Isaac gets complicated: Two circulation centers; Forecast tracks diverge

Dual centers observed today inside Tropical Storm Isaac

Growing divergence in various model forecast tracks

“Cone of uncertainty” grows bigger for Isaac

Westward trend? Overall in many model forecast tracks

Gulf of Mexico increasingly “in play” for Isaac landfall

Occasional rain & thunder & some sunshine for the opening weekend of the 2012 Minnesota State Fair

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Source: Twin Cities NWS

Isaac gets complicated:

I had a sense the tightly focused model forecast tracks yesterday were too good to be true.

Tropical Storm Isaac is throwing forecasters some curve balls today.

Two distinct centers of rotation (or vorticity) appeared inside Isaac Wednesday. The twin centers are “dueling” for overall control of what will eventually become the center of Isaac.

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Source: NOAA

Satellite images show one strong center swirling in the southwest part of the storm. A second defined center spins to the northeast.

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Source: NOAA

The appearance of twin centers poses some problems for computer models.

-Which center will ultimately emerge as the center of Isaac?

-What will the exact position of that center be in 24 hours?

-How strong will that center be?

-Which center is the model supposed to track?

Twin centers; multiple solutions:

The emergence of two vorticity centers in Isaac has thrown a major monkey wrench into the forecast tracks for various forecast models.

What was a “tight grouping” and high degree of consensus on forecast tracks Tuesday, turned into a wide range of possible tracks and intensities by late Wednesday.

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Source: NOAA via WxUnderground

The “official” NHC track shifts Isaac slightly west.

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Source: NHC

It appears that different models have locked onto the different centers with Isaac, and tracked them accordingly.

The NAM has grabbed the northern swirl and takes Isaac on a northward track, taking the storm east of Florida.

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The Euro continues the trend of favoring a left leaning track, and steers a powerful Isaac into the central Gulf. This track would pose a bigger threat to New Orleans than Tampa.

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Source: College of DuPage Weather Lab

The GFS plays the middle, with a potent hurricane sideswiping Florida’s Gulf Coast Monday & Tuesday.

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With so many possible track solutions that either bring Isaac over storm disrupting mountains or keep him over storm supercharging warm open water, accurate intensity forecasts become almost futile at this point.

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Overall the forecast for Isaac now looks like somebody just took a neatly stacked deck of cards and threw them into the air.

We may need another 24 hours at least to see which card comes up.

Stay tuned. Tracking Isaac may get more complicated before a credible soultion is clear.


  • Chris

    Large scale weather events tend to have weather trend effects far away from the actual event. I’m thinking el Nino/Nina, Bermuda high, polar circulations, cold in Siberia – warm here, etc. (I’m not a meteorologist so pardon if the examples are not accurate) Where I’m going is the tracks of Isaac all push directly at us here in MN. Of course it or the remnants won’t reach us. But with hurricanes in the SE does that push a certain pattern in our direction. I imagine the jet stream is pushed North so does that keep us in the nice and sunny area because lows can’t get to us? When they pull out to sea after going through the SE does that drag Canadian/polar air towards us giving us cooler than average? Or are hurricanes locally significant but don’t have the scale to really effect things outside the region they hit. Hopefully, the question makes sense.

  • Walter Weller

    Unless you’re near a big body of water that can be pushed onto you, hurricanes are not a big deal. Trees down, power out, roof damage, that’s about it. Been there, done that, several times. If you’re on low ground near the coast, though, you shouldn’t be. Move. Why’d you settle there in the first place?