A clear morning on Sunday could give way to a rainy and stormy afternoon the met office said.
After midday, gathering clouds are expected to give way to some rains, especially in mountain areas. Isolated storms are not ruled out.
Temperatures will rise to 31C inland, around 28C on the coasts and at 21C in the mountains.
Sunday night they will fall to 17C inland, and on the west and north coasts, around 19C on the southern and eastern coasts and at 12C in the mountains.
On Monday, Tuesday and Wednesday, more isolated storms are expected in the afternoons, especially inland and in the mountains. Isolated rains and thunderstorms are expected on the west coast Wednesday evening.
Temperatures on Monday and Tuesday could rise to slightly above average for this time of the year, the met office said.