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May was warmer and sunnier than usual. The mean temperature of 26.4 degrees was 0.5 degree above normal. The total bright sunshine duration of 183.4 hours was about 19% above normal. It was also slightly drier with a monthly rainfall of 288.3 millimetres, about 9% below normal. The accumulated rainfall since the beginning of the year was 477.9 millimetres, about 22% below normal for the same period.
The weather in Hong Kong was generally fine under the influence of a ridge of high pressure on the first three days of the month. The weather turned cloudy with some rain on May 4 and 5 when a trough of low pressure over southern China moved cross the coastal areas.
The weather became fine and dry on May 6 and 7 as another ridge of high pressure established over southern China. The relative humidity dropped below 40% during the day. In the following 10 days, it was generally fine and hot apart from a few brief showers on May 16 and 17. It was also hazy on May 13 and 14.
The weather deteriorated later on May 18 when a trough of low pressure developed over inland Guangdong and moved across the south China coast. A squall line swept across Hong Kong from northwest to southeast that evening, bringing heavy showers and severe gusts to the territory. A peak gust of more than 100 kilometres per hour was recorded at Waglan Island. In Tin Shui Wai, four people were injured when more than 20 stacked containers collapsed in gusty winds. With the tough of low pressure lingering along the south China coast, there were heavy showers and thunderstorms between May 19 and 22. During the heavy downpour on May 20, two landslips and 15 cases of flooding were reported.
Sunshine returned on May 23 when the trough of low pressure weakened. Under the influence of a southerly airstream, it was hot with sunny periods in the next three days.
The weather became unstable with heavy showers and squally thunderstorms on May 27, but improved with some sunny periods in the following day. Under the influence of a ridge of high pressure over the coastal areas of Guangdong, it was fine, clear and hot on May 29 and 30. Apart from a few showers in the morning, the weather stayed mainly fine and hot on the last day of the month.
Only one tropical cyclone occurred in the western North Pacific in the month.
Details of the issuance and cancellation of various warnings/signals in the month are summarised in Table 1.1. Monthly meteorological figures and departures from normal of May are tabulated in Table 1.2.
Ends/Monday, June 4, 2007
Issued at HKT 18:31
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