Mainly attributing to the warmer than normal sea surface temperature and stronger than usual southerly flow in the lower atmosphere over the northern part of the South China Sea, April 2024 was much warmer than usual.  The monthly mean maximum temperature of 28.9 degrees, monthly mean temperature of 26.4 degrees and monthly mean minimum temperature of 24.5 degrees were 3.3 degrees, 3.4 degrees and 3.4 degrees above their corresponding normals and all of them were the highest on record for April.  Affected by a number of troughs of low pressure, the month was also wetter than usual with a total rainfall of 257.1 millimetres, about 68 percent more than the normal figure of 153.0 millimetres.  The accumulated rainfall recorded in the first four months of the year was 289.5 millimetres, about 4 percent below the normal figure of 300.4 millimetres for the same period.

Under the influence of a southerly airstream, the weather was hot with sunny intervals during the day in Hong Kong on the first four days of the month.  The visibility was rather low in the morning and at night on 1 April.  The daily mean temperature of 27.2 degrees and daily minimum temperature of 26.5 degrees on 4 April were both the highest on record for Ching Ming Festival.  Affected by a trough of low pressure over Guangdong, local weather was mainly cloudy with a few showers and thunderstorms on 5 – 7 April.  The showers were heavier on 6 April with more than 40 millimetres of rainfall recorded over the northern and the eastern parts of the New Territories.  With the weakening of the trough of low pressure, showers eased off gradually in Hong Kong on 8 April.  The visibility was also rather low in some areas.

Under the influence of a fresh to strong easterly airstream, it was relatively cooler with a few light rain patches on 9 April.  With the band of clouds covering the coastal areas of Guangdong thinning out gradually, local weather became dry with sunny periods during the day on 10 April.  Affected by an anticyclone aloft and the subsequent southerly airstream, it was generally fine and hot during the day on 11 – 17 April.  With plenty of sunshine, the temperatures at the Observatory rose to a maximum of 31.9 degrees on the afternoon of 13 April, the highest of the month.  There was also coastal fog at first on 15 April.  Under the influence of a trough of low pressure, it was mainly cloudy with showers and squally thunderstorms on 18 April.  The showers were heavy at times and more than 30 millimetres of rainfall were recorded over the eastern part of the territory and parts of the New Territories.  A southerly airstream brought a few showers and isolated thunderstorms to Hong Kong on the next day. 

An active trough of low pressure over the northern part of south China edged south on 20 April and lingered along the coastal areas of Guangdong in the next three days.  There were heavy showers and squally thunderstorms in Hong Kong on 20 – 23 April.  More than 100 millimetres of rainfall were generally recorded over the territory and rainfall even exceeded 200 millimetres over North, Tai Po, Tsuen Wan and Sai Kung Districts on these four days.  Under the rain, temperatures at the Observatory dropped to a minimum of 21.5 degrees on 21 April, the lowest of the month but the highest monthly absolute minimum temperature on record for April.  Moreover, waterspout was spotted near Clear Water Bay on that morning.  With the trough of low pressure shifting to the south of Hong Kong and the onset of an easterly airstream over the coastal areas of Guangdong, local showers abated on 24 April.  

The trough of low pressure returned and lingered over the coast of Guangdong again on 25 – 28 April.  The weather of Hong Kong became unsettled with occasional showers and squally thunderstorms.  The showers were particularly heavy on 26 April.  More than 30 millimetres of rainfall were generally recorded over the territory and rainfall even exceeded 100 millimetres over Sai Kung and Sha Tin Districts on that day.  Besides, the daily mean temperature of 28.8 degrees and daily minimum temperature of 27.7 degrees on 27 April were both the highest on record for April.  Under the influence of a southerly airstream, local weather was hot with sunny intervals during the day on 29 April.  While there were sunny intervals during the day on the last day of the month, affected by an area of intense thundery showers associated with a trough of low pressure, the weather deteriorated with outbreaks of heavy showers and severe squally thunderstorms that night.  About 30 millimetres of rainfall were recorded over many places of the territory.  Hail was reported at Yuen Long.  Violent gusts of around 110 kilometres per hour were once recorded at Tai O.  A taxi in Aberdeen was damaged by a fallen tree.

There was no tropical cyclone over the South China Sea and the western North Pacific in April 2024.

Details of issuance and cancellation of various warnings/signals in the month are summarised 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 2024 Table 1.1   Strong Monsoon Signal Beginning Time Ending Time
Day/Month HKT Day/Month HKT
6 / 4   0725   6 / 4   1345  
28 / 4   0655   28 / 4   1345  


Table 1.2   Rainstorm Warning Signals Colour Beginning Time Ending Time
Day/Month HKT Day/Month HKT
Amber   18 / 4   1300   18 / 4   1405  
Amber   20 / 4   1935   20 / 4   2230  
Amber   21 / 4   1000   21 / 4   1345  
Amber   23 / 4   0830   23 / 4   1250  
Amber   26 / 4   0835   26 / 4   1345  
Amber   30 / 4   2130   30 / 4   2300  


Table 1.3   Thunderstorm Warning Beginning Time Ending Time
Day/Month HKT Day/Month HKT
5 / 4   1404   5 / 4   1515  
6 / 4   1019   6 / 4   1530  
7 / 4   1400   7 / 4   1630  
18 / 4   0726   18 / 4   1530  
19 / 4   0257   19 / 4   0400  
19 / 4   1200   19 / 4   1500  
19 / 4   2005   19 / 4   2230  
20 / 4   1515   21 / 4   0015  
21 / 4   0840   21 / 4   2230  
22 / 4   0815   22 / 4   0905  
22 / 4   1230   22 / 4   1630  
22 / 4   2025   22 / 4   2315  
23 / 4   0445   23 / 4   1530  
24 / 4   2100   24 / 4   2330  
25 / 4   0120   25 / 4   0700  
25 / 4   0815   25 / 4   1330  
25 / 4   1545   25 / 4   1645  
26 / 4   0150   26 / 4   0315  
26 / 4   0530   26 / 4   1530  
26 / 4   1925   26 / 4   2200  
27 / 4   1137   27 / 4   1300  
27 / 4   2210   28 / 4   0930  
28 / 4   1040   28 / 4   1530  
30 / 4   1635   30 / 4   1845  
30 / 4   1917   1 / 5   1300  


Table 1.4   Fire Danger Warnings Colour Beginning Time Ending Time
Day/Month HKT Day/Month HKT
Yellow   1 / 4   0600   1 / 4   1800  
Yellow   4 / 4   0600   4 / 4   1800  
Yellow   13 / 4   0745   13 / 4   1800  
Yellow   14 / 4   0600   14 / 4   1800  


Table 2   Figures and Departures from Normal - April 2024 Meteorological Element Figure of the Month Departure from Normal*
Mean Daily Maximum Air Temperature   28.9 degrees C   3.3 degrees above normal  
Mean Air Temperature   26.4 degrees C   3.4 degrees above normal  
Mean Daily Minimum Air Temperature   24.5 degrees C   3.4 degrees above normal  
Mean Dew Point Temperature   23.1 degrees C   3.4 degrees above normal  
Mean Relative Humidity   82 %   1 % below normal  
Mean Cloud Amount   81 %   4 % above normal  
Total Rainfall   257.1 mm   104.1 mm above normal  
Number of hours of Reduced VisibilityΔ   3 hours   65.2 hours below normal§  
Total Bright Sunshine Duration   87.5 hours   25.7 hours below normal  
Mean Daily Global Solar Radiation   10.27 Megajoule / square metre   2.25 Megajoule below normal  
Total Evaporation   66.4 mm   20.8 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.