The sun has come out and - as is tradition - the public has flocked to the outdoors to celebrate.
Sunday was the hottest day of the year, so far with temperatures hitting 20 degrees.
While in England, the temperature hit 27.
And the mercury appears not to have hit its peak yet as temperatures are set to reach higher than those in the party island of Ibiza, with 24oC forecast on Monday.
Emma Boorman, a Met Office forecaster said: "It's the warmest day of the year.
"There's lots of lovely sunshine out there to enjoy. The final temperatures are still coming in but all four countries in the United Kingdom have recorded their highest temperatures of the year."
Bookmaker Coral is offering even money that 2016 is the hottest year on record in the UK after the firm saw a sustained gamble over the last 48 hours leading them to slash the odds from 3-1.
It is also offering just 2-1 that the record high of 32.8C (91F) is broken in May, while it is 6-4 for 30C (86F) to be recorded this month.
Spokesman John Hill said: "Punters are convinced we are set for the hottest year on record in the UK as we've seen a sustained gamble in the betting over the last few days.
"We may not have to wait long for 30C or higher to be recorded in 2016 as the odds suggest it is likely to arrive this month."
Ladbrokes also said bets had been pouring in and it has been offering 2/1 for the mercury to reach 30C or higher before the weekend is out.
Jessica Bridge of Ladbrokes said: "It's getting hotter by the day and punters are convinced the sunshine's here to stay all summer."
Pollution levels are expected to peak on Sunday, with high levels possible locally and widespread moderate air pollution.
Those heading outdoors to enjoy the fine weather are also warned to be aware that UV levels will be high.
From Monday temperatures could hit 24 degrees in Northern Ireland and as the week progresses, temperatures are still likely to be mild, but will fall day on day.
But we should make the most of the good weather while it lasts as there is more cloud forecast for Wednesday.
Warnings have been issued to those with respiratory problems, as the continental heat will bring an unusually high dose of air pollution.
The change in temperature is expected to bring an increase in dirty particulate matter, caused by exhaust fumes, dust and other pollutants, according to Defra.
The heatwave will be a relief after Armagh Observatory reported the coldest April in 27 years.
A spokesman said April 2016 was slightly cooler than April 2012 and the coldest at Armagh since 1989. It was also drier and duller than average.
"There were several quite sharp ground frosts, and particularly towards the end of the month a cool breeze established containing showers in which were recorded sleet, snowflakes, snow and ice pellets, as well as hail," he said.
"There were 21 nights with ground frost and five with night-time air frosts. Buzzards were noted circling over the Astropark on the April 20 and 22."
The warm weather will also be good news for gardeners.
Horticulturist Gareth Austin said: "This weekend is looking like a key period for gardening, especially here in the North West. Ground conditions have warmed up recently and now is looking like a key time to get the first of the summer flowering dahlias planted.
"For many, it could be the first chance to get their lawns cut due to the persistent wet ground conditions in many gardens - although the abundance of dandelion flowers has been greatly appreciated by the bees in our gardens."