The Weather of July 2013

    Under the influence of unsettled weather respectively associated with an active maritime airstream and a trough of low pressure over the South China Sea during the second half of the month, July 2013 was wetter than usual in Hong Kong. The total rainfall of the month was 436.3 millimetres, about 16 percent above the normal figure of 376.5 millimetres.  The accumulated rainfall since 1 January was 1773.4 millimetres, about 20 percent above the normal figure of 1473.3 millimetres for the same period.  The number of days with thunderstorms observed at the Hong Kong Observatory in the month was 14 days, the highest since 1995.  The wet and cloudy weather also made July 2013 gloomier and cooler than usual.  The total duration of bright sunshine was only 156.9 hours, about 26 percent below the normal figure of 212.0 hours.  The mean temperature of the month was 28.0 degrees, 0.8 degree below the normal figure of 28.8 degrees. 

    Tropical cyclone Rumbia moved across the northern part of the South China Sea and intensified into a severe tropical storm on the first day of the month.  Affected by rainbands associated with Rumbia, the weather in Hong Kong was cloudy and windy with squally showers and thunderstorms.  Rumbia made landfall over Leizhou Peninsula the next morning, and local winds subsided gradually. 

    Under the influence of a ridge of high pressure, the weather was generally sunny and very hot apart from isolated showers from 3 to 5 July.  With the setting in of an active southerly airstream, the weather became more showery for the ensuing five days.  The showers eased off as mainly fine weather returned on 11 and 12 July apart from a few showers and isolated thunderstorms.  Over the western North Pacific, Severe Typhoon Soulik tracked west-northwestwards and swept across Taiwan on 13 July.  Under the influence of its outer subsiding air, the weather in Hong Kong was very hot with temperatures at the Hong Kong Observatory soaring to a maximum of 33.5 degrees on 13 July, the highest of the month. 

    An active maritime airstream brought scattered showers and a few thunderstorms to the territory over the next four days.  Meanwhile, tropical cyclone Cimaron intensified into a tropical storm over the Luzon Strait later on 17 July.  It entered the South China Sea, tracking generally northwestwards and making landfall over the coast of Fujian on the night of 18 July.  Cimaron weakened and dissipated over southeastern China the next morning, but its remnant rainbands continued to bring showers and squally thunderstorms to Hong Kong during the day. 

    Despite the presence of a ridge of high pressure over southern China, showers associated with a broad trough of low pressure over the South China Sea continued to affect Hong Kong for the ensuing four days.  Showers became heavier and more frequent on 24-26 July as the trough moved closer to the coast of Guangdong.  As a ridge of high pressure became well established over the region, the weather turned mainly fine apart from a few showers towards the end of the month.

    Four 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 summarized in Tables 1.1 to 1.5.  Monthly meteorological figures and departures from normal of July are tabulated in Table 2.