This winter’s unseasonably warm Christmas period came amid the fourth hottest December in the city on record, according to the Hong Kong Observatory.
A mean minimum temperature of 17.6 degrees Celsius (63 degrees Fahrenheit) was recorded last month – which was 1.7 degrees warmer than the normal figure of 15.9 degrees.
The hottest December was in 1968, when 21.3 degrees was recorded.
Dr Law Hiu-fai, a scientific officer at the Observatory, said the warm temperature had been expected because of the El Niño effect.
“In October and November, the temperature of the Pacific Ocean near the equator was getting warmer, it was expected that the El Niño would affect Hong Kong,” Law said.
The El Niño refers to a climate pattern that involves a slight warming of sea surface temperatures over the eastern equatorial Pacific Ocean every few years, because of a slackening of prevailing winds across it.
Under these conditions, Law said the temperature in Hong Kong would be normal or warmer.
Law said a replenishment northeast monsoon will arrive in Hong Kong on Sunday, bringing cooler weather.
The hottest day of the month was December 4, when the mercury peaked at 27.1 degrees, and the daily temperature averaged 24.8 degrees.
The temperature was eventually brought down by the northeast monsoon on December 7, but it climbed again 12 days later after Hong Kong was hit with a relatively warm and humid maritime airstream.
On December 22, Hong Kong’s daily temperature averaged 22.2 degrees, making it the hottest Winter Solstice ever recorded.
“A weaker than usual monsoon over southern China made Hong Kong unseasonably warm last month,” the observatory said.
In a summary of the weather in December, the forecaster said the mean temperature was the sixth highest recorded in the month, and 1.3 degrees above normal.
Apart from being warmer than usual, the observatory said December was also drier, with a total rainfall of just 11.9 millimetres – down from the usual 26.8 millimetres.
The cold only settled in after an intense winter monsoon washed over the city at the end of month, and a cold weather warning was issued on December 28.
A cold snap hit town after Christmas, when the daily average temperature dropped to 10.3 degrees on December 30 – the coldest day of the month.
During the chilly weather, a 90-year-old woman died from hypothermia, and at least 32 patients were sent to hospital between December 30 to January 1.
Conditions improved on Wednesday, and on Thursday, the average temperature was 17 degrees.
The mercury is expected to hit 20 degrees on Friday.