The Weather of September 2005

September 2005 was marked by the hazy weather in association with the northeast monsoon and approaching tropical cyclones. The number of hours of reduced visibility observed at the Hong Kong International Airport reached 195 hours in the month. The rainfall attributed to Typhoon Damrey made September 2005 a relatively wet month. The monthly rainfall of 352.6 millimetres was 52.9 millimetres above normal. The accumulated rainfall since 1 January was 3196.8 millimetres, about 59 per cent more than the normal figure of 2007.1 millimetres.

It was fine, hot and hazy on the first two days of the month. The weather became cloudy with thundery showers on 3 and 4 September as an area of low pressure affected the south China coastal areas. On 4 September, a man was swept away by sea waves which were whipped up by the gusty easterly winds around Shek O.

Dominated by a continental airstream, it was mainly fine and hazy on 5 September. Apart from a few isolated showers, the hazy condition continued in the following seven days. The visibilities in the Hong Kong International Airport dropped below 2000 metres on 11 and 12 September.

The outer rain band of a tropical depression over Vietnam brought some showers to Hong Kong on 13 September.

With the establishment of a ridge of high pressure over southeastern China, the weather turned fine on 14 September and remained so for the ensuing two days.

On 17 September, under the combined effect of a ridge of high pressure over southeastern China and Tropical Storm Vicente over the South China Sea, local winds were occasionally strong and there were some squally showers. Windy and showery weather continued on 18 September as Vicente drifted northwest towards the northern part of Vietnam. During the inclement weather in these two days, two men were drowned while swimming in the rough sea in Sai Kung.

Sunny weather returned when a ridge of high pressure set in on 19 September. The weather stayed fine in the next two days.

The Standby Signal No. 1 was issued on the morning of 22 September when Tropical Storm Damrey entered the South China Sea. With the air descending and warming up ahead of Damrey, it was very hot and hazy on 22 September. The maximum temperature rose to 34.3 degrees that afternoon, the highest in the month. As Damrey continued to intensify and moved across the northern part of the South China Sea, the first Strong Wind Signal No. 3 this year was issued on the morning of 24 September. Damrey intensified into a typhoon on 25 September and made landfall over Hainan Island on the early morning of 26 September. Locally, the weather started to deteriorate in the evening of 23 September. Strong winds and squally heavy showers buffeted the territory in the following two days. Over 100 millimetres of rainfall were recorded in some parts of the territory on 25 September. Right after the departure of Damrey, an intense northeast monsoon set in and maintained the windy and showery weather on 26 September. Although local winds abated gradually during the day, it was cloudy with scattered showers on 27 September.

The weather improved on 28 September. It was mainly fine for the rest of the month.

Eight tropical cyclones occurred in the western North Pacific and 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 September are tabulated in Table 2.

Warnings and Signals issued in September 2005

Table 1.1 Tropical Cyclone Warning Signals

Name of Tropical Cyclone	Signal Number	Beginning Time		Ending Time
Name of Tropical Cyclone	Signal Number	Day/Month	HKT	Day/Month	HKT
VICENTE	1	17 / 9	1440	18 / 9	0740
DAMREY	1	22 / 9	1040	24 / 9	0840
DAMREY	3	24 / 9	0840	26 / 9	0820

Table 1.2 Strong Monsoon Signal

Beginning Time		Ending Time
Day/Month	HKT	Day/Month	HKT
18 / 9	0755	18 / 9	2145
26 / 9	1245	27 / 9	1215

Table 1.3 Thunderstorm Warning

Beginning Time		Ending Time
Day/Month	HKT	Day/Month	HKT
31 / 8	2305	1 / 9	0100
3 / 9	0520	3 / 9	1145
3 / 9	1425	3 / 9	1630
4 / 9	0808	4 / 9	1530
6 / 9	1530	6 / 9	1830
7 / 9	2330	8 / 9	0600
8 / 9	1410	8 / 9	1630
9 / 9	1215	9 / 9	1415
9 / 9	1830	9 / 9	2000
10 / 9	1507	10 / 9	1730
10 / 9	1910	10 / 9	2130
12 / 9	1035	12 / 9	1130
13 / 9	0200	13 / 9	0600
13 / 9	1150	13 / 9	1300
14 / 9	0620	14 / 9	0830
17 / 9	1345	17 / 9	1700
18 / 9	1620	18 / 9	1815
18 / 9	1945	18 / 9	2245
19 / 9	0120	19 / 9	0600
20 / 9	0615	20 / 9	0915
25 / 9	0315	25 / 9	0600
25 / 9	0955	25 / 9	1200
25 / 9	1835	25 / 9	2000
25 / 9	2100	26 / 9	0030
26 / 9	0050	26 / 9	1100
27 / 9	0835	27 / 9	1130
27 / 9	1230	27 / 9	1600

Table 1.4 Very Hot Weather Warning

Beginning Time		Ending Time
Day/Month	HKT	Day/Month	HKT
1 / 9	0645	1 / 9	1630
22 / 9	1100	22 / 9	2000

Table 1.5 Special Announcement on Flooding
in the Northern New Territories

Beginning Time		Ending Time
Day/Month	HKT	Day/Month	HKT
8 / 9	1540	8 / 9	1630

Table 2 Figures and Departures from Normal - September 2005

Meteorological Element	Figure of the Month	Departure from Normal*
Mean Daily Maximum Air Temperature	30.4 degrees C	0.1 degree above normal
Mean Air Temperature	28.2 degrees C	0.6 degree above normal
Mean Daily Minimum Air Temperature	26.5 degrees C	1.0 degree above normal
Mean Dew Point Temperature	24.4 degrees C	1.1 degrees above normal
Mean Relative Humidity	81 %	3 % above normal
Mean Cloud Amount	69 %	6 % above normal
Total Rainfall	352.6 mm	52.9 mm above normal
Number of hours of Reduced VisibilityΔ	195 hours	108.6 hours above normal§
Total Bright Sunshine Duration	180.4 hours	1.3 hours below normal
Mean Daily Global Solar Radiation	14.32 Megajoule / square metre	2.17 Megajoule below normal
Total Evaporation	127.5 mm	22.8 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.
* 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 September 2005

Extract of Meteorological Observations in Hong Kong for September 2005