Mainly attributed to the stronger-than-usual subtropical ridge over southern China, the weather of May 2025 was drier than usual in Hong Kong. The total rainfall in the month was 81.6 millimetres, only about 28 per cent of the normal of 290.6 millimetres. The accumulated rainfall recorded in the first five months of the year was 207.1 millimetres, about 35 per cent of the normal of 590.9 millimetres for the same period and the eighth lowest on record for the same period. Moreover, the month was hotter than usual. The monthly mean minimum temperature of 25.5 degrees, monthly mean maximum temperature of 30.0 degrees and monthly mean temperature of 27.2 degrees were 1.0 degrees, 1.2 degrees and 0.9 degrees above their corresponding normals and were respectively one of the eighth, the ninth and the 10th highest on record for May. The spring of this year from March to May was also warmer than usual. The mean maximum temperature of 26.7 degrees and mean temperature of 23.7 degrees were respectively one of the fifth and one of the eighth highest on record for the same period.

     The weather in Hong Kong was mainly cloudy with a few showers on the first day of the month and turned fine the next day. Affected by a band of clouds, the weather became mainly cloudy again with a few showers in some areas on May 3 and 4. With light winds over the coast of Guangdong, local visibility was also relatively low on the first four days of the month with coastal fog on the mornings of May 3 and 4. While there were sunny intervals during the day on May 5, a trough of low pressure over inland Guangdong moved southwards gradually and brought a few showers and isolated thunderstorms to Hong Kong that night and the next day. More than 10 millimetres of rainfall were recorded over the northern part of the New Territories on the afternoon of May 6. The trough of low pressure continued to bring thundery showers to the vicinity of the Pearl River Estuary on May 7. Locally, it was cloudy with occasional showers and a few thunderstorms. Showers were heavy at times. More than 30 millimetres of rainfall were recorded over the New Territories, and rainfall even exceeded 70 millimetres over Chek Lap Kok, Tuen Mun, Tsuen Wan, Sha Tin and Tai Po districts.
      
     A fresh to strong easterly airstream affected the coast of Guangdong on May 8. Locally, there were sunny intervals and one or two showers. Around 10 millimetres of rainfall were recorded over Tai Po and Sha Tin Districts. Areas of intense thundery showers associated with a trough of low pressure moved across the vicinity of the Pearl River Estuary the next day. It was mainly cloudy with a few showers. Showers were heavier over some areas during the day with squally thunderstorms. More than 10 millimetres of rainfall were recorded over the eastern part of Hong Kong. A cold front formed over the northern part of southern China on May 10 and moved across the coast of Guangdong the next morning. Locally, it was mainly cloudy on May 10 with a few showers overnight and the next morning. The temperature at the Observatory dropped to a minimum of 21.0 degrees on May 11, the lowest of the month. The associated northeast monsoon brought very dry and generally fine weather that afternoon and the next day, with the relative humidity falling below 40 per cent over many places.
      
     Under the influence of an easterly airstream over the coast of Guangdong, local weather was hot during the day with sunny periods from May 13 to 15. A southerly airstream affected the coast of Guangdong in the following six days. The weather was mainly cloudy with one or two showers on May 16 and turned sunnier and very hot in the following two days. An upper-air disturbance affected the coast of Guangdong on May 19 and 20, bringing a few showers to some areas in Hong Kong. With the departure of the disturbance, the weather became very hot with sunny intervals on May 21.
      
     Under the influence of an anticyclone aloft over the coast of Guangdong and the northern part of the South China Sea, it remained very hot with sunny periods on May 22 and 23. The temperature at the Observatory rose to a maximum of 33.0 degrees on May 22, the highest of the month. With a trough of low pressure moving across the coast of Guangdong overnight on May 23 and 24, its associated showers and thunderstorms affected the territory on the night of May 23 and the next day. More than 20 millimetres of rainfall were recorded over many places on Hong Kong Island on May 24. With a broad band of clouds covering southern China, the weather was mainly cloudy on May 25 and 26. With the band of clouds thinning out, there were sunny periods during the day on May 27. An easterly airstream brought showers to the coast of Guangdong the next day. Locally, showers mainly affected the eastern part of the territory and brought more than 10 millimetres of rainfall to Sai Kung, Tseung Kwan O and the eastern part of Hong Kong Island. Meanwhile, a trough of low pressure edged closer to the coast of Guangdong that night, bringing showers and a few thunderstorms to Hong Kong on May 29. Showers were heavy in the afternoon with more than 30 millimetres of rainfall generally recorded over the territory. A strong easterly airstream affected the coast of Guangdong on the last two days of the month. Locally, it was cloudy with rain on May 30. Around 20 millimetres of rainfall were recorded over Hong Kong Island, Kowloon East, Sha Tin and Sai Kung districts. It was mainly cloudy on the last day of the month, with one or two rain patches in the morning and at night.     
      
     There was no tropical cyclone over the South China Sea and the western North Pacific in May 2025.
      
     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/Tuesday, June 3, 2025
Issued at HKT 15:00

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