Extreme Rainfall in the Carolinas during the Extratropical Transition of Hurricane Matthew (2016)

Hurricane Matthew locally generated more than 400mm of rainfall on 8–9 October 2016 over the eastern Carolinas and Virginia as it transitioned into an extratropical cyclone. The extreme rainfall totals caused flooding of Coastal Plain rivers days after the passage of Matthew, especially along the Tar River, and 24 people died as a result of freshwater flooding in North and South Carolina. The heaviest precipitation occurred 100–200 km inland from the coast and was collocated with enhanced low-tropospheric frontogenesis. Rapid Refresh (RAPv3) model analyses indicate that rapid frontogenesis occurred over eastern North and South Carolina and Virginia on 8 October, largely over a 12-h time period between 1200 UTC 8 October and 0000 UTC 9 October. The heaviest precipitation occurred along spiral rainbands near where they intersected with a near-surface front; this precipitation intensified as the temperature gradient along the near-surface front rapidly increased. Along the frontal boundary, conditional instability was released in rising parcels, and in contrast to Hurricane Floyd (1999), the release of conditional symmetric instability was minimally important. However, mid-tropospheric conditional symmetric instability release may have contributed to a secondary maximum in rainfall rate further inland over central North Carolina and Virginia. Cold-air damming was in place prior to the arrival of Matthew; however, it dissipated before the heaviest rainfall occurred over the Carolinas, and it did not impact the extreme rainfall totals observed there.