Hongkongers may see more extreme weather and cold winter spells in the future as the world's oceans warm up, scientists say.
The warning was issued as temperatures dropped dramatically from a warm and humid 21.5 degrees Celsius on Tuesday afternoon to a low of 7.9 yesterday morning.
Just a week ago Hong Kong was even colder than Sochi, Russia - where the Winter Olympics are being held - before temperatures rose rapidly to the low 20s.
The cold fronts hitting the city have been a result of a winter monsoon over southern China, caused by differential warming and cooling over land and sea.
This type of rapid fluctuation in temperature is quite common in the late winter and early spring, said Johnny Chan Chung-leun, dean of City University's school of energy and environment.
"During this period, the north-to-south temperature differences are smaller as the sun begins to warm the tropical parts of the northern hemisphere," said Chan, chair professor of atmospheric science.
Sandy Song Man-kuen, senior scientific officer at the Observatory, explained the phenomenon in terms of the change of a mild air mass to a cold one.
"Steep drops of more than 10 degrees have occurred on several occasions in the past. It is not the first time," she said.
The extent of the hot-cold fluctuations also depends on wave motions. As west-to-east wave amplitudes rose, some areas would get abnormally colder and others warmer, Chan said.
"Wave amplitudes are determined by the difference in temperatures between the northern and tropical parts of the northern hemisphere, which may also be affected by ocean temperatures," the professor said.
He noted that extreme differences in temperatures between the north and tropics were one of the causes of instability in the climate.
"With climate change, Hong Kong could see more cold snaps, extreme heat in the summer and much higher rainfall as warmer oceans release more atmospheric vapour," he warned.
The city has seen temperatures falling into the single digits for the second week this month, making this February the coldest in 18 years.
There was a bright spot in the gloom, however. Hong Kong's unusually chilly waters welcomed a group of visitors - a pod of about 100 false killer whales sighted over two days last week, although no firm link with the weather could be established.
The weatherman says cold weather will continue until the weekend, when the monsoon moderates gradually.
Observatory data shows that there is about one very cold day - where the temperature falls below 7 degrees - every two years.
The longest recorded cold snaps lasted six days, in the years 1893, 1951, 1955 and 1966.