Shortly after peaking, the hurricane turned to the north and gradually weakened as wind shear from an upper-level trough to its northwest increased. By early on November 17, the low-cloud circulation became partially exposed on the west side of the deep convection, and it is estimated that Sergio weakened to a tropical storm later that day. A ridge to its north and northeast turned the storm to the northwest and later to the west as Sergio gradually weakened.
Shortly after reaching its highest point, the hurricane began to move towards the north and gradually lost power due to increased wind shear from an upper-level trough in its northwest direction. By early November 17, the low-pressure system's cloud cover had partially lifted on the western side of a deep area of thunderstorms, and it is estimated that Sergio weakened into a tropical storm later that day. A ridge to the north and northeast then steered the storm westward as it continued to lose strength.