Northern Hemisphere tropical cyclone activity



[1] Recent historical Northern Hemisphere (NH) tropical cyclone (TC) inactivity is compared with strikingly large observed variability during the past three decades. Yearly totals of the combined active-basin NH accumulated cyclone energy (ACE) are highly correlated with boreal spring sea-surface temperature (SST) in the North Pacific Ocean and are representative of an evolving dual-gyre, trans-hemispheric correlation pattern throughout the calendar year. The observed offsetting nature of Eastern Pacific and North Atlantic basin ACE during the past three decades and a strong dependence of combined Pacific TC activity upon the El Niño-Southern Oscillation reflect the interrelated modulation of overall NH integrated TC energy by large-scale modes of climate variability. Thus, the quiescent period of overall integrated NH TC ACE continuing throughout 2008 is not unexpected in the context of previous periods of colder Pacific SSTs.