The Weather of March 2015

2 April 2015

    With a maritime airstream dominating over the coast of Guangdong during the latter half of the month, the weather of Hong Kong in March 2015 was warmer than usual. The monthly mean temperature was 19.9 degrees, 0.8 degrees higher than the normal figure of 19.1 degrees. The total rainfall in the month was 28.4 millimetres, only about 35 percent of the normal figure of 82.2 millimetres. The accumulated rainfall of 102.1 millimetres since 1 January was about 37 percent below the normal figure of 161.3 millimetres for the same period.

    A cold front over southern China moved across the coastal areas of Guangdong on the first day of the month and the strengthening of an easterly airstream brought cooler weather the next day. Another replenishment of the northeast monsoon on 4 and 5 March brought windy and even cooler conditions to Hong Kong, and the weather remained cloudy with light rain and mist patches till 8 March.

    Following a lull in the northeast monsoon that brought a warm and sunny day on 9 March, easterly winds strengthened again the next day as another replenishment of the northeast monsoon reached the coast of Guangdong. The weather became significantly cooler with light rain patches on 10-13 March. Temperatures at the Observatory fell to a minimum of 14.8 degrees on 12 March, the lowest of the month.

    As the northeast monsoon subsided, it was gradually replaced by a warmer maritime airstream on 14 and 15 March. Local weather turned increasingly humid with lingering clouds, mist and fog. As temperatures continued to rise, clouds finally dispersed during the day for some sunshine to break through on 19 March. Fine weather then prevailed in the next couple of days and temperatures at the Observatory climbed to a maximum of 28.3 degrees on 20 March, the highest of the month.

    With easterly winds strengthening and the northeast monsoon returning to the coast of Guangdong, the weather turned generally cloudy and windy with light rain patches from 22 to 26 March. After a rainy morning on 27 March, sunny intervals appeared in the afternoon as warm maritime air set in over the coast of Guangdong. Despite some coastal mist, clouds thinned out during the day with sunny periods coming through 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 1.2. Monthly meteorological figures and departures from normal for March are tabulated in Table 2.

Warnings and Signals issued in March 2015

Table 1.1 Strong Monsoon Signal

Beginning Time		Ending Time
Day/Month	HKT	Day/Month	HKT
5 / 3	0330	6 / 3	0545
10 / 3	0745	11 / 3	0745
23 / 3	0315	23 / 3	1345
24 / 3	2245	26 / 3	0745

Table 1.2 Fire Danger Warnings

Colour	Beginning Time		Ending Time
Colour	Day/Month	HKT	Day/Month	HKT
Yellow	1 / 3	0600	1 / 3	2315
Yellow	22 / 3	1200	22 / 3	2345
Yellow	29 / 3	0600	29 / 3	2145

Table 2 Figures and Departures from Normal - March 2015

Meteorological Element	Figure of the Month	Departure from Normal*
Mean Daily Maximum Air Temperature	22.0 degrees C	0.6 degree above normal
Mean Air Temperature	19.9 degrees C	0.8 degree above normal
Mean Daily Minimum Air Temperature	18.5 degrees C	1.3 degrees above normal
Mean Dew Point Temperature	17.1 degrees C	1.4 degrees above normal
Mean Relative Humidity	85 %	3 % above normal
Mean Cloud Amount	83 %	4 % above normal
Total Rainfall	28.4 mm	53.8 mm below normal
Number of hours of Reduced VisibilityΔ	72 hours	47.2 hours below normal§
Total Bright Sunshine Duration	69.9 hours	20.9 hours below normal
Mean Daily Global Solar Radiation	10.12 Megajoule / square metre	0.16 Megajoule above normal
Total Evaporation	69.2 mm	1.3 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. Before 10 October 2007, the number of hours of reduced visibility at the Hong Kong International Airport in 2005 and thereafter displayed in this web page was based on hourly visibility observations by professional meteorological observers. Since 10 October 2007, the data have been revised using the average visibility readings over the 10-minute period before the clock hour, as recorded by the visibility meter near the middle of the south runway.
* Departure from 1981 - 2010 climatological normal, except for number of hours of reduced visibility
§ Departure from mean value between 1997 and 2014

daily values of selected meteorological elements for HK for March 2015

The percentile map of mean temperature of March 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

Rainfall Map For March 2015 (isohyets are in millimetres)

Extract of Meteorological Observations in Hong Kong for March 2015