When travelling, it's generally smart to pack in preparation for rain or any other conditions that may arise. The rainfall in Tiree is roughly greater than that of Edinburgh. You can assume this to be the case over the next 28 days.
With an average temperature of 19 °C, peak weather can be found in July. As a traveller, expect to see changes in flight prices during that period. The temperatures in Edinburgh are hotter than in Tiree.