A warm and dry April

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     The weather of April 2018 was warmer than usual with a monthly mean temperature of 23.6 degrees, 1.0 degree above the normal figure of 22.6 degrees. The month was also much drier than usual with only 28.1 millimetres of rainfall recorded in the month, about one-sixth of the normal figure of 174.7 millimetres and the eighth lowest on record for April. The accumulated rainfall recorded in the first four months of the year was 117.5 millimetres, a deficit of 65 per cent compared to the normal figure of 336.1 millimetres for the same period.

     Under the influence of a ridge of high pressure, the weather in Hong Kong was generally fine and warm for the first five days of the month. A cold front moved across the coast of Guangdong on April 6, and the local weather turned cloudy with a few showers. As winds from the north strengthened in the afternoon, it became significantly cooler. The weather remained generally cloudy on April 7, with temperature at the Hong Kong Observatory dropping to a minimum of 16.1 degrees in the morning, the lowest of the month. Under the influence of the dry northeast monsoon, it was fine and dry in Hong Kong on April 8.

     With the moderation of the northeast monsoon and the onset of a southerly airstream, the temperatures rose gradually from April 9 to 13. With plenty of sunshine, the temperature at the Hong Kong Observatory reached a maximum of 30.6 degrees on April 13, the highest of the month.

     A cold front moved across the coast of Guangdong on the night of April 14 and the associated northeast monsoon brought cooler weather to Hong Kong over the next two days. Under the influence of an upper-air disturbance, there were showers and squally thunderstorms on April 15, with more than 10 millimetres of rainfall recorded generally over the territory.

     With a broad area of cloud band covering the coastal areas of Guangdong, it was mainly cloudy with a mixture of isolated showers and sunny intervals in Hong Kong from April 17 to 21. Under the influence of a southerly airstream, apart from coastal fog on the morning of April 23, the weather was hot with sunny periods on April 22 and 23.

     A trough of low pressure moved across the coast of Guangdong on April 24. The weather in Hong Kong turned cloudy with showers and a few thunderstorms during the day. More than 20 millimetres of rainfall were recorded over Hong Kong Island, Tuen Mun and Lantau Island. Under the influence of a broad cloud band over the south China coast, local weather remained cloudy with isolated showers from April 25 to 27.

     With the onset of an anticyclone aloft, the weather became mainly fine and hot towards the end of the month apart from some isolated showers.

     One tropical cyclone occurred over the South China Sea and the western North Pacific in April 2018.

     Details of the issuance and cancellation of various warnings/signals in April are summarised in Table 1. Monthly meteorological figures and departures from normal for April are tabulated in Table 2.

Ends/Thursday, May 3, 2018
Issued at HKT 16:22

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Table 1 (Warnings and signals issued in April 2018)

Table 2 (Figures and departures from normal - April 2018)