The Weather of April 2017

    April 2017 was warmer than usual with a mean temperature of 23.3 degrees, 0.7 degree above the normal of 22.6 degrees. The month was also drier than usual in terms of rainfall with 58.8 millimetres recorded in the month, only 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, a deficit of 60 percent compared to 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 1 April and the minimum temperature of 15.5 degrees recorded at the Hong Kong Observatory was the lowest of the month. With the moderation of the northeast monsoon, the weather turned cloudier on 5 April with a mixture of sunny periods, coastal fog patches and isolated showers over the next five days. Temperatures climbed steadily during the period, leading to a rather warm night on 9 April under the influence of a southerly airstream.

    Upon the passage of a trough of low pressure, widespread rain affected the territory on 11 April. Rain was heavy at times on 12 April, with more than 30 millimetres falling in some places, before easing off the next day. Meanwhile, the weather turned cooler as well, 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 14 to 19 April apart from some mist and haze. With plenty of sunshine, daytime conditions became rather hot with temperatures at the Hong Kong Observatory rising to a maximum of 30.7 degrees on 18 April, the highest of the month.

    The setting in of unsettled weather associated with a southerly airstream on 20 April marked the beginning of a showery spell that lasted for more than a week. Thundery showers brought over 3000 lightning strokes to the territory on 21 April ahead of the passage of a cold front later that day. The weather then became appreciably cooler on 22 and 23 April. A freshening of easterly winds on 24 April was followed by more showers and squally thunderstorms the next day. After a lull in the northeast monsoon and a relatively warm day on 26 April, the passage of a trough of low pressure brought another replenishment of the northeast monsoon to the coast of Guangdong and cooler weather to Hong Kong over the next couple of days.

    With the northeast monsoon subsiding, the weather was generally fine and rather warm on the last two days of the month.