September was the wettest month so far of 2025, and while there was above average sunshine in most places, there was no Indian summer as it was relatively cool overall.
In its preliminary climate statement for the month issued on Thursday, Met Éireann says all of its 25 weather stations recorded rainfall above their 1991-2020 long-term average (LTA) for the month, making it the 18th wettest September since 1940.
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The highest daily rainfall total was 31mm at Johnstown Castle, Co Wexford, on September 19th while the southeast, southwest and northwest experienced the highest rainfall overall.
Although September 2025 saw some warm temperatures, it was cool overall, with an average of 13.2 degrees. One station – Mount Dillon in Co Roscommon – on September 22nd experienced freezing conditions with the month’s lowest air and grass minimum temperatures at minus 0.6 and minus 4.4 degrees respectively.
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Most stations recorded above average sunshine. The highest number of daily sunshine hours recorded this month was 11.1 hours at Johnstown Castle, Co Wexford, on the 22nd.
The highest temperature was 20.9 degrees, recorded on September 9th at Shannon Airport, Co Clare, and again on September 17th at Oak Park, Co Carlow. The month was cooler than average with all stations recording temperatures below their LTA.
Atlantic low pressure weather systems dominated throughout the month. Ireland was often situated on the colder northern side of the jet stream in the upper atmosphere around the North Atlantic.
Of the top 10 warmest Septembers, six have occurred since 2001; which may be an indication of global warming.
Of the top 10 coolest Septembers, none have occurred since 2001. The most recent was in 1992 – the ninth coolest with an 11.8 degrees average.
The first third of the month saw “a mobile Atlantic set-up with low pressure, mostly situated to the north and west, steering several weather fronts across the country”. This brought scattered outbreaks of rain or showers on most days, sometimes heavy and thundery, interspersed with drier periods.
The second third of the month continued in a similar vein with the final third becoming drier when high pressure moved in from the west, preceded by a cool northerly wind. It slowly moved from west to east and brought several mostly dry days with plenty of sunshine.
The drier spell ended on the 27th as a frontal trough pushed in from the west. Pressure remained high for the following few days before Atlantic low pressure took control once again, while the first week of October will see the first named storm of the season with Storm Amy due on Friday.
