Storm and rain warnings are in place for four counties from 5pm as thundery conditions push in from the south.
Co Cork is subject to a yellow thunderstorm warning from 2.44pm to 6pm on Monday.
Met Éireann warned of possible lightning strikes along with heavy rain, spot flooding and difficult travel conditions.
Yellow rain warnings are also in place for Waterford, Wexford and Wicklow, also warning of spot flooding and difficult travel conditions.
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The latter warnings were due to come into place at 5pm and last until midnight.
Small craft warnings are in place for the northwest of the island from Slyne Head to Malin Head until midnight.
The UK’s Met Office has also issued a yellow thunderstorm warning for the six counties: Antrim, Armagh, Derry, Down, Fermanagh and Tyrone, for Tuesday, from noon until 9pm.
The Met Office warned of disruption to outdoor events and transport.
No further Met Éireann warnings for Tuesday were in place for counties between the south coast and Ulster by Monday afternoon, though the small craft warning on Tuesday extends around most of the island.
Monday’s highs have been between 19 and 24 degrees on a day that was warm for areas not yet affected by heavy rain.
A mild and humid night has been forecast, with lows of 16. Heavy rain was expected to spread northeastwards, dissipating to showers further inland.
Tuesday is set to have a cloudy start, with patchy rain in parts. Sunny spells will gradually develop, with scattered showers, some turning thundery over Connacht and Ulster.
It will continue to be humid, with highs of between 18 and 23 degrees, but coolest in the northwest.
Mixed and unsettled conditions look set to predominate for the rest of the week, with showers and moderate to fresh winds in places.
