4 July 2023

June 2023 was hotter than usual in Hong Kong due to the warmer than normal sea surface temperature over the northern part of the South China Sea and the prevalence of southerly flow. The monthly mean maximum temperature of 31.9 degrees and monthly mean temperature of 29.2 degrees were respectively 1.2 degrees and 0.9 degree above their normals, both ranking the fourth highest on record for June. Moreover, the monthly mean minimum temperature of 27.1 degrees was 0.6 degree above normal and one of the fifth highest on record. With all six months warmer than usual, the first half of 2023 was abnormally warm. The mean maximum temperature of 25.5 degrees was the third highest on record for the same period. Also, the mean temperature of 22.8 degrees and the mean minimum temperature of 20.8 degrees were both the fifth highest on record for the same period. The monthly rainfall of June 2023 was 490.9 millimetres, near the normal of 491.5 millimetres. The accumulated rainfall recorded in the first six months of the year was 841.3 millimetres, about 22 percent below the normal figure of 1082.5 millimetres for the same period.

Under the influence of an area of intense thundery showers moving southwards from inland Guangdong, there were heavy showers and severe squally thunderstorms in Hong Kong on the morning of 1 June with more than 50 millimetres of rainfall recorded over Tuen Mun and Sai Kung. Moreover, more than 10000 strokes of cloud-to-ground lightning were recorded within Hong Kong on that morning. With the departure of the area of thundery showers, sunshine emerged on that afternoon. Affected by an anticyclone aloft, it was generally fine apart from a few showers and isolated thunderstorms on 2 – 4 June. It was extremely hot on the afternoons of 2 – 3 June with maximum temperatures reaching 35 degrees or above in many places. The maximum temperature recorded at the Observatory on the afternoon of 2 June was 35.2 degrees, the highest of the month and the third highest monthly absolute maximum temperature on record for June.

Under the influence of the monsoon depression lingering over the northern part of the South China Sea and Beibu Wan and the trough of low pressure subsequently developed over the coast of southern China, local weather was a mixture of sunny periods, showers and thunderstorms on 5 – 11 June. The showers were particularly heavy on 6 and 10 June with more than 70 millimetres of rainfall recorded over Tuen Mun and the northeastern part of the New Territories on 6 June and over Ma On Shan on 10 June. With the departure of the trough of low pressure, there was more sunshine on 12 June. It was very hot on the afternoons of 8, 10 and 12 June.

With the trough of low pressure lingering over the coastal areas of Guangdong, the weather of Hong Kong deteriorated with occasional heavy showers and squally thunderstorms on 13 – 17 June. More than 200 millimetres of rainfall were recorded generally over the territory and rainfall even exceeded 300 millimetres over the eastern part of the territory and parts of Hong Kong Island and Lantau Island on these five days. The heavy rain on the afternoon of 17 June necessitated the issuance of Red Rainstorm Warning Signal. There were reports of serious flooding over some places in the New Territories on that day. Under the rain, temperatures at the Observatory dropped to a minimum of 25.1 degrees on 14 June, the lowest of the month.

Under the influence of a southwesterly airstream, it was mainly cloudy and showery on 18 – 19 June. The showers were heavier with a few squally thunderstorms on the morning of 18 June. Affected by an anticyclone aloft, there were sunny periods and a few showers on 20 – 22 June. Under the influence of an active southerly airstream, the weather turned mainly cloudy with thundery showers on the next two days. The showers were particularly heavy on 24 June with more than 50 millimetres of rainfall recorded over Lantau Island and parts of the western New Territories. Affected by an anticyclone aloft over southeastern China and a southerly airstream, local weather was a mixture of sunny periods, showers and isolated thunderstorms on 25 – 27 June. The showers were particularly heavy in some places on 26 June with more than 70 millimetres of rainfall recorded over Sha Tin. It was very hot on the afternoon of 27 June. Under the influence of the tropical disturbance over the northeastern part of the South China Sea and the subsequent southerly airstream, the weather of Hong Kong remained a mixture of sunny periods, showers and isolated thunderstorms on the last three days of the month. It was very hot on the afternoon of 29 June.

Two tropical cyclones occurred over the South China Sea and the western North Pacific in June 2023.

Lightning shot at Fanling on the morning of 1 June 2023. (Courtesy of Ching Tak FU)

Warnings and Signals issued in June 2023

Table 1.1   Rainstorm Warning Signals

Colour	Beginning Time		Ending Time
	Day/Month	HKT	Day/Month	HKT
Amber	1 / 6	0515	1 / 6	0800
Amber	6 / 6	1020	6 / 6	1335
Amber	10 / 6	2000	10 / 6	2115
Amber	13 / 6	2250	14 / 6	0550
Amber	14 / 6	2310	15 / 6	0530
Amber	16 / 6	0940	16 / 6	1400
Amber	17 / 6	1240	17 / 6	1405
Red	17 / 6	1405	17 / 6	1615
Amber	17 / 6	1615	17 / 6	1705
Amber	18 / 6	0835	18 / 6	1005

Table 1.2   Thunderstorm Warning

Beginning Time		Ending Time
Day/Month	HKT	Day/Month	HKT
1 / 6	0315	1 / 6	0955
2 / 6	1420	2 / 6	1500
3 / 6	1445	3 / 6	1815
3 / 6	2040	3 / 6	2300
4 / 6	0250	4 / 6	0830
4 / 6	0935	4 / 6	1230
5 / 6	0402	5 / 6	0945
6 / 6	0716	6 / 6	1830
7 / 6	0010	7 / 6	0310
7 / 6	0940	7 / 6	1900
8 / 6	0508	8 / 6	0700
8 / 6	0820	8 / 6	1100
8 / 6	1515	8 / 6	1615
8 / 6	1656	8 / 6	1900
8 / 6	2340	9 / 6	1500
10 / 6	0505	10 / 6	1150
10 / 6	1726	11 / 6	0030
11 / 6	0240	11 / 6	1315
11 / 6	1645	11 / 6	1745
12 / 6	1400	12 / 6	1645
13 / 6	1030	14 / 6	0820
14 / 6	1445	14 / 6	1645
14 / 6	2115	15 / 6	0700
15 / 6	1310	15 / 6	1830
15 / 6	2100	16 / 6	0300
16 / 6	0750	16 / 6	1800
17 / 6	0620	17 / 6	0830
17 / 6	0920	17 / 6	1800
18 / 6	0338	18 / 6	0600
18 / 6	0623	18 / 6	1330
18 / 6	1638	18 / 6	1845
19 / 6	0240	19 / 6	0915
19 / 6	1005	19 / 6	1130
20 / 6	0155	20 / 6	0400
20 / 6	1345	20 / 6	1445
23 / 6	0915	23 / 6	1800
23 / 6	1826	23 / 6	1930
24 / 6	0340	24 / 6	1930
24 / 6	1953	25 / 6	0500
25 / 6	0725	25 / 6	0845
25 / 6	1451	25 / 6	1600
26 / 6	0609	26 / 6	0845
26 / 6	1415	26 / 6	1515
28 / 6	0618	28 / 6	1500
28 / 6	2108	29 / 6	0100
29 / 6	2035	29 / 6	2130
30 / 6	0720	30 / 6	1500

Table 1.3   Very Hot Weather Warning

Beginning Time		Ending Time
Day/Month	HKT	Day/Month	HKT
29 / 5	0645	1 / 6	0530
2 / 6	0645	4 / 6	1745
8 / 6	1230	9 / 6	0950
10 / 6	1510	10 / 6	1840
12 / 6	1115	13 / 6	1620
21 / 6	0945	21 / 6	1745
22 / 6	1015	22 / 6	1815
25 / 6	1330	25 / 6	1620
27 / 6	1145	28 / 6	0720
29 / 6	1300	30 / 6	0900

Table 2   Figures and Departures from Normal - June 2023

Meteorological Element	Figure of the Month	Departure from Normal*
Mean Daily Maximum Air Temperature	31.9 degrees C	1.2 degrees above normal
Mean Air Temperature	29.2 degrees C	0.9 degree above normal
Mean Daily Minimum Air Temperature	27.1 degrees C	0.6 degree above normal
Mean Dew Point Temperature	25.9 degrees C	1.0 degree above normal
Mean Relative Humidity	83 %	1 % above normal
Mean Cloud Amount	82 %	5 % above normal
Total Rainfall	490.9 mm	0.6 mm below normal
Number of hours of Reduced VisibilityΔ	0 hour	13.7 hours below normal§
Total Bright Sunshine Duration	147.4& hours	3.1 hours above normal
Mean Daily Global Solar Radiation	15.17& Megajoule / square metre	0.56 Megajoule above normal
Total Evaporation	87.5 mm	26.3 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
&	Data incomplete

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