The Weather of December 2020
5 January 2021
The weather for December 2020 was cloudier than usual. The mean amount of cloud in the month was 62 percent, 10 percent above the normal of 52 percent. The mean temperature for December 2020 was 18.1 degrees, 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 percent of the normal figure of 26.8 millimetres. The annual total rainfall in 2020 was 2395.0 millimetres, near the annual normal of 2398.5 millimetres.
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 4-5 December. With a broad band of clouds covering the coast of Guangdong and the moderation of the winter monsoon, the weather became mainly cloudy and milder with a few light rain patches on 9-13 December.
Under the influence of an intense winter monsoon, the weather became appreciably cooler on 14 - 17 December. There were also a few light rain patches on 14 – 15 December. With the replenishment of dry winter monsoon, local weather became mainly fine and dry on 18 – 21 December. It was also cold on the mornings of 19 and 20 December. 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 23 December.
With clouds thinning out, the weather of Hong Kong turned mainly fine and dry during the day on 24 December. Visibility was rather low in some areas in that afternoon. Affected by an easterly airstream, local weather became cloudier with a few light rain and mist patches at first on the Christmas Day. Under the influence of a relatively dry easterly airstream, it was generally fine, dry and mild during the day on 26 – 29 December. With plenty of sunshine, the maximum temperature at the Observatory rose to 24.5 degrees on the afternoons of 27 and 29 December, the highest of the month.
Meanwhile, a cold front moved across southern China on the night of 29 December. Under the influence of the associated intense cold surge, the weather of Hong Kong became windy and significantly colder on 30 December. It was cold, windy and very dry on New Year’s Eve with the temperature at the Hong Kong Observatory falling to a minimum of 8.1 degrees in the morning, the lowest of the month. The temperature at Tai Mo Shan even dropped to -1.2 degrees.
One tropical cyclone occurred over the South China Sea and the western North Pacific in December 2020.
The weather for December 2020 was cloudier than usual. The mean amount of cloud in the month was 62 percent, 10 percent above the normal of 52 percent. The mean temperature for December 2020 was 18.1 degrees, 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 percent of the normal figure of 26.8 millimetres. The annual total rainfall in 2020 was 2395.0 millimetres, near the annual normal of 2398.5 millimetres.
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 4-5 December. With a broad band of clouds covering the coast of Guangdong and the moderation of the winter monsoon, the weather became mainly cloudy and milder with a few light rain patches on 9-13 December.
Under the influence of an intense winter monsoon, the weather became appreciably cooler on 14 - 17 December. There were also a few light rain patches on 14 – 15 December. With the replenishment of dry winter monsoon, local weather became mainly fine and dry on 18 – 21 December. It was also cold on the mornings of 19 and 20 December. 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 23 December.
With clouds thinning out, the weather of Hong Kong turned mainly fine and dry during the day on 24 December. Visibility was rather low in some areas in that afternoon. Affected by an easterly airstream, local weather became cloudier with a few light rain and mist patches at first on the Christmas Day. Under the influence of a relatively dry easterly airstream, it was generally fine, dry and mild during the day on 26 – 29 December. With plenty of sunshine, the maximum temperature at the Observatory rose to 24.5 degrees on the afternoons of 27 and 29 December, the highest of the month.
Meanwhile, a cold front moved across southern China on the night of 29 December. Under the influence of the associated intense cold surge, the weather of Hong Kong became windy and significantly colder on 30 December. It was cold, windy and very dry on New Year’s Eve with the temperature at the Hong Kong Observatory falling to a minimum of 8.1 degrees in the morning, the lowest of the month. The temperature at Tai Mo Shan even dropped to -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 the month are summarized in Tables 1.1 to 1.4. Monthly meteorological figures and departures from normal for December are tabulated in Table 2.
Warnings and Signals issued in December 2020
| Beginning Time | Ending Time | ||
|---|---|---|---|
| Day/Month | HKT | Day/Month | HKT |
| 29 / 12 | 2300 | 31 / 12 | 1225 |
| Colour | Beginning Time | Ending Time | ||
|---|---|---|---|---|
| Day/Month | HKT | Day/Month | HKT | |
| Yellow | 5 / 12 | 0600 | 6 / 12 | 1915 |
| Yellow | 13 / 12 | 1145 | 13 / 12 | 1900 |
| Yellow | 19 / 12 | 0600 | 20 / 12 | 0600 |
| Red | 20 / 12 | 0600 | 20 / 12 | 2330 |
| Red | 21 / 12 | 0600 | 21 / 12 | 2330 |
| Yellow | 25 / 12 | 0600 | 25 / 12 | 1800 |
| Yellow | 26 / 12 | 0600 | 26 / 12 | 1900 |
| Yellow | 27 / 12 | 0645 | 27 / 12 | 1900 |
| Red | 30 / 12 | 0600 | 2 / 1 | 2000 |
| Beginning Time | Ending Time | ||
|---|---|---|---|
| Day/Month | HKT | Day/Month | HKT |
| 31 / 12 | 1630 | 1 / 1 | 0945 |
| Beginning Time | Ending Time | ||
|---|---|---|---|
| Day/Month | HKT | Day/Month | HKT |
| 16 / 12 | 2200 | 17 / 12 | 1130 |
| 19 / 12 | 0515 | 21 / 12 | 0930 |
| 29 / 12 | 1620 | 3 / 1 | 0930 |
| Meteorological Element | Figure of the Month | Departure from Normal* |
|---|---|---|
| Mean Daily Maximum Air Temperature | 20.7 degrees C | 0.5 degree above normal |
| Mean Air Temperature | 18.1 degrees C | 0.2 degree above normal |
| Mean Daily Minimum Air Temperature | 15.9 degrees C | normal |
| Mean Dew Point Temperature | 12.1 degrees C | 0.2 degree above normal |
| Mean Relative Humidity | 69 % | normal |
| Mean Cloud Amount | 62 % | 10 % above normal |
| Total Rainfall | 1.5 mm | 25.3 mm below normal |
| Number of hours of Reduced VisibilityΔ | 60 hours | 139.4 hours below normal§ |
| Total Bright Sunshine Duration | 175.4 hours | 3.2 hours above normal |
| Mean Daily Global Solar Radiation | 12.69 Megajoule / square metre | 1.8 Megajoule above normal |
| Total Evaporation | 91.8 mm | 8.1 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 2019 |
|
| 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 |
