sentences:  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.