The Weather of August 2010

     Dominated by a relatively strong Pacific ridge, August 2010 was hotter and sunnier than usual.  The mean temperature for the month was 28.8 degrees, about 0.4 degrees above normal.  Meanwhile, the total bright sunshine duration for the month was 213.4 hours, about 12 percent above normal.  The month was also drier than usual.  The total rainfall in the month was 350.3 millimetres, about 21 percent below the normal figure of 444.6 millimetres.  The accumulated rainfall since 1 January was 1705.3 millimetres, about 9 percent below the normal figure of 1873.7 millimetres for the same period. 

     Affected by a ridge of high pressure extended from the Pacific, the weather was generally fine and hot for the first four days of the month.  Under generally light wind condition, it was very hot on 5 August.  The temperature at the Hong Kong Observatory rose to a maximum of 33.7 degrees, the highest of the month.  Intense day heating triggered off heavy and thundery showers that evening.  More than 50 millimetres of rainfall were recorded in the eastern part of Kowloon, Tseung Kwan O, Shatin and Sai Kung.  A weak ridge of high pressure brought sunny periods to the territory on 6 August. 

     A broad trough of low pressure extending from the northern part of the South China Sea brought thundery showers to the territory on 7 and 8 August.  As a weak ridge of high pressure re-establised over the coast of Guangdong, local weather became sunny and very hot again in the next two days.  The temperature at the Hong Kong Observatory rose to a maximum of 33.7 degrees again on 10 August, equalling the highest temperature of 5 August. 

     A trough of low pressure extending from the coast of western Guangdong brought cloudy condition with some thundery showers to the territory on 11 August.  With a southerly airstream gaining dominance, there were sunny periods with a few showers from 12 to 15 August.  Another trough of low pressure over the coast of western Guangdong brought showers and a few squally thunderstorms to Hong Kong for the following two days.  With a ridge of high pressure covering southern China, local weather turned mainly fine on 18 August.  Affected by an active easterly airstream, there were occasional showers and squally thunderstorms for the next two days.  The weather turned mainly fine on 21 and 22 August.

     A tropical depression formed over the South China Sea on 22 August.  While moving generally westwards, it intensified into a tropical storm and was named Mindulle on the morning of 23 August.  Mindulle further intensified into a severe tropical storm that night and made landfall over the northern part of Vietnam the next day.  Affected by the outer rainbands of Mindulle, local weather was cloudy with occasional showers and squally thunderstorms from 23 to 25 August.  With the dissipation of Mindulle, it became generally fine on the next two days.  Under light wind condition and with intense day heating, some locally developed heavy and thundery showers affected Hong Kong on the afternoon of 28 August (Figure 1).  More than 70 millimetres of rainfall were recorded in the western part of the New Territories, parts of Kowloon and Hong Kong Island.

     An area of low pressure over the South China Sea intensified into a tropical depression on 28 August.  It intensified into a tropical storm and was named Lionrock the next day.  It drifted slowly over the northern part of the South China Sea on 30 August.  Under the influence of the subsiding air mass ahead of Lionrock, local weather was sunny and very hot on 29 and 30 August.  Light wind condition brought hazy weather to the territory on the last day of the month.  

Figure 1.  Radar picture at 2 pm on 28 August 2010: Heavy thunderstorms were affecting the western part of
the New Territories, parts of Kowloon and Hong Kong Island

     Five 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 1.5.  Monthly meteorological figures and departures from normal for August are tabulated in Table 2.