The Weather of April 2023
April 2023 was warmer than usual with a mean temperature of 23.6 degrees, 0.6 degrees above the normal of 23.0 degrees. The month was also drier than usual with a total rainfall of 77.5 millimetres, about half of the normal of 153.0 millimetres. The accumulated rainfall recorded in the first four months of the year was 167.6 millimetres, about 44 percent below the normal figure of 300.4 millimetres for the same period.
With the prevalence of a fresh to strong easterly airstream, the weather of Hong Kong was mainly cloudy with a few showers and rather low visibility in some areas on the first three days of the month. Affected by upper air disturbances, there were also a few isolated thunderstorms on 2 April. The easterly airstream affecting the coast of Guangdong was replaced by a warm and humid southerly airstream on 4 April. Locally, the weather remained mainly cloudy with a few showers and rather low visibility in some areas on 4 – 6 April.
Meanwhile, a cold front moved across the coast of Guangdong on the night of 6 April and brought some rain to the territory. The weather of Hong Kong became cooler with sunny intervals during the day on 7 April. Under the influence of the northeast monsoon, it was mainly cloudy with bright periods during the day on the next three days. There were also a few rain patches on the morning of 9 April. Under the rain, temperatures at the Observatory dropped to a minimum of 18.0 degrees on that morning, the lowest of the month. With the moderation of the northeast monsoon and under light wind conditions, apart from some coastal mist in the morning, the weather was generally fine and hot during the day on 11 – 12 April.
While the easterlies picked up slightly, the weather of Hong Kong remained generally fine on 13 April. With the easterly flow abating and under the influence of a cloud band, the weather became cloudier with a few light rain patches and relatively low visibility in some areas at first on 14 April. Affected by a weak continental airstream, local weather turned sunnier and hot during the day on 15 – 17 April. There was also some haze on 15 April. With plenty of sunshine, temperatures at the Observatory rose to a maximum of 30.8 degrees on the afternoon of 16 April, the highest of the month.
Under the influence of a southerly airstream, apart from a few showers and mist patches, it was hot with sunny intervals during the day on 18 April. Affected by a trough of low pressure, the weather of Hong Kong became unsettled with occasional showers and squally thunderstorms on 19 – 21 April. A band of intense squally thunderstorm associated with the trough of low pressure brought violent gusts to many places on the morning of 19 April. Gusts of around 100 kilometres per hour were once recorded at Star Ferry. A row of hoardings in Sha Tin collapsed on that morning with six persons injured. Moreover, hails were reported at Yuen Long and Fanling during the passage of the intense thunderstorms in the small hours of 21 April. On these three days, more than 30 millimetres of rainfall were recorded generally over Hong Kong and rainfall even exceeded 70 millimetres over the southern part of the territory.
Under the influence of a fresh to strong easterly airstream and the subsequent trough of low pressure over Guangdong, it was mainly cloudy with a few showers and the visibility was rather low in some areas on 22 – 24 April. With the arrival of the northeast monsoon, the weather became slightly cooler with a few rain and mist patches on 25 April. While it remained cooler in the morning, the weather turned brighter and dry during the day on 26 April. Affected by the northeast monsoon, apart from a few rain patches, it was mainly cloudy with sunny intervals during the day the next day. With the moderation of the northeast monsoon, while it was mainly cloudy with a few rain patches at first, the weather became fine during the day on 28 April. Under the influence of a trough of low pressure over inland Guangdong, local weather turned cloudier with a few showers on 29 April. The trough of low pressure then developed into a cold front and moved across the coastal areas on that night. Affected by the associated northeast monsoon, it was dry with sunny periods during the day on the last day of the month.
Two tropical cyclones occurred over the South China Sea and the western North Pacific in April 2023.
A row of hoardings in Sha Tin collapsed due to violent gusts on the morning of 19 April 2023, resulting in six injuries. (Courtesy of Radio Television Hong Kong)
Hail was reported near Yuen Long on 21 April 2023 (Courtesy of Toby Wong)(Left)
Image of radar echoes at 3 a.m. on 21 April 2023.(Right)
Details of issuance and cancellation of various warnings/signals in the month are summarized in Tables 1.1 to 1.4. Monthly meteorological figures and departures from normal for April are tabulated in Table 2.
Warnings and Signals issued in April 2023
|Beginning Time||Ending Time|
|3 / 4||1945||4 / 4||0945|
|21 / 4||2230||23 / 4||0945|
|Colour||Beginning Time||Ending Time|
|Amber||19 / 4||1015||19 / 4||1215|
|Amber||21 / 4||0200||21 / 4||0630|
|Amber||24 / 4||1615||24 / 4||1715|
|Beginning Time||Ending Time|
|2 / 4||0700||2 / 4||0925|
|19 / 4||0945||19 / 4||1430|
|19 / 4||1635||19 / 4||1845|
|19 / 4||1912||20 / 4||0830|
|20 / 4||1622||20 / 4||1800|
|20 / 4||1915||21 / 4||1200|
|21 / 4||1320||21 / 4||2245|
|22 / 4||2117||22 / 4||2300|
|24 / 4||1515||24 / 4||1830|
|Colour||Beginning Time||Ending Time|
|Yellow||7 / 4||0600||7 / 4||1900|
|Yellow||8 / 4||0600||8 / 4||1800|
|Yellow||16 / 4||0600||16 / 4||2000|
|Yellow||30 / 4||0600||30 / 4||2000|
|Meteorological Element||Figure of the Month||Departure from Normal*|
|Mean Daily Maximum Air Temperature||26.0 degrees C||0.4 degree above normal|
|Mean Air Temperature||23.6 degrees C||0.6 degree above normal|
|Mean Daily Minimum Air Temperature||21.7 degrees C||0.6 degree above normal|
|Mean Dew Point Temperature||20.3 degrees C||0.6 degree above normal|
|Mean Relative Humidity||82 %||1 % below normal|
|Mean Cloud Amount||82 %||5 % above normal|
|Total Rainfall||77.5 mm||75.5 mm below normal|
|Number of hours of Reduced VisibilityΔ||15 hours||55.3 hours below normal§|
|Total Bright Sunshine Duration||92.3 hours||20.9 hours below normal|
|Mean Daily Global Solar Radiation||11.02 Megajoule / square metre||1.5 Megajoule below normal|
|Total Evaporation||65.3 mm||21.9 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.
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.
|*||Departure from 1991 - 2020 climatological normal, except for number of hours of reduced visibility|
|§||Departure from mean value between 1997 and 2022|
|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
Extract of Meteorological Observations in Hong Kong for April 2023