The weather station at Mount Dillon in Roscommon recorded the lowest May temperature on record early last month.
The rainfall levels recorded in May were above average at all of Met Eireann's weather stations.
The most rain fell over Valentia Observatory in Kerry which had its wettest May since 2006.
Met Eireann says it was also colder than usual last month, with the lowest temperature of minus four degrees recorded in Roscommon.
The temperature at Mount Dillon on May 6th was its lowest May temperature on record.