May 2024 was characterized by cloudier than usual weather with localized heavy rain over parts of the New Territories.  The mean amount of cloud in the month was 83 percent, 7 percent above the normal of 76 percent.  As for monthly rainfall, while over 700 millimetres of rainfall were recorded over parts of the Sai Kung, the monthly rainfall recorded at the Observatory was only 292.6 millimetres, near the normal figure of 290.6 millimetres.  The accumulated rainfall recorded in the first five months of the year was 582.1 millimetres, slightly below the normal figure of 590.9 millimetres for the same period.  The monthly mean temperature of 26.0 degrees was slightly below the normal figure of 26.3 degrees.  Attributing to the well above normal temperatures in March and April, the spring of this year from March to May was much warmer than usual.  The mean temperature of 24.5 degrees, mean minimum temperature of 22.7 degrees and mean maximum temperature of 27.0 degrees were respectively the second, one of the second and the fourth highest on record for the same period.

Under the influence of a trough of low pressure, the weather of Hong Kong was unsettled with heavy showers and severe squally thunderstorms on the morning of 1 May.  More than 30 millimetres of rainfall were generally recorded over Hong Kong and rainfall even exceeded 50 millimetres over the eastern part of the territory.  Violent gusts exceeding 100 kilometres per hour were also recorded at Cheung Chau.  Under the rain, temperatures at the Observatory dropped to a minimum of 22.4 degrees that morning, the lowest of the month.  Affected by a fresh to strong easterly airstream, it was mainly cloudy with a few showers on 2 – 3 May.  

The upper-air disturbances associated with the southern branch of a westerly trough affected southern China on 4 May.  Coupled with significant low-level convergence and upper-level divergence, persistent thundery showers affected the vicinity of the Pearl River Estuary areas on that day.  Locally, it was mainly cloudy with heavy showers and severe squally thunderstorms on 4 May.  More than 100 millimetres of rainfall were recorded over many places and rainfall even exceeded 400 millimetres over parts of Tseung Kwan O on that day.  There was exceptionally severe rainstorm over some areas in the eastern part of the territory in the morning with an hourly rainfall of 145.5 millimetres recorded at Tseung Kwan O.  The heavy rain also necessitated the issuance of the first Red Rainstorm Warning Signal of the year.  Besides, violent gusts of about 110 kilometres per hour were once recorded at Cheung Chau Beach on that afternoon.  According to preliminary reports, there were 16 reports of flooding including 12 cases in Sai Kung and Tseung Kwan O and 15 reports of landslides in Sai Kung area.  In the midst of downpour, the temperature at the Observatory dropped to the month’s lowest of 22.4 degrees again on that day.

With the departure of the upper-air disturbance, apart from thundery showers in the morning, the weather improved with sunny intervals during the day on 5 May.  Under the influence of an anticyclone aloft, it was mainly fine and hot during the day on 6 May.  While there were sunny periods on the morning of 7 May, the weather became cloudier with a few showers and thunderstorms in the afternoon with the setting in of an easterly airstream. The easterly airstream strengthened gradually and continued to affect the coast of Guangdong, local weather was mainly cloudy with sunny intervals on 8 – 11 May.    While the local weather was hot with sunny intervals during the day on 12 May, a trough of low pressure edged closer to the coast of southern China and brought heavy showers and thunderstorms to some areas of Hong Kong in the afternoon.  More than 30 millimetres of rainfall were recorded over Sha Tin and Sai Kung.  With the weakening of the trough of low pressure, the weather became less showery with sunny intervals during the day on 13 May.

With the setting in of a fresh to strong easterly airstream on the night of 13 May, apart from a few showers on that night and at first the next day, the weather was mainly fine on 14 – 16 May.  It was very dry during the day on 16 May and the relative humidity over most parts of the territory once fell below 40 per cent.  The weather turned cloudier on 17 – 18 May.  Affected by a trough of low pressure lingering over the coastal areas of Guangdong and the subsequent upper-air disturbance, local weather became mainly cloudy with occasional showers and a few thunderstorms on 19 – 25 May.  The showers were particularly heavy on 21 May.  More than 50 millimetres of rainfall were recorded over most parts of the territory and rainfall even exceeded 200 millimetres over parts of Lantau Island.  With the departure of the upper-air disturbance, the showers abated with bright periods on the afternoon of 26 May.  

Under the influence of an active southerly airstream, it was mainly cloudy with showers and a few thunderstorms on 27 May.  Another trough of low pressure moved across the coast of Guangdong on the early morning of 28 May and brought heavy showers and thunderstorms to Hong Kong. Around 30 millimetres of rainfall were recorded over many places of the territory and rainfall even exceeded 50 millimetres over Tai Po and Sai Kung.  With the trough of low pressure moving to the northern part of the South China Sea, local weather was hot with sunny intervals during the day that day with the temperatures at the Observatory rising to a maximum of 32.0 degrees, the highest of the month.  Affected by a strong easterly airstream, it was dry with sunny intervals on 29 May.  The weather was mainly cloudy with a few showers on 30 May.  Meanwhile, a broad area of low pressure over the central to northern part of the South China Sea strengthened into a tropical depression on the afternoon of 30 May and the Observatory issued the first tropical cyclone warning signal of this year.  The tropical depression intensified into a tropical storm and was named Maliksi on 31 May.  With Maliksi edging towards the coast of western Guangdong, local weather deteriorated gradually with occasional showers later that day.  More than 10 millimetres of rainfall were recorded over most parts of the territory and rainfall even exceeded 50 millimetres over parts of the New Territories on that day.

Two tropical cyclones occurred over the South China Sea and the western North Pacific in May 2024.