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The Weather of July 2023

2 August 2023

With a stronger than usual subtropical ridge dominating over southern China for most of the time in the month, July 2023 was exceptionally hot in Hong Kong. The monthly mean maximum temperature of 33.0 degrees, monthly mean temperature of 30.1 degrees and monthly mean minimum temperature of 28.0 degrees were respectively 1.4 degrees, 1.2 degrees and 1.1 degrees above their normals and all were the third highest on record for July. The month was also much drier than usual with only 175.2 millimetres of rainfall, about 45 percent of the normal of 385.8 millimetres. The accumulated rainfall recorded in the first seven months of the year was 1016.5 millimetres, about 31 percent below the normal figure of 1468.2 millimetres for the same period.

Under the influence of a broad trough of low pressure and the subsequent southwesterly airstream, the weather of Hong Kong was mainly cloudy with occasional showers and squally thunderstorms on the first four days of the month. More than 40 millimetres of rainfall were recorded over most parts of the territory and rainfall even exceeded 100 millimetres over Tai Po, Sha Tin and parts of Lantau Island on these four days. Under the rain, temperatures at the Observatory dropped to a minimum of 26.2 degrees on 1 and 2 July, the lowest of the month. Dominated by an anticyclone aloft, apart from isolated showers, local weather turned generally fine and very hot on 5 July and remained so till 14 July. It was also extremely hot on the afternoons of 13 - 14 July with maximum temperatures reaching 35 degrees or above in many places.

Meanwhile, an area of low pressure near northern Luzon intensified into a tropical depression on 14 July and later named as Talim. It tracked west-northwestwards across the northern part of the South China Sea towards the coast of western Guangdong and intensified into a typhoon gradually on 15 – 17 July. Talim moved across Leizhou Peninsula and Beibu Wan on the night of 17 July and the next morning. It then moved into the inland areas of Guangxi on 18 July and eventually weakened into an area of low pressure over the northern part of Vietnam on 19 July.

Under the influence of the outer subsiding air of Talim, it was mainly fine and extremely hot during the day on 15 July. Squally thunderstorms triggered by high temperatures also affected parts of the territory later on that day. With Talim edging closer to the western Guangdong and further intensifying, local winds strengthened gradually with occasional squally showers and thunderstorms on 16 July. Strong to gale force winds generally affected the territory with occasional storm force winds on high ground on 17 July, necessitating the issuance of the first No.8 Gale or Storm Signal this year. As Talim departed from Hong Kong and weakened over inland, local winds moderated gradually later on 17 July and the next day. The outer rainbands of Talim brought occasional heavy squally showers to Hong Kong on 17 – 18 July. More than 40 millimetres of rainfall were generally recorded over most parts of the territory on these two days and rainfall even exceeded 90 millimetres in parts of Tai Po and North Districts.

Under the influence of a broad trough of low pressure, the weather was mainly cloudy with a few showers on 19 July. Affected by an anticyclone aloft, apart from a few showers, generally fine and very hot weather persisted in Hong Kong on 20 – 25 July. It was extremely hot on the afternoons of 24 - 25 July with maximum temperatures reaching 35 degrees or above in many places. Meanwhile, tropical cyclone Doksuri moved across the Luzon Strait and entered the northeastern part of the South China Sea on 26 – 27 July. It then moved north-northwestwards across the northeastern part of the South China Sea and made landfall over Jinjiang, Fujian on 28 July.

Under the influence of the outer subsiding air of Doksuri, it was generally fine and extremely hot during the day on 26 - 27 July. The maximum temperature at the Observatory soared to 36.1 degrees on the afternoon of 27 July, the highest of the month and one of the highest monthly absolute maximum temperatures on record for July. Moreover, the daily mean temperature on that day was 32.2 degrees and the highest on record for July. The oppressive heat also triggered squally thunderstorms on that evening. It was very hot with sunny periods and isolated showers on 28 July. Affected by an active southerly airstream, the weather turned showery with squally thunderstorms on 29 – 30 July. More than 40 millimetres of rainfall were recorded over most parts of the territory and rainfall even exceeded 100 millimetres over parts of Tai Po, Sha Tin, Tuen Mun and North Districts in these two days. Under the influence of a broad trough of low pressure, it was showery with thunderstorms in the small hours of 31 July. The weather improved with sunny periods during the day.

Three tropical cyclones occurred over the South China Sea and the western North Pacific in July 2023.

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 2023

Table 1.1   Tropical Cyclone Warning Signals
Name of
Tropical Cyclone
Signal
Number
Beginning Time Ending Time
Day/Month HKT Day/Month HKT
TALIM 1 15 / 7 0440 16 / 7 0540
3 16 / 7 0540 17 / 7 0040
8 NE 17 / 7 0040 17 / 7 0640
8 SE 17 / 7 0640 17 / 7 1620
3 17 / 7 1620 18 / 7 0240
1 18 / 7 0240 18 / 7 0840
DOKSURI 1 26 / 7 2040 28 / 7 1240


Table 1.2   Strong Monsoon Signal
Beginning Time Ending Time
Day/Month HKT Day/Month HKT
18 / 7 0841 18 / 7 1440


Table 1.3   Rainstorm Warning Signals
Colour Beginning Time Ending Time
Day/Month HKT Day/Month HKT
Amber 17 / 7 1750 17 / 7 1930
Amber 29 / 7 0810 29 / 7 0910
Red 29 / 7 0910 29 / 7 1010
Amber 29 / 7 1010 29 / 7 1040
Amber 29 / 7 2245 30 / 7 0030
Amber 31 / 7 0100 31 / 7 0320


Table 1.4   Thunderstorm Warning
Beginning Time Ending Time
Day/Month HKT Day/Month HKT
1 / 7 1145 1 / 7 1430
1 / 7 2155 1 / 7 2315
2 / 7 0715 2 / 7 1700
3 / 7 1358 3 / 7 1530
4 / 7 0357 4 / 7 0500
4 / 7 1340 4 / 7 1600
5 / 7 0601 5 / 7 0700
12 / 7 1429 12 / 7 1530
14 / 7 0543 14 / 7 0645
15 / 7 1300 15 / 7 1545
15 / 7 1700 15 / 7 1945
15 / 7 2240 16 / 7 0200
16 / 7 1240 16 / 7 2130
17 / 7 1636 17 / 7 1845
18 / 7 0128 18 / 7 0330
18 / 7 2330 19 / 7 0030
20 / 7 0325 20 / 7 0530
21 / 7 1202 21 / 7 1530
26 / 7 1510 26 / 7 1645
27 / 7 1746 27 / 7 2400
29 / 7 0435 29 / 7 1345
29 / 7 1840 30 / 7 1800
30 / 7 1950 31 / 7 0430
31 / 7 1155 31 / 7 1620


Table 1.5   Very Hot Weather Warning
Beginning Time Ending Time
Day/Month HKT Day/Month HKT
5 / 7 1145 16 / 7 1700
20 / 7 1525 27 / 7 2030
28 / 7 0645 28 / 7 2250


Table 2   Figures and Departures from Normal - July 2023
Meteorological Element Figure of the Month Departure from Normal*
Mean Daily Maximum Air Temperature 33.0 degrees C 1.4 degrees above normal
Mean Air Temperature 30.1 degrees C 1.2 degrees above normal
Mean Daily Minimum Air Temperature 28.0 degrees C 1.1 degrees above normal
Mean Dew Point Temperature 25.8 degrees C 0.6 degree above normal
Mean Relative Humidity 78 % 3 % below normal
Mean Cloud Amount 74 % 2 % above normal
Total Rainfall 175.2 mm 210.6 mm below normal
Number of hours of Reduced VisibilityΔ 0 hour 11.7 hours below normal§
Total Bright Sunshine Duration 219.2 hours 21.9 hours above normal
Mean Daily Global Solar Radiation 19.13 Megajoule / square metre 1.91 Megajoule above normal
Total Evaporation 124.7 mm 17.3 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 1991 - 2020 climatological normal, except for number of hours of reduced visibility
  § Departure from mean value between 1997 and 2022



daily values of selected meteorological elements for HK for July 2023

The percentile map of mean temperature of July 2023

  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