Irma path far from certain, but FLA… 

Posted: 8:33 am Tuesday, September 5th, 2017

By Kirk Mellish

Large and dangerous top category Irma will continue to impact the Caribbean islands this week, but when where and what the WORST of the storm will do to the United States remains uncertain. However, FLORIDA is clearly the current greatest worry, at least for starters.

As you can see, where and WHEN it starts to turn north will have huge implications for Florida AND Georgia/Carolina’s.

The pattern is highly complex and small changes in subtle features aloft will have big changes in the strength and future path of Irma:


Canadian ensemble is an outlier:


Good tip from NHC: focus on cone of uncertainty, NOT the center or eye location. Average track errors are 175 miles at Day 4, 225 miles at Day 5!

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Strongest winds in Atlantic hurricane since Wilma in 2005, only 6 other Atlantic hurricanes got this strong on record.



GFS ensembles bunched closer over FL while the ECMWF has much greater spread (uncertainty) in the spaghetti plot:

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NHC seems to be following the “Megacluster” ensemble:

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The 06Z ensembles came in with an east shift, although I am not a fan of 06 runs, worth watching:

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I would factor in the 12Z GFS ensembles:

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Warm waters in Ocean surface are the FUEL:

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As per NHC’s official list of landfalling going back to 1851, continental USA has never had two Cat 4s in one year.

Just about all of the generally reliable guidance keep as a category 4 or more for the next 5 days- Super rare Atlantic forecast! Only 4 storms have done this in the past 50 years…so about a once per decade run of prolonged intensity (if it verifies).

Has the “buzzsaw” look on Satellite:

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The max winds verified puts it in rare company:


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Hurricanes Allen and Ivan hold the Atlantic record for longest time at Category 5 strength (3 days). Irma may approach that record. Irma is the strongest Atlantic storm since Felix in 2007 on winds and lowest pressure since Igor in 2010.

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ECMWF on left, GFS ensemble on right:

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Irma is the 17th hurricane in the Atlantic on record to have max winds >= 175 mph. Atlantic max wind record is Allen (1980) at 190 mph.

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Mountain effect would be bad for them, but good news for U.S.:

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Previous blog post on Irma here