Sunday, Monday and Tuesday will be "exceptionally warm” with daytime temperatures of 25C to 30C generally and possibly up to 32C in places on Monday.
A nationwide Yellow weather alert has been issued with Met Éireann warning of a risk of water-related incidents, an impact of heat stress especially for more vulnerable people, and a high UV index.
The warning comes into effect from 6am on Sunday and lasts until 9pm on Tuesday.
The country will also experience ‘tropical nights’ with night-time temperatures ranging from 15 to 20 degrees.
The weather warning comes as forecaster Evelyn Cusack said Monday could be the hottest day on record.
“We’re in for a hot spell - we won’t call it a heat wave because it won’t last long enough - but certainly for Sunday, Monday and Tuesday, we’ll have temperatures widely across Ireland of at least 27C and 28C,” she told Newstalk.
“So, on Sunday it could get up to 30C and then on Monday it will be the hottest day and we could get up to 32C.
“So, we are even looking at possibly breaking our record, but it will certainly be very hot for Ireland – although our continental friends think we’re crazy thinking that 30C is hot, as that is just a normal summer’s day for most of southern Europe.”
The highest temperature ever recorded in Ireland was the 33.3C recorded at Kilkenny Castle in 1887, while the hottest July temperature ever recorded by Met Éireann was the 32.3C recorded in Roscommon in 2006.
Meanwhile, despite some early cloud today, it will brighten up this afternoon and evening, with widespread sunny spells developing.
Highest temperatures will be between 18C to 24C, warmest in the south and southeast.
It will be cooler across western and northern coasts due to a light to moderate northwesterly breeze. Tonight will be dry with long clear spells. Patches of mist and fog will form near calm conditions, with low temperatures of 8C to 12C.
Tomorrow morning, the fog will clear and there will be some hazy sunshine.
It will turn cloudier in some areas during the day but will remain mainly dry with some possibly isolated showers.
Ireland will see temperatures rise tomorrow, with highs of 21C to 26C, warmest in central parts of the country, with a light to moderate southerly breeze.
It will be dry tomorrow night with a chance of isolated showers.
For Sunday’s All-Ireland hurling final at Croke Park, it will be very warm and dry with widespread hazy sunshine.
Highest temperatures will be between 22C to 28C, warmest in central parts and the east, while south to southeast breezes will be light to moderate.
Sunday will be a rather warm night with temperatures remaining above 14C to 17C. It will be dry and clear with light southerly winds.
According to Met Éireann, Monday could surpass last Tuesday as the hottest day of the year so far as temperatures rise between 26C to 29C degrees – with a chance of 30C to 32C degrees in some parts.
The warm weather will continue into Tuesday but is expected to end in the early days of next week as temperatures fall back to normal.