An unseasonably warm and dry April

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     With relatively less cold air intrusion from the north in April 2021, local weather continued to be much warmer than usual. The monthly mean minimum temperature of 22.4 degrees, the monthly mean maximum temperature of 27.0 degrees and the monthly mean temperature of 24.1 degrees were 1.3 degrees, 1.4 degrees and 1.1 degrees above their corresponding normal figures (or 1.6 degrees, 2.0 degrees and 1.5 degrees above their corresponding 1981-2010 normal figures) respectively, making them the fifth, the seventh and the ninth highest on record for April respectively. With the dominance of an upper-air anticyclone over southern China for most of the time in the month, the month was also much drier than usual with a total rainfall of only 32.5 millimetres, about 21 per cent of the normal of 153.0mm (or about 19 per cent of the 1981-2010 normal of 174.7mm). The accumulated rainfall recorded in the first four months of the year was 98.1mm, a decrease of about 67 per cent compared to the corresponding normal of 300.4mm (or about 71 per cent below the 1981-2010 normal of 336.1mm), making it the 10th lowest on record for the same period.

     With the establishment of an anticyclone aloft and the departure of the cloud band from the South China coast, the weather of Hong Kong was generally fine with hot afternoons from April 1 to 3. Under the influence of a fresh to strong easterly airstream, local weather became mainly cloudy and slightly cooler with a few rain patches from April 4 to 5.

     Affected by an anticyclone aloft southern China, local weather improved with sunny periods from April 6 to 7. Under the influence of an easterly airstream, the weather became cloudier on April 8. With the strengthening of the easterly airstream and affected by the upper-air disturbance, local weather was cloudy and cooler with a few showers on April 9. More than 5mm of rainfall were recorded over most parts of the territory. The temperature recorded at the Hong Kong Observatory dropped to 19.7 degrees under the rain in that morning, the lowest of the month.

     With the setting in of a relatively dry easterly airstream, the weather of Hong Kong turned generally fine and dry during the day from April 10 to 11. Under the influence of an anticyclone aloft, the weather remained generally fine and hot during the day from April 12 to 13. Affected by a fresh to strong easterly airstream, local weather became cloudier with a few rain patches on April 14. With a trough of low pressure edging towards the coast of Guangdong, it was cloudy with some showers in Hong Kong from April 15 to 17.

     Under the influence of a strong easterly airstream, the weather of Hong Kong was mainly cloudy with sunny intervals from April 18 to 20. With the moderation of the easterly airstream and the dominance of an anticyclone aloft, local weather became generally fine from April 21 to 23. With plenty of sunshine, the temperature recorded at the Hong Kong Observatory soared to a maximum of 32.6 degrees on the afternoon of April 23, the highest of the month. The onset of an easterly airstream brought cloudier weather and a few rain patches to Hong Kong on April 24. With a trough of low pressure edging closer to the coastal areas of Guangdong, the weather of Hong Kong was cloudy with some showers from April 25 to 28. More than 5mm of rainfall were generally recorded over the territory on April 27. With the departure of the trough of low pressure and the setting in of a dry continental airstream, local weather improved with sunny periods on April 29 and became generally fine and hot during the day on the last day of the month.

     One tropical cyclone occurred over the South China Sea and the western North Pacific in April 2021.

     Details of the issuance and cancellation of various warnings/signals in April are summarised in Table 1. Monthly meteorological figures and departures from normal for April are tabulated in Table 2.

Ends/Tuesday, May 4, 2021
Issued at HKT 15:00

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Table 1 (Warnings and signals issued in April 2021)

Table 2 (Figures and departures from normal - April 2021)