 In the second week of December , a frontal trough stalled south of Bermuda . An upper level disturbance moved over the area on December 9 , and produced widespread convection along the frontal wave . The system moved to the northeast , and based on a developing circulation within the convection , the National Hurricane Center classified the system as a subtropical storm on December 12 while located 275 miles ( 440 km ) northeast of Bermuda . 
