 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.
