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The Weather of September 2022

5 October 2022

With much sunnier weather than usual in the month, September 2022 was exceptionally hot in Hong Kong. The monthly mean maximum temperature of 32.7 degrees, mean temperature of 29.6 degrees and mean minimum temperature of 27.3 degrees were 2.2 degrees, 1.7 degrees and 1.2 degrees above their corresponding normals and all of them were the second highest on record for September. There were 3 days with daily maximum temperatures at the Hong Kong Observatory equal to or higher than 35.0 degrees in the month, the highest number on record for September. The total duration of bright sunshine of 237.4 hours in the month was about 36 percent higher than the normal of 174.4 hours and the eighth highest on record for September. The month was also drier than usual with a monthly rainfall of only 171.2 millimetres, about 53 percent of the normal of 321.4 millimetres. The accumulated rainfall this year up to September was 1999.0 millimetres, about 11 percent lower than the normal figure of 2242.8 millimetres for the same period.

Under the influence of a weak northeast monsoon, it was very hot with sunny periods on the first day of the month in Hong Kong. High temperatures also triggered thundery showers over the territory in the afternoon. More than 70 millimetres of rainfall were recorded over Tai Po and North District of the New Territories. Affected by a dry continental airstream, the weather of Hong Kong was fine and dry on 2 – 6 September. It was also very hot during the day on 3 – 6 September.

Under the influence of an easterly airstream along the coast of Guangdong and a broad trough of low pressure over the South China Sea, local weather turned mainly cloudy with occasional showers and a few thunderstorms on 7 September. More than 20 millimetres of rainfall were recorded over many places in the New Territories and rainfall even exceeded 40 millimetres in Tai Po. Dominated by a ridge of high pressure, apart from isolated showers, it was generally fine and very hot during the day on 8 – 9 September. Under light wind conditions, apart from sunny intervals, high temperatures triggered a few showers the next day.

With the prevalence of a dry continental airstream, apart from a few showers, the weather of Hong Kong was generally fine and very hot on 11 – 17 September. It was also very dry during the day on 13 – 15 September and there were some haze on 12 – 13 and 16 – 17 September. With plenty of sunshine, the maximum temperature at the Observatory soared to 35.9 degrees on 13 September, the highest of the month and the highest maximum temperature for September on record. Moreover, the daily mean temperature at the Observatory reached 31.7 degrees on 13 and 14 September, both were the highest on record for September. The daily minimum temperature of 29.6 degrees on 14 September was also the highest on record for September.

Under light wind conditions, apart from sunny periods on 18 – 19 September, high temperatures triggered a few showers and squally thunderstorms over the territory on these two days. In particular, the isolated severe squally thunderstorms on the afternoon of 18 September brought intense gusts to Sai Kung, Lau Fau Shan and Tai O. With the onset of a fresh to strong northeast monsoon, there were sunny intervals and a few showers on 20 September. Apart from a few morning showers, the weather of Hong Kong turned generally fine on the next two days.

With the arrival of a replenishment of the northeast monsoon, local weather was mainly fine at first but became cloudy gradually with a few showers and thunderstorms later on 23 September. More than 20 millimetres of rainfall were recorded over the western part of the New Territories. Under the influence of the drier northeast monsoon, apart from a few showers, it was generally fine and dry on 24 – 26 September. Local weather turned cloudier and windier on 27 – 28 September. Affected by a broad trough of low pressure, it was mainly cloudy with showers and squally thunderstorms on 29 – 30 September. Showers were heavy at times on 30 September, with more than 100 millimetres of rainfall recorded over many places of the territory. Under the rain, the temperature at the Observatory dropped to a minimum of 24.8 degrees on that day, the lowest of the month.

Eight tropical cyclones occurred over the South China Sea and the western North Pacific in September 2022.

Details of issuance and cancellation of various warnings/signals in the month are summarized in Tables 1.1 to 1.6.  Monthly meteorological figures and departures from normal for September are tabulated in Table 2.

 

Warnings and Signals issued in September 2022

Table 1.1   Strong Monsoon Signal
Beginning Time Ending Time
Day/Month HKT Day/Month HKT
27 / 9 0145 29 / 9 0245


Table 1.2   Rainstorm Warning Signals
Colour Beginning Time Ending Time
Day/Month HKT Day/Month HKT
Amber 30 / 9 1025 30 / 9 1415
Amber 30 / 9 2010 30 / 9 2110


Table 1.3   Thunderstorm Warning
Beginning Time Ending Time
Day/Month HKT Day/Month HKT
1 / 9 1400 1 / 9 1930
7 / 9 0235 7 / 9 1015
10 / 9 1523 10 / 9 1630
16 / 9 1434 16 / 9 1555
17 / 9 1550 17 / 9 1700
18 / 9 1445 18 / 9 2045
18 / 9 2123 19 / 9 0930
19 / 9 1430 19 / 9 1930
20 / 9 1015 20 / 9 1330
23 / 9 1540 23 / 9 1830
23 / 9 2145 23 / 9 2345
24 / 9 0040 24 / 9 0300
29 / 9 0630 29 / 9 1245
29 / 9 2305 30 / 9 0500
30 / 9 0820 30 / 9 2145


Table 1.4   Fire Danger Warnings
Colour Beginning Time Ending Time
Day/Month HKT Day/Month HKT
Red 2 / 9 1130 4 / 9 2330
Red 5 / 9 0600 6 / 9 1900
Red 9 / 9 0600 9 / 9 1945
Yellow 10 / 9 0600 10 / 9 1745
Yellow 11 / 9 0600 11 / 9 1800
Yellow 12 / 9 0600 12 / 9 2030
Red 13 / 9 0600 16 / 9 1900
Yellow 17 / 9 0600 17 / 9 1830
Yellow 18 / 9 0615 18 / 9 1645
Yellow 24 / 9 0845 24 / 9 1900
Yellow 25 / 9 0600 25 / 9 1945


Table 1.5   Very Hot Weather Warning
Beginning Time Ending Time
Day/Month HKT Day/Month HKT
1 / 9 1110 1 / 9 1545
2 / 9 0645 2 / 9 1620
3 / 9 0645 3 / 9 1930
4 / 9 0645 6 / 9 1745
8 / 9 1130 9 / 9 1620
11 / 9 0645 11 / 9 1730
12 / 9 0645 19 / 9 1700
26 / 9 1235 26 / 9 1730


Table 1.6   Special Announcement on Flooding
in the Northern New Territories
Beginning Time Ending Time
Day/Month HKT Day/Month HKT
1 / 9 1630 1 / 9 1920


Table 2   Figures and Departures from Normal - September 2022
Meteorological Element Figure of the Month Departure from Normal*
Mean Daily Maximum Air Temperature 32.7 degrees C 2.2 degrees above normal
Mean Air Temperature 29.6 degrees C 1.7 degrees above normal
Mean Daily Minimum Air Temperature 27.3 degrees C 1.2 degrees above normal
Mean Dew Point Temperature 22.8 degrees C 0.8 degrees below normal
Mean Relative Humidity 69 % 9 % below normal
Mean Cloud Amount 54 % 12 % below normal
Total Rainfall 171.2 mm 150.2 mm below normal
Number of hours of Reduced VisibilityΔ 5 hours 63.0 hours below normal§
Total Bright Sunshine Duration 237.4 hours 63.0 hours above normal
Mean Daily Global Solar Radiation 18.33 Megajoule / square metre 3.34 Megajoule above normal
Total Evaporation 135.6 mm 12.8 mm above 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 1991 - 2020 climatological normal, except for number of hours of reduced visibility

  §   Departure from mean value between 1997 and 2021

Daily values of selected meteorological elements for Hong Kong for September

The percentile map of mean temperature of September

  Remarks : Extremely high: above 95th percentile
Above normal: between 75th and 95th percentile
Normal: between 25th and 75th percentile
Below normal: between 5th and 25th percentile
Extremely low: below 5th percentile
Percentile and 5-day running average values are
computed based on the data from 1991 to 2020


Extract of Meteorological Observations in Hong Kong for September 2022