The Weather of August 2012

     August 2012 was one of the hottest Augusts on record which was mainly attributed to the prevalence of the continental subsiding airstream associated with tropical cyclones Saola, Kai-tak and Tembin.  The monthly mean temperature rose to 29.5 degrees which was 0.9 degrees above normal, equaling the records set in 1990, 1998 and 2011.  It was also the driest August since 1992.  The monthly total rainfall was 149.8 millimetres, only about 35 percent of the normal figure of 432.2 millimetres.  The accumulated rainfall since 1 January was 1545.4 millimetres, a deficit of 19 percent comparing to the normal figure of 1905.5 millimetres for the same period.
 
     Under the influence of the outer subsiding airstream of Typhoon Saola, the weather was generally fine and very hot apart from some haze for the first three days of the month.  Saola made landfall over the coast of Fujian on 3 August and weakened into an area of low pressure on the morning of 4 August.  Affected by the rainband associated with the remnants of Saola, it became mainly cloudy with a few showers on 4 and 5 August.   On 6 August, a trough of low pressure brought cloudy weather with a few showers and thunderstorms to the territory at first.  The weather turned fine in the afternoon when the trough dissipated.
 
     Affected by a continental airstream, the weather was mainly fine and very hot apart from a few isolated thunderstorms from 7 to 9 August.  An active southwesterly airstream brought cloudy weather with showers and squally thunderstorms to Hong Kong for the ensuing four days.  The showers were heavier on the morning of 11 August.  More than 80 millimetres of rainfall were recorded over parts of Hong Kong Island.  Affected by the anticyclone aloft over southern China, it was mainly fine and hot apart from a few isolated showers on 14 August.
 
     Over the sea east of the Philippines, tropical cyclone Kai-tak intensified into a severe tropical storm and moved across the northern part of Luzon, entering the South China Sea on 15 August.  Affected by its outer subsiding airstream, local weather became very hot on that day.  With Kai-tak further intensifying into a typhoon and edging closer to the coast of western Guangdong, the weather in Hong Kong turned cloudy with occasional squally showers on 16 August, with winds strengthening gradually in the afternoon and reaching gale force occasionally in the southwestern part of the territory and on high ground that night and the early morning of 17 August.  As Kai-tak moved away from Hong Kong, making landfall near Zhanjiang over western Guangdong, local winds weakened gradually during the day.  Kai-tak moved across northern Vietnam and dissipated inland on 18 August.  Local weather was mainly fine apart from a few showers on 18 August and the ensuing three days.   
 
     A trough of low pressure brought cloudy weather with showers and thunderstorms to Hong Kong on 22 August.  With the winds turning northerly gradually, it became mainly fine with some haze the next day. 

     Over the sea east of Taiwan, tropical cyclone Tembin intensified into a severe typhoon on 23 August and moved across the southern part of Taiwan, entering the northeastern part of the South China Sea on 24 August.  Tembin became slow-moving and lingered over the northeastern part of the South China Sea the next two days.  Under the influence of the circulation of another tropical cyclone Bolaven over the western North Pacific, Tembin turned east-northeastward on 27 August and accelerated northeastward towards the sea east of Taiwan the next day.  Affected by the subsiding continental airstream associated with Tembin, it was very hot in Hong Kong from 24 to 28 August.  The temperature at the Observatory soared to a maximum of 34.5 degrees on 28 August, the highest of the month.   Under a southerly airstream over the coast of Guangdong, there were sunny periods and a few showers in Hong Kong on 29 and 30 August.  A broad trough of low pressure over the northern part of the South China Sea brought some showers to the territory on the last day of the month. 

     Seven tropical cyclones occurred over the western North Pacific and the South China Sea in the month.

     Details of issuance and cancellation of various warnings/signals in the month are summarized in Tables 1.1 to 1.4.  Monthly meteorological figures and departures from normal for August are tabulated in Table 2.