A drier May
With the northeast monsoon affecting southern China and a band of clouds covering the coast of Guangdong, it was mainly cloudy with sunny intervals in Hong Kong on the first two days of the month. There were also a few light rain patches on the morning of May 1. Under the influence of an anticyclone aloft, apart from isolated showers on the morning of May 3, the weather of Hong Kong became hot with sunny periods on May 3 to 5. Affected by a southerly airstream, the weather turned cloudier with isolated showers on May 6.
A trough of low pressure moved across the south China coastal area and brought showery weather and squally thunderstorms to Hong Kong on May 7 and 8. The rain was particularly heavy on the afternoon of May 7 and necessitated the issuance of the first Red Rainstorm Warning Signal of the year. More than 50 millimetres of rainfall were recorded generally over the territory and rainfall even exceeded 100 millimetres over parts of Hong Kong Island on these two days. Affected by a fresh to strong easterly airstream, there were sunny intervals and a few rain patches on May 9 to 11. With a band of clouds covering Guangdong, it was mainly cloudy with a few showers on May 12 and 13.
Under the influence of a trough of low pressure, the showers affecting Hong Kong became more frequent during the day on May 14. More than 30 millimetres of rainfall were recorded over most parts of the territory and rainfall even exceeded 50 millimetres over Lantau Island on that day. Under the rain, temperatures at the Observatory dropped to a minimum of 20.2 degrees on that morning, the lowest of the month. With the departure of the trough of low pressure, the weather improved with sunny periods during the day on May 15 and 16.
With the setting in of a southerly airstream, local weather turned showery with a few thunderstorms on May 17. The showers were heavier around noon on that day with more than 30 millimetres of rainfall recorded over many places. With the showers petering out, it was hot with sunny periods in Hong Kong on May 18 to 20. Visibility was also rather low in some areas on May 18 to 20. With abundant sunshine, it was very hot on the afternoon of May 22. Affected by a trough of low pressure, local weather became cloudy with showers and squally thunderstorms on May 23 and 24. The rain was particularly heavy in some areas on the morning of May 23. More than 30 millimetres of rainfall were recorded over parts of the territory and rainfall even exceeded 70 millimetres over Yuen Long. It remained mainly cloudy with a few showers on May 25.
With the strengthening of the anticyclone aloft, apart from a few showers, local weather gradually turned mainly fine and hot on May 26 to 29. Meanwhile, over the western North Pacific, tropical cyclone Mawar moved across the sea areas to the east of Luzon and Taiwan on May 28 to 31. Under the influence of the outer subsiding air of Mawar, it was mainly fine and extremely hot on the afternoons of last two days of the month. Temperatures over many places rose to 35 degrees or above. The maximum temperature recorded at the Observatory was 34.7 degrees on the afternoon of May 31, the highest of the month. Moreover, the daily minimum temperature of 29.6 degrees and daily mean temperature of 31.4 degrees on that day were also the highest and one of the highest on record for May. Showers and thunderstorms triggered by high temperatures also affected parts of the territory on the afternoons of May 30 and 31. The showers were heavier in some places on the afternoon of May 31 with more than 30 millimetres of rainfall recorded over North District and Tai Po District.
One tropical cyclone occurred over the South China Sea and the western North Pacific in May 2023.
Details of issuance and cancellation of various warnings/signals in the month are summarised in Table 1. Monthly meteorological figures and departures from normal for May are tabulated in Table 2.
Ends/Friday, June 2, 2023
Issued at HKT 15:00
Issued at HKT 15:00