SIGNIFICANCE OF TROPICAL STORM TRACKS AND CYCLES TO FLOODING IN THE LOWER TAR, NEUSE, AND CAPE FEAR BASINS, NORTH CAROLINA

In September-October 1999 three hurricanes made landfall in eastern North Carolina triggering a prolonged and complex flood event (i.e., flash flooding, backwater flooding, and downstream flooding) in the Lower Neuse and Tar River Basins. Examination of recorded historical flood events for the lower Tar, Neuse, and Cape Fear River Basins shows that a spatial and temporal relationship exists between major downstream flood events and the tracks and timing of landfalling hurricanes-tropical storms in the lower portions of these drainage basins. Also, a strong temporal relationship exists between the ~20-30 year wet cycle periods in West Africa and the occurrence of the landfalling hurricanes-tropical storms, that trigger the major downstream flood events in these drainage basins.

In the Lower Tar River Basin at Greenville, NC (116 years of record) and at Tarboro, NC (107 years of record) the seven and six largest floods occurred respectively at these two locations during the hurricane season. Five of these downstream flood events correspond spatially and temporally to the tracks of landfalling hurricanes-tropical storms. The two, that do not correspond, occurred before the WWII era so the lack of correspondence is perhaps due to lack of complete records. Additionally, six of these seven downstream flood events were triggered by landfalling hurricanes-tropical storms that were generated during the West Africa wet cycle periods from 1890 to present. In the lower Neuse and Cape Fear Basins an equally strong spatial and temporal relationship exists between landfalling hurricanes-tropical storms, generated during the West Africa wet cycles, to the timing and frequency of major downstream flood events.

Hence, we should expect most, if not all, of the high magnitude downstream flood events in the lower Tar, Neuse, and Cape Fear River Basins in the future to occur during the hurricane season (June 01 to November 30) and also to occur during the ~20-30 years West Africa wet cycles. Furthermore, because these large downstream flood events are related to specific shifts in tropical storm-generating climate, perhaps these large magnitude downstream flood events have shorter recurrence intervals than have been previously suggested.