An exceptionally warm January

     With fewer cold air outbreaks from the north reaching the south China coast, January 2019 was much warmer than usual in Hong Kong. The monthly mean temperature of 18.1 degrees and the monthly mean minimum temperature of 16.4 degrees, both the third-highest on record for January, were 1.8 degrees and 1.9 degrees above their corresponding normal figures respectively. The mean maximum temperature was 20.4 degrees which was 1.8 degrees above the normal figure and was the fifth-highest on record for January. January 2019 was also drier than usual, with only 4.7 millimetres of rainfall recorded in the month, about one-fifth of the normal figure of 24.7 millimetres for January.
 
     The intense winter monsoon that started to affect the south China coastal areas in late December 2018 brought cold weather to Hong Kong on the first day of January 2019. The minimum temperature recorded at the Hong Kong Observatory on that day was 11.4 degrees, the lowest of the month. The weather on the next two days was cool and cloudy with a few rain patches. Sunny intervals with gradual rises in local temperatures occurred on January 4 and 5 as the monsoon moderated. A weak replenishment of the northeast monsoon brought generally cloudy weather with a few rain patches from January 6 to 8.
 
     The weather of Hong Kong turned windy when a fresh to strong easterly airstream affected the south China coastal areas on January 9. With the easterlies subsiding, local weather from January 10 to 12 became milder with sunny periods and low visibility episodes. The easterlies strengthened again on January 13 and 14, leading to cloudy weather, light rain patches and morning mist.
 
     The weather was cooler with some rain patches on January 15 due to the northeast monsoon over the south China coastal areas. Local weather remained cloudy and cool the next day. While the clouds covering the coastal areas dissipated, the weather turned fine gradually during the day on January 17. The monsoon was gradually replaced by an easterly airstream on January 18, bringing mostly cloudy weather and a few light rain patches to Hong Kong on January 18 and 19. As the easterly winds moderated, it was warm with sunny periods during the day on January 20 with a few light rain patches in the morning and at night.
 
     The dry northeast monsoon reaching the south China coastal areas on the night of January 20 and its subsequent replenishment on January 26 brought fine and dry weather with cool mornings to Hong Kong from January 21 to 28. With the northeast monsoon moderating gradually, the weather was mild with sunny periods towards the end of the month. It was rather warm on January 31 with the maximum temperature at the Hong Kong Observatory soaring to 24.5 degrees, the highest of the month.
 
     One tropical cyclone occurred over the South China Sea and the western North Pacific in January 2019.
 
     Details of 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.