The Weather of June 2011 - A hot and wet June

     Under the prevalence of a warm southerly airstream punctuated by episodes of inclement weather especially during the latter half of the month, June 2011 was hotter and wetter than usual.  The mean temperature of the month was 28.6 degrees, 0.7 degrees above the normal figure of 27.9 degrees.  Amber rainstorm warnings were issued for periods of heavy rain associated with Tropical Storm Sarika and a convective disturbance around mid June and an active trough of low pressure towards the end of the month.  The monthly total rainfall recorded at the Hong Kong Observatory was 446.1 millimetres, about 15 percent above normal.  In spite of a wet June, the accumulated rainfall since 1 January was only 718.4 millimetres, a deficit of 32 percent compared to the normal figure of 1054.7 millimetres for the same period. 

     With a balmy southerly airstream prevailing, the weather in Hong Kong was generally fine and hot apart from one or two showers for the first eight days of the month.  Under light wind condition, it was very hot on 9 and 10 June.  The temperatures at the Hong Kong Observatory soared to a maximum of 34.5 degrees on 9 June, the highest record in June since 1980.  

     A tropical depression developed over the seas west of Luzon and was named Sarika on 9 June.  While moving northwards and edging closer to southeastern China, Sarika intensified into a tropical storm on 10 June.  It made landfall near Shantou on the morning of 11 June and weakened into an area of low pressure during the day.  Affected by Sarika and its remnant, local weather became cloudy with occasional showers and squally thunderstorms on 11 and 12 June.  A southerly airstream continued to bring some showers to the territory for the ensuing three days.  

     Under the influence of a convective disturbance, local weather deteriorated again with occasional heavy rain and a few squally thunderstorms on 16 and 17 June.  Over 200 millimetres of rainfall were recorded over parts of the urban area and Sha Tin on these two days.  With the dissipation of the convective disturbance, the rain eased off and it became mainly fine on 18 and 19 June.  

     Meanwhile, a tropical depression crossed the Luzon Strait on 20 June, entered the northern part of the South China and was named Haima on 21 June.  Affected by the subsidence air mass ahead of Haima, local weather was very hot for these two days, apart from a few squally showers.  Haima crossed the northern part of the South China Sea and intensified into a tropical storm on 22 June.  Locally, there were heavy squally showers with strong east to southeasterly winds, reaching gale force offshore and on high ground occasionally on that day.  Haima made landfall over the coast of western Guangdong the next day.  Under the influence of its outer rain bands, it remained cloudy with a few squally showers in Hong Kong on 23 June.  

     As Haima moved west-southwestwards further away from Hong Kong, local weather turned generally fine and hot on 24 and 25 June.  Affected by a southerly airstream, there were a few isolated showers and thunderstorms for the next two days.  An active trough of low pressure brought occasional heavy rain and squally thunderstorms to the territory on 28 and 29 June.  More than 120 millimetres of rainfall were recorded over the western part of Hong Kong Island on 28 June and more than 100 millimetres over Yuen Long, Sha Tin and the northeastern part of the New Territories on 29 June.  The trough of low pressure weakened gradually during the last day of the month but local weather remained cloudy with showers and a few squally thunderstorms.

     Three tropical cyclones occurred over the South China Sea and the western North Pacific 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 June are tabulated in Table 2.