Met Eireann says temperatures in Newport, Co Mayo have exceeded 28 degrees today, and high temperatures will continue for the rest of the week.
The latest data from 3pm this afternoon shows Mount Dillon in Roscommon was the hottest spot nationally at 29 degrees, followed by Newport and Athenry at 28 degrees.
Claremorris recorded 27 degrees, with 24 degrees in Belmullet.
A status yellow weather warning is in effect until Friday morning, with Met Eireann forecasting daytime highs of 27 to 30 degrees, while at night it's not expected to fall below 17 to 20 degrees.
Even hotter temperatures are expected in Roscommon, south Leitrim, Longford, Westmeath, Cavan and Monaghan with a status orange weather alert in these areas, and temperatures of over 30 degrees in places.
The Mayo Fire Service is reminding the public that a level orange high fire warning is in place at present for bog, forest and gorse fires, and is appealing to people to be vigilant.
The fire crew from Kilkelly attended a gorse fire near the town earlier today, and quickly brought it under control.