issued in November 2009


Table 1.1   Strong Monsoon Signal

Beginning Time Ending Time
Day/Month HKT Day/Month HKT
2 / 11 0610 2 / 11 1145
2 / 11 1720 3 / 11 0840
11 / 11 2130 12 / 11 0715
13 / 11 0000 13 / 11 0935
13 / 11 1230 13 / 11 1615
15 / 11 1945 16 / 11 0145
16 / 11 1910 18 / 11 0445
20 / 11 1230 21 / 11 0945


Table 1.2   Fire Danger Warnings

Colour Beginning Time Ending Time
Day/Month HKT Day/Month HKT
Yellow 31 / 10 0600 1 / 11 1800
Red 1 / 11 1800 5 / 11 0600
Yellow 8 / 11 0600 8 / 11 1800
Yellow 14 / 11 0600 14 / 11 1800
Yellow 21 / 11 0600 22 / 11 1130
Red 22 / 11 1130 23 / 11 1215
Yellow 28 / 11 0610 30 / 11 0600


Table 1.3   Cold Weather Warning

Beginning Time Ending Time
Day/Month HKT Day/Month HKT
16 / 11 1620 19 / 11 1130
20 / 11 1615 21 / 11 1145


Table 2   Figures and Departures from Normal - November 2009

Meteorological Element Figure of the Month Departure from Normal*
Mean Daily Maximum Air Temperature 23.2 degrees C 0.8 degree below normal
Mean Air Temperature 20.5 degrees C 0.9 degree below normal
Mean Daily Minimum Air Temperature 18.3 degrees C 1.1 degrees below normal
Mean Dew Point Temperature 15.1 degrees C 0.2 degree below normal
Mean Relative Humidity 72 % 2 % above normal
Mean Cloud Amount 61 % 8 % above normal
Total Rainfall 60.4 mm 25.3 mm above normal
Number of hours of Reduced VisibilityΔ 141 hours 12.0 hours below normal§
Total Bright Sunshine Duration 171.4 hours 6.8 hours below normal
Mean Daily Global Solar Radiation 12.75 Megajoule / square metre 0.11 Megajoule above normal
Total Evaporation 97.6 mm 14.9 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 2008

daily values of selected meteorological elements for HK for November 2009

Extract of Meteorological Observations in Hong Kong for November 2009