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September was wetter than normal. The monthly rainfall of 365.7 millimetres was 22 per cent higher than the normal figure. The total rainfall since January 1 was 2 041.7 millimetres, two per cent above the normal for the same period.
Three tropical cyclones affected Hong Kong in the month and the Hurricane Signal No 10 was hoisted during the passage of Typhoon York. This was the first time since 1983 that the Hurricane Signal was hoisted. The Red Rainstorm Warning Signal and the Landslip Warning were issued on September 16.
It was fine on the morning of September 1. Isolated thunderstorms developed in the afternoon and a fisherman was struck by lightning near Lei Yue Mun. Hazy conditions occurred the following morning and there were isolated showers in the afternoon. It was again hazy on the morning of September 3 but the weather became fine and hot in the afternoon with temperatures rising to 32.8 degrees, the highest in the month.
As Tropical Storm Wendy made landfall near Shanwei early on September 4, local weather turned cloudy with a few showers. Isolated thunderstorms developed on September 5. However, it was mainly fine apart from some isolated showers for the next few days.
The weather became fine and hot on September 10. Hot weather persisted the next few days and it was reported that two hikers died of heatstroke on September 12. Hazy conditions were observed at the airport on September 13 and 14. Temperatures rose to 32.8 degrees again on September 14.
On September 15, Typhoon York approached Hong Kong from the southeast and weather became cloudy to overcast with some rain patches. Strong winds started to affect offshore areas in the evening. York crossed the southwestern part of Lantau around noon the following day. Winds of hurricane force and heavy rain buffeted the territory resulting in the death of two people. The daily rainfall of 276.0 millimetres recorded on September 16 was the second highest for September.
As York moved away, rain eased off and sunny periods developed on September 18. Isolated heavy showers returned the following day. It was hazy on the morning of September 20 and there were isolated thunderstorms in the afternoon.
A northeast monsoon brought dry weather to the southern China coastal areas on September 21. It became fine with long sunny periods on September 22.
Fine weather persisted until September 25 when Severe Tropical Storm Cam approached from the southeast. Cam swept across the New Territories the following day. Gales and a few squally showers were experienced. Temperatures dropped to 22.8 degrees that morning in heavy showers, the lowest in the month. Weather remained mainly cloudy.
Easterly winds strengthened offshore on the evening of September 27 as the northeast monsoon intensified, bringing along some rain patches. Cloudy and rainy weather continued the following day. It became fine and sunny on September 29. Fine weather prevailed till the end of the month.
Six tropical cyclones occurred in the South China Sea and the western North Pacific in the month.
Details of the issuance/hoisting and cancellation/lowering of various warnings/signals in the month are summarized in Table 1.1. Monthly meteorological figures and departures from normal of September are tabulated in Table 1.2.
Table 1.1 Warnings and Signals in September 1999
Beginning Time Ending Time
Type of Warnings/Signals day/month hour day/month hour
Tropical Cyclone Warning Signals
Name of Signal
Tropical Cyclone Number
Wendy 1 3/9 0345 4/9 1120
York 1 13/9 1045 15/9 1015
3 15/9 1015 16/9 0315
8 NW 16/9 0315 16/9 0520
9 16/9 0520 16/9 0645
10 16/9 0645 16/9 1745
8 SW 16/9 1745 16/9 2210
3 16/9 2210 17/9 0045
Cam 1 24/9 0940 25/9 1540
3 25/9 1540 26/9 0520
8 NW 26/9 0520 26/9 1120
8 SW 26/9 1120 26/9 1410
3 26/9 1410 26/9 1520
Strong Monsoon Signals 22/9 0725 22/9 0945
27/9 2225 28/9 1402
Rainstorm Warning Signals
Amber 16/9 0450 16/9 0527
Red 16/9 0527 16/9 1840
Amber 26/9 0955 26/9 1320
Landslip Warning 16/9 0610 17/9 0950
Thunderstorm Warnings 1/9 1340 1/9 2100
2/9 1340 2/9 1540
3/9 1455 3/9 1755
3/9 1940 3/9 2140
5/9 0435 5/9 0635
5/9 0805 5/9 1005
5/9 1212 5/9 1412
6/9 0600 6/9 0700
6/9 1350 6/9 1550
8/9 1240 8/9 1440
9/9 0900 9/9 1500
10/9 1240 10/9 1540
11/9 1135 11/9 1335
12/9 1400 12/9 1800
13/9 1800 13/9 2100
14/9 1608 14/9 1808
17/9 1905 17/9 2105
18/9 0220 18/9 0720
18/9 0755 18/9 0955
19/9 1700 19/9 1900
20/9 1130 20/9 2130
26/9 0840 26/9 1140
28/9 0145 28/9 0645
Fire Danger Warning
Yellow 23/9 1800 25/9 0615
Table 1.2 Figures and Departures from Normal - September 1999
Meteorological Element Figure of Departure from normal
the month above normal below normal
Total Bright Sunshine 148.5 ---- 33.2
Duration(hours)
Mean Daily Global Solar 13.39 ---- 3.10
Radiation (MJ/Square Metre)
Total Rainfall (mm) 365.7 66.0 ----
Mean Cloud Amount (%) 70 7 ----
Mean Relative Humidity (%)78 ---- ----
Mean Daily Maximum Air 30.4 0.1 ----
Temperature (Degree Celsius)
Mean Air Temperature 27.8 0.2 ----
(Degree Celsius)
Mean Daily Minimum Air 25.9 0.4 ----
Temperature (Degree Celsius)
Mean Dew Point 23.5 0.2 ----
(Degree Celsius)
Total Evaporation (mm) 123.0 ---- 27.3
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.
End/Tuesday, October 12, 1999
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