 A cold front moved off the continent of North America in early September . The system spawned a low pressure area that gradually developed into a subtropical depression at 1800 UTC on September 10 , while located about 325 miles ( 525 km ) west @-@ southwest of Bermuda . It rapidly acquired tropical characteristics and became Tropical Depression Ten at 0600 UTC on September 11 . Thereafter , the depression strengthened into Tropical Storm Florence at 1200 UTC on that day and reached hurricane status only six hours later . Drier mid @-@ tropospheric air weaken Florence to a tropical storm , but re @-@ strengthen into a hurricane later on September 12 . 
