Complex sentence: November 9--13,2009 marked a significant extratropical storm surge event on the US east coast when the remnants of Hurricane Ida developed into a Nor'easter off the Southeast US coast.
Split into simpler sentences: November 9--13,2009 marked a significant extratropical storm surge event on the US east coast. The extratropical remnants of Hurricane Ida developed into a Nor'easter off the Southeast US coast.