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  • The Weather of July 2018

  • 2 August 2018

    The weather in Hong Kong was cloudier than usual in July 2018. The mean amount of cloud in the month was 77 percent, 8 percent above the normal of 69 percent. The duration of bright sunshine in the month was only 181.1 hours, about 15 percent below the normal figure of 212.0 hours. The month was also warmer than usual with the mean temperature of 29.1 degrees, 0.3 degrees above the normal of 28.8 degrees. Despite the cloudy and rather showery conditions for most part of the month, the monthly rainfall was 341.1 millimetres, about 9 percent below the normal of 376.5 millimetres in July. The accumulated rainfall recorded in the first seven months of the year was 974.9 millimetres, a deficit of 34 percent compared to the normal of 1473.3 millimetres for the same period.

    Under the influence of the southwest monsoon, local weather was a mixture of sunshine and showers on 1 - 7 July. There were also occasional heavy showers and squally thunderstorms in isolated areas during these few days. During the localized heavy showers on 5 July, more than 200 millimetres of rainfall were recorded over Tai Po District. A broad trough of low pressure continued to bring showery weather to Hong Kong on 8 - 9 July.

    Apart from one or two morning showers on 10 July, the subsiding air associated with the outer circulation of tropical cyclone Maria brought generally fine weather to Hong Kong on 10 - 11 July. While it was generally fine and very hot on 12 July, with a broad trough of low pressure edging closer to the coast of Guangdong and the picking up of easterly winds, there were heavy showers and squally thunderstorms in Hong Kong on 13 - 15 July. During the downpour, the temperature at the Hong Kong Observatory fell to a minimum of 25.0 degrees on 15 July, the lowest in the month.

    A ridge of high pressure maintained a strong easterly airstream over the coast of Guangdong on 16 July and the showery activities subsided gradually. Meanwhile, an area of low pressure near Luzon developed into a tropical storm, named Son-Tinh, on 17 July. Son-Tinh moved generally westward across the northern part of the South China Sea and entered Beibu Wan on 18 July. It made landfall over the northern part of Vietnam and weakened into an area of low pressure inland on 19 July. Locally, with plenty of sunshine, it was very hot with temperature at the Hong Kong Observatory soaring to 34.3 degrees on the afternoon of 17 July, the highest in the month. Affected by the outer rainbands of Son-Tinh, the weather in Hong Kong became mainly cloudy with occasional squally showers and thunderstorms that night and on the next day. Under the combined effect of the ridge of high pressure over the southeast coast of China and Son-Tinh, it was also windy on 17 - 18 July.

    While the easterly airstream affecting the coast of Guangdong moderated gradually, a broad trough of low pressure continued to bring a few squally showers to Hong Kong on 19 - 20 July. Under the influence of the subsiding air ahead of tropical cyclone Ampil, local weather became generally fine and very hot on 21 July. After a fine and very hot morning, the weather became mainly cloudy with some squally showers over the western part of Hong Kong on the afternoon of 22 July.

    Meanwhile, an area of low pressure associated with the remnant of Son-Tinh re-intensified into a tropical depression over Beibu Wan on 22 July. It moved slowly over Beibu Wan and skirted past the northwestern part of Hainan Island. The tropical depression then made landfall over Leizhou Peninsula on 23 July and dissipated over inland Guaugxi on 24 July. Locally, with active showery activities over the northern part of the South China Sea, it was mainly cloudy with heavy showers and a few squally thunderstorms on 23 July. Showers gradually subsided with more sunshine in the following two days.

    As an anticyclone aloft southeastern China strengthened gradually, the local weather remained generally fine and very hot apart from isolated showers towards the end of the month with the maximum temperature reaching the month’s highest of 34.3 degrees again on 29 July.


     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 July are tabulated in Table 2.
 

Warnings and Signals issued in July 2018

Table 1.1   Tropical Cyclone Warning Signals
Name of
Tropical Cyclone
Signal
Number
Beginning Time Ending Time
Day/Month HKT Day/Month HKT
SON-TINH 1 17 / 7 0240 17 / 7 1620
3 17 / 7 1620 18 / 7 0940
no name 1 23 / 7 1540 24 / 7 1040


Table 1.2   Strong Monsoon Signal
Beginning Time Ending Time
Day/Month HKT Day/Month HKT
14 / 7 0845 16 / 7 1615
18 / 7 0940 18 / 7 2100


Table 1.3   Rainstorm Warning Signals
Colour Beginning Time Ending Time
Day/Month HKT Day/Month HKT
Amber 2 / 7 1215 2 / 7 1315
Amber 15 / 7 1235 15 / 7 1400


Table 1.4   Thunderstorm Warning
Beginning Time Ending Time
Day/Month HKT Day/Month HKT
1 / 7 1350 1 / 7 1600
2 / 7 0203 2 / 7 0315
2 / 7 1048 2 / 7 1615
3 / 7 0725 3 / 7 1500
4 / 7 0050 4 / 7 0300
5 / 7 0952 5 / 7 1500
6 / 7 1512 6 / 7 1615
7 / 7 0922 7 / 7 1400
7 / 7 1455 7 / 7 1530
8 / 7 1450 8 / 7 1730
8 / 7 2255 9 / 7 0100
9 / 7 1755 9 / 7 1945
13 / 7 0350 13 / 7 1200
14 / 7 0245 14 / 7 1030
14 / 7 1140 14 / 7 2230
15 / 7 1220 15 / 7 1530
15 / 7 1557 15 / 7 2100
17 / 7 1945 18 / 7 1515
19 / 7 1005 19 / 7 1230
19 / 7 1425 19 / 7 1630
21 / 7 1520 21 / 7 1730
22 / 7 1400 22 / 7 1510
23 / 7 1355 24 / 7 0700
24 / 7 1000 24 / 7 1400
24 / 7 2005 24 / 7 2200
25 / 7 1300 25 / 7 1400
25 / 7 2050 25 / 7 2300
26 / 7 0535 26 / 7 0900
26 / 7 1140 26 / 7 1500
26 / 7 1627 26 / 7 1730
27 / 7 1305 27 / 7 1430


Table 1.5   Very Hot Weather Warning
Beginning Time Ending Time
Day/Month HKT Day/Month HKT
28 / 6 0645 1 / 7 1620
6 / 7 1110 6 / 7 1800
11 / 7 0645 11 / 7 1845
12 / 7 1130 12 / 7 1800
17 / 7 1210 17 / 7 1815
21 / 7 0645 21 / 7 1730
22 / 7 0645 22 / 7 1620
26 / 7 1215 26 / 7 1800
27 / 7 0645 2 / 8 1700


Table 2   Figures and Departures from Normal - July 2018
Meteorological Element Figure of the Month Departure from Normal*
Mean Daily Maximum Air Temperature 31.8 degrees C 0.4 degree above normal
Mean Air Temperature 29.1 degrees C 0.3 degree above normal
Mean Daily Minimum Air Temperature 27.0 degrees C 0.2 degree above normal
Mean Dew Point Temperature 25.4 degrees C 0.3 degree above normal
Mean Relative Humidity 81 % normal
Mean Cloud Amount 77 % 8 % above normal
Total Rainfall 341.1 mm 35.4 mm below normal
Number of hours of Reduced VisibilityΔ 0 hour 14.2 hours below normal§
Total Bright Sunshine Duration 181.1 hours 30.9 hours below normal
Mean Daily Global Solar Radiation 17.62 Megajoule / square metre 0.45 Megajoule above normal
Total Evaporation 141.1 mm 5.1 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 2017

daily values of selected meteorological elements for HK for July 2018

The percentile map of mean temperature of July 2018

  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



Rainfall Map For July 2018 (isohyets are in millimetres)