Isiolo itself is a practical stop year-round — the town functions regardless of season. What changes is the accessibility and quality of the reserves to the north. The best time to visit Samburu, Buffalo Springs, and Shaba is during the dry seasons: January to February and June to October. In dry conditions, animals concentrate at water sources and are easier to spot, and the roads are passable. The long rains (April to May) can make some northern roads impassable and wildlife harder to find. The short rains (November) are lighter and usually manageable. If your main purpose is the reserves, aim for the dry months.