Temperatures inland on Sunday could hit as high as 39C and will remain at this level at least until Wednesday, the met office said.
On Sunday, there may be some cloud and isolated brief showers in the mountains where the temperature will hover around 29C.
Inland however will be hot at 39C, while in coastal areas, the temperature will be around 31C.
Sunday night temperatures will drop to 23C inland and on the coast, and 19C in the mountains.
Little will change between Sunday and Wednesday, the met office said.