Meteorological History of Hurricane Wilma - Formation

Formation

During the second week of October, an unusually large, monsoon-like lower-level circulation and a broad area of disturbed weather developed over much of the Caribbean Sea. The system was enhanced by diffluence from an upper-level low across the southwestern Atlantic. By October 13, a broad area of low pressure developed and persisted about 150 miles (240 km) southeast of Jamaica, possibly aided by the passage of tropical waves through the area at the time. Convection increased and became slightly better organized, though upper-level wind shear initially prevented development. The system drifted westward, and early on October 14 the convection became more concentrated and a little better organized as upper-level wind shear lessened slightly.

Later on October 14, the system became much better defined, with increasingly organized shower and thunderstorm activity, as conditions in the upper levels of the atmosphere became significantly more favorable. It was then that the National Hurricane Center first indicated that it was possible for a tropical depression to develop in the area. Dvorak classifications were initiated on October 15. The system continued to organize, with the National Hurricane Center remarking the system could ultimately become a hurricane. By late on October 15, the surface circulation became defined well enough, with sufficiently organized deep convection, for the National Hurricane Center to designate the system as Tropical Depression Twenty-Four while it was located about 220 miles (350 km) east-southeast of Grand Cayman.

The depression tracked slowly westward, a motion due to weak steering currents caused by a high pressure area to its north across the Gulf of Mexico. Initially, the center of circulation was broad without a defined inner core; forecaster Lixion Avila remarked, "The area of minimum pressure could anywhere within 60 miles (97 km) of its ." Initially, the tropical depression was forecast to drift west-southwestward before turning to the north; within five days of the forecast's issuance, the system was predicted to be located about 80 miles (130 km) south of the Isle of Youth as a 105 mph (169 km/h) hurricane. However, the National Hurricane Center noted in the first advisory on the depression that there were "all indications that there could a dangerous hurricane in the northwestern Caribbean Sea in 3 to 5 days." This was due to the depression being located within an environment very conducive for development, specifically low amounts of wind shear and very warm water temperatures.

As Tropical Depression Twenty-Four drifted southwestward, it steadily organized; by early on October 16, rainbands began to gradually consolidate with well-established outflow, and a large upper-level anticyclone developed over the depression. Although deep convection and banding features increased, mid-level dry air from the north prevented significant organization, and the convection was split into two primary areas. Surface buoy reports indicated that, due to its large size, the system failed to strengthen beyond tropical depression status, even though it received tropical storm strength Dvorak classifications from The National Hurricane Center's Tropical Analysis and Forecast Branch and the National Oceanic and Atmospheric Administration's Satellite Analysis Branch. Continued reconnaissance flights reported peak winds of about 30 mph (48 km/h).