Tropical Storm Ana (2003) - Meteorological History

Meteorological History

A non-tropical low pressure area developed about 240 miles (390 km) south-southwest of Bermuda on April 18 through the interaction of an upper-level trough and a surface frontal trough. The surface trough, which extended from the gale center to Hispaniola, brought a plume of moisture northward from the Caribbean Sea into the circulation, which caused heavy rainfall in Puerto Rico. The non-tropical low tracked generally northward, with a ridge to its east and west, and on April 19 the system began producing sporadic convection near its center; early that day, satellite imagery indicated the presence of a tight inner core of winds. After turning to the northwest, it looped southeastward and gradually became separated from the surface frontal system, due to the deepening of the upper-level trough over the system. Convection became better organized over the center, and it is estimated the system developed into Subtropical Storm Ana early on April 20 while located about 250 miles (400 km) west of Bermuda. Operationally, the subtropical cyclone was not classified by the National Hurricane Center until 21 hours later.

The subtropical storm tracked east-southeastward and continued to organize, and by late on April 20 an upper-level warm core was present over the system. Based on its organization, Ana is estimated to have become a tropical storm by 0000 UTC on April 21. Upon becoming a tropical storm, Ana attained a peak intensity of 60 mph (95 km/h), which was based on estimates from the Hebert-Poteat technique and data from QuikSCAT. Shortly thereafter, it made its closest point of approach to Bermuda, when it passed about 130 miles (210 km) southwest of the island. Operationally, the cyclone was first classified by the National Hurricane Center around this time, when it was considered a subtropical cyclone. Strong upper-level wind shear removed much of the convection, though a small area of thunderstorms persisted near the center. The storm became completely separated from the upper-level system, and the cyclone re-organized, developing an eye feature late on April 21. Embedded within the flow of a cyclone to its north, Ana continued eastward, and early on April 22 the wind shear again removed the convection from the center. Convection waxed and waned throughout the day, and by April 23 the circulation had deteriorated in organization. After turning to the northeast, the circulation center merged with an approaching cold front on April 24, and Tropical Storm Ana completed the transition into an extratropical cyclone. The extratropical storm accelerated east-northeastward before losing its identity within the frontal zone on April 27 southeast of the Azores.