The warning comes as a temperature of 30.1 degrees was recorded on Wednesday - the highest of the year so far.
Met Éireann has issued a thunderstorm warning for four counties on what is officially the hottest day of the year so far.
The yellow warning could see localised thunderstorms with a risk of lightning and spot flooding across Donegal, Leitrim, Mayo, and Sligo and is valid until 11pm on Wednesday night.
The warning comes as a temperature of 30.1 degrees was recorded at Mount Dillon in Roscommon, making it the highest temperature of the year so far.
Conditions are set to continue very warm and sunny on Wednesday evening, with the heat potentially sparking the aforementioned thunderstorms across north Connacht and Ulster.
It is also expected to be "uncomfortably warm and humid" on Wednesday nigh,t with any thunderstorms expected to clear, leaving behind dry and clear spells, with temperatures remaining at at least 17 degrees overnight.
Thursday will be another hot and mostly dry day with plenty of sunshine and highest temperatures of 26 to 29 degrees generally, reaching 30 degrees locally.
The rest of the week is also expected to be very warm and humid with above average daytime temperatures, sunny spells and some thundery showers.
However, things are expected to become slightly cooler over the weekend and into next week as high pressure will weaken and somewhat unsettled weather may make a return.
Friday will be another very warm day with highest temperatures of 25-29 degrees.
Current indications suggest that Saturday will be slightly cooler than previous days with highest temperatures ranging from 18 to 25 degrees, with the possibility of rain.
Sunday is also expected to be a warm day with sunny spells and the chance of scattered showers developing yet again. Highest temperatures will reach between 22-25 degrees.
The heatwave may be coming to an end from next week as Monday will see conditions become closer to average in the west, extending to all areas from Tuesday with the risk of some heavy showers developing throughout the country.