La Niña’s impact on hurricane season

The National Oceanic and Atmospheric Administration has forecast an above average Atlantic hurricane season in 2020. In fact, two storms, Arthur and Bertha, have been named even before the technical beginning of the season on June 1st.

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A chain reaction of atmospheric events may to blame for the expected increase in hurricane activity. In the last month, ocean temperatures have substantially decreased along the east equatorial Pacific Ocean. This quick cooling shows a transition from an El Niño to a La Niña pattern.

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In a neutral to La Niña ENSO phase, the trade winds along the equator intensify, pushing warm surface waters to west. As a result, cool water from the subsurface “upwells” to the surface. This creates cool and dry conditions along the east equatorial Pacific Ocean and along the west coast of South America.

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The pattern resulting from La Niña creates a change in the weather across the Gulf of Mexico, Caribbean Sea and Atlantic Ocean. Westerly winds in the Atlantic Basin weaken, causing vertical wind shear to decrease.

Hurricanes thrive in an atmosphere with minimal vertical wind shear. The weakening westerlies also increase the atmospheric instability. The final takeaway is the La Niña translates to suitable atmospheric conditions in the Atlantic Ocean for hurricane formation and strengthening.

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