Tropics Tracker: What La Nina’s return means for end of hurricane season

Tropics remain quiet

June 2021 sea surface temperature departure from the 1991-2020 average.
June 2021 sea surface temperature departure from the 1991-2020 average. (Data Snapshots on Climate.gov.)

ORLANDO, Fla. – The Atlantic is nice and quiet as we venture through the middle of October. That could change in the final week or so of the month. More on that to come.

The National Oceanic and Atmospheric Administration officially declared Thursday that La Nina conditions are present. La Nina typically favors an active Atlantic basin during hurricane season. La Nina was declared in September of last year and the tropics unsurprisingly went crazy.

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To be declared an official La Nina or its warmer counterpart El Nino, sea surface temperature anomalies in the equatorial Pacific have to be greater than 0.5 degrees Celsius in a specific region. For La Nina, that would be below average.

Sea surface temperature anomaly

What is La Nina?

La Nina is a seasonal ocean/atmospheric pattern that develops in the tropical Pacific. La Nina is the cool phase of El Nino Southern Oscillation, or ENSO. During hurricane season, the phase ENSO is in can strongly impact tropical development far away in the Atlantic Basin.

When El Nino, the warm phase, is present, tropical development is suppressed with increased wind shear and poor atmospheric conditions in the Atlantic Basin.

When La Nina is present, waters along the equatorial Pacific, off of the coast of Peru, are cooler than normal. This happens because the trade winds strengthen in that region, pushing warm water toward Australia, allowing cooler water deeper in the ocean to come to the surface. This is known as upwelling.

Rest of October

Indications are that there could still be development during the last week to 10 days of the month or to start November. The place to watch would be the Caribbean as large-scale features come into play to enhance development in this area.

After this entity known as the Madden-Julian Oscillation passes by, the Atlantic should abruptly shut down for the season other than a stray storm developing.


About the Author:

Jonathan Kegges joined the News 6 team in June 2019 as the Weekend Morning Meteorologist. Jonathan comes from Roanoke, Virginia where he covered three EF-3 tornadoes and deadly flooding brought on by Hurricanes Florence and Michael.