Projected Increase in Extremely Active Atlantic Hurricane Seasons

Abstract

Abstract Future changes to the year-to-year swings between active and inactive North Atlantic tropical cyclone (TC) seasons have received little attention, yet may have great societal implications in areas prone to hurricane landfalls. This work investigates past and future changes in North Atlantic TC activity, focusing on interannual variability and evaluating the contributions from anthropogenic forcing. We show that interannual variability of Atlantic TC activity has already increased, evidenced by a significant increase in the occurrence of both extremely active and inactive TC seasons since the 1980s. Consistent with the observed trend, TC-resolving general circulation models project a 58 - 64% increase in the variance of North Atlantic TC activity, measured by accumulated cyclone energy, by the middle of the 21st Century. Further analysis indicates that these changes are the result of increased variability in vertical wind shear and atmospheric stability, in response to enhanced Pacific-to-Atlantic interbasin sea surface temperature variations. Therefore, we conclude that robust anthropogenic-forced intensification in the variability of Atlantic TC activity has already emerged from natural variability and will continue to intensify in the future, with important implications for emergency planning and societal preparedness.