After spots of early fog dissipated, Wednesday opened up to clear skies but it may not last as increased cloud inland and over the mountains is expected later in the day, the met office said.
The temperature will rise to 33C inland, to 26C on the west coast, around 28C on the south and east coastlines, and 23C degrees in the higher mountains.
Wednesday night the weather will be mostly clear with some increased low clouds with more fog expected in the early hours of Thursday.
Temperatures will drop to around 18C inland and on the coast and to 14C in the higher mountains.
On Thursday the temperature will rise gradually and fluctuate above the average seasonal levels.
Friday will see more cloud coverage but the temperature will remain at higher levels.