The Weather of July 2018

    The weather in Hong Kong was cloudier than usual in July 2018. The mean amount of cloud in the month was 77 percent, 8 percent above the normal of 69 percent. The duration of bright sunshine in the month was only 181.1 hours, about 15 percent below the normal figure of 212.0 hours. The month was also warmer than usual with the mean temperature of 29.1 degrees, 0.3 degrees above the normal of 28.8 degrees. Despite the cloudy and rather showery conditions for most part of the month, the monthly rainfall was 341.1 millimetres, about 9 percent below the normal of 376.5 millimetres in July. The accumulated rainfall recorded in the first seven months of the year was 974.9 millimetres, a deficit of 34 percent compared to the normal of 1473.3 millimetres for the same period.

    Under the influence of the southwest monsoon, local weather was a mixture of sunshine and showers on 1 - 7 July. There were also occasional heavy showers and squally thunderstorms in isolated areas during these few days. During the localized heavy showers on 5 July, more than 200 millimetres of rainfall were recorded over Tai Po District. A broad trough of low pressure continued to bring showery weather to Hong Kong on 8 - 9 July.

    Apart from one or two morning showers on 10 July, the subsiding air associated with the outer circulation of tropical cyclone Maria brought generally fine weather to Hong Kong on 10 - 11 July. While it was generally fine and very hot on 12 July, with a broad trough of low pressure edging closer to the coast of Guangdong and the picking up of easterly winds, there were heavy showers and squally thunderstorms in Hong Kong on 13 - 15 July. During the downpour, the temperature at the Hong Kong Observatory fell to a minimum of 25.0 degrees on 15 July, the lowest in the month.

    A ridge of high pressure maintained a strong easterly airstream over the coast of Guangdong on 16 July and the showery activities subsided gradually. Meanwhile, an area of low pressure near Luzon developed into a tropical storm, named Son-Tinh, on 17 July. Son-Tinh moved generally westward across the northern part of the South China Sea and entered Beibu Wan on 18 July. It made landfall over the northern part of Vietnam and weakened into an area of low pressure inland on 19 July. Locally, with plenty of sunshine, it was very hot with temperature at the Hong Kong Observatory soaring to 34.3 degrees on the afternoon of 17 July, the highest in the month. Affected by the outer rainbands of Son-Tinh, the weather in Hong Kong became mainly cloudy with occasional squally showers and thunderstorms that night and on the next day. Under the combined effect of the ridge of high pressure over the southeast coast of China and Son-Tinh, it was also windy on 17 - 18 July.

    While the easterly airstream affecting the coast of Guangdong moderated gradually, a broad trough of low pressure continued to bring a few squally showers to Hong Kong on 19 - 20 July. Under the influence of the subsiding air ahead of tropical cyclone Ampil, local weather became generally fine and very hot on 21 July. After a fine and very hot morning, the weather became mainly cloudy with some squally showers over the western part of Hong Kong on the afternoon of 22 July.

    Meanwhile, an area of low pressure associated with the remnant of Son-Tinh re-intensified into a tropical depression over Beibu Wan on 22 July. It moved slowly over Beibu Wan and skirted past the northwestern part of Hainan Island. The tropical depression then made landfall over Leizhou Peninsula on 23 July and dissipated over inland Guaugxi on 24 July. Locally, with active showery activities over the northern part of the South China Sea, it was mainly cloudy with heavy showers and a few squally thunderstorms on 23 July. Showers gradually subsided with more sunshine in the following two days.

    As an anticyclone aloft southeastern China strengthened gradually, the local weather remained generally fine and very hot apart from isolated showers towards the end of the month with the maximum temperature reaching the month’s highest of 34.3 degrees again on 29 July.