The depression slowly moved southwestward, and in conditions that were good for strengthening, it strengthened into Tropical Storm Wilma on October 17. In the beginning, development was slow because of its large size, although thunderstorms slowly organized. From October 18, and over the next day, Wilma underwent explosive deepening over the open waters of the Caribbean; in a 30-hour period, the system's central atmospheric pressure dropped from 982 mbar (29.00 inHg) to the record-low value of 882 mbar (26.05 inHg), while the winds increased to 185 mph (300 km/h). At its strongest, the pinhole eye of Wilma was about 3 miles (5 km) in diameter, the smallest known eye in an Atlantic hurricane. After the inner eye died off because of an eyewall replacement cycle, Wilma weakened to Category 4 status, and on October 21, it made landfall on Cozumel and on the Mexican mainland with winds of about 150 mph (240 km/h).