139th Anniversary of Ireland’s hottest day – 33.3oC at Kilkenny Castle on 26th June 1887
Today marks the 139th Anniversary of the highest air temperature ever recorded in Ireland, 33.3°C recorded at Kilkenny Castle on 26 June 1887. This long-standing record puts Ireland as an outlier in Europe, the fastest warming continent in the world, with all other countries more recently breaking their all-time national temperature records. Given the extraordinary length of time this record has stood, Met Éireann recently conducted a comprehensive study of the validity of the 33.3oC measurement.
In 2025 Met Éireann researchers conducted the widest evaluation of the Kilkenny Castle record temperature to date. In this most recent study, authors digitised historic temperature measurements from Kilkenny Castle as well as neighbouring weather stations in order to complete a comprehensive analysis of the record.
Daily Weather Reports from 1887 at 8 AM. The contours show estimated height of mercury (in inches) at that location. 30.1 in. of mercury is approximately 1019.3 hPa, 30.2 in. is approximately 1022.7 hPa, 30.3 in. is approximately1026.1 hPa, 30.4 in. is approximately 1029.5 hPa and 30.5 in. is approximately 1032.8 hPa.
The analysis found:
- an inspector’s report from the time suggested the instruments were in a good location, the thermometer was calibrated correctly and housed in a double louvred screen meeting all the international requirements of the time.
- a report from September 1887 mentions no concerns regarding the record temperature in June of that year.
- a synoptic weather analysis from past observations and reanalysis shows the potential for a significant warming event at the end of June 1887.
- a modern analysis of data across the island shows (in many cases) that the differences between Kilkenny and neighbouring stations on that day were entirely plausible.
- a statistical model for extreme data fits well to the dataset of annual maximum temperatures at Kilkenny Castle.
- and an analysis of rainfall records (taking evapotranspiration into account) shows how much of a deficit there was across the country, particularly in the east and southeast – these are ideal conditions for an extreme heat event.
- many contemporaneous sources found cited the unprecedented drought and the intense heat of 1887.
The World Meteorological Organization recommends that old climate records should only be removed if there is sufficient and significant evidence of error. While the review uncovered some reservations, no clear evidence of error was identified.
Following the review, and acknowledging some reservations with such an old measurement, Met Éireann, international meteorological services and scientific peer reviewers recommend that the original 33.3oC Kilkenny temperature should remain.
Keith Lambkin, Head of Climate Services at Met Éireann notes:
“This year Ireland saw its highest ever temperature in May. Last year Ireland experienced its warmest ever Summer and 2023 was Ireland’s warmest year on record. With national temperature records continuing to fall due to our changing climate, unfortunately it is only a matter of time before the long-standing Kilkenny Castle temperature record is broken.”
Ciaran Kelly, Met Éireann Meteorologist and co-author of the 2025 research on this topic commented:
“We are indebted to the weather observers at Kilkenny Castle and the thousands of weather observers around the country over the last century and a half, whose diligence and expertise are allowing us to better understand how Ireland’s climate is changing.”
The full peer reviewed scientific paper appears in the International Journal of Climatology and can be found here.
A summary talk of the findings presented by lead researcher John O’Sullivan to the Irish Meteorological Society is available here.