Hurricane Matthew impacted Haiti and the Southeastern United States in October 2016, killing at least 600 people and 47 in the United States. Many of the U.S. deaths were related to drivers trying to drive their cars through high water, which appeared abruptly in parts of eastern North and South Carolina after over 400 mm (15.75 in.) of rainfall fell in a day in some locations. As the center of Matthew approached the Carolinas, it transitioned into an extratropical cyclone, and the precipitation associated with the storm extended well north of the center. This is a common occurrence, and a trough to the northwest in such cases helped to support heavy rainfall over much of North Carolina.
Of particular interest was the particularly heavy rainfall that fell in a corridor over inland eastern North Carolina. It was here that rainfall in excess of 15 inches was in some places observed. What caused this narrow region of extreme rainfall? As the hurricane transitioned into an extratropical cyclone, a surface frontal boundary developed to the north of and extended from the circulation center. To the east of the boundary was warm, moist oceanic air. To the west, was cooler, drier continental air. At the boundary, the warm air being pushed in from the ocean rises and supports intense rainfall. But why did the temperature boundary occur where it did, or at all? Did cold air damming east of the Appalachians contribute to the frontal boundary?
Because Matthew paralled the U.S. Southeast Coast, a wealth of dual-polarimetric radar data was collected. With it, we can see differences in the structure of rain drops in oceanic vs land convection. The changes in convective characteristics as rain bands moved onshore may also contribute to the greater rain rates over land than over ocean.