Throughout October 13, marked intensification of the cyclone occurred. Over a 24‑hour span, ending at 18:00 UTC, its central pressure fell from 1005 mb (hPa; 29.68 inHg) to 979 mb (hPa; 28.91 inHg) which was reflected in Isbell's winds more than doubling from 35 mph (55 km/h) to 90 mph (150 km/h). Shortly thereafter, the storm made landfall in extreme western Cuba, near Guane, before emerging over the southeastern Gulf of Mexico. Isbell's brief stint over land did not hinder development, which continued unabated until 12:00 UTC on October 14 at which time it reached its maximum intensity. Situated to the south of Key West, Florida, Isbell attained winds of 125 mph (205 km/h) which ranks it as a Category 3 hurricane on the modern-day Saffir–Simpson hurricane wind scale. Additionally, its central pressure bottomed out at 964 mb (hPa; 28.47 inHg). Around this time, a new low-pressure area formed to Isbell's northwest over the Gulf in response to a powerful cold-core low over the Mississippi Valley. The cyclonic flow of this second system brought cool, dry air from the north and circulated it into the hurricane. This in turn caused the storm to become asymmetric in structure with radar imagery indicating little to no reflectivity along the western periphery of the hurricane.