Thu Sep 21 2017 12:52 PM

While a technical La Niña for the coming fall and winter is not a sure bet (forecast is about a 55-60% chance), even the cooler bias is useful in forecasting activity trends in the Atlantic basin for at least the rest of this year.

ENSO neutral conditions actually tend to be even somewhat more favorable for big-time banner years (2005, 2017, etc.) overall, but La Niña is very supportive of active to hyperactive Atlantic seasons.

Speaking just about the months of October, Octobers during La Niñas are usually about 50% more active than neutral - and October is right around the corner.

A few other things La Niñas can usually be counted on for: Increasing odds of sub-tropical cyclone formation, many of which go on to become fully tropical. Also, lowering of shear over the Caribbean, thus helping cook up and fuel deeply warm-cored tropical cyclones there.

This lowering of shear over the Caribbean heading into the back-half of this already hyperactive 2017 season raises some alarm bells, especially for the Yucatan, Cuba, Florida, the Bahamas, Georgia, the Carolinas, and Bermuda. Many late-season tropical cyclones that begin in the Caribbean go on to impact these areas. (See image below)

Dr. Ryan Truchelut recently touched on all this with a good article in the Tallahassee Democrat (Link).

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