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  • The Weather of July 2019

  • 2 August 2019

    July 2019 was much hotter than usual in Hong Kong, mainly attributing to the warmer than normal sea surface temperature over the northern part of the South China Sea. The monthly mean minimum temperature of 27.7 degrees was 0.9 degree above the normal figure of 26.8 degrees, the highest on record for July. The monthly mean temperature of 29.5 degrees was 0.7 degree above the normal figure of 28.8 degrees, one of the sixth highest on record for July. The month was also cloudier than usual with the mean amount of cloud of 79%, about 10% above the normal figure of 69% and one of the fifth highest on record for July. The duration of bright sunshine in the month was only 150.5 hours, about 29% below the normal figure of 212.0 hours and the seventh lowest on record for July. The monthly rainfall was 328.5 millimetres, about 13 percent below the normal of 376.5 millimetres. The accumulated rainfall recorded in the first seven months of the year was 1437.9 millimetres, slightly lower than the normal figure of 1473.3 millimetres for the same period.

    Affected by an area of low pressure over the northern part of the South China Sea, there were sunny periods and showers as well as isolated thunderstorms on the first day of the month. Meanwhile, the area of low pressure developed into a tropical depression and was named Mun on 2 July. It moved generally westward across Hainan Island and entered Beibu Wan on 3 July. Mun made landfall over the northern part of Vietnam and weakened into an area of low pressure over inland on 4 July. Under the influence of the rainbands associated with Mun, it was cloudy with occasional heavy showers and thunderstorms on 2 – 4 July. More than 100 millimetres of rainfall were recorded over most parts of the territory in these three days.

    With the prevalence of a southwesterly airstream, the weather of Hong Kong was a mixture of sunshine and showers on 5 – 9 July. Under the influence of a trough of low pressure, local weather became showery with a few thunderstorms on 10 – 11 July. More than 60 millimetres of rainfall were recorded over Lantau Island and parts of the New Territories in these two days.

    Dominated by an anticyclone aloft southeastern China, apart from a few showers, local weather turned fine and progressively became very hot from 12 – 18 July. With plenty of sunshine and light winds, the maximum temperature at the Observatory soared to 35.0 degrees on 18 July, the highest of the month. The oppressive heat also triggered thundery showers in that evening. While the weather remained very hot with sunny intervals on the morning of 19 July, high temperature again triggered heavy showers and squally thunderstorms in that afternoon. More than 30 millimetres of rainfall were recorded over many places, and rainfall even exceeded 50 millimetres over the western part of the New Territories. A trough of low pressure continued to bring showery weather with localized heavy rain to Hong Kong on 20 – 21 July. During these two days, more than 40 millimetres of rainfall were recorded over North District, Sai Kung and Southern District, rainfall even exceeded 100 millimetres over Sha Tau Kok.

    Affected by an upper-air disturbance, the weather of Hong Kong was a mixture of sunshine and showers on 22 – 24 July. With the strengthening of the anticyclone aloft southeastern China, local weather became generally fine and very hot apart from isolated showers in the next three days. As the anticyclone aloft weakened, it was mainly cloudy with a few showers and thunderstorms on 28 – 29 July. Meanwhile, an area of low pressure developed into a tropical cyclone over the northern part of the South China Sea on 30 July and was named Wipha. With Wipha moving towards Hainan Island, local weather deteriorated gradually and became windy with outbreaks of squally heavy showers and thunderstorms on the last two days of the month. The outer rainbands associated with Wipha brought more than 100 millimetres of rainfall to most parts of the territory on 31 July and the rainfall over Tseung Kwan O, Wong Tai Sin and Tai Wai even exceeded 200 millimetres. In the midst of the downpour, the temperature at the Observatory dropped to a minimum of 24.5 degrees on 31 July, the lowest of the month.


     Four 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 1.6.  Monthly meteorological figures and departures from normal for July are tabulated in Table 2.
 

Warnings and Signals issued in July 2019

Table 1.1   Tropical Cyclone Warning Signals
Name of
Tropical Cyclone
Signal
Number
Beginning Time Ending Time
Day/Month HKT Day/Month HKT
MUN 1 2 / 7 1615 3 / 7 0540
WIPHA 1 30 / 7 1540 30 / 7 2115
3 30 / 7 2115 31 / 7 1340
8 NE 31 / 7 1340 31 / 7 2340
3 31 / 7 2340 1 / 8 1920


Table 1.2   Rainstorm Warning Signals
Colour Beginning Time Ending Time
Day/Month HKT Day/Month HKT
Amber 3 / 7 0045 3 / 7 0205
Amber 19 / 7 1405 19 / 7 1515
Amber 19 / 7 1845 19 / 7 1945
Amber 20 / 7 1210 20 / 7 1330
Amber 31 / 7 1155 31 / 7 1435
Amber 31 / 7 1730 31 / 7 2000
Red 31 / 7 2000 31 / 7 2130


Table 1.3   Landslip Warning
Beginning Time Ending Time
Day/Month HKT Day/Month HKT
31 / 7 2040 2 / 8 0915


Table 1.4   Thunderstorm Warning
Beginning Time Ending Time
Day/Month HKT Day/Month HKT
1 / 7 0225 1 / 7 0600
1 / 7 0940 1 / 7 1045
1 / 7 1245 1 / 7 1345
2 / 7 0245 2 / 7 0415
2 / 7 1023 2 / 7 1120
2 / 7 2110 3 / 7 1745
4 / 7 0050 4 / 7 0300
4 / 7 0325 4 / 7 0640
10 / 7 0215 10 / 7 0415
10 / 7 0910 10 / 7 1115
10 / 7 1155 10 / 7 1800
11 / 7 0615 11 / 7 0715
11 / 7 1425 11 / 7 2130
18 / 7 1405 18 / 7 1600
18 / 7 1735 18 / 7 2045
19 / 7 1220 19 / 7 1600
19 / 7 1755 19 / 7 2040
20 / 7 1035 20 / 7 1500
20 / 7 1545 20 / 7 1930
21 / 7 0905 21 / 7 1345
22 / 7 1015 22 / 7 1500
22 / 7 1738 23 / 7 0020
23 / 7 0420 23 / 7 0735
28 / 7 0715 28 / 7 1100
28 / 7 1330 28 / 7 1600
29 / 7 0500 29 / 7 1030
29 / 7 1420 29 / 7 1500
29 / 7 1725 29 / 7 1830
30 / 7 0525 30 / 7 1115
30 / 7 1925 30 / 7 2030
30 / 7 2125 31 / 7 0200
31 / 7 0345 31 / 7 1500
31 / 7 1845 31 / 7 2245


Table 1.5   Very Hot Weather Warning
Beginning Time Ending Time
Day/Month HKT Day/Month HKT
1 / 7 1350 1 / 7 2015
7 / 7 1220 7 / 7 1610
13 / 7 0645 18 / 7 1945
19 / 7 1045 19 / 7 1345
20 / 7 0950 20 / 7 1205
25 / 7 0700 27 / 7 1900


Table 1.6   Special Announcement on Flooding
in the Northern New Territories
Beginning Time Ending Time
Day/Month HKT Day/Month HKT
31 / 7 2025 31 / 7 2400


Table 2   Figures and Departures from Normal - July 2019
Meteorological Element Figure of the Month Departure from Normal*
Mean Daily Maximum Air Temperature 32.1 degrees C 0.7 degree above normal
Mean Air Temperature 29.5 degrees C 0.7 degree above normal
Mean Daily Minimum Air Temperature 27.7 degrees C 0.9 degree above normal
Mean Dew Point Temperature 25.9 degrees C 0.8 degree above normal
Mean Relative Humidity 81 % normal
Mean Cloud Amount 79 % 10 % above normal
Total Rainfall 328.5 mm 48.0 mm below normal
Number of hours of Reduced VisibilityΔ 1 hour 12.5 hours below normal§
Total Bright Sunshine Duration 150.5 hours 61.5 hours below normal
Mean Daily Global Solar Radiation 15.51 Megajoule / square metre 1.66 Megajoule below normal
Total Evaporation 114.4 mm 31.8 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 1981 - 2010 climatological normal, except for number of hours of reduced visibility

  §   Departure from mean value between 1997 and 2018

daily values of selected meteorological elements for HK for July 2019

The percentile map of mean temperature of July 2019

  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


Extract of Meteorological Observations in Hong Kong for July 2019