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May 2009 was drier and sunnier than usual. The total rainfall of 245.2 millimetres in the month, which was mainly recorded in the last 10 days, was about 26% below the normal figure of 329.5 millimetres. The accumulated rainfall since January 1 was 475.7 millimetres, about 29% below the normal figure of 666.6 millimetres for the same period. The total bright sunshine duration was 169.8 hours, about 23% above normal. The mean temperature was 25.5 degrees, 0.3 degrees below the normal figure of 25.8 degrees.
Under the influence of a ridge of high pressure over southeastern China, the weather in Hong Kong was fine and dry on the first three days of the month. A cloud band developed over southern China, moved southwards to the coastal areas and brought a few light rain patches to Hong Kong on May 4. With dissipation of the cloud band, local weather turned fine on May 5. Fine and dry weather persisted for the ensuing four days.
Another cloud band moved from west to east across southern China and brought a few light rain patches to Hong Kong on May 10. After the passage of the cloud band, the weather turned fine again on May 11. It was sunny and hot for the following two days. Affected by an easterly airstream, local weather turned mainly cloudy with a few rain patches from May 14-16.
The easterly airstream was replaced by a southwesterly airstream on May 17. Local weather became sunny and hot apart from a few showers from May 17-19. A trough of low pressure developed over the south China coastal areas and brought cloudy weather and a few thundery showers to the territory for the next three days.
Affected by an area of low pressure near Hainan, local weather became more unsettled with occasional heavy downpours and squally thunderstorms from May 23-25. The rain eased off gradually with some bright periods on May 26. A fresh to strong easterly airstream associated with a ridge of high pressure over southeastern China brought cloudy and rainy weather to the territory for the following three days. Under the influence of a dry continental airstream, it was dry and mainly fine for the last two days of the month.
Two tropical cyclones occurred in the western North Pacific and the South China Sea in the month.
Details of the issuance and cancellation of various warnings/signals in the month are summarised in Table 1.1. Monthly meteorological figures and departures from normal of May are tabulated in Table 1.2.
Ends/Tuesday, June 2, 2009
Issued at HKT 18:22
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