The Weather of May 2025 - A relatively dry and hot May
3 June 2025
Mainly attributing 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 percent 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 percent 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 tenth 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 3 – 4 May. 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 3 – 4 May. While there were sunny intervals during the day on 5 May, 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 6 May. The trough of low pressure continued to bring thundery showers to the vicinity of the Pearl River Estuary on 7 May. 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 8 May. 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 10 May and moved across the coast of Guangdong the next morning. Locally, it was mainly cloudy on 10 May with a few showers overnight and the next morning. The temperature at the Observatory dropped to a minimum of 21.0 degrees on 11 May, 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 percent 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 on 13 – 15 May. A southerly airstream affected the coast of Guangdong in the following six days. The weather was mainly cloudy with one or two showers on 16 May and turned sunnier and very hot in the following two days. An upper-air disturbance affected the coast of Guangdong on 19 – 20 May, 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 21 May.
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 22 – 23 May. The temperature at the Observatory rose to a maximum of 33.0 degrees on 22 May, the highest of the month. With a trough of low pressure moving across the coast of Guangdong overnight on 23 – 24 May, its associated showers and thunderstorms affected the territory on the night of 23 May and the next day. More than 20 millimetres of rainfall were recorded over many places on Hong Kong Island on 24 May. With a broad band of clouds covering southern China, the weather was mainly cloudy on 25 – 26 May. With the band of clouds thinning out, there were sunny periods during the day on 27 May. 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 29 May. 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 30 May. 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.
Coastal fog near Waglan Island on the morning of 4 May 2025
Extract of Meteorological Observations in Hong Kong for May 2025
Details of issuance and cancellation of various warnings/signals in the month are summarised in Tables 1.1 to 1.5. Monthly meteorological figures and departures from normal for May are tabulated in Table 2.
Warnings and Signals issued in May 2025
| Beginning Time | Ending Time | ||
|---|---|---|---|
| Day/Month | HKT | Day/Month | HKT |
| 7 / 5 | 2340 | 8 / 5 | 0945 |
| 30 / 5 | 1900 | 31 / 5 | 1615 |
| Colour | Beginning Time | Ending Time | ||
|---|---|---|---|---|
| Day/Month | HKT | Day/Month | HKT | |
| Amber | 7 / 5 | 1322 | 7 / 5 | 1425 |
| Amber | 29 / 5 | 1625 | 29 / 5 | 1845 |
| Beginning Time | Ending Time | ||
|---|---|---|---|
| Day/Month | HKT | Day/Month | HKT |
| 1 / 5 | 1435 | 1 / 5 | 1600 |
| 4 / 5 | 1445 | 4 / 5 | 1600 |
| 5 / 5 | 2159 | 6 / 5 | 0030 |
| 6 / 5 | 1045 | 6 / 5 | 1830 |
| 6 / 5 | 2010 | 6 / 5 | 2230 |
| 7 / 5 | 0835 | 7 / 5 | 2100 |
| 9 / 5 | 1010 | 9 / 5 | 1315 |
| 10 / 5 | 2030 | 10 / 5 | 2230 |
| 19 / 5 | 1620 | 19 / 5 | 1800 |
| 20 / 5 | 1026 | 20 / 5 | 1200 |
| 23 / 5 | 1815 | 24 / 5 | 0030 |
| 24 / 5 | 1121 | 24 / 5 | 1615 |
| 28 / 5 | 2315 | 29 / 5 | 0215 |
| 29 / 5 | 0920 | 29 / 5 | 1900 |
| Colour | Beginning Time | Ending Time | ||
|---|---|---|---|---|
| Day/Month | HKT | Day/Month | HKT | |
| Red | 11 / 5 | 0945 | 12 / 5 | 2230 |
| Beginning Time | Ending Time | ||
|---|---|---|---|
| Day/Month | HKT | Day/Month | HKT |
| 17 / 5 | 1330 | 17 / 5 | 1620 |
| 18 / 5 | 1405 | 18 / 5 | 1620 |
| 21 / 5 | 1145 | 23 / 5 | 1800 |
| Meteorological Element | Figure of the Month | Departure from Normal* |
|---|---|---|
| Mean Daily Maximum Air Temperature | 30.0 degrees C | 1.2 degrees above normal |
| Mean Air Temperature | 27.2 degrees C | 0.9 degrees above normal |
| Mean Daily Minimum Air Temperature | 25.5 degrees C | 1.0 degrees above normal |
| Mean Dew Point Temperature | 22.6 degrees C | 0.4 degrees below normal |
| Mean Relative Humidity | 77 % | 6 % below normal |
| Mean Cloud Amount | 81 % | 5 % above normal |
| Total Rainfall | 81.6 mm | 209.0 mm below normal |
| Number of hours of Reduced VisibilityΔ | 0 hours | 35.9 hours below normal§ |
| Total Bright Sunshine Duration | 123.2 hours | 15.6 hours below normal |
| Mean Daily Global Solar Radiation | 15.28 Megajoule / square metre | 0.82 Megajoule above normal |
| Total Evaporation | 116.0 mm | 6.2 mm above normal |
| Remarks : | All measurements were made at the Hong Kong Observatory except sunshine, solar radiation and evaporation which were recorded at King's Park Meteorological Station and visibility which was observed at the Hong Kong International Airport. |
| Δ |
The visibility readings at the Hong Kong International Airport are based on hourly observations by professional meteorological observers in 2004 and before, and average readings over the 10-minute period before the clock hour of the visibility meter near the middle of the south runway from 2005 onwards. The change of the data source in 2005 is an improvement of the visibility assessment using instrumented observations following the international trend. |
* Departure from 1991 - 2020 climatological normal, except for number of hours of reduced visibility |
|
§ Departure from mean value between 1997 and 2024 |
|
| Remarks : | Extremely high: above 95th percentile Above normal: between 75th and 95th percentile Normal: between 25th and 75th percentile Below normal: between 5th and 25th percentile Extremely low: below 5th percentile Percentile and 5-day running average values are computed based on the data from 1991 to 2020 |
Extract of Meteorological Observations in Hong Kong for May 2025