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The mean temperature for May 2010 was 25.6 degrees, close to the normal figure of 25.8 degrees. The rainfall over the territory was highly uneven. The total rainfall recorded at the Hong Kong Observatory Headquarters in the month was only 176.6 millimetres, about 54% of the normal figure of 329.5 millimetres, whereas over 400 millimetres and 300 millimetres of rainfall were recorded at the eastern part of the New Territories and western Lantau respectively. The accumulated rainfall since January 1 was 410.7 millimetres, about 38 percent below the normal figure of 666.6 millimetres for the same period.
Under the influence of a ridge of high pressure, the weather was generally fine for the first three days of the month. An easterly airstream brought mist and light rain patches to the territory for the next two days. Affected by a trough of low pressure over southern China, local weather became cloudy with showers on May 6. With the trough approaching the coast of Guangdong, local weather deteriorated further with heavy rain and squally thunderstorms on the morning of May 7. Dominated by a humid maritime airstream over the coastal areas of Guangdong, it was mainly cloudy with coastal fog on May 8.
A trough of low pressure formed over southern China on May 8. It moved southwards and brought some showers to the territory the next day. With the passage of the trough of low pressure across the coast of Guangdong, it was rainy and thundery on May 10. Although there were still some showers, local weather improved with some sunny intervals from May 11 to 13 with the establishment of a weak ridge of high pressure over the coastal areas of southeastern China. Affected by a humid easterly airstream, there were a few light rain and fog patches on May 14. Another trough of low pressure over southern China brought some thundery showers to Hong Kong the next day. Affected by an easterly airstream, the weather became mainly cloudy with a few rain patches and coastal mist on May 16 and 17.
A ridge of high pressure over the south China coastal areas brought generally fine and hot weather to the territory on May 18. Under the influence of a trough of low pressure, it turned rainy with a few squally thunderstorms for the ensuing two days.
A moist maritime airstream affected the coastal areas of Guangdong and brought hot weather to Hong Kong on May 21. The temperature at the Hong Kong Observatory rose to a maximum of 30.7 degrees on that day, the highest of the month. Local weather became cloudy with some showers and thunderstorms on May 22 and 23 as an active trough of low pressure crossed the south China coast on the morning of May 23. After its passage, a dry continental airstream brought fine and dry conditions to the territory for the next three days.
Dominated by an easterly airstream over the south China coastal areas, local weather turned mainly cloudy with a few rain patches on May 27. There were some sunny periods on May 28. A trough of low pressure over the south China coastal areas brought an episode of thundery showers to Hong Kong on the evening of May 29. Local weather remained showery with squally thunderstorms the next day. Over 100 millimetres of rainfall was recorded at Sha Tin and Sai Kung that afternoon. There were still a few rain patches on the last day of the month.
There was no tropical cyclone over the South China Sea and the western North Pacific in the month.
Details of the issuance and cancellation of various warnings/signals in the month are summarised in Table 1. Monthly meteorological figures and departures from normals of May are tabulated in Table 2.
Ends/Wednesday, June 2, 2010
Issued at HKT 19:19
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