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  • The Weather of October 2016

  • 2 November 2016

    October 2016 was marked by record-breaking high mean temperatures, despite a succession of cyclonic systems passing by in the vicinity of Hong Kong and the duration of sunshine falling under 80 percent of the October normal. The monthly mean maximum temperature of 29.1 degrees, monthly mean temperature of 26.8 degrees and monthly mean minimum temperature of 25.0 degrees were all 1.3 degrees above their respective normals and were the highest ever on record for October. After the passage of the remnant circulation of Severe Typhoon Megi over southern China in late September, Tropical Storm Aere hovered for days over the coastal waters of Guangdong at the doorstep of Hong Kong in early October. Then came Super Typhoon Sarika and Super Typhoon Haima in less than a week between 16 and 21 October. The former brought torrential rain that broke the October hourly rainfall record and triggered the Black Rainstorm Warning on 19 October, while the latter led to the issuance of the No. 8 Gale or Storm Signal on 21 October. The monthly rainfall recorded at the Hong Kong Observatory was 624.4 millimetres, more than six times the October normal of 100.9 millimetres and the second highest on record for October. The accumulated rainfall of 2888.9 millimetres up to the end of October was about 24 percent above the normal figure of 2334.0 millimetres for the same period.

    In the wake of Megi, unsettled weather prevailed over the coastal waters of Guangdong, with heavy showers and thunderstorms affecting Hong Kong early in the morning on 1 October. The Red Rainstorm Warning was issued as more than 70 millimetres of rainfall generally fell over the urban areas and the eastern part of the New Territories. Local weather was a combination of increasing sunshine and decreasing showers over the following four days as a weak low pressure system drifted southwestward off the coast of Guangdong and passed by to the south of Hong Kong. Meanwhile, Aere followed the weak low into the northeastern part of the South China Sea on 6 October and lingered for days to the southeast of Hong Kong before weakening into an area of low pressure on the night of 10 October. Locally, it was generally fine and hot during the day on 6 October and temperature at the Hong Kong Observatory rose to a maximum of 32.4 degrees, the highest of the month. After some showers that night, the weather gradually turned sunnier over the next four days.

    As Aere weakened and drifted away towards Xisha, cooler air associated with the northeast monsoon gradually spread south towards the coastal areas of Guangdong. Temperature at the Hong Kong Observatory fell to a minimum of 22.0 degrees on 11 October, the lowest of the month. Local weather turned windier under a strong easterly airstream, and after some rain patches on 11 and 12 October, it became mainly fine over the next four days as the winds gradually subsided.

    Meanwhile, Severe Typhoon Sarika moved across Luzon and entered the South China Sea on the morning of 16 October. Tracking west-northwestwards, Sarika made landfall over Hainan Island on the morning of 18 October and moved across Beibu Wan on 19 October. Under the combined effect of Sarika and the northeast monsoon over southern China, local weather became windy with squally showers on 17-19 October. The convergence between the northeast monsoon and the southerly airstream associated with Sarika triggered prolonged periods of heavy rain and thunderstorms on 18 and 19 October. The rain was most intense on the afternoon of 19 October, with more than 100 millimetres of rainfall falling generally over Hong Kong and rainfall even exceeding 200 millimetres over the urban areas, Shatin and Tai Po, necessitating the issuance of the first ever Black Rainstorm Warning in October since the Rainstorm Warning System commenced operation in 1992. The hourly rainfall of 78.7 millimetres recorded at the Hong Kong Observatory between 3 and 4 p.m. that day was also the highest in October since records began in 1884.

    As Sarika dissipated over inland Guangxi, Super Typhoon Haima moved across Luzon and entered the northern part of the South China Sea on the morning of 20 October. Affected by the subsiding air ahead of Haima, it was mainly fine and hazy in Hong Kong that day. Haima weakened gradually into a typhoon as it edged towards the coast of eastern Guangdong and made landfall near Shanwei around noon on 21 October. With the approach of Haima, local winds strengthened significantly and reached gale force in many places during the day. The rainbands of Haima also brought squalls and heavy rain to Hong Kong. More than 100 millimetres of rainfall fell over Kowloon City, Wong Tai Sin and the eastern part of the New Territories. As Haima moved further inland, local weather improved with sunny periods and a few isolated showers over the next three days.

    With the establishment of an upper-air anticyclone over southern China, local weather became fine and hot on 25-28 October. The passage of a cold front on 29 October brought cooler weather and some showers. The weather remained windy with sunny intervals the next day before mainly fine weather returned on the last day of the month as the monsoon winds subsided.

Severe flooding at Ching Cheung Road (left) and Chai Wan Road (right) on 19 October 2016
Severe flooding at Ching Cheung Road (left) and Chai Wan Road (right) on 19 October 2016
(courtesy of Drainage Services Department)


Tree blown down near Lai Chi Kok Fire Station during the passage of Haima
Tree blown down near Lai Chi Kok Fire Station during the passage of Haima
(photo provided by member of the public)


Radar echoes at 10 a.m. on 21 October 2016 as Haima made landfall east of Hong Kong
Radar echoes at 10 a.m. on 21 October 2016 as Haima made landfall east of Hong Kong


    Five 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 1.7.  Monthly meteorological figures and departures from normal for October are tabulated in Table 2.
 

Warnings and Signals issued in October 2016

Table 1.1   Tropical Cyclone Warning Signals
Name of
Tropical Cyclone
Signal
Number
Beginning Time Ending Time
Day/Month HKT Day/Month HKT
AERE 1 6 / 10 2040 9 / 10 0345
SARIKA 1 16 / 10 2120 17 / 10 1340
3 17 / 10 1340 18 / 10 2210
HAIMA 1 20 / 10 0820 20 / 10 2040
3 20 / 10 2040 21 / 10 0610
8 NW 21 / 10 0610 21 / 10 1415
8 SW 21 / 10 1415 21 / 10 1720
3 21 / 10 1720 21 / 10 2210


Table 1.2   Strong Monsoon Signal
Beginning Time Ending Time
Day/Month HKT Day/Month HKT
12 / 10 2045 13 / 10 0745
13 / 10 2245 14 / 10 0740
18 / 10 2211 19 / 10 0845
29 / 10 1930 29 / 10 2215


Table 1.3   Rainstorm Warning Signals
Colour Beginning Time Ending Time
Day/Month HKT Day/Month HKT
Amber 1 / 10 0525 1 / 10 0555
Red 1 / 10 0555 1 / 10 0700
Amber 1 / 10 0700 1 / 10 0735
Amber 18 / 10 1525 18 / 10 1815
Amber 19 / 10 1300 19 / 10 1530
Red 19 / 10 1530 19 / 10 1600
Black 19 / 10 1600 19 / 10 1715
Red 19 / 10 1715 19 / 10 1815
Amber 19 / 10 1815 19 / 10 1930


Table 1.4   Landslip Warning
Beginning Time Ending Time
Day/Month HKT Day/Month HKT
19 / 10 0920 19 / 10 2200


Table 1.5   Thunderstorm Warning
Beginning Time Ending Time
Day/Month HKT Day/Month HKT
1 / 10 0325 1 / 10 1015
1 / 10 1410 1 / 10 1445
4 / 10 0940 4 / 10 1115
4 / 10 1615 4 / 10 1715
6 / 10 2225 7 / 10 0130
19 / 10 1030 19 / 10 1830


Table 1.6   Fire Danger Warnings
Colour Beginning Time Ending Time
Day/Month HKT Day/Month HKT
Yellow 9 / 10 0600 9 / 10 2045
Yellow 10 / 10 0600 10 / 10 2100
Yellow 16 / 10 0600 16 / 10 1800
Yellow 30 / 10 0600 30 / 10 2230


Table 1.7   Special Announcement on Flooding
in the Northern New Territories
Beginning Time Ending Time
Day/Month HKT Day/Month HKT
18 / 10 1730 18 / 10 2015
19 / 10 1325 19 / 10 2150


Table 2   Figures and Departures from Normal - October 2016
Meteorological Element Figure of the Month Departure from Normal*
Mean Daily Maximum Air Temperature 29.1 degrees C 1.3 degrees above normal
Mean Air Temperature 26.8 degrees C 1.3 degrees above normal
Mean Daily Minimum Air Temperature 25.0 degrees C 1.3 degrees above normal
Mean Dew Point Temperature 22.9 degrees C 2.7 degrees above normal
Mean Relative Humidity 80 % 7 % above normal
Mean Cloud Amount 74 % 16 % above normal
Total Rainfall 624.4 mm 523.5 mm above normal
Number of hours of Reduced VisibilityΔ 28 hours 114.8 hours below normal§
Total Bright Sunshine Duration 152.6 hours 41.3 hours below normal
Mean Daily Global Solar Radiation 12.91 Megajoule / square metre 1.14 Megajoule below normal
Total Evaporation 95.2& mm 28.7 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 October 2016

The percentile map of mean temperature of October 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