Climate Fact: El Niño and North Atlantic Cyclones
The El Niño-Southern Oscillation, the periodic “sloshing” back and forth of warm water between the eastern and western tropical Pacific, is believed to affect the frequency of tropical cyclone development in the North Atlantic. Specifically, during La Niña phases (when the waters off the west coast of South America are unusually cool) circulation in the upper atmosphere reduces the amount of wind shear, favoring tropical cyclone development. El Niño phases (when the waters off the west coast of South America are unusually warm) increase the amount of vertical wind shear over the Atlantic, which suppresses tropical cyclone development. While this two-phase model has been useful for making weather predictions, a closer analysis of tropical Pacific sea-surface temperature records reveals that not all events that have been classified as El Niño events were the same. During some El Niño events, the warmest waters were indeed directly off the west coast of South America (an eastern Pacific warming or EPW), while during others, the warmest waters were instead concentrated in the central Pacific (a central Pacific warming or CPW ). CPW events have the same basic impact on North Atlantic tropical cyclone development frequency as La Niña phases do and CPW events tend to steer storms on more southerly tracks towards the U.S. Gulf Coast and Central America. Eighty percent of the CPW events that have occurred since 1950 have happened in the last 20 years.
Seasons: Spring, Summer, Fall
Sources: Holland, G. “Predicting El Niño’s Impacts.” Science 325 (2009): 47 and Kim, HM et al. “Impact of Shifting Patterns of Pacific Ocean Warming on North Atlantic Tropical Cyclones.” Science 325 (2009): 77-80.
