2nd June 2023 – (Hong Kong) Hong Kong experienced drier than usual weather in May 2023, with the monthly rainfall recorded at 182.8 millimetres, which is about 37 percent below the normal figure of 290.6 millimetres. The accumulated rainfall recorded in the first five months of the year was 350.4 millimetres, which is about 41 percent below the normal figure of 590.9 millimetres for the same period. The month was also slightly warmer than usual with the mean temperature of 26.6 degrees, 0.3 degrees above the normal of 26.3 degrees. The spring of this year, from March to May, was exceptionally warm, with a mean minimum temperature of 22.0 degrees, a mean temperature of 23.8 degrees, and a mean maximum temperature of 26.5 degrees, which were respectively one of the fourth, sixth, and eighth highest on record for the same period.
During the first two days of May, Hong Kong experienced mainly cloudy weather with sunny intervals. There were also a few light rain patches on the morning of May 1 due to the northeast monsoon affecting southern China and a band of clouds covering the coast of Guangdong. However, under the influence of an anticyclone aloft, the weather became hot with sunny periods from 3rd to 5th May, with isolated showers on the morning of 3rd May. Affected by a southerly airstream, the weather turned cloudier with isolated showers on 6th May.
On 7th and 8th May, a trough of low pressure moved across the south China coastal area, bringing showery weather and squally thunderstorms to Hong Kong. The rain was particularly heavy on the afternoon of 7th May, necessitating 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 9th to 11th May. With a band of clouds covering Guangdong, it was mainly cloudy with a few showers on 12th and 13th May.
Under the influence of a trough of low pressure, the showers affecting Hong Kong became more frequent on 14th May with more than 30 millimetres of rainfall recorded over most parts of the territory. 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 15th and 16th May.
On 17th May, local weather turned showery with a few thunderstorms due to the setting in of a southerly airstream. 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 18th to 20th May. Visibility was also rather low in some areas on 18th to 20th May. With abundant sunshine, it was very hot on the afternoon of 22nd May. Affected by a trough of low pressure, local weather became cloudy with showers and squally thunderstorms on 23rd and 24th May. The rain was particularly heavy in some areas on the morning of 23rd May, with more than 30 millimetres of rainfall recorded over parts of the territory, and rainfall even exceeded 70 millimetres over Yuen Long. It remained mainly cloudy with a few showers on 25th May.
With the strengthening of the anticyclone aloft, local weather gradually turned mainly fine and hot from 26th to 29th May, apart from a few showers. Meanwhile, over the western North Pacific, tropical cyclone Mawar moved across the sea areas to the east of Luzon and Taiwan from 28th to 31st May. Under the influence of the outer subsiding air of Mawar, it was mainly fine and extremely hot on the afternoons of the last two days of the month. Temperatures over many places rose to 35 degrees or above, with the maximum temperature recorded at the Observatory being 34.7 degrees on the afternoon of 31st May, 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 30th and 31st May. The showers were heavier in some places on the afternoon of 31st May, with more than 30 millimetres of rainfall recorded over North District and Tai Po District.