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The Weather of March 2006

    March 2006 was marked by low visibility, humid weather and rapidly fluctuating temperatures. The mean relative humidity of 86 percent was 5 percent above normal. The number of hours of reduced visibility observed at the Hong Kong International Airport reached 180 hours (i.e. about 24 % of time) in the month. In spite of the humid weather, the monthly total rainfall of 48.4 millimetres was 18.5 millimetres below the normal amount. The accumulated rainfall since the beginning of the year was 102.4 millimetres, about 26 percent below the normal figures of 138.3 millimetres.

    Under the influence of the northeast monsoon, it was fine and cold on the first three days of March. With a broad cloud band covering southern China, local weather turned cloudy on 4 March. A humid maritime airstream set in on 5 March, bringing mist and rain patches to the territory. The weather remained humid with fog patches the next day. While it was foggy on the morning of 7 March, sunshine streamed through the clouds during the day. Apart from the relatively low visibility, it was mild with sunny periods in the following four days.

    A cold front crossed the south China coast on the evening of 12 March, bringing rain patches and appreciably cooler weather to Hong Kong. It was cold with some rain in the ensuing two days. The temperature fell to 9.0 degrees on 14 March, the lowest in the month. The weather stayed cloudy and cool on 15 March. It became hazy as the local winds subsided on 16 March, with visibility in the harbour dropping below 2000 metres at times.

    Humid and foggy weather returned on 17 March when a moist easterly airstream affected the south China coast. With plenty of sunshine during the day, the temperature rose to 26.2 degrees on 18 March, the highest in the month. The arrival of a northeast monsoon brought mainly cloudy weather to the territory in the next two days.

    Under the influence of a maritime airstream, it was foggy on 21 and 22 March. Thick fog in the harbour on the morning of 23 March reduced the visibility to about 200 metres. The weather became rainy as a rain bearing cold front moved across the coast of Guangdong that night. It was overcast with rain in the following four days.

    The weather became mainly fine on 28 March and remained so for the rest of the month.

    Only one tropical cyclone occurred in 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 1.5.  Monthly meteorological figures and departures from normal for March are tabulated in Table 2.


 

Warnings and Signals issued in March 2006


Table 1.1   Strong Monsoon Signal

Beginning Time Ending Time
Day/Month HKT Day/Month HKT
28 / 2 2020 1 / 3 1615
12 / 3 2045 13 / 3 0445
19 / 3 1400 20 / 3 0640


Table 1.2   Thunderstorm Warning

Beginning Time Ending Time
Day/Month HKT Day/Month HKT
23 / 3 1035 23 / 3 1400
24 / 3 0255 24 / 3 0900
24 / 3 1230 24 / 3 1530
25 / 3 1300 25 / 3 1500


Table 1.3   Fire Danger Warnings

Colour Beginning Time Ending Time
Day/Month HKT Day/Month HKT
Yellow 1 / 3 0600 3 / 3 0600
Yellow 3 / 3 1130 3 / 3 1800
Yellow 19 / 3 1200 19 / 3 1800


Table 1.4   Frost Warning

Beginning Time Ending Time
Day/Month HKT Day/Month HKT
1 / 3 1630 2 / 3 0705


Table 1.5   Cold Weather Warning

Beginning Time Ending Time
Day/Month HKT Day/Month HKT
28 / 2 0730 3 / 3 0930
12 / 3 1615 14 / 3 1610


Table 2   Figures and Departures from Normal - March 2006

Meteorological Element Figure of the Month Departure from Normal*
Mean Daily Maximum Air Temperature 20.5 degrees C 0.8 degree below normal
Mean Air Temperature 18.5 degrees C normal
Mean Daily Minimum Air Temperature 16.6 degrees C 0.1 degree above normal
Mean Dew Point Temperature 16.0 degrees C 1.0 degree above normal
Mean Relative Humidity 86 % 5 % above normal
Mean Cloud Amount 76 % normal
Total Rainfall 48.4 mm 18.5 mm below normal
Number of hours of Reduced VisibilityΔ 180 hours 73.7 hours above normal§
Total Bright Sunshine Duration 93.3 hours 3.1 hours below normal
Mean Daily Global Solar Radiation 10.95 Megajoule / square metre 0.29 Megajoule below normal
Total Evaporation 64.4 mm 27.8 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.


 

The calibration factors of the pyranometer at King's Park in 2006 and 2007 have been re-computed based on the results of a regional instrument comparison in Asia in 2007. The readings of total global solar radiation at King's Park in 2006 and 2007 displayed in this web page before 13 June 2008 have been revised on 13 June 2008 using the new calibration factors.

  *   Departure from 1961-1990 climatological normal, except for number of hours of reduced visibility.
  §   Departure from mean value between 1997 and 2005.


daily values of selected meteorological elements for HK for March 2006

Extract of Meteorological Observations in Hong Kong for March 2006