The Weather of December 2016
4 January 2017
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 and the third highest for December since record began in 1884. The total rainfall recorded in the month was only 6.6 millimetres, less than one quarter of the normal figure of 26.8 millimetres. But in terms of rainfall for the whole year, the annual total of 3026.8 millimetres was about 26 percent above the yearly normal of 2398.5 millimetres.
Under the influence of the northeast monsoon, the month started off with fine and dry conditions in Hong Kong on the first two days. The weather became cloudy on 3 December as a band of clouds 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 couple of days as temperatures climbed to a rather warm 25.9 degrees on 5 December, the highest of the month.
Apart from a lull in the northeast monsoon with relatively warm weather on 12 and 13 December, further replenishments of continental air brought a spell of generally fine and dry conditions to the territory from 6 to 16 December. Easterly winds freshened over the south China coastal areas on 11 December, but temperatures only began falling significantly as the winds turned northerly on 14 December. It was only then that the weather became appreciably cooler over the next couple of days.
After a cool and cloudier day on 17 December, the weather soon warmed up again as sunny skies emerged on 18 and 19 December. With moist maritime air edging back towards the coast of Guangdong, increasing cloudiness on 20 December was followed by a day of humid conditions and light rain on 21 December. 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 23 December, and the weather remained mostly cloudy till Christmas Day.
Despite a fine and relatively warm day on 26 December during another break in the northeast monsoon, the passage of a cold front brought strengthening northerly winds that night and falling temperatures the next day. Windy conditions were enhanced by the presence of a 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 27 December, while the first issuance of the Cold Weather Warning this winter saw temperatures plummeting to a minimum of 11.5 degrees the next morning, the lowest in the month.
After a cloudy day on 28 December, the northeast monsoon started to subside and temperatures gradually recovered 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 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 December are tabulated in Table 2.
Warnings and Signals issued in December 2016
| Beginning Time | Ending Time | ||
|---|---|---|---|
| Day/Month | HKT | Day/Month | HKT |
| 24 / 12 | 0210 | 24 / 12 | 1145 |
| 26 / 12 | 2310 | 28 / 12 | 0745 |
| Colour | Beginning Time | Ending Time | ||
|---|---|---|---|---|
| Day/Month | HKT | Day/Month | HKT | |
| Yellow | 4 / 12 | 0600 | 4 / 12 | 1800 |
| Red | 6 / 12 | 0830 | 7 / 12 | 2000 |
| Red | 8 / 12 | 0615 | 8 / 12 | 1800 |
| Yellow | 11 / 12 | 0600 | 11 / 12 | 1900 |
| Yellow | 17 / 12 | 0600 | 17 / 12 | 1945 |
| Yellow | 18 / 12 | 0600 | 18 / 12 | 1800 |
| Yellow | 25 / 12 | 0600 | 25 / 12 | 1800 |
| Yellow | 26 / 12 | 0600 | 27 / 12 | 1145 |
| Red | 27 / 12 | 1145 | 28 / 12 | 0045 |
| Red | 29 / 12 | 0600 | 30 / 12 | 2315 |
| Yellow | 31 / 12 | 1130 | 31 / 12 | 1800 |
| Beginning Time | Ending Time | ||
|---|---|---|---|
| Day/Month | HKT | Day/Month | HKT |
| 27 / 12 | 1620 | 29 / 12 | 0930 |
| Meteorological Element | Figure of the Month | Departure from Normal* |
|---|---|---|
| Mean Daily Maximum Air Temperature | 21.8 degrees C | 1.6 degrees above normal |
| Mean Air Temperature | 19.6 degrees C | 1.7 degrees above normal |
| Mean Daily Minimum Air Temperature | 17.7 degrees C | 1.8 degrees above normal |
| Mean Dew Point Temperature | 13.9 degrees C | 2.0 degrees above normal |
| Mean Relative Humidity | 70 % | 1 % above normal |
| Mean Cloud Amount | 62 % | 10 % above normal |
| Total Rainfall | 6.6 mm | 20.2 mm below normal |
| Number of hours of Reduced VisibilityΔ | 89 hours | 135.9 hours below normal§ |
| Total Bright Sunshine Duration | 168.2 hours | 4.0 hours below normal |
| Mean Daily Global Solar Radiation | 12.25 Megajoule / square metre | 1.36 Megajoule above normal |
| Total Evaporation | 82.7 mm | 1.0 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.
|
* Departure from 1981 - 2010 climatological normal, except for number of hours of reduced visibility |
|
§ Departure from mean value between 1997 and 2015 |
|
| Remarks : | Extremely high: above 95th percentile Above normal: between 75th and 95th percentile Normal: between 25th and 75th percentile Below normal: between 5th and 25th percentile Extremely low: below 5th percentile Percentile and 5-day running average values are computed based on the data from 1981 to 2010 |
