Sensitivity of North Atlantic Tropical Cyclone Tracks to Climate Variability and Climate Change

This study examines the impact of natural climate variability and long-term climate change on North Atlantic tropical cyclone (TC) tracks. Using data from HURDAT for the period 1950-2007, we categorize Atlantic TCs that form in the Main Development Region into one of three track types: Straight-Moving (SM), Recurving Landfall (RCL), and Recurving Ocean (RCO) TCs. As expected, the SM storms are associated with a westward extension and strengthening of the North Atlantic Subtropical High (NASH) whereas the RCO storms coincide with a weakening of the NASH. The presence of El Nino conditions in the tropical Pacific is found to be associated with a weakening and eastward retreat of the NASH, an increase in the percentage of RCO TCs, and a decrease in the percentage of RCL TCs. Using 6-hourly wind fields from NCEP-NCAR Reanalyses, simulated tracks are computed for each historical storm in the sample using the Beta Advection Model (BAM). Using observed genesis locations, the BAM successfully reproduces the differences in TC tracks between SM, RCO and RCL storm types. When storm genesis is uniformly distributed over the MDR we find that RCL and RCO storms still exhibit a distinct difference in tracks, suggesting that differences in the large-scale steering flow over the tropical Atlantic are primarily responsible for their track differences. However the SM TCs exhibit a more northward track under the uniform genesis experiment, indicating that the more southern and western genesis location of these storms is an important contributor in determining their tracks. The observed difference between TC tracks during El Nino and La Nina events is also reproduced by the BAM under both observed and uniformly seeded genesis experiments, suggesting that it is the changes in the large-scale steering flow over the Atlantic that is responsible the larger percentage of RCO storm tracks during El Nino events. The influence of anthropogenic warming is examined using a 7 member ensemble comparing the 2xCO2 experiment to a pre-industrial control. Increased sea level pressure over the northeast and northwest quadrants of the Atlantic does not alter the average TC track