The alert, which covers Cavan, Monaghan, Longford, Louth, Meath, Offaly and Westmeath, is valid until 6pm this evening.
A separate warning is also in place for Leitrim, Roscommon and Sligo, which is valid until 8pm.
Localised thunderstorms this afternoon may result in frequent lightning in affected counties.
This comes as the national forecaster issued a high temperature warning due to “very warm and humid weather” across the country.
The warning is in place since 8am this morning until the same time on Saturday morning.
While daytime temperatures may rise in excess of 27C, even nighttime temperatures will not fall below 15 degrees.
Met Éireann has warned that potential impacts of such weather include heat stress, uncomfortable sleeping conditions and an increased risk of water related incidents.
Temperatures today are expected to hit highs of 24C to 26C while it will remain dry and sunny this morning.
Showers will develop in the southeast and spread northwards over Leinster and may become heavy with thunderstorms and spot flooding possible.
This afternoon may bring both sunshine and isolated heavy or thundery showers.
Tonight will be warm, close and mainly dry with some patches of mist and fog.
Ireland’s weather forecast
Lowest temperatures of 15 to 17 degrees are expected overnight.
Friday will also bring highs of 24 to 28 degrees, though some areas may experience even warmer.
It will be dry with sunny spells and some mist or fog in some coastal areas.
Isolated heavy or thundery showers may develop tomorrow afternoon before a warm and humid night.
Some showers are possible.
This weekend will see further warm, sunny days that bring with them high temperatures and the chance of thunderstorms.
Met Éireann forecasts temperatures of 21 to 25 degrees on Saturday, while Sunday will see a slight drop in temperatures of 19 to 24 degrees.
Monday will offer slight respite from the heat, as temperatures will drop to 15 to 19 degrees with outbreaks of rain and cooler, less humid air.
Met Éireann says current indications for next week show weather is likely to become more unsettles with rain or showers at times and temperatures in their mid to high teens.