Invest 91L more organized, but has little time to develop

By: Dr. Jeff Masters , 2:31 PM GMT on April 22, 2011

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Hurricane season is more than a month away, but we have a tropical disturbance (91L) typical of what one might see in June or November. 91L is spinning over the waters a few hundred miles south of Bermuda, and has improved considerably in organization since yesterday, thanks to a drop in wind shear. The latest SHIPS model output is showing shear of 40 - 55 knots over 91L, but shear analyses from the University of Wisconsin CIMSS group is showing lower shear values of 20 - 30 knots over the main circulation center and to 91L's north, where the heaviest thunderstorms are. The system has a warm core at low levels, but a trough of low pressure lies over the storm at upper levels, and this trough is pumping cold, dry air into 91L, making it not completely tropical. One characteristic of subtropical systems like 91L is the presence of the main band of heavy thunderstorms removed several hundred miles from the circulation center, and 91L fits that description. 91L has two centers of circulation competing to be dominant, and this competition is slowing the storm's development. The storm was headed north at 5 - 10 mph early this morning, but that motion has halted, and 91L appears to be moving more south-southwesterly now, away from Bermuda. Sea surface temperatures are 23°C, which are very cold for a tropical storm to form in, but could support development of a subtropical storm.

As 91L moves south today, shear will steadily rise, and the storm likely has only until Friday night before shear grows too high to permit development. NHC is giving 91L a 20% chance of developing into a subtropical or tropical depression, which is a reasonable forecast. There has been only been one named April storm in the Atlantic since 1851, Tropical Storm Ana of 2003. The formation of a tropical disturbance at this location this time of year is unusual, but is not a harbinger of a active season ahead. Had this been going on in the Caribbean, that would be a different story.


Figure 1. Morning satellite image of the Atlantic tropical disturbance 91L. Note the two centers of circulation competing to be dominant. I expect the northern center will become dominant.

Jeff Masters

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Quoting Ameister12:
What's going on in St. Louis. I heard a tornado hit there.


Extensive damage reported @ Lambert Int. Airport. Glass blown into terminal C, minor injuries reported and another terminal with damage. Homes destroyed multi level buildings collapsed with people trapped. 2 confirmed tornado's, one north & one south of downtown.
Member Since: January 30, 2010 Posts: 0 Comments: 3259
Quoting cat5hurricane:

Hey, do you blog on CP?

No unfortunately I am only an unknown engineer in the lower reaches of Europe who has a little bit of an idea about what is going on!
I'd love to advance a few theories, if anybody had time to listen.
My life long ambition is to achieve total synthesis with global weather systems.
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Quoting KEEPEROFTHEGATE:
the april tease will be gone may get some widly scattered showers from it and a little breeze that will be it
I was really hoping for 1-2 inches between Sun and Tues... just enough to give the ground a thorough wetting down....

Anyway, it ain't over til the fat lady sings, and I don't hear any women singing right now....
Member Since: October 25, 2005 Posts: 19 Comments: 20733
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It looks like Mother Nature is taking a new medication or something, what with all this weather happening early, and all these quakes...
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Quoting BahaHurican:


Starting to wonder if there'll be enough left to bring moisture...
the april tease will be gone may get some widly scattered showers from it and a little breeze that will be it
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Quoting cat5hurricane:

I wouldn't exactly call that and some broken glass 'major damage'.


NO, not what you just described. But the entire roof blown off Concorce C I would probably classify Major damage as reported by fire crews on scene.
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What's going on in St. Louis. I heard a tornado hit there.
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Starting to wonder if there'll be enough left to bring moisture...
Member Since: October 25, 2005 Posts: 19 Comments: 20733
Just hanging out off the top of the parking garage at Lambert Field ( ST LOUIS )

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airport was full of easter travelers
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damage at lambert airport at st louis and in north st louis. homes destroyed in south st louis from another tornado.. 2 tornados are about 25 miles apart and is now in western illinois.
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Blame it on the blogs Groth......


ST. LOUIS (KMOV) – Brutal storms that whipped through north St. Louis County Friday night caused extensive damage to St. Louis Lambert International Airport.

Airport spokesperson Jeff Lea says high winds caused the glass to break and blow into Concourse C and Terminal One on the upper floors. Minor injuries were reported.

A News 4 viewer also reported damage as seen through an airport photo showing a vehicle dangling over a parking garage wall.

There are also reports of damage to other vehicles in the airport parking lots. Emergency vehicles are on the scene.
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Quoting Grothar:
Here is the vorticity.




i think ya might want to stick with the black and white world :)
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Quoting cat5hurricane:

When is your buddy JFLORIDA coming back?


Don't know. And thanks for letting me know who my buddies are :-|
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We can only wish you the wishes of those who are not there to wish with you.
To those of the USA and neighbouring regions, please hold on and survive stronger through any trial you are enduring.
God speed to tranquility. Please surmount whatever blocks are placed to trip you.
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Quoting Seastep:
I know exactly what you were doing Gro. ;)


Just like old time, eh. Seastep? Any word on St. Louis? Situation doesn't look to good. Haven't seen anything on the TV yet.
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Quoting CyclonicVoyage:



You sure you know how to do this Grothar???


Yes I do you twit. LOL But they are having a problem with their website and the images do not always post properly.


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Here is the shear

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I know exactly what you were doing Gro. ;)
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Quoting Grothar:


If you can't start a little argument on the blog what's the sense.


Monty Python - Argument Clinic
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Quoting Grothar:
Here is the vorticity.




Here is the shear:




You sure you know how to do this Grothar???
Member Since: January 30, 2010 Posts: 0 Comments: 3259
Here is the vorticity.




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What do we have to do for a little laugh around here Grothar?
Member Since: January 30, 2010 Posts: 0 Comments: 3259
Quoting Hurricanes101:


the red lines are showing vorticity, which shows you the that the vorticity with 91L is very strong

wind shear is the yellow lines



I was being sarcastic, I know. 91L has improved it's circulation greatly today. Interesting to note the remnant circulation is kicking back up in the NE quad of 91L, though it had been absorbed earlier. Kinda highlights the disorganization though.
Member Since: January 30, 2010 Posts: 0 Comments: 3259
Quoting Seastep:


That's not wind shear. That's vorticity.


I know sea. That is why I posted both. Just wanted to see who was paying attention. You know me by now. LOL. If you can't start a little argument on the blog what's the sense.
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Quoting emcf30:
Major damage now being reported at Lambert Airport. C Terminal destroyed, Main terminal major damage



For those who don't know that is St. Louis International. Man, the tornadoes this year.
Member Since: January 30, 2010 Posts: 0 Comments: 3259
Quoting CyclonicVoyage:


100kts of windshear???

Why doesn't the NHC just name the wind shear. It does cause a lot of deaths every year.


the red lines are showing vorticity, which shows you the that the vorticity with 91L is very strong

wind shear is the yellow lines
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How is everyone? Happy Easter.

Been crazy busy at work.
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CBS News live
Link
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Quoting Grothar:
Just got word that the CIMSS website has been fixed. Here is the first image. Notice the 100kt windshear.




100kts of windshear???

Why doesn't the NHC just name the wind shear. It does cause a lot of deaths every year.
Member Since: January 30, 2010 Posts: 0 Comments: 3259
the yellow lines on the CIMSS site is the shear, I believe the red is the vorticity

looking at the up to date shear map I use on CIMSS, it indicates 20-30 knots over the center, not 100
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Major damage now being reported at Lambert Airport. C Terminal destroyed, Main terminal major damage
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Quoting Grothar:
Just got word that the CIMSS website has been fixed. Here is the first image. Notice the 100kt windshear.




That's not wind shear. That's vorticity.
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Quoting KEEPEROFTHEGATE:
it has taken me years to master the plymouth state its a great site little difficult learning all the different ways to get info but once in its good easy info to get


If they would add a little color, the site would be much more interesting. I lived in a black and white world for so long, that I want more color.
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On and off but, surely there. Cell K0, figures.
Member Since: January 30, 2010 Posts: 0 Comments: 3259
Link

Multiple persons trapped inside various buildings that are collapsed. Major damage being reported by various commands throughout the area. Live audio of rescues.
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Quoting Grothar:
Just got word that the CIMSS website has been fixed. Here is the first image. Notice the 100kt windshear.


chomp chomp chomp chomp burp
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20 folks trapped in Collapsed Homes in N. St. Louis, TWC reports
Member Since: July 3, 2005 Posts: 414 Comments: 125613
Quoting cat5hurricane:

You really love your Plymouth State there, chief.
it has taken me years to master the plymouth state its a great site little difficult learning all the different ways to get info but once in its good easy info to get
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Just got word that the CIMSS website has been fixed. Here is the first image. Notice the 100kt windshear.


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About JeffMasters

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.