The fierce heatwave affecting large parts of Europe is known as an Omega block, because it takes the shape of the Greek letter, with a bulge of hot air in the middle and cooler air on either side, according to an expert. 

“It’s drawing warm air up from North Africa, from the Sahara, and that’s why we have this really intense heat,” said Clair Barnes, a climate scientist at Imperial College in London, quoted by Reuters.

Met Éireann has issued a status yellow high temperature warning for the whole of Ireland, from 12pm on Tuesday until 9am on Friday. It is warning of heat stress and water safety issues due to increased use of lakes and beaches.

An advisory for "exceptionally warm weather" is also in place until 9am on Friday. 

Met Éireann has warned that the heat will peak on Thursday, when temperatures could hit 33C or 34C. If the mercury does hit 34C, it would be a new record temperature for the country. 

The all-time high Irish temperature record is 33.3C, which was set at Kilkenny Castle in 1887.

The National Directorate Fire and Emergency Management's Keith Leonard has called on the public to check on elderly people during the high temperatures, especially those living alone.

“These weather conditions can be a real strain for older people, so just check their houses are cool and that they have plenty of cold drinks and that they appear comfortable and check the HSE website for advice,” he told RTÉ's Morning Ireland.

He said drowning is a known risk during warm weather, and he urged people to swim only in areas where there is a lifeguard.

“If there's no life guard, don't get in. Swim where you can be seen. Lakes, reservoirs, and disused quarries are much colder than the sea, and they often hide a lot of hazards and can trap swimmers, or where swimmers can get out of their depth very quickly.

“If you see somebody in trouble, call 999 and ask for the coast guard. Don't delay.” 

Me Leonard said that unfortunately, every time there was hot weather, there was an increase in drownings in areas like disused quarries, lakes and reservoirs.

There was also a risk of wildfire and he called on people not to light barbeques in wildland areas.

Meanwhile, in France, at least 18 people have died, including two children left in a hot car, since the weekend. French prime minister Sebastien Lecornu is scheduled to hold a crisis meeting on Tuesday, an aide said. More than 1,350 schools have been shut due to the heat.

In the UK, some parts of England and Wales are set to see the mercury hit 38C to 40C, smashing the June record set in 1976. 

National Outlook

More generally for this week's weather, Tuesday will see highs of between 22C and 29C. It will be warmest in the south and east, but cooler in parts of the northeast, with the mercury sitting between 19C and 21C. Nighttime lows will drop to 12C across parts of the west and the north, but it will be milder and humid elsewhere, with 15C to 18C expected. 

Wednesday will be very warm or hot and humid with highs of 23C to 29C. It will be warmest across the southern half of the country. Nighttime temperatures will not fall below 14C for the northwest and 18C or 19C for the southwest. 

Thursday is going to be an "exceptionally hot and humid day across Ireland." Temperatures will range from the high twenties and could get up to around 33C or 34C, with the hottest weather across the midlands and west. 

A long, persistent spell of rain will come into the coastal parts of the northwest and west on Thursday night, with some spot flooding and frequent lightning expected. It will stay dry elsewhere, but it will be an exceptionally mild and muggy night with temperatures not falling under 15C to 22C. 

Persistent heavy thundery rain will affect Connacht and Ulster for a time on Friday, with sunshine elsewhere. It will still be very warm or hot and humid elsewhere with temperatures ranging between 23C and 30C. 

It will be another mild and muggy night on Friday with a mix of clear spells and some showers, and lows of 15C to 19C. 

Looking into the weekend, Saturday will see some sunny spells before rain starts to come in from the west. Highs of 17C to 24C are expected. Sunday will see the rain clear with sunny spells developing and highs of 15C to 20C/21C - returning to average for the time of year. 

-Additional reporting from the Guardian