Fig. 2

Observed low frequency anomalies in Atlantic major hurricane frequency and associated climate variables. a Coherent variations are shown for Atlantic major hurricane frequency (grey shading), Inverted Hurricane Shear Index during the Atlantic hurricane season (JJASON) (solid red with stars), Atlantic Multidecadal Variability (AMV) Index (dashed magenta) and Atlantic Meridional Overturning Circulation (AMOC) Fingerprint (solid blue). The AMOC Fingerprint is shifted backward by 4 years to represent the AMOC anomalies at mid-high latitudes. Also shown are the unfiltered annual mean RAPID AMOC Index at 26°N for 2004–2014 (solid black line) and its linear trend (dashed black line) with a unit of Sverdrup (Sv, right y-axis) (b) Variations of Atlantic major hurricane frequency (grey shading) and AMV index (dashed magenta) are compared with the main development region (MDR: 80°W–20°W, 10°N–20°N) averaged SST anomalies (solid red) and relative SST (solid blue with dots) during the Atlantic hurricane season (JJASON). The relative SST is defined as the difference between MDR SST anomalies and tropical (TROP: 30°S-30°N) mean SST anomalies. All time series are 10-year low-pass filtered and normalized by their own standard deviation over the period 1957–2005. The key focus period (2005–2015) is highlighted by the line segment/arrows on plot