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One of the hottest August on record

     Under the prolonged dominance of the sub-tropical ridge, Hong Kong experienced one of the hottest August since records began in 1884.  The monthly mean temperature soared to 29.5 degrees, equalling the record set in 1990 and 1998 and was 1.1 degrees above normal.  The month was sunnier than usual.  The monthly total duration of bright sunshine was 242.0 hours, 52.3 hours higher than normal.

     The month was also dry with a total rainfall of 157.6 millimetres, only 35 percent of the normal figure.  The accumulated rainfall since January 1 amounted to  1092.3 millimetres, suffering a deficit of 42 percent compared with the normal figure of 1873.7 millimetres for the same period.

     Under the influence of a persistent anticyclone aloft southern China, the weather in Hong Kong was sunny and very hot in the first seven days of the month.  The temperatures at the Hong Kong Observatory rose to a maximum of 35.0 degrees in the afternoon on August 7, the highest of the month.

     A trough of low pressure developed near the South China coast and brought thundery showers to the territory for the next two days.  As the trough of low pressure became more active, there were occasional heavy rain and squally thunderstorms over the territory on August 10.  With the weakening of the trough of low pressure on August 11, the rain eased off and there were sunny periods during the day.

     Dominated by a ridge of high pressure over southern China, local weather became sunny and hot apart from a few showers from August 12 to 16.  With a temporary retreat of the ridge, there were thunderstorms in the afternoon on August 17.  As the ridge re-established over southern China, local weather became generally fine and very hot in the ensuing three days.  Despite the weakening of the ridge of high pressure, the weather was generally fine apart from a few showers and isolated thunderstorms from August 21 to 23.  A trough of low pressure over southern China edged towards the coast of Guangdong on August 24 and brought showers to the territory.  Under the influence of the trough of low pressure, thundery showers developed locally in the afternoon on August 25.  

     Affected by a continental airstream, the weather was generally fine and very hot apart from a few isolated showers and some haze from August 26 to 28.  Meanwhile, Typhoon Namadol over the Luzon Strait headed northwards towards Taiwan on August 28, crossing the southern part of the island on August 29.  It moved towards Fujian the following day while weakening into a tropical storm.  Namadol subsequently made landfall over the province and weakened further on August 31.  During this period, Hong Kong remained outside the core circulation of Namadol and was under the influence of a dry west to northwesterly airstream.  Local weather continued to be very hot with haze for the last three days of the month.

     Five tropical cyclones 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 of August are tabulated in Table 2.

Ends/Thursday, September 1, 2011
Issued at HKT 20:58


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