Dangerous Florence 

Posted: 11:00 am Wednesday, September 12th, 2018

By Kirk Mellish

Remember the “Cone of Uncertainty” I’ve been talking about all week? How important it is to note at 5 days ahead it’s very large with the error on the track last year being 150 miles? The reason I’ve been pointing that out is so that those paying attention would NOT be surprised when projected track and intensity level change to something new.

I pointed out days ago that even Georgia could not be given an all clear. That is still very much the case!

AIR FORCE HURRICANE HUNTER AIRCRAFT FINDS FLORENCE HAS CHANGED LITTLE WHILE MOVING TOWARD THE U.S. SOUTHEAST COAST… LIFE-THREATENING STORM SURGE AND RAINFALL EXPECTED ACROSS PORTIONS OF THE CAROLINAS.  Currently a Category 4.

Satellite this morning measured a max wave height under the cyclone of 83 feet. No waves that high are not forecast for the East Coast. Eye is over 400 miles SE of Wilmington, NC:

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How big?

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Expected to strengthen today into tomorrow but weaken to a Cat 3 or 2 as the eye gets to land, still a dangerous hurricane (Cone of uncertainty in white):

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Keep in mind looking at map below, this does NOT mean Atlanta WILL get tropical storm force winds at or after the time indicated, it means it’s possible. The point of the map is to give people an idea of when they should have storm prep completed just in case it started that early. The NHC continues to slow down the storm as it approaches the coast of North C Carolina or South Carolina on Thu & Fri and move slowly near the coastline thru Sat.

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7-DAY ACCUMULATED RAINFALL AVERAGE ESTIMATE:

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Screen Shot 2018-09-12 at 11.40.48 AMScreen Shot 2018-09-12 at 11.41.28 AM

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Although Athens, Ga and the DAWGS look alright as of now they would be wise to have a Plan B just in case.

Our ATLANTA forecast Sunday through Tuesday is subject to the whims of Florence, and could change for the WORSE! Given the current official NHC track we look OK. However, given the NHC keeps shifting their track south (I think because they give the GFS model too much weight) I would not be surprised for a track more into Georgia than currently shown, so stay tuned. This obviously includes a threat to Savannah.

The reason the forecast becomes so tricky is because the “steering currents” in the upper levels of the atmosphere collapse as it nears the coast and tries to move inland. Think of it this way, if the steering wheel of a car comes off while moving how would you know where its going to end up?

Uncertainty remains high on the end game due to the unprecedented track possibilities.

ECMWF Model Output track guidance (blue line deterministic, black is ensemble):

ECMWF_06L_2018091112

Read prior blogs on Florence if you missed them.

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EXPERIMENTAL PRODUCT Guikema Research UNIVERSITY OF MICHIGAN ENGINEERING:

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Follow me on Twitter @MellishMeterWSB.

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