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Decoupling strikes again: Karen “decapitated”

October 4th, 2013 - 11:31 pm

As expected, the weather story of the day was not Tropical Storm Karen, but a damaging tornado outbreak in Nebraska, Iowa and extreme southeastern South Dakota, and an epic early-season blizzard in Wyoming and western South Dakota (up to 3 feet of snow already in Lead, SD, and maybe 5 feet total before it’s over!). Both of these events were caused by the same storm over the Plains, which absolutely dwarfs puny Karen in the Gulf right now:

That said, this blog’s focus is on tropical weather (notwithstanding my #SNOWFIREICANENADO references), so I’ll defer to Mike Smith, Jeff Masters and others to wrap up those events.

As for Karen, well, it looks like she’s just about finished. I tweeted earlier (shortly after my last blog update) that, according to the National Hurricane Center’s 5pm EDT discussion, Karen had a chance to restrengthen after 24 hours if she could hold together that long, but first there was a significant chance the storm could completely “decouple,” with its thunderstorms totally separating from its low-level center — much like what happened with Flossie and Gabrielle earlier this season. Flash forward six hours, and it appears that is indeed happening:

The NHC’s 11pm EDT discussion explains:

KAREN HAS BEEN DECAPITATED BY STRONG SOUTHWESTERLY SHEAR AND NOW CONSISTS OF A VERY TIGHT SWIRL OF LOW CLOUDS WITH SOME LINEAR CONVECTION TO THE EAST OF THE CENTER. DATA FROM RECONNAISSANCE PLANES INDICATE THAT THERE IS A WELL-DEFINED CIRCULATION…BUT THE
WINDS ARE GRADUALLY DECREASING. ON THIS BASIS…THE INITIAL INTENSITY HAS BEEN LOWERED TO 40 KNOTS IN THIS ADVISORY. TROPICAL STORMS RARELY RECOVER AFTER BEING STRONGLY DAMAGED BY SHEAR…ESPECIALLY IF THE ENVIRONMENT IS AS DRY AS IT IS OVER THE WESTERN GULF OF MEXICO.

Officially, the NHC is keeping Karen as a tropical storm for now, and even forecasting marginal strengthening after 24 hours, given its “vigorous circulation” at low levels. However: “AS PREVIOUSLY INDICATED…AN ALTERNATIVE SCENARIO IS THAT KAREN REMAINS DECOUPLED FROM THE DEEP CONVECTION AND WEAKENS AT A FASTER PACE. THE LATTER SCENARIO IS BECOMING MORE REALISTIC GIVEN THE CURRENT ORGANIZATION OF THE CYCLONE.” Reading between the lines, and in light of respected meteorologists’ thoughts on Twitter, it’s pretty clear that rapid weakening and dissipation is what the forecasters truly expect, but the NHC is going to wait a few more hours to be sure before making that official.

Here at Weather Nerd, though, we don’t stand on ceremony, so I am hereby treating this storm as basically “dead until proven alive.” Accordingly, this will be my last blog update on Karen unless I wake up in the morning and learn to my surprise that she’s making a comeback. Even if that does happen, my updates will be limited because of weekend family plans — but I’ll at least keep tweeting about Karen if she survives, which you will be able see below. Once Karen officially dies, however, I’ll go back on Twitter #hiatus, and you won’t hear from me again until another U.S. tropical threat arises.

As always, Amy Sweezey’s Twitter list of “Wx Tweeps” is a good resource in my absence.

Anyway, without further ado, here are my most recent tweets, updating live:


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I'm certain this happened because I stayed up late & drove the 40 miles to my girlfriend's place to help her get ready for the storm.
45 weeks ago
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