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A colder and drier December

     Due to the frequent replenishment of the winter monsoon, December 2011 was colder than usual with a monthly mean temperature of 16.9 degrees, 0.9 degrees below the normal figure of 17.8 degrees.  There were six cold days (daily minimum temperature at 12.0 degrees or below) in the month, about two days more than normal.  The prevalence of the continental airstream also brought drier than usual weather to the territory in December.  The total rainfall recorded in the month was 2.8 millimetres, less than a tenth of the monthly norm.  The annual rainfall for 2011 was 1476.7 millimetres, a deficit of about 38 per cent compared to the annual norm of 2382.7 millimetres.

     A cold front crossed the coast of Guangdong on the morning of the first day of the month and the associated intense winter monsoon brought significantly cooler weather with sunny periods to Hong Kong on that day.  Dominated by the winter monsoon, it remained rather cool, fine and dry for the ensuing three days.  Affected by a fresh easterly airstream, the weather became cloudy with rain patches on December 5 and 6.  With the moderation of the easterly airstream, there were sunny intervals on December 7.

     An intense winter monsoon reached the south China coast on the morning of December 8 and brought significantly cooler weather to the territory on December 8 and 9.  Affected by the intense winter monsoon, it was cold, fine and very dry for the next three days.  The temperatures at the Hong Kong Observatory fell to a minimum of 9.6 degrees on December 11, the lowest of the month.  While the winter monsoon moderated gradually on December 13, daytime temperatures rose to above 20 degrees generally from December 13 to 15.

     With the arrival of a replenishment of the winter monsoon in southern China, it remained generally fine and dry from December 16 to 19.  Affected by a broad band of clouds, the weather became mainly cloudy for the ensuing two days.

     Another replenishment of the winter monsoon reached southern China on the morning of December 22 and brought fine and dry weather to the territory on December 22 and 23.  With the strengthening of the winter monsoon, local weather was cold and very dry over the next two days.   With the persistence of the winter monsoon, it remained cool and dry with localised haze for the rest of the month.

     One tropical cyclone occurred over the South China Sea and the western North Pacific in the month.

     Details of the issuance and cancellation of various warnings/signals in the month are summarised in Table 1.  Monthly meteorological figures and departures from normal of December are tabulated in Table 2.

Ends/Wednesday, January 4, 2012
Issued at HKT 19:25


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