The latest data from Met Éireann shows that a temperature of 33 degrees was recorded at Phoenix Park today, making it the hottest day of the year so far.
"Highest air temperature recorded today was 33.0 degrees at the Phoenix Park, Co. Dublin," said the forecaster.
"This is a new all-time national record for the month of July, and the highest air temperature recorded in Ireland in the 20th and 21st centuries."
The previous July record for Phoenix Park was 29.5 degrees in 1989.
The highest temperature ever recorded for Ireland was 33.3 degrees at Kilkenny Castle in June 1887.
Earlier the weather station in Phoenix Park hit 30.1 degrees with Met Éireann warning the public to be vigilant to scorching conditions across the country.
According to Carlow Weather, temperatures at Dublin Airport also broke an all-time record, reaching 28.9 degrees, just after noon today.
Head of Forecasting at Met Éireann Evelyn Cusack said today will be the hottest day of the summer.
It comes as Irish water has been forced to impose night-time restrictions on water supplies in 15 areas across the midlands and southeast as demand increases, particularly in holiday hotspots, during the current hot spell.
And it is urging families to cut back using paddling pools, and asked people to take shorter showers where possible to conserve water supplies.
There are 12 areas currently most at risk of drought, mainly in the midlands and south-east of the country including Bennettsbridge and Clogh, Castlecomer, in Kilkenny, Coalbrook in Tipperary, Clonakilty, Roberts Cove, Whitechurch and Coppeen in Cork, Wexford Town and Bunclody in Wexford, Inis Oirr in Galway and Swan in Laois.
Since the middle of last week, Irish Water said it has seen a “noticeable increase” particularly in seaside resorts and agricultural areas with demand likely to remain high throughout July and August.
The utility said that although the vast majority of its 750 water treatment plants continue to meet the demand, despite the pressure on water supplies, it has implemented a range of measures in affected areas such as tankering and/or night-time restrictions to protect supplies and ensure water keeps flowing to homes and businesses.
Supplies in the Greater Dublin Area are healthy, but the demand for treated water has increased by 4pc on average in the last week alone.
Irish Water's Head of Operations Tom Cuddy said that in some areas, ground water sources are slow to recover, and so could not rule out restrictions being imposed in other counties.
In addition to the areas where measures have had to be taken, the utility has a "watch list" of a further 65 water supply schemes they are keeping an eye on, he told RTÉ’s News at One.
He urged parents to keep paddling pools very shallow if they have to be used to cool children down, while householders are also asked to avoid power washing and keep the garden hose in the shed in order to reduce their water usage during the hot weather.
Met Éireann’s Status Yellow temperature warning will remain in place until midnight tomorrow.
The forecaster has warned people to be aware of heat stress, the risk of water related incidents and the high solar UV index, especially for the more vulnerable of the population.
The head of forecasting, Evelyn Cusack, said this is extreme heat for Ireland as the country’s average maximum temperature during the summer months is usually 21 degrees.
“Today will be the hottest day of the current mini heat wave affecting Ireland, so we’re expecting temperatures of about five degrees to up to 10 degrees above average,” she told RTÉ’s Morning Ireland.
“This is a very, very hot day, it’s going to be probably the hottest day of the summer. The highest yesterday was 29.3 degrees in Phoenix Park, the July record is actually 32.3 degrees and that was set in Elphin on July 19, 2006.
“So, I don’t think we’re going to breach that because at the moment while it is warm the temperature is about 18or 19 degrees at the moment.
“That little bit of cloud is depressing it, so we might get to 32 degrees, I doubt if we’ll breach the record but perhaps, we might.
“I think we should call it a mini heat wave, it’s a hot spell and some people will be glad to hear it isn’t going to last.
“During tomorrow, it’s going to be really warm and humid across Leinster, a little bit fresher weather will be coming in from the Atlantic and there’s a risk of thunderstorms breaking out especially across Leinster tomorrow."
Tonight will be warm with temperatures ranging between 14 to 18 degrees, or locally warmer, especially in the east.
It will be mainly dry with a mix of cloud and some clear spells, but a few showers could develop in the west by morning.
Some mist and fog will develop in mostly light variable winds, however, winds will increase moderate to occasionally fresh northwesterly over the western half of the country by morning.
Tuesday will continue very warm over the eastern half of the country with highest temperatures of between 22 to 26 degrees. It will be cooler further west with highs of 16 to 22 degrees.
In the east there will be hazy sunny spells and the chance of a few isolated heavy showers or thunderstorms developing throughout the day.
To the west it will be cloudier with some showery outbreaks of rain mostly along Atlantic coasts, and the chance of a few heavy bursts.
Winds will increase moderate to fresh veering northwesterly throughout the day.
The forecaster predicts that temperatures will return to normal from Wednesday onwards with a fair amount of dry weather and a few showers for the rest of the week.
Temperatures will return to average on Wednesday with a mix of cloud and sunny spells and some scattered light showers during the morning, becoming mostly confined to western fringes during the afternoon.
There will be highest temperatures of between 16 to 20 degrees generally, warmest in the southeast in mostly moderate northwest winds, fresh along Atlantic coasts.
Meanwhile, Water Safety Ireland has urged people to swim at beaches where there is a lifeguard on duty following a third water-related death in the past week amid a spell of warm weather.
A man in his 60s died on Saturday after getting into difficulty while swimming in a lake near Portarlington, Co Laois.
Water safety chiefs have advised people to swim within their depth and stay within their depth and only swim between the red and yellow flags at a lifeguarded waterway.
People should never use inflatable toys in open water as a gentle breeze can quickly bring a person away from shore.
Children should always be supervised closely and never left alone near water.
The charity recommends that if people see someone in trouble in the water, they should shout, reach and throw
Shout to calm, encourage and orientate them, reach with anything that prevents you from entering the water such as clothing or a stick and throw a ring buoy or any floating object to them.