The dry, cooler months from May to September are the most forgiving time for Iona. Days can still be hot, but conditions are generally easier for long drives, camping, and wildlife watching than in the hotter months.
October to April brings higher heat and the possibility of difficult local conditions after rain, especially around riverbeds and tracks. The coast can be foggy and cool even when the inland desert is harsh, so pack for both cold damp mornings and fierce sun.