The Climatological Influence of ENSO and Hurricane Frequency in North Carolina

Phenomena such as the El Niño-Southern Oscillation (ENSO) and variability in tropical cyclone activity are known to induce significant seasonal-to-interannual fluctuations in precipitation across the world. In order to increase the accuracy of precipitation prediction on these times scales, it is imperative for atmospheric scientists to understand the localized effects of these large-scale patterns.  At the State Climate Office of North Carolina, research is performed to determine how ENSO and tropical cyclones directly impact North Carolina’s seasonal-to-interannual precipitation budget.  Daily precipitation data for this project was collected from roughly 150 stations across North Carolina through the National Weather Service’s Cooperative Observer network from two notable ENSO events: a strong La Niña in 1988-1989, and a strong El Niño in 1997-1998.  To examine the impacts of tropical cyclones on precipitation, data from the peak of the 2004 hurricane season was compared to the 1981-2010 climate normals.  The results showed 32.0 percent less precipitation than normal during the winter of 1988-1989 and 56.1 percent more precipitation than normal for the winter of 1997-1998. During the 2004 hurricane season, June through November, North Carolina received 22.8 percent more precipitation than normal.  In the eight different climate divisions of North Carolina, these known precipitation differences can influence seasonal outlooks for weather and drought conditions.  In the future, this research will become a basis for a web-based tool that will display precipitation comparison plots for user-selected time periods.