Heat records are not the same as measured records
The final days of September could be exceptionally warm, but official records are only established after validated measurements.
Temperatures of around 28 or 29 degrees are expected in the south-east on Tuesday 29 September. That could break daily records, but a forecast is not yet a climate measurement: KNMI validates the observations only afterwards.
The Netherlands is set for another summer-like heat peak at the end of September. According to current forecasts, temperatures could reach 28 or 29 degrees, particularly in Limburg and parts of Brabant. That would bring several stations close to existing daily records for 29 and 30 September.
Whether a record is actually set depends on the exact temperature at the measuring stations and on the definition used. A national record in De Bilt is different from a local daily record in Maastricht or Eindhoven. KNMI also distinguishes between current, as yet unvalidated data and verified climate data.
Official KNMI statistics for De Bilt show that September 2026 averaged 16.6 degrees up to and including the 25th. The normal average for September in the 1991–2020 period is 14.7 degrees. Those figures describe the month so far and do not yet definitively indicate how warm the final days will be.
The warmth follows an exceptionally warm summer. KNMI calculated an average temperature of 19.3 degrees for June, July and August, compared with a normal 17.5 degrees. This made the summer of 2026 the warmest since measurements began in 1901. In June, temperatures in Ell reached 39.4 degrees.
A warm day in itself is not proof of climate change. The climate picture emerges from long series of measurements. Nevertheless, the succession of warm periods fits the picture KNMI paints of a warmer Netherlands, with more frequent extreme heat and major differences in rainfall.
The social consequences depend on more than the daily maximum. Warm nights, drought, water quality, and pressure on healthcare and infrastructure also play a role. The record-dry summer and earlier heatwaves mean that governments and businesses are looking not only at today's thermometer, but also at the consequences for agriculture, nature and public health.
According to the current forecast, a shift to cooler and wetter weather will follow Tuesday. The news value of the coming days will therefore remain mainly meteorological: old daily records may be broken, but the definitive assessment will only come after the measurements have been checked.
One story, several perspectives
What is established
- High temperatures are expected on 29 September, particularly in the south-east.
- September 2026 was warmer than normal up to and including 25 September.
- According to KNMI, the summer of 2026 was the warmest since 1901.
- A forecast is not the same as a validated record.
Left
Arguments Emphasises that recurring heat calls for rapid climate adaptation: cool public spaces, protection for vulnerable people, and investment in water management and nature.
Values Public health, social equality, prevention and protection of ecosystems.
Consequences Advocacy for public spending and stringent climate policy, even when an individual warm day does not appear exceptional.
Centre
Arguments Wants policy to be based on validated trends and regional risk analyses, not on a single weather forecast. Adaptation and emissions reduction can coexist.
Values Scientific rigour, feasibility and long-term planning.
Consequences Targeted measures for the most vulnerable areas and sectors, evaluated on the basis of new measurements.
Right
Arguments Emphasises practical adaptation and individual responsibility, such as adequate ventilation, water availability, and protection of agriculture and infrastructure.
Values Resilience, affordability, local control and continuity of economic activity.
Consequences Preference for concrete measures with demonstrable effects and caution towards broad, costly rules not directly linked to today's weather.
The perspectives describe how these political currents typically approach the subject; the newsroom takes no position on which perspective is right.
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The measured temperature and summer records were checked directly with KNMI and NOS. Forecasts for 29 September are described as forecasts, not as established records.
- confirmed September 2026 had averaged 16.6 degrees in De Bilt up to and including 25 September. — This appears in the KNMI table of monthly extremes. source
- confirmed The normal September average in De Bilt is 14.7 degrees for 1991–2020. — Listed in the same KNMI table. source
- confirmed The summer of 2026 averaged 19.3 degrees and was the warmest since 1901. — KNMI and NOS report this figure and record. source
- confirmed A temperature of 39.4 degrees was measured in Ell on 26 June. — KNMI names Ell as the summer's highest temperature. source
- confirmed Official climate data are validated after measurement. — KNMI describes the checking and validation of daily data. source
Editor's note
The heat peak and possible daily records are forecasts; the monthly and summer figures are official KNMI measurements. The text makes this distinction explicit.Sources
More on this in Dutch media
- Het Parool — „hitte warmterecord”
- de Volkskrant — „hitte warmterecord”
- NU.nl — „hitte warmterecord”