The Weather of January 2015
3 February 2015
With the northeast monsoon bringing dry continental air mass to the south China coast during the month, the weather of January 2015 was sunnier than usual. The total duration of sunshine in the month was 198.8 hours, 39 percent above the normal figure of 143.0 hours. The monthly mean amount of cloud was 45 percent, against a normal figure of 61 percent. As a result of the rain on 12 and 13 January, the monthly total rainfall of 41.7 millimetres was 69 percent above the January normal of 24.7 millimetres. Overall, the mean temperature of the month was 16.4 degrees, only 0.1 degree above normal.
Under the influence of a dry winter monsoon, Hong Kong started off with cool and dry conditions on the first four days of the month. Affected by a mild and humid maritime airstream, it turned cloudy with mist and coastal fog on 5 January. With the clouds thinning out, the weather became generally fine and warm on the afternoon of 6 January. Temperatures at the Observatory rose to a maximum of 23.9 degrees that day, the highest of the month.
Following some morning fog early on 7 January, temperatures fell during the day by 4 to 5 degrees compared with the previous day as a cold front crossed the coast of Guangdong in the morning. Affected by a dry continental air mass behind the cold front, mainly fine weather prevailed for the next three days.
A broad band of clouds covered southern China and brought a few rain patches to Hong Kong on 11 January. The weather became cold and rainy on 12 and 13 January as an intense winter monsoon reached the south China coastal areas. Most of the rain in the month, about 40 millimeters in total, fell during the two-day period. As the broad rainband moved eastward away from the Pearl River Estuary, the rain eased off and the weather became fine on the night of 13 January. Under clear night skies, it remained cold in the morning over the next two days. Temperatures at the Observatory fell to a minimum of 10.3 degrees early on 14 January, the lowest of the month. Dominated by a dry winter monsoon, local weather remained generally fine and dry up to 23 January. Relative humidity at the Observatory dropped below 40 percent on 19 and 22 January.
Affected by a humid easterly airstream, the weather turned mainly cloudy with light rain and mist patches on 24-25 January. After a fine and relatively mild day on 26 January, a strengthening of the easterly winds brought windy and slightly cooler weather to the territory over the next three days. The weather turned cloudier again as a cold front approached the south China coast on 30 January, and temperatures dropped further the next day with some light rain patches.
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One tropical cyclone occurred over the South China Sea and the western North Pacific in the month. |
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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 January are tabulated in Table 2. |
Warnings and Signals issued in January 2015
| Beginning Time | Ending Time | ||
|---|---|---|---|
| Day/Month | HKT | Day/Month | HKT |
| 28 / 1 | 0750 | 29 / 1 | 0545 |
| Colour | Beginning Time | Ending Time | ||
|---|---|---|---|---|
| Day/Month | HKT | Day/Month | HKT | |
| Yellow | 1 / 1 | 0600 | 1 / 1 | 1100 |
| Red | 1 / 1 | 1100 | 1 / 1 | 1945 |
| Yellow | 3 / 1 | 0600 | 3 / 1 | 2045 |
| Yellow | 10 / 1 | 0600 | 10 / 1 | 1900 |
| Yellow | 11 / 1 | 1150 | 11 / 1 | 1800 |
| Red | 15 / 1 | 0600 | 15 / 1 | 2100 |
| Yellow | 17 / 1 | 0600 | 18 / 1 | 2400 |
| Red | 19 / 1 | 0000 | 19 / 1 | 2145 |
| Red | 22 / 1 | 0600 | 22 / 1 | 2315 |
| Yellow | 30 / 1 | 0600 | 31 / 1 | 0600 |
| Beginning Time | Ending Time | ||
|---|---|---|---|
| Day/Month | HKT | Day/Month | HKT |
| 31 / 12 | 1620 | 2 / 1 | 0600 |
| 12 / 1 | 1200 | 16 / 1 | 0800 |
| Meteorological Element | Figure of the Month | Departure from Normal* |
|---|---|---|
| Mean Daily Maximum Air Temperature | 18.9 degrees C | 0.3 degree above normal |
| Mean Air Temperature | 16.4 degrees C | 0.1 degree above normal |
| Mean Daily Minimum Air Temperature | 14.5 degrees C | normal |
| Mean Dew Point Temperature | 11.2 degrees C | 0.2 degree below normal |
| Mean Relative Humidity | 72 % | 2 % below normal |
| Mean Cloud Amount | 45 % | 16 % below normal |
| Total Rainfall | 41.7 mm | 17.0 mm above normal |
| Number of hours of Reduced VisibilityΔ | 172 hours | 80.1 hours below normal§ |
| Total Bright Sunshine Duration | 198.8 hours | 55.8 hours above normal |
| Mean Daily Global Solar Radiation | 13.27 Megajoule / square metre | 3.1 Megajoule above normal |
| Total Evaporation | 81.9 mm | 10.6 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 |
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§ Departure from mean value between 1997 and 2014 |
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| 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 January 2015