Recent historical Northern Hemisphere tropical cyclone inactivity is compared with the strikingly large observed variability during the past three decades. Yearly totals of Northern Hemisphere ACE are highly correlated with boreal spring sea-surface temperatures in the North Pacific Ocean and are representative of an evolving dual-gyre, trans-hemispheric correlation pattern throughout the calendar year. The offsetting nature of EPAC and NATL basin integrated energy and the strong dependence of combined Pacific TC activity upon ENSO suggest a hypothesis that overall Northern Hemisphere TC behavior is largely modulated by global-scale, non-local climate variability.

Northern Hemisphere tropical cyclone ACE remains at currently historically low levels reflective of global-scale climate conditions that are considerably less favorable for frequent, long-lived, intense tropical cyclones.