This image of subtropical storm Ana was taken by the SeaWiFS instrument onboard the OrbView-2 satellite on April 20, 2003, two days before Ana was classified as a tropical system.
Subtropical storms are non-frontal low pressure systems that have characteristics of both tropical and extratropical cyclones. The most common type is an upper-level cold low with circulation extending to the surface layer and maximum sustained winds generally occurring at a radius of about 100 miles or more from the center. In comparison to tropical cyclones, such systems have a relatively broad zone of maximum winds that is located farther from the center, and typically have a less symmetric wind field and distribution of convection.
Tropical Storm Ana is only the second tropical or subtropical storm to form in April since forecasters began tracking hurricanes in 1871. The only other known April subtropical system formed in 1992.