Marco and Laura in the Gulf of Mexico

Negligible influence on Atlanta weather

If you read my blog post back on August 10th I explained how the upper-level pattern was going to open up the Coastal U.S. to potential tropical cyclones during this period into September based on the blocking high pressure cells West and East.

I explained in my blog post of August 22nd how different steering currents at different levels influence the two systems differently. You miss a Tweet you miss a lot. You miss a blog you miss a lot lol.

If you follow me on Twitter you know I pointed out many days ago that if we got two hurricanes in the Gulf simultaneously it would be the first time ever recorded but that the odds were against it.

Marco has weakened to a tropical storm and is not expected to become a hurricane again, but as Laura moves into the Gulf, IF Marco is not on land then it will be the first time we have two named systems in the Gulf at the same time since 1959 having happened only one other time in 1933.

The GENERAL steering flow across both systems is IN THE MEAN roughly the same, from the Southeast to the Northwest:

However, the two storms are in different locations and are at different intensity levels and have different structures, hence there is no reason they should would or could move in the exact same direction or speed.

The weaker system Marco, being shorter in the atmosphere is more readily influenced by low to mid level air flow (850mb):

Laura on the other hand, being hundreds of miles away and being more intense and thus taller up in the atmosphere, is influenced more by stronger air currents higher up in the atmosphere around the clockwise air flow of the blocking high pressure ridge to its Northeast (500mb):

And the stronger Laura gets the more it can influence and be influenced by upper level winds even higher up in the atmosphere.

The exact strength AND configuration of those winds and high pressure blocking ridges in the days ahead will determine whether the ultimate path is more North or more West and our numerical equations in the computer models give us guidance on the future options to make a forecast.

These include specialized hurricane models and general forecast global models, and their ensembles which produce the so-called “spaghetti” charts showing the range of possible outcomes. (For in depth google Lorenz Chaos Theory and Ensemble Weather Forecasting).



The longer Laura is over the warm gulf waters the more intense it can get, so the more West it goes toward Galveston Bay the stronger it can get, if it goes more North toward Louisiana it at least MIGHT be less intense. I think the track is going to end up being shifted farther West than current NHC as a CAT 2-4 hurricane.

I’ll add my usual admonition that while forecast track accuracy is good especially out to 3 days, we lack skill at predictions of tropical cyclone intensity one way or another.

For more Follow me on Twitter @MellishMeterWSB .

Kirk Mellish


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