The Weather of August 2013

    The weather of August 2013 was rather gloomy, mainly due to a prolonged period of cloudy and rainy weather associated with tropical cyclones Utor and Trami in mid-August.  The total duration of bright sunshine recorded in the month was 148.1 hours, the 10th lowest on record for the month of August and about 22 percent below the normal figure of 188.9 hours.  The monthly total rainfall of 445.4 millimetres was slightly above the normal figure of 432.2 millimetres.  The accumulated rainfall since 1 January was 2218.8 millimetres, about 16 percent above the normal figure of 1905.5 millimetres for the same period.  

    As Tropical Storm Jebi tracked northwestwards across the South China Sea towards Hainan Island, its combined effect with the ridge of high pressure over the coast of southeastern China caused local winds to strengthen gradually at the beginning of the month.  The outer rainbands of Jebi also brought scattered squally showers and thunderstorms to Hong Kong.  Jebi intensified into a severe tropical storm and moved towards Hainan Island on the morning of 2 August, making landfall near Wenchang during the night.  More than 50 millimetres of rainfall were recorded on the first two days of the month over most parts of the territory, with rainfall over the western part of Hong Kong Island exceeding 100 millimetres.  With Jebi weakening gradually over the northern part of Vietnam, showery activities affecting Hong Kong abated on 3 August and sunny intervals appeared in the afternoon. 

    Under the dominance of a ridge of high pressure, it was sunny and very hot from 4 to 6 August.  An active southerly airstream brought a few showers and squally thunderstorms to Hong Kong on 7 August.  With the re-establishment of the ridge of high pressure, sunny and very hot conditions returned for the ensuing five days.  Temperatures at the Hong Kong Observatory rose to a maximum of 34.9 degrees on 12 August, the highest of the month. 

    Over the western North Pacific, Utor intensified into a super typhoon on 11 August.  It moved cross Luzon and weakened to a severe typhoon the next morning.  On 13 August, Utor entered the northern part of the South China Sea and edged towards the coast of western Guangdong.  Affected by the outer rainbands of Utor, the weather in Hong Kong became overcast and windy with heavy squally showers and a few thunderstorms.  With Utor making landfall near Yangjiang on 14 August, local winds weakened gradually.  Winds in Hong Kong moderated further the next day as Utor continued to move inland and weakened into a tropical depression.  Thundery showers associated with the remnant of Utor continued to affect Hong Kong from 15 to 20 August.  

    Another tropical cyclone Trami crossed the seas east of Taiwan and moved towards the coast of Fujian on 21 August.  In Hong Kong, under the influence of a continental airstream, there were sunny intervals with relatively low visibility in some areas.  Affected by the outer rainbands of Trami, the weather in Hong Kong became showery with a few squally thunderstorms on 22 August.  In the wake of Trami, an active southwesterly airstream brought heavy showers and squally thunderstorms to the territory for the next two days.

    A ridge of high pressure extended westward from the Pacific and brought generally fine weather to southeastern China on 25 August.  Locally, the weather improved gradually and there were sunny periods in the afternoon.  Under generally fine and very hot weather, temperatures in Hong Kong reached 33 degrees or above over many places in the afternoon for the ensuing four days.

    Affected by a trough of low pressure, local weather deteriorated with heavy rain and squally thunderstorms on the last two days of the month.  The rain was particularly heavy on the morning of 30 August when more than 50 millimetres of rainfall were recorded over many places of the New Territories and Hong Kong Island, with rainfall over Tai Po exceeding 150 millimetres.