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The Weather of October 2007

    October 2007 was warmer and drier than usual. The monthly mean temperature of 25.6 degrees was 0.4 degrees above normal. The monthly total rainfall of 51.7 millimetres was about 64 per cent below the normal figure of 144.8 millimetres. The accumulated rainfall since the beginning of the year was 1687.3 millimetres, about 22 percent below the normal figure of 2151.9 millimetres for the same period.

    The combined effect of the northeast monsoon and the Severe Tropical Storm Lekima over the South China Sea brought strong winds and occasional squally showers to Hong Kong on the first three days of the month. Under windy conditions, a cargo ship sank near Tolo Harbour on 2 October. There were also at least 17 reports of collapsed tree in the territory. As Lekima moved further west and made landfall over Vietnam, local winds moderated gradually later on 3 October.

    The weather turned fine on 4 October and remained so in the ensuing three days. With plenty of sunshine, the temperature rose up to 31.6 degrees on 6 October, the highest in the month. Under light wind conditions, it was hazy on 8 October. Visibility dropped below 3000 metres in many parts of the territory. The visibility improved when a replenishment of the northeast monsoon reached the south China coast on 9 October.

    Under the influence of an area of rain over the northern part of the South China Sea, the weather became mainly cloudy with a few rain patches on 10 October and the following four days. Dry and sunny weather returned on 15 October when the northeast monsoon over southern China strengthened. The weather stayed mainly fine in the next three days. A continental airstream brought very dry weather to Hong Kong during the Chung Yeung holiday on 19 October. Over 100 reports of hill fire were reported. Apart from some haze, generally fine weather persisted in the next ten days.

    The weather became cloudy with rain on the last two days of the month when a broad band of cloud over the South China Sea moved north to cover the coastal area.

    Seven 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 1.2.  Monthly meteorological figures and departures from normal for October are tabulated in Table 2.


 

Warnings and Signals issued in October 2007


Table 1.1   Strong Monsoon Signal

Beginning Time Ending Time
Day/Month HKT Day/Month HKT
30 / 9 2145 1 / 10 0630
1 / 10 1630 3 / 10 1715


Table 1.2   Fire Danger Warnings

Colour Beginning Time Ending Time
Day/Month HKT Day/Month HKT
Yellow 29 / 9 0600 1 / 10 0600
Yellow 6 / 10 0600 7 / 10 0600
Red 7 / 10 0600 8 / 10 0600
Red 9 / 10 0600 10 / 10 0600
Yellow 13 / 10 1130 13 / 10 1645
Yellow 14 / 10 1130 14 / 10 1800
Red 16 / 10 0600 16 / 10 1800
Red 17 / 10 0600 17 / 10 1800
Red 19 / 10 0600 21 / 10 0600
Yellow 21 / 10 0600 22 / 10 0600
Yellow 27 / 10 0600 28 / 10 1800


Table 2   Figures and Departures from Normal - October 2007

Meteorological Element Figure of the Month Departure from Normal*
Mean Daily Maximum Air Temperature 28.4 degrees C 0.5 degree above normal
Mean Air Temperature 25.6 degrees C 0.4 degree above normal
Mean Daily Minimum Air Temperature 23.8 degrees C 0.7 degree above normal
Mean Dew Point Temperature 20.0 degrees C 0.2 degree above normal
Mean Relative Humidity 72 % 1 % below normal
Mean Cloud Amount 65 % 9 % above normal
Total Rainfall 51.7 mm 93.1 mm below normal
Number of hours of Reduced VisibilityΔ 299 hours 147.3 hours above normal§
Total Bright Sunshine Duration 178.8 hours 16.2 hours below normal
Mean Daily Global Solar Radiation 14.31 Megajoule / square metre 1.15 Megajoule below normal
Total Evaporation 118.1 mm 34.1 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.


 

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 2006


daily values of selected meteorological elements for HK for October 2007

Extract of Meteorological Observations in Hong Kong for October 2007