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A relatively warm April
     April 2017 was warmer than usual with a mean temperature of 23.3 degrees, 0.7 degrees above the normal of 22.6 degrees. The month was also drier than usual with 58.8 millimetres of total monthly rainfall recorded, about one-third of the normal of 174.7 millimetres. The accumulated rainfall recorded in the first four months of the year was 134.5 millimetres, 60 per cent below the normal of 336.1 millimetres for the same period.
     Under the influence of a continental airstream brought by the northeast monsoon, the weather in Hong Kong was sunny and dry on the first four days of the month. The month started off with a cool morning on April 1 and a minimum temperature of 15.5 degrees was recorded at the Hong Kong Observatory, the lowest of the month. With the moderation of the northeast monsoon, the weather turned cloudier on April 5 with a mixture of sunny periods, coastal fog patches and isolated showers over the next five days. Meanwhile, under the influence of a southerly airstream, temperatures climbed steadily during the period, leading to a rather warm night on April 9.
     Upon the passage of a trough of low pressure, widespread rain affected the territory on April 11. Rain was heavy at times on April 12, with more than 30 millimetres of rain recorded in some areas, before easing off the next day. Meanwhile, the weather turned cooler as a replenishment of the northeast monsoon reached the south China coast. Following the moderation of the northeast monsoon, the weather was mainly fine from April 14 to 19, with some mist and haze. With plenty of sunshine, it was rather hot during the day on April 18, with temperatures at the Hong Kong Observatory rising to a maximum of 30.7 degrees, the highest of the month.
     A southerly airstream brought unsettled weather conditions to the territory on April 20. Showery conditions persisted in Hong Kong for more than a week, and thundery showers brought over 3 000 lightning strokes to the territory on April 21. After the passage of a cold front later that day, the weather became appreciably cooler on April 22 and 23. A freshening of easterly winds on April 24 brought more showers and squally thunderstorms the next day. After the northeast monsoon subsided, the weather turned relatively warm on April 26. Following the passage of a trough of low pressure, the arrival of another replenishment of the northeast monsoon affected the coast of Guangdong and brought cooler weather to Hong Kong over the next two days. 
     With the northeast monsoon subsiding, the weather was generally fine and rather warm on the last two days of the month.
     Two tropical cyclones occurred over the South China Sea and the western North Pacific in April 2017.
     Details of 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 4, 2017
Issued at HKT 16:26
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