Empirical Modes of Landfalling Tropical Cyclones in North Carolina

Recent studies of Atlantic tropical cyclone (TC) activities indicated that the frequency of landfalling TCs is on the rise along the U.S. East Coast, whereas not so along the Gulf Coast. There is also a significant state-by-state variation of the number of landfalling TCs along the East Coast in the past century, with Florida being the first and North Carolina the second. For the user community, particularly planners and emergency management officals at the state level, the information of landfalling hurricanes on state-by-state basis would be valuable and complementary to that of Atlantic Hurricane activity.

This study documents the frequency variation of landfalling-hurricanes and tropical storms in North Carolina (NC) from 1987-1999 using Empirical Mode Decomposition (EMD) method. Four principal modes, which include an interannual mode, an intra-decadal mode, a decadal mode and a multi-decadal mode, have been extracted from the NC TC landfall time series. There is evidence that the interannual mode is influenced by the El Nino/Southern Oscillation (ENSO) cycle, whereas the decadal mode is affected by the dipole mode of the Atlantic sea-surface temperature (SST) anomalies. The physical mechanisms of the intra-decadal and multi-decadal modes are not yet well understood. However, the latter seems correlated with the multi-decadal signal of West Africa rainfall anomalies. We also note that, on century time scale, the annual number of landfalling TCs in NC experienced a slight downward trend from 0.85 in the late nineteenth century to a low of 0.79 in 1950s, and has been slowly rising to about 0.81 in 1999. On decadal time scales, late 1880s-1890s, 1920s-early 1930s, late 1940s-1950s, and late 1980s-1990s experienced more than normal landfall TCs in NC, whereas 1910s-early 1920s, 1930s-early 1940s, and late 1960s-early 1980s experienced below normal TC activity in NC. All modes except the interannual mode seem to remain as positive anomalies in the early 21st century. Thus, unless interannual-time scale forcing which is unfavorable for TCs making landfall in NC exists, North Carolinians will likely brace for more than normal landfalling TCs in the early 21st century.