An unusually warm December

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     With the northeast monsoon over the south China coastal areas remaining relatively weak for most of the month, December 2016 was warmer than usual. The monthly mean temperature of 19.6 degrees was 1.7 degrees above the normal figure of 17.9 degrees, the third highest for December since records began in 1884. The total rainfall for the month was only 6.6 millimetres, less than one quarter of the normal figure of 26.8 millimetres. But the annual total rainfall recorded was 3026.8 millimetres, about 26 per cent above the yearly normal of 2398.5 millimetres.

     Under the influence of the northeast monsoon, the weather in Hong Kong was fine and dry for the first two days of the month. It became cloudy on December 3 as a band of cloud covered the south China coast and the northern part of the South China Sea. Under light wind conditions, it was hazy with sunny periods over the next two days. It was rather warm on December 5 with temperatures rising to 25.9 degrees, the highest of the month.

     Further replenishments of continental air brought a spell of generally fine and dry conditions to the territory from December 6 to 16. Easterly winds freshened over the south China coastal areas on December 11, and a moderation of the northeast monsoon brought relatively warm weather on December 12 and 13. Temperatures began falling significantly as the winds turned northerly on December 14, and the weather became appreciably cooler over the next two days.

     After a cool and cloudier day on December 17, the weather soon warmed up again as sunny skies emerged on December 18 and 19. With a moist maritime airstream setting in over the coast of Guangdong, December 20 was cloudier and followed by humid conditions with light rain on December 21. The rain eased off the next day and the weather turned fine again as dry continental air returned to the south China coastal areas after the passage of a cold front. The strengthening of easterly winds brought patches of light rain on the night of December 23, and the weather remained mostly cloudy till Christmas Day.

     Despite a fine and relatively warm day on December 26 as the northeast monsoon moderated, the passage of a cold front brought strengthening northerly winds that night and falling temperatures the next day. Windy conditions strengthened due to the presence of weakening tropical cyclone Nock-Ten over the central part of the South China Sea, with winds reaching gale force on high ground in Hong Kong. Under the influence of the intense northeast monsoon, a continental airstream brought fine and very dry weather to the territory on December 27. The Hong Kong Observatory issued the first Cold Weather Warning Signal this winter as temperatures dropped to a minimum of 11.5 degrees the next morning, the lowest of the month.

     After a cloudy day on December 28, the northeast monsoon started to subside and temperatures gradually rose with sunny periods towards the end of the month.

     Two tropical cyclones 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 the normal for December are tabulated in Table 2.

Ends/Wednesday, January 4, 2017
Issued at HKT 15:31

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Table 1 (Warnings and Signals issued in December 2016)

Table 2 (Figures and Departures from Normal - December 2016)