The weather for December 2020 was cloudier than usual in Hong Kong. The mean amount of cloud in the month was 62 per cent, 10 per cent above the normal figure of 52 per cent. The monthly mean temperature of 18.1 degrees was 0.2 degrees above the normal figure of 17.9 degrees. The month was also much drier than usual with a total rainfall of only 1.5 millimetres, about 6 per cent of the normal figure of 26.8mm. The annual total rainfall in 2020 was 2395.0mm, similar to the annual normal figure of 2398.5mm.
Dominated by a dry winter monsoon, the weather of Hong Kong was generally fine and dry on the first eight days of the month with rather cool mornings on December 4 and 5. With a broad band of clouds covering the coast of Guangdong and the moderation of the winter monsoon, the weather became milder and mainly cloudy with a few light rain patches from December 9 to 13.
Under the influence of an intense winter monsoon, local weather became appreciably cooler from December 14 to 17. There were also a few light rain patches from December 14 to 15. With the replenishment of a dry winter monsoon, local weather became mainly fine and dry from December 18 to 21. It was also cold on the mornings of December 19 and 20. Affected by a cloud band over the coast of Guangdong, the weather became cloudier in the next two days with a few rain patches on December 23.
With clouds thinning out, the weather of Hong Kong turned mainly fine and dry during the day on December 24. Visibility was rather low in some areas in that afternoon. Affected by an easterly airstream, local weather became cloudier with a few light rain patches and mist at the beginning on the Christmas Day. Under the influence of a relatively dry easterly airstream, it was generally fine, mild and dry during the day from December 26 to 29. With plenty of sunshine, the temperature at the Hong Kong Observatory soared to 24.5 degrees on the afternoons of December 27 and 29, the highest of the month.
Meanwhile, a cold front moved across southern China on the night of December 29. Under the influence of the associated intense cold surge, the weather of Hong Kong became windy and significantly colder on December 30. It was cold, windy and very dry on the New Year's Eve with the temperature at the Hong Kong Observatory dropping to 8.1 degrees in the morning, the lowest of the month. The temperature at Tai Mo Shan even dropped to minus 1.2 degrees.
One tropical cyclone occurred over the South China Sea and the western North Pacific in December 2020.
Details of issuance and cancellation of various warnings/signals in December are summarised in Table 1. Monthly meteorological figures and departures from normal for December are tabulated in Table 2.
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