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  • The Weather of September 2016

  • 4 October 2016

    With rainy weather dominating the first part of the month, September 2016 was gloomier than usual. The total duration of sunshine recorded in the month was 135.7 hours, 36.6 hours below the normal figure of 172.3 hours and the seventh lowest on record for September. However, the month was slightly warmer than usual with a monthly mean temperature of 27.9 degrees, 0.2 degree higher than the normal figure of 27.7 degrees. The monthly total rainfall was 323.1 millimetres, slightly below the normal figure of 327.6 millimetres. The accumulated rainfall of 2264.5 millimetres for the first nine months was about 1 percent above the normal figure of 2233.1 millimetres for the same period.

    With a trough of low pressure lingering over the South China coast, the weather in Hong Kong was unstable with showers and thunderstorms on the first ten days of the month. The showers were particularly heavy on 1, 5 and 10 September with over 30 millimetres of rainfall generally over the territory. With the trough of low pressure weakening gradually, there were sunny periods and a few showers on 11 September.

    Under the dominance of the anticyclone over southern China, local weather became generally fine apart from a few isolated showers on 12-13 September. Meanwhile, Super Typhoon Meranti moved across the Luzon Strait on the night of 13 September and swept across the coastal waters of southwestern Taiwan the next day. Affected by the outer subsiding air associated with Meranti, the weather in Hong Kong was very hot and dry on 14 September with temperatures rising to about 33 degrees over most parts of the territory. With Meranti making landfall near Xiamen and weakening over inland, the cloud band associated with Meranti covered eastern Guangdong and there were a few isolated showers in Hong Kong on 15 September.

    Under the influence of a relatively dry continental airstream, it was mainly fine, hot and dry in Hong Kong on 16-18 September. While it remained generally fine during the day on 19 September, with the northeast monsoon setting in, local weather turned cloudy with some rain that night. Affected by the northeast monsoon, the weather became cooler and rainy on 20 September. With the gradual thinning of cloud covering the south China coastal areas, the weather became mainly fine on 21-26 September.

    Over the western North Pacific, Severe Typhoon Megi moved across Taiwan on the afternoon of 27 September and made landfall at Fujian the next morning. Megi moved westward across Fujian and weakened gradually on 28 September. It degenerated into an area of low pressure over Jiangxi on the morning of 29 September. Under the subsidence effect ahead of Megi, local weather was very hot and hazy on 27 September with temperatures at the Observatory reaching a maximum of 34.9 degrees, the highest of the month and the second highest on record for September. With Megi taking a more westerly track and edging closer to Guangdong, local winds strengthened from the northwest and cleared the haze on 28 September. Under the influence of the northeast monsoon, it was mainly cloudy and cooler for the rest of the month.

    Seven tropical cyclones occurred over the South China Sea and the western North Pacific 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 2016

Table 1.1   Tropical Cyclone Warning Signals
Name of
Tropical Cyclone
Signal
Number
Beginning Time Ending Time
Day/Month HKT Day/Month HKT
MERANTI 1 14 / 9 1010 15 / 9 0420
MEGI 1 28 / 9 0840 28 / 9 2310


Table 1.2   Rainstorm Warning Signals
Colour Beginning Time Ending Time
Day/Month HKT Day/Month HKT
Amber 1 / 9 0655 1 / 9 0745
Amber 9 / 9 1145 9 / 9 1320
Amber 10 / 9 1235 10 / 9 1355


Table 1.3   Thunderstorm Warning
Beginning Time Ending Time
Day/Month HKT Day/Month HKT
1 / 9 0105 1 / 9 1600
2 / 9 0340 2 / 9 0445
2 / 9 0715 2 / 9 0915
2 / 9 1220 2 / 9 1530
2 / 9 2130 3 / 9 0030
3 / 9 0230 3 / 9 0400
3 / 9 1405 3 / 9 1515
5 / 9 1240 5 / 9 2015
6 / 9 0005 6 / 9 0300
8 / 9 0740 8 / 9 0945
9 / 9 0915 9 / 9 1400
10 / 9 0755 10 / 9 1500
11 / 9 0855 11 / 9 1100
11 / 9 1805 11 / 9 2015
11 / 9 2105 11 / 9 2215
13 / 9 0245 13 / 9 0345


Table 1.4   Fire Danger Warnings
Colour Beginning Time Ending Time
Day/Month HKT Day/Month HKT
Yellow 15 / 9 0600 18 / 9 1930
Yellow 25 / 9 0600 25 / 9 1800


Table 1.5   Very Hot Weather Warning
Beginning Time Ending Time
Day/Month HKT Day/Month HKT
12 / 9 1330 12 / 9 1810
13 / 9 0645 13 / 9 1620
14 / 9 0645 14 / 9 1700
27 / 9 0715 27 / 9 2345


Table 2   Figures and Departures from Normal - September 2016
Meteorological Element Figure of the Month Departure from Normal*
Mean Daily Maximum Air Temperature 30.4 degrees C 0.3 degree above normal
Mean Air Temperature 27.9 degrees C 0.2 degree above normal
Mean Daily Minimum Air Temperature 26.1 degrees C 0.3 degree above normal
Mean Dew Point Temperature 23.9 degrees C 0.5 degree above normal
Mean Relative Humidity 79 % 1 % above normal
Mean Cloud Amount 72 % 6 % above normal
Total Rainfall 323.1 mm 4.5 mm below normal
Number of hours of Reduced VisibilityΔ 45 hours 38.1 hours below normal§
Total Bright Sunshine Duration 135.7 hours 36.6 hours below normal
Mean Daily Global Solar Radiation 13.38 Megajoule / square metre 1.23 Megajoule below normal
Total Evaporation 103.6& mm 22.3 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 1981 - 2010 climatological normal, except for number of hours of reduced visibility

  §   Departure from mean value between 1997 and 2015

  &   Data incomplete

daily values of selected meteorological elements for HK for September 2016

The percentile map of mean temperature of September 2016

  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 1981 to 2010