The Hong Kong Observatory recorded a high of 36.9°C in August—the highest daily temperature on local record. August also saw the rare occurrence of three nights with minimum temperatures of 30°C or above, underscoring the severity of extreme hot-night conditions. Meteorological agencies are forecasting that a very strong El Niño may be imminent. Dr. Cheng Luk-ki, Director of Green Power, analyzed temperature data from Hong Kong's two recent very strong El Niño events and estimates that Hong Kong could face prolonged high temperatures this autumn. Average autumn temperatures may reach a record 27°C or above, and he urges the Government and the public to prepare for the heat-related risks in the months ahead.
El Niño is a natural phenomenon in which abnormally warm sea surface temperatures in the eastern equatorial Pacific Ocean trigger climate anomalies worldwide. It typically occurs every two to seven years. When its intensity (RONI) reaches 2.0°C or above, it is classified as a "Very Strong El Niño". The two most recent very strong El Niño events occurred in 1997/1998 (peak RONI = 2.38) and 2015/2016 (peak RONI = 2.37).
Dr. Cheng noted that during both very strong El Niño episodes, Hong Kong's autumn (September to November) average temperatures increased. In 1998, the average autumn temperature reached 25.7°C, 0.7°C higher than the 25.0°C average over the preceding five years. In 2015, the average autumn temperature reached 26.1°C, 0.9°C higher than the 25.2°C average over the preceding five years.
Over the past five years (2021–2025), Hong Kong's average autumn temperature was 26.3°C. Based on the warming pattern observed during the previous two very strong El Niño events, this autumn's average temperature could rise by around 1°C compared with the most recent five-year average—bringing the seasonal average to a record 27°C or above.
Dr. Cheng further pointed out that in recent years, even as Hong Kong enters autumn, the number of Very Hot Weather(1) and Hot nights(2) has shown an upward trend. Last year (2025), Hong Kong recorded 19 very hot weather days and 20 hot nights during autumn—both the highest on record. With the additional influence of a very strong El Niño, the number of Very Hot days and Hot nights this autumn could set new records again.
In view of an approaching very strong El Niño, Dr. Cheng urged the Government, the public, and all sectors not to be complacent, and to prepare early to address the health risks and wider impacts associated with sustained high temperatures in autumn.
(1) Daily maximum temperature of 33.0°C or above; (2) Daily minimum temperature of 28.0°C or above
