The current above-average temperatures are expected to remain over the next three days, the met office said.
On Wednesday, the temperature will rise to around 37C inland, around 25C on the west and east coasts, 29C on the south and north coasts and around 26C in the higher mountains.
On Wednesday night, it will be mostly clear with some cloud on the northern and western coasts with isolated fog patches in the early hours of Thursday.
The temperature will drop to around 18C inland and on the north coast, around 19C on the remainder of the coast and around 16C in the higher mountains.
On Thursday and Friday the weather will be mostly clear with some early fog patches but temperatures will remain high. Saturday may see some increased cloud coverage in the afternoon.