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What is El Nino and why does it matter during hurricane season?

What is El Nino, and why does it matter during hurricane season? Here’s a look at the naturally occurring phenomenon.

What is El Nino?

An El Nino is a change in the climate pattern that leads to unusual warming of surface waters and the atmosphere. The change happens in the Pacific Ocean near the equator and is temporary.

What causes El Nino?

Strong trade winds usually blow from east to west across the Pacific near the equator, causing warm water to be pulled westward and pile up in the western part of the Pacific. The winds also pull the deeper, colder water in the eastern Pacific to the surface as they move westward.

During an El Nino, the usually strong trade winds are weaker. The weaker winds don’t pull warm waters westward and the warm water they do pull tends to fall back toward the east, making the waters near South America warmer.

What does it matter if the water is warmer in the eastern part of the Pacific?

Warmer water in the eastern Pacific tends to make trade winds weaker. Weaker westerly winds lead to increased rainfall in the eastern Pacific, while at the same time causing dryer conditions in the western Pacific.

How does that affect hurricane season in the Atlantic?

If the El Nino effect is strong in a particular year, it can suppress the formation of hurricanes in the Atlantic.

The main way that happens is by wind shear. Wind patterns produced by El Nino align to cut off a tropical storm's source of power – warm water and air. Wind shear, a change in wind speed and/or direction with altitude, is increased over the Caribbean and Atlantic in years where the El Nino is strong.

What is La Nina?

La Nina is the opposite of El Nino. National Geographic explains how La Nina works.

How often do El Ninos happen?

They happen about every three to seven years.