Hong Kong recorded 54 days at or above 33C in both 2021 and 2023, against an average of 13.4 such days a year through the 2000s, according to Hong Kong Observatory figures compiled this week.
Every completed year since 2020 has topped 50 very hot days. By 28 August 2026 it had logged 30, with a further four between 1 and 28 September.
The warnings have stretched with them. Annual hours under the Observatory's very hot weather warning have tripled since 2000, from 464 hours to a peak of more than 1,400 in 2021. Since 2020 the warnings have covered at least 13 per cent of the calendar year, against just over 5 per cent in 2000.
Extremely hot days, at 35C or above, were until recently close to unknown. There were five in 1963, an outlier, and typically none to two a year until 2016. Across 2016 to 2026 the average is 4.6 a year. There had been three by 28 August.
Nights have moved too. Minimum temperatures at or above 28C occurred about 20 times a year in 2000 to 2009. From 2015 the average is 46, with a record 61 in 2021. By 28 August 2026 there had been 35.
The Observatory defines 28.7C as the normal mean temperature for August. Since 2016, only two years have come in below it: 2016 at 28.4C and 2018 at 28.6C.
The season has also lengthened at both ends. Very hot days now fall outside the traditional June-to-August window: every September from 2021 to 2025 recorded double figures, where single figures or none had been usual, and October 2025 had four, where there had been none at all before 2021.
Rain has been doing something similar. 2026 brought 15 red rainstorm warnings and three black ones, both the second-highest on record, and 82 warnings in total, mostly amber, which is a historic high. July rainfall was the second-highest on record, and June produced the first two black warnings in a single day.
Two of these figures should be read together. A warning is, by construction, notice of a departure from the ordinary. Hong Kong's very hot weather warning now runs for at least 13 per cent of the year, and in 2021 ran for more than 1,400 hours.
On that basis the Department of Unnecessary Research proposes a straightforward correction. The warning is not warning of the climate. It is the climate, issued in instalments, and the quiet periods between warnings are the anomaly.
The August figure settles the point. The Observatory's normal for August is 28.7C. August has come in above that in nine of the last eleven years. A normal exceeded nine times out of eleven is not a description of August. It is a description of 2016.
Our analysts accordingly recommend inverting the scheme. Issue a warning when the temperature falls below 33C, and a black rainstorm warning when, over the course of an hour, it fails to rain.
Eighty-two warnings have been issued this year, a historic high. The year has three months to run.