By John Morales 

We have had a very active Atlantic hurricane season this year. Record hot sea surface temperatures have already driven the storm count past the yearly average (14), with a good chunk of the season still ahead.  

I’ve had many people in Miami and Puerto Rico ask, “if it’s been so busy, how come we haven’t had any impacts, or even a significant threat? How come ‘all’ the hurricanes are turning out into the North Atlantic?”

It is time we talk about the deflector shield, or in this year’s case, shields (plural).

The shields have been “activated” this year. The east coast of the U.S., the Leeward and Virgin Islands and Puerto Rico all have been mostly protected from tropical storms, even in this very busy 2023 season.

You’ve heard me talk about the “deflector shield” on television from time to time. It’s the term I’ve coined to describe a semipersistent dip in the jet stream positioned along the Eastern Seaboard. Occasionally this summer it’s been a little further east in the western Atlantic, and sometimes a little closer to the Midwest. Other times it’s been replaced by the opposite—a ridge of high pressure.

But times in which high pressure has been strong in the west Atlantic have been few and far between this year. The Bermuda high, typically a consistently strong summer feature, has also been weak.

Dips in the jet stream, known as troughs, have eroded the strength of the high pressure systems by driving cold fronts much further south than you’d expect in the height of summer. You can see the weakness of the highs compared to the June to August normal in the areas shaded in blue in the image below. This condition persists even as we now transition to fall.

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