Hong Kong saw the latest issuance of a Very Hot Weather warning in a year on Wednesday, as the city sweltered during an exceptionally hot October.

Temperatures across Hong Kong at 1:45pm on Wednesday, October 21, 2026. Photo: weatherhongkong.com via HKO.

The warning – which was raised at 6.45am – is triggered based on a heat index threshold and generally when the mercury is set to reach, or exceed, 33 degrees Celsius.

Wednesday breaks the previous record of October 19, 2024 for the Observatory’s latest issuance.

Temperatures had reached 36 degrees Celsius in Yuen Long by Wednesday lunchtime, with a high of 33.8 degrees Celsius recorded at the Observatory’s Tsim Sha Tsui headquarters.

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“Winds are weak over the coast of Guangdong. Meanwhile, under the influence of an anticyclone aloft, the weather is generally fine and very hot over Guangdong,” the Observatory said on Wednesday. “Besides, pressure is rising over northern Guangdong. A surge of the northeast monsoon is expected to reach the coastal areas tonight.”

Pedestrians in Hong Kong during hot weather. File Photo: Kyle Lam/HKFP.

Professor Amos Tai from the Chinese University of Hong Kong’s Department of Earth and Environmental Sciences said on a radio programme on Wednesday that the super El Niño – which sees sea surface temperatures in the central and eastern equatorial Pacific Ocean rise – has weakened the northeast monsoon.

Tai also pointed to Super Typhoon Champi, located east-northeast of Manila, as contributing to subsiding air currents locally.

According to iCable, he added that Hongkongers should expect a hotter winter this year – or perhaps the hottest in history – as the super El Niño phenomenon is expected to last until next spring.

The Observatory predicts that the city will continue to see highs of above 30 degrees Celsius until next Wednesday.

Changing climate

According to HKFP’s weatherhongkong.com, Wednesday also marked the hottest October 21 on record, beating 31.5 degrees Celsius recorded in 2024.

Data from the Observatory shows that record after record is being broken, from the number of “hot nights” a year to the average temperature through August, the final month of summer.

The number of Very Hot Days in Hong Kong has quadrupled since the 2000s. Back then, the city recorded a yearly average of 13.4. But, since 2020, there have been more than 50 Very Hot Days a year.

The number of hours annually that Hong Kong has spent under heat warnings has also tripled since 2000.

Climate crisis

The Intergovernmental Panel on Climate Change has warned that the intensity and frequency of heatwaves have continued to increase since the 1950s due to human-caused climate change. The prevalence of greenhouse gases like carbon dioxide – which trap heat in the atmosphere – raises the planet’s surface temperature, with hotter, longer heatwaves putting lives at risk.

See also: How extreme heat became the deadliest silent killer among world weather disasters

Hong Kong has already warmed by 1.7 degrees Celsius since the Industrial Revolution, research NGO Berkeley Earth says. Heat and humidity may reach lethal levels for protracted periods by the end of the century, according to a 2023 study, making it impossible to stay outdoors in some parts of the world.