The outlook into the weekend projected showers or some longer outbreaks of rain on Friday and Saturday.
Thursday is set to be the hottest day of the week in Ireland with temperatures up to 31C in parts.
A status yellow high temperature warning has been in place for every county in the Republic of Ireland since midday on Tuesday.
Met Éireann said the warning, which is due to expire at 9am on Friday, includes water safety issues due to increased use of lakes and beaches, uncomfortable sleeping conditions, heat stress and possible forest fires.
Mark Bowe, a meteorologist with the agency, has projected “very high” temperatures will continue.
He said Wednesday would see highs of around 27-28C and overnight lows above 15C.
Looking later in the week, Mr Bowe said: “Thursday – that’s set to be the hottest day of the week.
“All that warm air will have fully arrived from Europe and temperatures are expected to be widespread over 25C – reaching around 30 or possibly 31C in parts of the Midlands and Connacht.”
Mr Bowe said this also carried the risk of some thunderstorms, with the north west possibly experiencing heavy showers on Friday afternoon.
He said temperatures would take a “bit of a slide” on Friday, with a “few more showers moving in”.
The UK Met Office forecast maximum temperatures of 24C in Northern Ireland on Wednesday, potentially rising to 27C for Thursday.
The outlook into the weekend projected showers or some longer outbreaks of rain on Friday and Saturday, with the rain “perhaps heavy and thundery at times”.
