A Co Cavan weather station is one of three nationwide that recorded its highest October temperature since 2001.
The Ballyhaise station recorded a mean temperature of 11.4 degrees Celsius last month, 1.3 degrees above its Long-Term average.
Meanwhile, the latest Met Éireann monthly report reveals every weather station recorded an October mean temperature that is above average.
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Dublin Airport and Mullingar, Co Westmeath, were the other two stations that had their warmest October in 20 years.
It comes amid a warning at the Cop 26 Climate Summit that Europe's hottest summer on record wouldn't have happened without human-induced climate change.
A new European record was set in Sicily - where it got to 48.8 degrees Celsius.
