Hong Kong’s winter season will see average to above-average temperatures, due to the influences of both global warming and weather patterns, according to the Hong Kong Observatory.
An observatory spokesman said that the weather pattern La Nina usually brings colder-than-average temperatures to Hong Kong, but because of the warming effect of climate change, the city’s winter will have temperatures closer to historical averages.
La Nina and El Nino are natural weather events which occur when the atmosphere above the Pacific Ocean changes from its neutral state, due to the cooling or warming of the Pacific’s surface waters.
During El Nino, the decrease in trade winds over the Pacific Ocean sends warm seawater to the Western hemisphere, while La Nina causes the opposite to happen. The ocean and the atmosphere interact, reinforcing the changes in the state of the ocean and the atmosphere. This cycle is called the El Nino-Southern Oscillation (ENSO).
Typically, El Nino increases Hong Kong’s average winter temperature by 0.2 degrees Celsius, but La Nina cools it down by 0.7 degrees Celsius. The average winter temperature in Hong Kong during La Nina is 16.2 degrees Celsius.
But because the effect of La Nina has been counteracted by that of global warming, which sees “a significant long-term rising trend,” the observatory predicts that Hong Kong will see temperature levels that “tend toward normal to above-normal”.
Both El Nino and La Nina will bring increased rainfall during the winter and spring seasons. The forecast for winter is just over 100mm of rainfall. La Nina almost doubled the chances of tropical cyclones hitting Hong Kong back in autumn.