September appears to rank among the six warmest on record
Provisional calculations place September 2026 high in the Dutch rankings, but the month has not yet officially ended.
September 2026 looks set to finish among the six warmest Septembers in the Netherlands since records began. The provisional calculation is based on data up to and including 27 September and a weather forecast for the final days.
A current calculation based on KNMI data provisionally puts September’s average temperature at around 16.5 degrees. This would make the month clearly warmer than the long-term September average of 14.7 degrees.
The calculation is not yet a definitive KNMI ranking. The final days of the month could still change the average. Depending on the temperature during that period, September is expected to finish around sixth place according to the scenarios consulted, but a higher or lower position remains possible.
The official record for the warmest September belongs to 2006, with an average temperature of around 17.9 degrees in De Bilt. The provisional figure for 2026 is therefore below that level. The month could nevertheless come close to the warmest Septembers in the record series.
The high September temperatures follow an exceptionally warm and dry summer. The KNMI previously reported that June, July and August were very warm together, and that the national precipitation deficit stood at around 285 millimetres at the end of August. According to the institute, this places 2026 among the driest 5 per cent of years with recorded measurements.
A warm month is not in itself evidence of climate change. Climate conclusions are based on long-term series and changes in the likelihood of extremes. A run of warm months is, however, consistent with the broader trend of rising average temperatures in the Netherlands.
The effects are not the same everywhere either. A warm September can extend the growing season, but drought can put pressure on agriculture, nature and water management. Heat and sunshine can also contribute to ozone formation affecting air quality; the RIVM describes this relationship as a recurring pattern.
The definitive position of September 2026 must be established by the KNMI after the end of the month. Until then, the safest formulation is that the month probably ranks among the six warmest, not that it is definitively the sixth warmest.
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The provisional ranking is carefully presented as an expectation rather than a definitive record. The KNMI context on the warm and dry summer and the RIVM explanation of heat and ozone were checked separately.
- uncertain September 2026 ranks around sixth place based on provisional calculations. — The calculation uses data up to and including 27 September and weather forecasts for the remaining days. source
- confirmed The long-term average for September is 14.7 degrees. — The provisional ranking refers to the KNMI average for 1991–2020. source
- confirmed September 2006 is the warmest September, at around 17.9 degrees. — The provisional KNMI ranking lists 2006 as number one. source
- confirmed The precipitation deficit stood at around 285 millimetres at the end of August. — The KNMI cites this national deficit in its summer report. source
Editor's note
The provisional place in the top six is a calculation and not yet a definitive KNMI publication. The broader summer and drought figures have been published by the KNMI.Sources
- September 2026: op weg naar een warmterecord? — MScha, op basis van KNMI-gegevens
- Recordwarme en droge zomer — KNMI
- Luchtverontreiniging — RIVM
More on this in Dutch media
- RTL Nieuws — „september temperatuur”
- FD — „september temperatuur”
- AD — „september temperatuur”