We could see record temperatures today as the sizzling hot spell continues.
A Status Yellow high temperature warning remains in place for the whole country with the mercury set to hit 32C in places.
The highest heat in the country yesterday was recorded at Dublin’s Phoenix Park, which hit 29.3C.
“A very hot day ahead today,” he said.
“The hottest day of this brief hot spell. Temperatures will get close to record-breaking temperatures, with potentially 33C in the east of the country.
“It will widely get up to 30C in many parts of the country; just that little bit cooler near the coasts.”
Officially the highest temperature ever recorded in Ireland was the 33.3C recorded at Kilkenny Castle in 1887.
The hottest July temperature ever recorded by Met Éireann was the 32.3C recorded in Roscommon in 2006.
Mr O’Reilly said there is “certainly a chance” the all-time record will be broken today.
“We will get very close to it,” he said. “Whether we’ll get over that record, it is hard to know.
“It will be all eyes on the Phoenix Park weather station, which is most likely to see the record, but we could see it in some other areas.”
Meanwhile, an Orange Fire Warning is in place with people urged not to light outdoor fires and avoid other open ignition sources.
The Irish Coastguard is also warning people not to swim in an area they're not familiar with.
Three people died while swimming last week, including a man in his 60s who got into difficulty while swimming at Derryounce Lake in County Laois on Saturday.
The Coastguard said people should always wear a lifejacket in boats and kayaks and should never swim alone.