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Under the influence of cold spells brought by the winter monsoon during the second half of the month, the weather in December 2013 was significantly colder than usual. The monthly mean temperature of 16.1 degrees was 1.8 degrees below the normal figure of 17.9 degrees, the lowest for December since 1975. The active winter monsoon also maintained generally dry conditions for most of the month. Yet the month turned out to be much wetter than usual in terms of rainfall due to the rainy episode between December 14 and 17. The total rainfall of the month was 88.3 millimetres, more than three times the normal figure of 26.8 millimetres and the 10th highest for December on record. The annual total rainfall of 2013 was 2847.3 millimetres, about 19 per cent above the normal figure of 2398.5 millimetres.
Dominated by the northeast monsoon, fine and very dry weather persisted over Hong Kong for the first seven days of the month. Affected by a cloud band over the northern part of the South China Sea and the coast of southeastern China, local weather turned cloudier with rain patches on December 8. Ahead of the arrival of a replenishment of the northeast monsoon, temperatures at the Hong Kong Observatory reached 24.9 degrees on December 9, the highest of the month. The northeast monsoon brought a dry continental airstream to Hong Kong and the weather was mainly fine with haze on December 9 and 10.
Clouds returned to the south China coastal areas on December 11 and brought a few light rain patches to the territory on December 12 and 13. With the approach of an upper level disturbance, the rain became heavier and more frequent in Hong Kong over the next four days. Coupled with the arrival of an intense winter monsoon, temperatures fell significantly and it was gloomy, rainy and cold on December 16 and 17. As the rainbands associated with the upper level disturbance moved away on December 18, local weather turned mainly fine and dry. Temperatures at the Hong Kong Observatory fell to a minimum of 9.2 degrees that morning, the lowest of the month, and the weather remained cold in the next two days.
After a cool and cloudier day on December 21, further replenishment of the winter monsoon kept the weather generally cold, fine and very dry till the end of the month. Under a clear sky and light wind conditions, nocturnal cooling caused temperatures to drop below 3 degrees at Ta Kwu Ling, where frost was reported on the mornings of December 28 to 30.
No 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/Friday, January 3, 2014
Issued at HKT 18:50
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