The Weather of December 2014
Monday, 5th January 2015
Affected by frequent replenishments of the winter monsoon, the weather of December 2014 was cooler than normal, with spells of cloudy and rainy weather. The mean temperature for the month was 16.3 degrees, 1.6 degrees below the normal figure of 17.9 degrees. The total duration of bright sunshine in the month was 115.3 hours, 33 percent below the normal figure of 172.2 hours. The monthly total rainfall was 44.7 millimetres, about 67 percent above the normal figure of 26.8 millimetres. The annual rainfall of 2014 was 2638.3 millimetres, about 10 percent above the normal of 2398.5 millimetres.
After the passage of a cold front early on 1 December, an intense winter monsoon swept through the coastal areas of Guangdong and brought appreciably cooler weather to Hong Kong in the early part of the month. Cloudy conditions prevailed with some rain patches before the weather turned sunnier following the dissipation of clouds on 8 and 9 December.
As Tropical Storm Hagupit made its way across the South China Sea, a broad band of clouds extended over the coastal waters of Guangdong and cloudy skies returned on 10 - 12 December with a few rain patches. Coupled with the arrival of a surge of the winter monsoon, the weather turned colder as temperatures fell progressively. As a dry continental air mass reached the south China coastal areas, the weather became sunny on 13 and 14 December. Despite a cloudy day on 15 December, further replenishments of the winter monsoon in the next few days brought even colder and drier air to Hong Kong. The relative humidity plunged below 30 percent on 17 December and temperatures fell to a minimum of 10.7 degrees, the lowest of the month, before midnight on 19 December as another cloud band moved in from the northern part of the South China Sea and brought significant rain to the territory.
The ebb and flow between dry and moist air masses across the south China coast continued in the latter part of the month. Following three days of fine and dry weather on 20 - 22 December, the return of moist and milder air mass brought the clouds and rain patches back in the next five days. The rain patches lasted till the morning of 28 December before the arrival of a surge of the winter monsoon later that day brought drier conditions to Hong Kong. Following a cold morning on 29 December, the weather remained generally fine, dry and cool 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 2014
| Beginning Time | Ending Time | ||
|---|---|---|---|
| Day/Month | HKT | Day/Month | HKT |
| 1 / 12 | 0345 | 2 / 12 | 0745 |
| 4 / 12 | 0315 | 4 / 12 | 1500 |
| 6 / 12 | 2245 | 7 / 12 | 0600 |
| 8 / 12 | 2315 | 9 / 12 | 0845 |
| 16 / 12 | 0500 | 17 / 12 | 1145 |
| Colour | Beginning Time | Ending Time | ||
|---|---|---|---|---|
| Day/Month | HKT | Day/Month | HKT | |
| Yellow | 6 / 12 | 1105 | 6 / 12 | 1800 |
| Red | 12 / 12 | 0600 | 14 / 12 | 2300 |
| Red | 16 / 12 | 0600 | 18 / 12 | 1800 |
| Yellow | 20 / 12 | 0600 | 21 / 12 | 0600 |
| Red | 21 / 12 | 0600 | 22 / 12 | 1800 |
| Red | 29 / 12 | 0600 | 29 / 12 | 2145 |
| Beginning Time | Ending Time | ||
|---|---|---|---|
| Day/Month | HKT | Day/Month | HKT |
| 3 / 12 | 1620 | 5 / 12 | 1145 |
| 13 / 12 | 0425 | 13 / 12 | 1145 |
| 16 / 12 | 1620 | 20 / 12 | 1030 |
| 21 / 12 | 1620 | 22 / 12 | 1145 |
| 28 / 12 | 1620 | 30 / 12 | 1130 |
| 31 / 12 | 1620 | 2 / 1 | 0600 |
| Meteorological Element | Figure of the Month | Departure from Normal* |
|---|---|---|
| Mean Daily Maximum Air Temperature | 18.5 degrees C | 1.7 degrees below normal |
| Mean Air Temperature | 16.3 degrees C | 1.6 degrees below normal |
| Mean Daily Minimum Air Temperature | 14.2 degrees C | 1.7 degrees below normal |
| Mean Dew Point Temperature | 9.9 degrees C | 2.0 degrees below normal |
| Mean Relative Humidity | 67 % | 2 % below normal |
| Mean Cloud Amount | 67 % | 15 % above normal |
| Total Rainfall | 44.7 mm | 17.9 mm above normal |
| Number of hours of Reduced VisibilityΔ | 115 hours | 123.6 hours below normal§ |
| Total Bright Sunshine Duration | 115.3 hours | 56.9 hours below normal |
| Mean Daily Global Solar Radiation | 9.41 Megajoule / square metre | 1.48 Megajoule below normal |
| Total Evaporation | 85.8 mm | 2.1 mm above 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 2013 |
|
| 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 |
Extract of Meteorological Observations in Hong Kong for December 2014