Despite some mild interludes, January 2018 was dominated by the northeast monsoon with two episodes of cold weather during the first half and towards the end of the month. In general, the month was slightly cooler than usual with a mean temperature of 16.1 degrees, 0.2 degrees below the normal figure of 16.3 degrees. There was also more rain than usual with 62.2 millimetres of rainfall recorded in the month, more than double the normal figure of 24.7 millimetres.

     Under the influence of an easterly airstream, the weather in Hong Kong was mainly cloudy with sunny periods on the first two days of the month. After a generally fine and mild day on January 3, a broad band of clouds moved in from the northern part of the South China Sea, bringing cloudy weather and light rain patches to the territory over the next two days. The weather turned windy and cooler, and the rain became heavier on January 6 and 7 as a strong easterly airstream affected the south China coastal areas.

     A cold front over southern China moved across the coastal areas of Guangdong on January 8, bringing gloomy conditions and more rain to Hong Kong. Under the strengthening northerly winds, the weather became significantly colder and temperature at the Hong Kong Observatory fell to around 8 degrees in the morning of January 9. As a continental air mass spread towards the south China coast, the clouds thinned out and the weather turned brighter and drier on January 10. With fine and sunny weather settling in, dry conditions persisted for a further two days as daytime relative humidity fell below 40 per cent. Meanwhile, under the influence of another replenishment of the winter monsoon, cold weather in Hong Kong persisted till January 14.

     With the northeast monsoon weakening, the weather in Hong Kong was persistently fine and the temperature rose significantly. The day was warm and hazy on January 17. Temperature at the Hong Kong Observatory climbed to the month's highest of 25.5 degrees that day. Apart from a cloudy interlude on January 19 with rain patches in the morning, generally fine and mild weather persisted for a further four days. There was mist on January 21 and haze on January 22 under light wind conditions.

     The weather remained mostly fine on January 24 and 25, then turned windy and appreciably cooler as easterly winds strengthened along the south China coast. The weather became increasingly cloudy with light rain patches affecting the territory on January 26 and 27. Following the passage of a cold front on January 28, northerly winds set in and an intense winter monsoon brought a spell of cold weather with overcast skies and rain patches that persisted till the end of the month. Rain was particularly heavy during the day on January 31 and temperature at the Hong Kong Observatory dropped to the month's lowest of 7.8 degrees before midnight.

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

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

Ends/Friday, February 2, 2018
Issued at HKT 17:40

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