A June with rejuvenating rain
After a very dry May, the rainbands of tropical cyclone Ewiniar in early June, as well as showery activities associated with troughs and an active southerly airstream later in the month, brought significant amount of rainfall to the territory. The monthly rainfall was 458.8 millimetres, slightly above the normal figure of 456.1 millimetres for June. However, as rainfall in the first five months was far below normal, the accumulated rainfall recorded in the first half of the year was 633.8 millimetres, a deficit of 42 per cent compared to the normal figure of 1096.9 millimetres for the same period. The month was also hotter than usual with a mean temperature of 28.6 degrees, 0.7 degrees above the normal figure 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 June 1. The heat 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 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 June 2 and was later named Ewiniar. It skirted past the east coast of Hainan Island and moved 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 June 4. The Observatory issued the tropical cyclone warning signal for the first time this year on the morning of June 5. After making landfall near Yangjiang on the night of June 7, the 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 recorded over the territory from June 6 to 8. The heavy downpour necessitated the issuance of the first rainstorm warning signal on June 6 this year, and the Red Rainstorm Warning Signal was issued on June 8. A waterspout was spotted near Cheung Chau in the evening on June 7. The weather became generally fine on June 9 as local winds gradually subsided and the showers eased off.
After two fine and very hot days on June 10 and 11, a trough of low pressure brought heavy showers and thunderstorms to the coast of Guangdong over the next two days. There was a report of waterspout near the Ninepin Islands on the morning of June 12, and more than 100 millimetres of rain fell over Sai Kung, Hong Kong Island and Cheung Chau on June 13. As the trough moved to the south of Hong Kong, local weather improved with a mixture of sunshine and isolated showers on June 14 and 15. A low pressure area along the trough developed over the northern part of the South China Sea, and the weather in Hong Kong remained mostly fine but windy on June 16 and 17.
Under the influence of the southwest monsoon, there was a mixture of sunny periods and showers in Hong Kong from June 18 to 21. An active southerly airstream brought more clouds and some heavy showers to the territory on June 22 and 23. Another waterspout was observed near Cheung Chau on the morning of June 22, and the temperature at the Observatory fell to the month’s lowest of 24.4 degrees on June 23 during heavy showers. Despite a sunny day on June 24, there were showers that night and the next day in Hong Kong.
As a subtropical ridge established itself over southeastern China, showery activities gradually reduced on June 26. Under the influence of the southwest monsoon, despite some showers at times, the weather in Hong Kong remained mostly fine and hot till the end of the month.
Four tropical cyclones occurred over the South China Sea and the western North Pacific in June 2018.
Details of issuance and cancellation of various warnings/signals in June are summarised in Table 1. Monthly meteorological figures and departures from normal for June are tabulated in Table 2.