Hongkongers have long complained of the city’s summers getting hotter and longer – and the numbers show they’re not wrong.
Hong Kong saw a record-breaking heatwave in summer 2026. File photo: Kyle Lam/HKFP.Data from the Hong Kong Observatory (HKO) 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.
HKFP looks at the city’s warming climate over the decades in seven charts.
1. ‘Very hot days’ on the rise
In the 2000s, the city recorded a yearly average of 13.4 “very hot days” – when the daily maximum temperature reaches 33 degrees or above. Since the 2020s, there have been more than 50 very hot days a year.
Records were set in 2021 and 2023, when Hong Kong experienced 54 very hot days. By the end of August, there had already been 30 very hot days so far this year.
As of September 21, there have been four very hot days this month.
The number of very hot days in August has generally risen in proportion with the annual figure.
2. Heat warnings in force more than ever
Annual hours under the HKO’s “very hot weather warning” have tripled since 2000 – climbing from 464 hours to a peak of over 1,400 hours in 2021.
Since 2020, heat warnings have been in force for at least 13 per cent of every calendar year. In 2000, it was just over 5 per cent.
The very hot weather warning is triggered not by a specific temperature, but by a heat index threshold that takes into account temperature, humidity, and airflow.
3. ‘Extremely hot days’ prevalent
The HKO defines extremely hot days as days when the maximum temperature reaches or exceeds 35 degrees.
With the exception of one abnormally hot year in 1963, when there were five “extremely hot days,” the city had never seen a year with more than two such days until the past decade.
Most years, in fact, had no extremely hot days.
That’s changed since 2016. Hong Kong has recorded an average of 4.6 extremely hot days annually for the last 10 years. So far this year, there have been three, all of them in August.
4. Summers getting longer
The city is not just seeing more “very hot days” – it’s also experiencing them across a wider timeframe, beyond the traditional summer months.
Before the 2010s, very hot days were concentrated in June, July and August. In other months, they were rare. But over the past decade, very hot days have increasingly been starting as early as May, and spilling into September and October.
Between 2021 and 2025, the city recorded a double-digit number of very hot days in September, compared to typical single-digit figures or even zero in previous years.
Last year, there were four very hot days in October. Before 2021, there were usually none.
5. August temperatures soar above ‘normal’
The mean temperature in August used to regularly sit below 28.7 degrees, which the HKO defines as the “normal” mean temperature for the month.
But in the past decade, temperatures above that threshold have become the norm. Since 2016, there were only two years that the mean temperature in August dipped below the “normal” level – and not by much.
In 2016, the mean August temperature was 28.4, and in 2018, it was 28.6.
In comparison, across the 35-year span from 1980 to 2015, there were a total of 22 years in which the mean temperature was below normal.
6. Number of ‘hot nights’ doubles
The HKO defines “hot nights” as ones when the daily minimum temperature is 28 degrees or above. From 2015 onwards, there have been an average of 46 hot nights a year, with 2021 setting an all-time record of 61.
In contrast, there were only around 20 hot nights annually from 2000 to 2009.
As of the end of August, there have been 35 hot nights so far this year, putting it on par with last year. By the end of August 2025, there were 34 hot nights.
But there have not been any hot nights in September so far. Last year, there were 13 – a historical record for that month.
7. Rainstorm warnings more frequent
There have been 15 red rainstorm warnings and three black rainstorm warnings so far this year – both the second-highest numbers on record. Last year, the HKO issued 16 red rainstorm warnings and five black rainstorm warnings – a record for both.
The 82 warnings issued so far this year – among which the vast majority are the lowest-level amber alerts – are the most in history.
The city was particularly rainy in June, July and August, with July’s rainfall being the second-highest on record for the month.
June also saw the HKO issue two black rainstorm warnings in one day for the first time.
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