Overnight between August 24 and August 25, Ioke strengthened rapidly, becoming a Category 5 hurricane on the 25th - the first system originating from the Central Pacific to reach that intensity while still in the Western Hemisphere. Ioke then began to travel over a large environment highly favorable for hurricane development, and would maintain its strength for an extended period of time. Ioke also became the most intense hurricane ever to develop in the Central Pacific, with a central pressure of 921 mbar (27.19 inHg) at that point (which dropped to 920 mbar at its Central Pacific peak).