El Nino/La Nina Influence on Hurricane Season

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One of the driving factors in determining the magnitude of a hurricane season is forecasting the phase of a naturally occurring climate cycle across the waters of the equatorial Pacific Ocean. The phase changes over the equatorial Pacific Ocean are known as La Nina and El Nino. A cooler-than-average phase in the equatorial Pacific is referred to as "La Nina" while a warmer-than-average phase is called "El Nino."

Trends in the Atlantic Hurricane Season from year to year can be traced back to the La Nina and El Nino phases over the Pacific. Through extensive research, Dr. William Gray of Colorado State University discovered that La Nina cycles produce more Atlantic hurricanes while El Nino cycles produce fewer Atlantic hurricanes.

One of the main reasons this conclusion was drawn is that the wind shear is typically lower across the Atlantic during La Nina than in El Nino years. Lower levels of wind shear allow tropical waves to organize more frequently and develop into tropical cyclones and hurricanes. In El Nino years, there is increased wind shear across the Atlantic Basin which will tend to prevent tropical waves from organizing into cyclones and hurricanes.

Another correlation that can be drawn between La Nina and El Nino is the number of hurricanes that threaten the Caribbean and the United States. As one might expect, research shows that La Nina years feature an increased threat of hurricanes striking land in the Caribbean or the United States than years with an El Nino.

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