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January 2016 was characterised by an intense cold surge in the latter part of the month and exceptionally high monthly rainfall. The unseasonably warm weather in the first three weeks of the month was totally offset by the freezing temperatures during the three-day period of January 23 to 25. The mean sea level pressure of 1,037.7 hectopascals on January 24 was the highest ever recorded at the Observatory. Yet the monthly average temperature of 16.0 degrees turned out to be deceptively unremarkable, only 0.3 degree below normal. With upper-air disturbances repeatedly affecting the south China coastal areas and bringing outbreaks of heavy rain, the Observatory recorded an all-time high monthly rainfall of 266.9 millimetres, more than 10 times the normal figure of 24.7 millimetres for January, and breaking the previous record of 214.3 millimetres set way back in January 1887. The heavy rain on January 5 also broke the hourly rainfall record for January.
Under the influence of a dry northeast monsoon, the weather in Hong Kong was mainly fine and dry on the first day of the month. A broad band of clouds over the northern part of the South China Sea brought a few rain patches on January 2 and the weather remained cloudy with mist and fog patches in the next two days as a humid maritime airstream set in over the territory. The visibility at Waglan Island once fell below 500 metres in the morning on January 3.
An area of heavy rain and thunderstorms associated with an upper-air disturbance affected Hong Kong in the afternoon on January 5 and brought more than 30 millimetres of rainfall to the urban areas, the eastern part of Lantau Island and the eastern part of the New Territories. The rain was particularly heavy between 1pm and 2pm with 37.0 millimetres of rainfall reported at the Observatory, the highest hourly rainfall for January on record. It also necessitated the issuance of the Amber Rainstorm Warning, the earliest of the year since the rainstorm warning system commenced operation in 1992.
Despite some rain and mist patches in the morning on January 6, the weather turned mainly fine during the day as a drier air mass reached the south China coastal areas, and remained so over the next couple of days. Meanwhile, easterly winds freshened on January 9 and the weather turned cloudier and cooler with rain on January 10 and 11. A replenishment of the northeast monsoon reached the coast of Guangdong and temperatures dropped further in Hong Kong with relatively cool mornings on January 12 and 13.
After a sunny day on January 13, a prolonged spell of cloudy weather set in over the next 11 days. Rainbands associated with an upper-air disturbance and a cold front affected Hong Kong from January 15 to 17 with more than 75 millimetres of rainfall recorded at the Observatory during the period. After a rather cold morning and some sunny periods on January 18, easterly winds strengthened over the next couple of days and brought more clouds and rain to Hong Kong.
Meanwhile, an intense surge of cold air poured southwards across Mainland China and reached the coast of Guangdong on January 22, bringing appreciably colder weather with occasional rain. Temperatures in the urban areas fell to about 10 degrees that night and plunged further in the next couple of days as strong to gale force northerly winds raged across the coastal areas. Under bitterly cold and rainy conditions, the mean sea level pressure at the Observatory climbed to an all-time record high of 1,037.7 hectopascals on January 24 and temperatures dropped further during the day to the month's lowest level of 3.1 degrees that afternoon, the coldest day since 1957 and the sixth lowest on record. Sub-zero temperatures were recorded on high ground with temperatures at Tai Mo Shan falling to a minimum of -6.0 degrees that day. There was widespread frost, rime, icing, freezing rain and ice pellets on high ground and in some parts of the New Territories. More than 120 people, mostly hikers and runners in a cross-country race stranded on Tai Mo Shan and nearby peaks due to icy roads and wintry weather, had to be rescued or led to safety, and more than 60 were taken to hospitals for treatment with a number of them suffering from hypothermia.
Following a very cold morning on January 25, sunny skies emerged that day as the northerly winds eventually brought a dry continental air mass to Hong Kong with relative humidity falling below 40 per cent during the day. However, clouds and rain patches soon returned the next day as the dry air mass retreated, and the weather remained cold in the mornings on January 26 and 27 despite a gradual rise in temperatures. Conditions became even more humid and unsettled on January 28 and 29 as another upper-air disturbance brought heavier rain and thunderstorms to the south China coastal areas. Under the influence of the northeast monsoon, generally cloudy and cool weather prevailed till the end of the month.
There was no tropical cyclone over the South China Sea and the western North Pacific in the month.
Details of issuance and cancellation of various warnings/signals in the month are summarised in Table 1. Monthly meteorological figures and departures from normal for January are tabulated in Table 2.
Ends/Tuesday, February 2, 2016
Issued at HKT 20:29
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