The Weather of June 2018

    After a very dry May, the long awaited rainfall eventually returned to Hong Kong in June 2018, mainly due to the passage of tropical cyclone Ewiniar in early June, as well as showery activities associated with troughs and an active southerly airstream later in the month. The monthly rainfall was 458.8 millimetres, slightly above the normal of 456.1 millimetres in June. However, with well below normal rainfall in the first five months, the accumulated rainfall recorded in the first half of the year was 633.8 millimetres, a deficit of 42 percent compared to the normal of 1096.9 millimetres for the same period. The month was also warmer than usual with a mean temperature of 28.6 degrees, 0.7 degree above the normal of 27.9 degrees.

    The heat wave in the latter half of May extended into early June. With plenty of sunshine in the morning, the temperature at the Hong Kong Observatory soared to the month’s highest of 35.1 degrees around noon on 1 June. The heat also triggered some isolated heavy showers and thunderstorms near Tai Po. An easterly airstream then reached the coastal area of Guangdong later in the day and the intense heat was slightly relieved by the windy conditions over the next couple of days.

    Meanwhile, an area of low pressure over the South China Sea intensified into a tropical depression on 2 June and was later named Ewiniar. It skirted past the east coast of Hainan Island and then turned in the general direction of the coastal areas of western Guangdong. The weather in Hong Kong became cloudy with some squally showers and thunderstorms on 4 June and tropical cyclone warning signal was issued for the first time this year on the morning of 5 June. After making landfall near Yangjiang on the night of 7 June, a weakening Ewiniar continued to drift towards the Pearl River Delta. Its rainbands brought heavy squally showers and thunderstorms to Hong Kong with more than 170 millimetres of rainfall generally recorded over the territory on 6 - 8 June. The heavy downpour necessitated the issuance of the first rainstorm warnings this year, including the Red Rainstorm Warning on 8 June. A waterspout was also spotted near Cheung Chau in the evening on 7 June. Local winds gradually subsided and the showers eased off on 9 June as generally fine weather returned.

    After a couple of fine and very hot days on 10 and 11 June, a trough of low pressure brought heavy showers and thunderstorms to the coast of Guangdong on 12 - 13 June. There was a report of waterspout near Ninepin Islands on the morning of 12 June, and more than 100 millimetres of rain fell over Sai Kung, Hong Kong Island and Cheung Chau on 13 June. The trough passed to the south of Hong Kong and local weather improved with a mixture of sunshine and isolated showers on 14 - 15 June. Despite the development of a low pressure area along the trough over the northern part of the South China Sea, the weather in Hong Kong remained mostly fine but windy on 16 – 17 June.

    Under the influence of the southwest monsoon, local weather was a mixture of sunny periods and showers on 18 - 21 June. An active southerly airstream brought more clouds and some heavy showers to the territory on 22 – 23 June. Another waterspout was observed near Cheung Chau on the morning of 22 June, and the temperature at the Hong Kong Observatory fell to the month’s lowest of 24.4 degrees on 23 June during heavy showers. Despite a sunny day on 24 June, more showers affected the territory that night and the next day.

    As the subtropical ridge became established over southeastern China, showery activities gradually decreased on 26 June. Under the influence of the southwest monsoon and despite still some showers around at times, the weather in Hong Kong remained mostly fine and hot till the end of the month.