Following a pass through the storm by a United States Navy reconnaissance plane, Ethel was declared a "severe hurricane" with winds reaching 115 mph (190 km/h), equivalent to a modern-day Category 3 hurricane on the Saffir–Simpson Hurricane Scale. At the time these winds were measured, a barometric pressure of 974 mbar (hPa; 28.7 inHg) was recorded, the lowest in relation to the hurricane. However, shortly thereafter, cool, dry air began to entrain the storm, causing it to rapidly weaken. In a six-hour span, the storm suddenly weakened to a Category 1 hurricane, a decrease of 25 mph (110 km/h).