A high of 22C was recorded in Derrylin, Co Fermanagh, while the mercury tipped 23C in Valentia, Co Kerry.
Further highs are forecast for the remainder of the week, with the Met Office predicting a dry and sunny day for NI on Wednesday, alongside light winds and a maximum temperature of 23C.
Cloudier weather with occasional isolated showers may follow in the afternoon.
Thursday though will bring a cooler and cloudier day with occasional showers, brightening up as the day progresses, with dry and often cloudy weather to follow on Friday and Saturday.
It comes as the UK overall recorded its highest temperature of the year, with 24.9C reached in Ross-on-Wye in Herefordshire.
The previous hottest temperature this year was 24.5C recorded in St James’s Park, London, on Monday – which peaked at 24.7C on Tuesday.
It is predicted the warm weather could see temperatures hit 27 or 28C on Wednesday in southern England and the Midlands.
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The warm weather could also exceed the record for the highest April temperature in Wales – which is 26.2C.
In NI, the record sits at 24.5C, recorded on April 26 1984 in Boom Hall, Derry, while the Republic of Ireland record is 25.8C, recorded in Glenties, Co Donegal on April 26 1984.
Meteorologist Craig Snell said the most likely places to see the highest temperatures on Wednesday were “in a line from London over towards the West Country and into the Midlands”.
The meteorologist told the PA news agency: “The central southern parts of the UK are probably going to be where the highest temperatures will be tomorrow.”
NI also saw a spell of warm, sunny weather earlier this month. Pic: Arthur Allison/Pacemaker Press
News Catch Up – Tuesday 29 April
Mr Snell said Thursday would be “the peak of the heat”.
He added: “We are likely to see 28 or 29 degrees.
“And again, it’s going to be a corridor from the west of London over towards Bristol which will probably be the most likely places to see the highest temperatures.”
The meteorologist said the high temperatures on Thursday would result in one of the “warmest starts to May on record”.