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The Weather of October 2008

    October 2008 was unseasonably warm. Both the monthly mean temperature of 26.5 degrees and the mean daily minimum temperature of 24.9 degrees broke the records set in 1983 by 0.1 degrees and 0.2 degrees respectively. The accumulated rainfall since 1 January was 3002.9 millimetres, about 30 percent above the normal figure of 2313.1 millimetres for the same period.

    Under the influence of a ridge of high pressure over southern China, local weather was mainly fine for the first two days of the month. Tropical Depression Higos entered the South China Sea on 2 October and intensified into a Tropical Storm the next day. Affected by the outer rainbands of Higos, it became cloudy with a few showers on 3 October. Higos weakened into a Tropical Depression and made landfall over the western part of Guangdong on 4 October. Local weather remained showery on that day. Higos weakened further into an area of low pressure the next morning and moved eastwards along the coast of Guangdong. Under the influence of the remnant of Higos and a cooler airstream over the south China coastal areas, there were some heavy squally showers and thunderstorms in the territory on 5 October.

    A weak northeast monsoon reached southern China on the evening of 5 October and brought mainly cloudy condition to Hong Kong from 6 to 8 October. Clouds thinned out gradually and the weather turned generally fine for the ensuing three days. A replenishment of northeast monsoon reached southern China on 11 October and brought windy, rainy and slightly cooler weather to the territory on 12 and 13 October. A dry continental airstream brought generally fine and dry conditions to the territory for the next three days.

    Affected by an area of low pressure over the northern part of the South China Sea, the weather became mainly cloudy with a few showers on 17 and 18 October. A ridge of high pressure dominated over the south China coastal areas and brought mainly fine weather to the territory from19 to 23 October.

    A weak cold front moved across the coastal areas of Guangdong on the morning of 24 October. Affected by the northeast monsoon behind the cold front, local weather became mainly cloudy with a few rain patches on 24 and 25 October. Under the influence of a continental airstream over southern China, local weather turned mainly fine for the last six days of the month.

    Four tropical cyclones occurred in the western North Pacific and the South China Sea 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 October are tabulated in Table 2.


 

Warnings and Signals issued in October 2008


Table 1.1   Tropical Cyclone Warning Signals

Name of
Tropical Cyclone		 Signal
Number		 Beginning Time Ending Time
Day/Month HKT Day/Month HKT
HIGOS 1 2 / 10 1930 4 / 10 2230


Table 1.2   Strong Monsoon Signal

Beginning Time Ending Time
Day/Month HKT Day/Month HKT
5 / 10 1745 5 / 10 2340
12 / 10 0945 12 / 10 1200


Table 1.3   Rainstorm Warning Signals

Colour Beginning Time Ending Time
Day/Month HKT Day/Month HKT
Amber 5 / 10 0850 5 / 10 1130
Amber 5 / 10 1815 5 / 10 2040


Table 1.4   Thunderstorm Warning

Beginning Time Ending Time
Day/Month HKT Day/Month HKT
4 / 10 0210 4 / 10 0600
4 / 10 1700 4 / 10 1800
5 / 10 0010 5 / 10 1200
5 / 10 1700 5 / 10 2100


Table 1.5   Fire Danger Warnings

Colour Beginning Time Ending Time
Day/Month HKT Day/Month HKT
Yellow 1 / 10 0600 1 / 10 2315
Yellow 7 / 10 0000 7 / 10 2100
Yellow 11 / 10 0600 12 / 10 1645
Yellow 15 / 10 1115 15 / 10 1800
Yellow 19 / 10 0600 19 / 10 2345
Yellow 26 / 10 0600 26 / 10 1800


Table 2   Figures and Departures from Normal - October 2008

Meteorological Element Figure of the Month Departure from Normal*
Mean Daily Maximum Air Temperature 29.1 degrees C 1.4 degrees above normal
Mean Air Temperature 26.5 degrees C 1.2 degrees above normal
Mean Daily Minimum Air Temperature 24.9 degrees C 1.5 degrees above normal
Mean Dew Point Temperature 22.1 degrees C 2.2 degrees above normal
Mean Relative Humidity 77 % 3 % above normal
Mean Cloud Amount 69 % 12 % above normal
Total Rainfall 144.6 mm 7.3 mm below normal
Number of hours of Reduced VisibilityΔ 230 hours 64.9 hours above normal§
Total Bright Sunshine Duration 180.6 hours 10.5 hours below normal
Mean Daily Global Solar Radiation 14.53 Megajoule / square metre 0.07 Megajoule above normal
Total Evaporation 115.7 mm 20.7 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 1971 - 2000 climatological normal, except for number of hours of reduced visibility

  §   Departure from mean value between 1997 and 2007
daily values of selected meteorological elements for HK for October 2008

Extract of Meteorological Observations in Hong Kong for October 2008