The Weather of May 2017

    Due to the heavy rain on the morning of 24 May, the month was wetter than usual. The total rainfall recorded in the month was 399.3 millimetres, about 31 percent above of the normal figure of 304.7 millimetres. The accumulated rainfall recorded in the first five months of the year was 533.8 millimetres, a deficit of about 17 percent compared to the normal figure of 640.8 millimetres for the same period.

    Under the influence of a maritime airstream, the weather in Hong Kong was hot with sunny periods on the first three days of the month. There was also coastal fog on the morning of 2 May. Upon the passage of a trough of low pressure, local weather deteriorated with heavy showers and squally thunderstorms on 4 May. More than 30 millimetres of rainfall were recorded over widespread areas. With the weakening of the trough of low pressure, the weather became mainly fine and hot in the next couple of days apart from some mist and haze.

    A fresh easterly airstream brought cloudier weather and a few showers to the territory on 7-8 May. With the passage of a trough of low pressure, there were thundery showers on the early morning of 9 May. Under light wind condition, the visibility was rather low on the next day. With the setting up of a ridge of high pressure over the coast of Guangdong and the northern part of the South China Sea, the weather became mainly fine and hot on 11 May, with temperatures at the Hong Kong Observatory rising to a maximum of 31.6 degrees, the highest of the month.

    With a trough of low pressure lingering over the coastal areas of Guangdong and the northern part of the South China Sea, the weather became more showery in mid May. The showers were heavy at times on 15 May, bringing over 50 millimetres of rainfall to Kowloon and Shatin. With the trough of low pressure moving to the northern part of the South China Sea and the onset of a relatively dry easterly airstream, mainly fine weather returned on 17 May. Under the influence of a maritime airstream, the weather turned generally cloudy with a few showers over the next six days.

    With the passage of a trough of low pressure across the coast of Guangdong, local weather deteriorated with heavy showers and squally thunderstorms on 24 May. The heavy rain, which necessitated the issuance of the first Black Rainstorm Warning this year, brought more than 70 millimetres of rainfall to widespread areas with rainfall exceeding 300 millimetres in Kwai Tsing and Sham Shui Po. Serious flooding were reported in many places over the territory including Lai Chi Kok, Tseung Kwan O, Ho Man Tin, central and western parts of the Hong Kong Island.

    With the trough of low pressure moving towards the northern part of the South China Sea, local weather improved with sunny intervals on 25 May. An easterly airstream brought mainly cloudy weather with one or two isolated showers to the territory the next day. Affected by a dry continental airstream, it was mainly fine and dry on 27-29 May. With the continental airstream weakening and being gradually replaced by a southwesterly airstream, the weather was hot with a few showers towards the end of the month.