With drier northeast monsoon affecting Hong Kong for most of the time and less moisture supply to the coast of southern China in the month, April 2025 was drier than usual in Hong Kong. The monthly mean relative humidity was 74 per cent, the second lowest on record for April since 1947. Moreover, the total rainfall in the month was 57.1 millimetres, only about 37 per cent of the normal of 153.0 millimetres. The accumulated rainfall recorded in the first four months of the year was 125.5 millimetres, about 42 per cent of the normal of 300.4 millimetres for the same period. The month was also sunnier than usual. The monthly total sunshine duration was 155.6 hours, about 37 per cent above the normal of 113.2 hours. April 2025 was warmer than usual with a mean temperature of 23.7 degrees, 0.7 degrees above the normal of 23.0 degrees.

     Under the influence of the northeast monsoon and a broad band of clouds covering southern China, the weather was mainly cloudy and cold with one or two light rain patches on the morning of the first day of the month. The temperatures at the Observatory fell to a minimum of 12.9 degrees that morning, the lowest of the month. With the band of clouds thinning out, there were sunny periods during the day. The weather became fine and dry the next day. Under the influence of a dry easterly airstream, it remained fine and very dry on the afternoon of April 3. While it was generally fine at first on April 4, a band of clouds gradually covered the coast of Guangdong, leading to cloudier weather that afternoon and the following two days. There were occasional showers on April 5, with around 10 millimetres of rainfall recorded over many places. With the band of clouds thinning out, the weather became mainly fine on April 7. It was dry and rather warm during the day. Winds were weak over the coast of Guangdong on April 8 and 9. The weather in Hong Kong was rather warm with sunny periods.

     A southerly airstream brought humid weather in the following three days. Locally, there were fog patches on the morning of April 11, with the visibility in the harbour once falling below 1 000 metres. Moreover, a trough of low pressure over northern Guangdong developed into a cold front on the morning of April 12. As the cold front edged closer to the coastal region, local showers increased with a few squally thunderstorms that afternoon. More than 10 millimetres of rainfall was recorded over many places, and rainfall even exceeded 20 millimetres over Tai Po District. The cold front moved across the coastal areas around that evening. Under the influence of the associated intense and dry northeast monsoon, showers eased off with temperatures falling gradually that night. Strong northerly winds also affected many parts of Hong Kong that night and at first the next day, with winds occasionally reaching gale force offshore and on high ground. The intense monsoon also transported sand and dust southwards from Mongolia and brought widespread sandstorms to many inland areas in China. Under the influence of the very dry continental airstream and the sand and dust weather, the weather was very dry with visibility slightly dropping to around 5 to 6 kilometres over parts of the territory from April 13 to 15. The relative humidity over many places on these three days fell below 40 per cent. The relative humidity recorded at the Observatory on April 13 once fell to 21 per cent, the lowest record in April since the establishment of the automatic weather station at the Observatory's Headquarters in 1984. With plenty of sunshine and weaker winds on April 15, the temperatures at the Observatory soared to a maximum of 33.0 degrees that afternoon, the highest of the month. It also marked the earliest occurrence of very hot weather in a year and the second highest maximum temperature for April on record.

     An easterly airstream affected the coast of Guangdong on April 16 and 17. While the local weather was mainly fine and dry during the day on April 16, it became mainly cloudy the next day with coastal fog in the morning and at night. The visibility at Waglan Island once fell below 1 000 metres. With a humid southerly airstream replacing the easterly airstream that afternoon, the weather was cloudy with a few showers in the following two days. There was coastal fog from April 18 to 21. The southerly airstream continued to affect the coast of Guangdong and brought hot weather to Hong Kong from April 20 to 24. The maximum temperature recorded at the Observatory was 30.6 degrees on April 20, making it one of the warmest day of Easter on record.

     A trough of low pressure affected inland Guangdong on April 24 and edged closer to the coastal areas in the evening, bringing showers and a few squally thunderstorms that night and the next day. Showers were heavy on the morning of April 25. More than 30 millimetres of rainfall was recorded over many places, and rainfall even exceeded 50 millimetres over the eastern part of Hong Kong Island, Kwun Tong and Tseung Kwan O. With a fresh to strong easterly airstream setting in that night, the weather was cloudy with a few showers and became cooler in the following two days. There were also fog patches on April 27. The visibility at Waglan Island once fell below 1 000 metres. Another trough of low pressure over inland Guangdong edged closer to the coastal areas gradually that night. Apart from coastal fog on the morning of April 28, there were showers and one or two thunderstorms that day with rainfall exceeding 10 millimetres over many places, and around 30 millimetres of rainfall was even recorded over the northern part of the New Territories. Affected by a relatively dry easterly airstream, the weather was generally fine on the last two days of the month.

     There was no tropical cyclone over the South China Sea and the western North Pacific in April 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 April are tabulated in Table 2.

Ends/Tuesday, May 6, 2025
Issued at HKT 15:00

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