On Ibiza, you will never be much more than 10Km from the sea, and although the hills to the north east and south west rise to 4-500m, the climate will be very much tempered by the surrounding water.
Daily average temperatures will be similar to the south coast of the mainland but there will be less variation between the maximum and minimum
The rainfall will be higher than the mainland south coast but with very little falling in June July or August.
Daily average temperatures for Ibiza
Source: World Climate