The Met service has issued a yellow weather warning for Saturday as temperatures may edge over 40C inland.
The warning will be in place between 1pm and 4.30pm.
On Saturday evening, temperatures are expected to drop to 25C inland and the south and east coasts, 22C in the remaining coastal areas, and 18C in the mountains.
Clear weather is expected early on Sunday with some clouds in certain areas later in the day.
Temperature will again reach 40C inland, 32C in the west and north coasts, around 35C in other coastal areas, and 30 in the higher regions.
Mostly clear weather is forecast for next week although there may be some isolated showers or a storm inland and the mountains.
Temperatures will remain unchanged, above average, mainly inland and the higher regions.