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A mixture of rainstorms and hot weather in May

     May 2014 was characterised by gloomy and rainy conditions during the first part of the month and persistent hot weather in the latter part. The total rainfall of 687.3 millimetres was more than double the normal amount for May and the seventh highest May rainfall on record. The accumulated rainfall from January to May of 1066.8 millimetres was about 67 per cent above the normal figure of 640.7 millimetres for the same period.  With about three quarters of the sunshine occurring in the second half of the month, the total duration of bright sunshine of the month was 107.8 hours, about 23 per cent below the normal figure of 140.4 hours. Sunny and hot weather in the last week of the month also brought the average temperature for the month up to 26.4 degrees, half a degree above the normal figure of 25.9 degrees.

     The weather in the early part of the month was dominated by late-season northeast monsoon. With a cloud band covering Guangdong and the northern part of the South China Sea, it was cloudy with a few showers in Hong Kong on May 1. The clouds thinned out gradually and there were sunny periods in the next two days. A trough of low pressure over southern China edged towards the coast on May 4, moving across the coastal areas of Guangdong the next morning and bringing thunderstorms and heavy showers to the territory. More than 30 millimetres of rainfall were recorded on May 5 over widespread areas in Hong Kong, and rainfall over Sha Tin, Tai Po, Tsuen Wan and Yuen Long even exceeded 50 millimetres. Rain patches continued to affect Hong Kong in the next couple of days. With replenishment of cooler air brought by the northeast monsoon, temperatures at the Hong Kong Observatory fell to a minimum of 18.8 degrees on the morning of May 6, the lowest of the month.  

     Intense thunderstorms associated with a trough of low pressure swept across the coast of Guangdong on the night of May 8 and brought widespread heavy rain and squalls to Hong Kong.  The Black Rainstorm Warning was issued at 10.30pm and more than 70 millimetres of rainfall were generally recorded over the territory. Affected by troughs of low pressure near the south China coastal areas, the weather remained unsettled with outbreaks of heavy showers and squally thunderstorms in the following five days. The rain was particularly heavy and persistent over the northern part of the New Territories on May 11 with more than 200 millimetres of rainfall recorded over Tai Po, Sha Tau Kok and Sheung Shui. There were 26 reports of flooding and 33 reports of landslides in Hong Kong during the heavy rain episodes.  

     After more than a week of gloomy skies, sunny intervals appeared in the afternoon on May 12 and 13 following some morning thundery showers. With an active south to southwesterly airstream prevailing over the south China coastal areas, the weather remained cloudy with a few showers and thunderstorms in the ensuing six days. Showers became heavier and squally thunderstorms more frequent as another trough of low pressure affected Hong Kong from May 20 to 23.   

     With the weakening of the trough, sunny periods returned on May 24. The weather then became generally fine and hot despite a few showers in the latter part of the month. With plenty of sunshine, temperatures at the Hong Kong Observatory rose to a maximum of 32.8 degrees on May 31, the highest of the month.

     One tropical cyclone occurred 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 normal for May are tabulated in Table 2.

Ends/Wednesday, June 4, 2014
Issued at HKT 18:35


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