Tropical Storm Wilma began to turn to the west-northwest on October 18, during which the storm developed a small, intermittent and ragged eye feature as well as a mid-level eye feature. It continued to strength, and at 1200 UTC on October 18, Wilma strengthened into a Category 1 hurricane while about 225 miles (360 km) south-southeast of Grand Cayman. Shortly after reaching hurricane strength, the hurricane began undergoing explosive deepening, subsequent to the development of a "pinhole" eye 9 miles (14 km) in diameter. This small eye was surrounded by a ring of deep convection, with cloud-top temperatures of about -125 °F (-87 °C).