Met Éireann has said last night was the warmest November night on record, with a temperature of 15.5C recorded at Shannon Airport.
The forecaster said it has been exceptionally mild over the past two days, with temperatures five degrees above normal for November in some areas.
It said 17.5 degrees was recorded in West Mayo today.
Meteorologist Emer Flood said: "Last night we had the highest lowest temperature overnight, effective the warmest November night."
Provisional new highest minimum temperature record for November in Ireland last night. Between 21:00UTC and 09:00UTC, the temperature at Shannon Airport, Co Clare didn't fall below 15.5°C. The previous record was 14.6°C. Five other synoptic stations also broke the previous record pic.twitter.com/RmrtOmd9eC— Irish Observational Climatology (@METclimate) November 11, 2022
Ms Flood added events like this "are more likely to occur and be more frequent due to climate change".
Meanwhile, balmy November temperatures have seen the UK experience its warmest Armistice Day on record.
The temperature rose to almost 20C today, almost two degrees higher than the previous record set 45 years ago.
The unseasonably high temperatures have led to "exceptionally mild" conditions across the UK, the Met Office said.
The warm conditions are forecast to continue into the weekend.
The Met Office said tomorrow will again be "unseasonably mild" while Sunday will be "very mild" across the UK with a high of 20C possible.
Today the UK has seen the warmest Armistice Day on record, provisionally breaking the previous record of 17.8 Celsius set in 1954 and 1977— Met Office (@metoffice) November 11, 2022
England, Scotland and Northern Ireland also set provisional new individual records
Here are the top temperatures from the four nations pic.twitter.com/x9TfRguS4C
The effects of the unseasonably mild weather are being felt at the National Botanic Gardens in Dublin where some flowers were in full bloom today.
Dr Colin Kelleher, a research botanist, said dahlias were amongst the flowers having an extended flowering season, which is very unusual for November.
"It looks like a summer scene, lots of varieties are in flower," Dr Kelleher said.
Another rare sight was a Callery pear tree, which blossomed a few weeks ago, something that normally happens in Spring.
"We're getting the light levels going down, the tree is bedding down for the winter but temperature is conflicting, the temperature is high and it started flowering," he siad.
"You can see that the leaves are senescing, that means the leaves are turning red as the nutrients are being taken from them."
Dr Kelleher said it is very unusual to have it flowering and senescing at the same time and if there are "multiple events like this it will suffer and potentially die".
He said the exotic trees that are in the Botanic Gardens, which is managed by the OPW, can act as a "sentinel for climate change".
"We can see what interaction is happening with them and use them as a predictors of what's going to change."
Dr Kelleher said they may have to alter what is planted in future to ensure suitability for future climates.
Today, Myerscough in Lancashire enjoyed a high of 19.5C, while Lossiemouth in Scotland saw a top temperature of 19.1C.
Magilligan in Northern Ireland had a high of 17.4C, and Hawarden in Wales reached 16.9C.
The Met Office tweeted: "Today the UK has seen the warmest Armistice Day on record, provisionally breaking the previous record of 17.8 Celsius set in 1954 and 1977.
"England, Scotland and Northern Ireland also set provisional new individual records."
The weather service said warm air drawn up from the south west has led to mild conditions for the time of year.
Additional reporting PA