On August 11, 2007, a tropical wave moved off the west coast of Africa, and, encountering favorable conditions, quickly developed into Tropical Depression Four about 520 miles (835 km) west-southwest of Cape Verde on August 13. The depression moved briskly westward, and was upgraded to Tropical Storm Dean at 1500 UTC on August 14. The storm's intensity continued to build although dry air and cooler air inflow from the north were slowing structural development. Ragged bands formed on August 15 and the formation of a partial eyewall was observed later that day.
Image of Hurricane Dean at category 5 hurricane strength on August 18, 2007.
Intensification continued and the storm was upgraded to Hurricane Dean at 5 a.m. EDT (0900 UTC) August 16. The deep-layered ridge to the north continued to steer the system west, towards the Caribbean Sea. The storm quickly strengthened to a Category 2 hurricane on the Saffir-Simpson Hurricane Scale. The storm's development slowed slightly but a reconnaissance aircraft discovered a closed eyewall on August 17 as the storm passed through the Lesser Antilles. Data from the aircraft indicated that Hurricane Dean had strengthened to a Category 3 hurricane and its trailing bands were still over the Lesser Antilles. During the evening of August 17, Dean strengthened into a Category 4 hurricane and continued to steadily grow in both size and intensity through the night. On August 18 the presence of a double eyewall was noted, indicating an eyewall replacement cycle and causing short term fluctuations in intensity. These fluctuations did not affect the storm's well defined satellite presentation. Operationally, Dean was thought to have only been a Category 4 on the 18th, but post-storm analysis shows that Dean had become a 165 miles per hour (265 km/h) Category 5 that day. Dean weakened very slightly on the morning of August 19 as it finished the eyewall replacement cycle and began to interact with the island of Jamaica