 A cold front stalled a couple hundred miles southeast of Bermuda on October 10 . During that day , a strong upper @-@ level trough moved southeastward off the southeast coast of the United States . Due to several factors , including upward motion and strong diffluence — the rate at which a fluid moves — the area became baroclinically unstable . This caused the interaction between the trough and the front to develop into an extratropical low about 345 miles ( 555 km ) southeast of Bermuda on October 11 . The low moved quickly northward , then northwestward , strengthening quickly due to the instability of the atmosphere . Late on October 11 , the system slowed , and the upper @-@ level circulation became aligned with the low @-@ level circulation . The extratropical storm began to develop tropical characteristics late on October 11 , including surface temperatures warmer than the surrounding environment , and vertical wind characteristics of a tropical cyclone . Based on its organization , the system developed into Subtropical Storm One early on October 12 while located about 35 miles ( 55 km ) south of Bermuda . 
