Dr. Gary Lackmann-October 17 Colloquium

Hurricane Joaquin’s role in the South Carolina Flood of October 2015

Catastrophic flooding took place across South Carolina in early October 2015, while Hurricane Joaquin was located offshore to the south-east of the heavy precipitation. Prior research, storm summary reports, satellite imagery, and media accounts all suggested that Joaquin contributed to the flooding event. We utilize numerical simulations to elucidate Joaquin’s role in the flooding. Specifically, we investigate: (i) whether the presence of Joaquin enhanced atmospheric water vapor content over the southeastern U.S., and (ii) if Joaquin altered the synoptic-scale and mesoscale forcing for ascent during the flood through changes in the upper-level flow. Given that precipitation greatly exceeds evaporation in the vicinity of tropical cyclones, and that the lower-tropospheric flow is strongly convergent in such systems, our working hypothesis was that Joaquin’s role, if any, was due to upper-level dynamical alterations. Having a robust and slow-moving upper trough located to the west of the flooding region, we further hypothesized that heavy precipitation would have taken place even in the absence of Joaquin. In order to test these hypotheses, we compare control simulations using the Weather Research and Forecasting (WRF) model with experimental simulations, in which Joaquin is removed from the initial conditions. Without Joaquin, heavy rain still occurs, but there is a pronounced northward shift in the axis of heaviest precipitation into North Carolina, a modest reduction in area-averaged rainfall, and increased atmospheric water vapor content over the Southeastern U.S. In summary, the dynamical influences of Joaquin dominate over changes to water vapor content.

Dr. Lackmann earned B.S. and M.S. degrees from the University of Washington (1986 and 1989), and a Ph.D. from the SUNY Albany (1995). He joined the faculty of North Carolina State in 1999. His research focuses on high-impact synoptic, mesoscale, and tropical weather systems, and effect on climate change on these systems. He currently serves as the Chief Editor of Weather and Forecasting and is co-chair of the UCACN, an external NCEP review committee.