After becoming an extratropical low, the remnants of Ivan turned to the southeast and entered into the Atlantic Ocean, due to the building of an upper-level ridge to its east. As an extratropical cyclone, Ivan remained identifiable in both surface and upper-level data, and the system turned south and southwestward over the next few days. By September 20, the system was off the east coast of Florida, creating scattered thunderstorms; unfavorable wind shear stopped tropical redevelopment, though forecasters mentioned the possibility for more favorable conditions a few days later. On September 21 the low crossed southern Florida and emerged into the Gulf of Mexico, and as it moved across the warm waters of the region the low began to re-acquire tropical characteristics; the low-level circulation became increasingly better defined, and convection redeveloped over the center. Based on reports from Hurricane Hunters, it is estimated the low redeveloped into Tropical Depression Ivan late on September 22 while about 175 miles (280 km) south-southeast of the mouth of the Mississippi River.