The Weather of April 2005

April 2005 was much drier than normal. The monthly rainfall of 32.3 millimetres was the ninth lowest for April. The accumulated rainfall of the first four months this year was 110 millimetres, 63 percent below the normal figure of 299.8 millimetres. April 2005 was also warmer than usual. The mean temperature of 23.1 degrees was 0.9 degree above normal.

It was cloudy with some rain on the first day of April 2005. The cloudy and wet condition gave way to fine and dry weather on 2 April when a northeast monsoon arrived at the south China coast. While the weather was generally fine and dry in the following two days, it was hazy on 4 April. A broad cloud band moved over southern China on 5 April, bringing cloudy and misty weather to Hong Kong. Dominated by a maritime airstream, local weather was warm with sunny periods in the ensuing six days. It was also foggy on 10 and 11 April.

A cold front moved across the coast of Guangdong on 12 April, bringing significantly cooler weather to Hong Kong that night. Coupled with the rain, the northerly winds brought the temperature down to 14.6 degrees on the morning of 13 April, the lowest in the month. The weather remained cloudy with a few rain patches until 17 April.

Under the influence of a maritime airstream, warm and sunny weather returned on 18 April. Apart from some cloudy periods on 21 April, the weather stayed fine in the next five days. With plenty of sunshine, it was hot with maximum temperatures exceeding 30 degrees in the New Territories on 20 April. The weather became cloudy with some showers on 25 April when a trough of low pressure edged towards the south China coast. It remained cloudy with a few showers 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 1.3. Monthly meteorological figures and departures from normal for April are tabulated in Table 2.

Warnings and Signals issued in April 2005

Table 1.1 Strong Monsoon Signal

Beginning Time		Ending Time
Day/Month	HKT	Day/Month	HKT
4 / 4	0655	4 / 4	1245

Table 1.2 Thunderstorm Warning

Beginning Time		Ending Time
Day/Month	HKT	Day/Month	HKT
13 / 4	0420	13 / 4	0730
25 / 4	2035	25 / 4	2235

Table 1.3 Fire Danger Warnings

Colour	Beginning Time		Ending Time
Colour	Day/Month	HKT	Day/Month	HKT
Yellow	3 / 4	0000	4 / 4	0600
Yellow	5 / 4	0000	5 / 4	2315

Table 2 Figures and Departures from Normal - April 2005

Meteorological Element	Figure of the Month	Departure from Normal*
Mean Daily Maximum Air Temperature	25.4 degrees C	0.5 degree above normal
Mean Air Temperature	23.1 degrees C	0.9 degree above normal
Mean Daily Minimum Air Temperature	21.3 degrees C	1.1 degrees above normal
Mean Dew Point Temperature	19.9 degrees C	0.9 degree above normal
Mean Relative Humidity	83 %	normal
Mean Cloud Amount	79 %	1 % above normal
Total Rainfall	32.3 mm	129.2 mm below normal
Number of hours of Reduced VisibilityΔ	198 hours	130.1 hours above normal§
Total Bright Sunshine Duration	104.3 hours	4.6 hours below normal
Mean Daily Global Solar Radiation	11.40 Megajoule / square metre	1.74 Megajoule below normal
Total Evaporation	77.8 mm	29.1 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 1961-1990 climatological normal, except for number of hours of reduced visibility.
§ Departure from mean value between 1997 and 2004.

daily values of selected meteorological elements for HK for April 2005

Extract of Meteorological Observations in Hong Kong for April 2005