The Weather of June 2017

    As a result of the very hot weather in early June and the rainy spell in mid-June, the month was overall warmer and wetter than usual. The monthly mean temperature was 28.8 degrees, 0.9 degree above the normal of 27.9 degrees. The total rainfall recorded in the month was 656.0 millimetres, about 44 percent above the June normal of 456.1 millimetres. The accumulated rainfall recorded in the first half year was 1189.8 millimetres, a surplus of 8 percent compared to the normal of 1096.9 millimetres for the same period.

    Under the influence of an active southwest monsoon, the weather was mainly cloudy and showery on the first two days of the month. The weather turned brighter on 3 June, and with winds subsiding and more sunshine, the weather became very hot on 5 – 7 June. Despite the fine conditions, a lingering trough over the inland areas of Guangdong also led to some significant development of showery activities along the coast that affected the territory on 6 and 7 June. Generally fine weather persisted till 11 June with temperature at the Hong Kong Observatory that day soaring to a maximum of 34.1 degrees, the highest of the month.

    Meanwhile, an area of low pressure over the South China Sea developed into a tropical storm, named Merbok, on 11 June. Merbok moved across the northern part of the South China Sea on 12 June and intensified further into a severe tropical storm that night. It traversed the eastern part of Hong Kong waters and made landfall over the Dapeng Peninsula before midnight. With the approach of Merbok, local winds strengthened significantly with heavy squally showers later on 12 June, leading to the issuance of the No.8 Gale or Storm Signal for the first time in June since 2012. As Merbok weakened over land, its rainbands continued to affect the south China coastal region with gusty winds and heavy rain, with temperature at the Hong Kong Observatory falling to the month’s lowest of 24.3 degrees in rain and the issuance of the Red Rainstorm Warning Signal on the morning of 13 June. More than 150 millimetres of rainfall were generally recorded over the territory on 13 – 14 June, with rainfall over the urban areas exceeding 250 millimetres.

    Under the influence of an enhanced southwest monsoon in the wake of Merbok on 15 and 16 June and with the development of a lingering trough of low pressure along the coastal areas of the Guangdong, the weather remained unstable and rainy till 21 June. In particular, outbreaks of heavy rain and squally thunderstorms on 17 June brought more than 100 millimetres of rainfall to the territory and again led to the issuance of the Red Rainstorm Warning Signal.

    After the dissipation of the trough, the weather turned fine and hot on 22 June. A mixture of sunshine and showers then persisted for the next five days. Despite the development of another trough over southern China, showery activities over the coastal region gradually subsided and daytime conditions became very hot as generally fine weather prevailed over the territory towards the end of the month.