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  • Writer's pictureBryan Norcross

Everybody wants to know if hurricane season is over

The short answer is… maybe but probably not.

The non-tropical system off the Carolina coast had strong enough winds yesterday to be named Tropical Storm Wanda, but it was missing the organized circulation that a tropical system has to have. Hurricane Hunters flew through the system and found 50 mph winds nearby, but they weren't really related to the sloppy, broad circulation.

Now today, it has a better-defined circulation, but few strong thunderstorms.

Upper-level winds are going to become increasingly hostile today. So wanna-be Wanda’s opportunity has likely passed. Although there is still a brief window today when the disturbance could technically become a tropical depression or low-end storm before the upper winds blow it apart.

The main consequence, no matter the technical definition, will be coastal flooding in eastern North Carolina caused by a combination of the winds blowing off the ocean and the King Tides.

By tomorrow, the system should get absorbed into a frontal system and be moving out to sea.

Elsewhere in the Atlantic, there are no developing systems on the horizon.

Why would that be? Is the season over? There is no way to be 100% sure, but we can point to a couple of factors.

There's a type of wave we don't talk about very much that rotates around the earth in the upper atmosphere. It alternately increases and decreases the ability of thunderstorms and tropical disturbances to develop. Systems need tall thunderstorms to strengthen and organize. When the thunderstorms are suppressed, tropical systems are less likely to come together.

The phenomenon is called the MJO for the Madden-Julian Oscillation. It was discovered in the early 70’s by a couple of atmospheric scientists named Madden and Julian working at NCAR – the National Center for Atmospheric Research in Boulder, Colorado.

Currently, the MJO favors tropical systems developing in the western Pacific and is suppressing development in the Atlantic. So that’s likely one factor keeping things quiet.

In addition, this time last year, the phenomenon called La Niña – the opposite of El Niño – was ramping up. A La Niña, when there is unusually cold water in the equatorial Pacific, tends to encourage tropical development in the Atlantic. A strong La Niña was forecast to develop this fall as well, so a long hurricane season was expected like in 2020.

It hasn’t quite happened, however. There is a large pool of cool water under the surface of the Pacific, but the ocean-water temperature in the important part of the ocean is not drastically cooling. In 2020, a strong La Niña kept the hurricane season going late into November. But this year, we haven’t seen the big La Niña boost.

Third, the weather pattern over the Atlantic has been fairly hostile. Upper-level winds have generally been less than conducive for development over the typically favored areas.

If these trends continue, we shouldn’t expect any more systems to develop in the tropical Atlantic. But there is no way to know what might happen in the northwest Caribbean or the Gulf of Mexico. There is still plenty of time for a random system to develop there.

A dangling cold front could trigger a tropical system, for example. Or a non-tropical system could hang around over the warm water and become tropical enough to get a name.

The bottom line is, there is no way to be 100% sure why the hurricane season suddenly paused – it’s likely a combination of factors. And there’s no way to be sure if it’s going to start up again due to a random front in the wrong place.

Playing the odds, we should still be ready for something else to form this month. After all, we’re only one-third done with October.

Still, the long-range forecast models show low chances of any development over the next two weeks. If that works out, we’ll be nearing the end of October when the odds significantly decrease.


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