Atlantic tropical disturbance 91L poses little threat

By: Dr. Jeff Masters , 2:15 PM GMT on April 21, 2011

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A tropical disturbance (91L) near 24N, 63W, midway between the Virgin Islands and Bermuda, is moving north-northwest at about 8 mph. The system's heavy thunderstorm activity has increased since yesterday, but 91L has an elongated and poorly-organized circulation, thanks to a hefty 80 knots of wind shear. The storm is over waters of 25°C, and these waters will cool to 24°C by Friday as the storm continues to the north-northwest. Before 91L reaches Bermuda, steering currents will reverse and force 91L to the south-southwest on Saturday, into a region of higher wind shear. The latest SHIPS model forecast predicts wind shear will drop to 50 knots over 91L by Friday, then increase again to 70 knots by Sunday. The high shear and relatively cool water temperatures will make it difficult for 91L to organize into a subtropical depression. I give 91L a 10% of becoming a subtropical depression. Climatology argues against 91L becoming the first named storm of the year; there has only been once 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 necessarily a harbinger of a active season ahead.


Figure 1. Morning satellite image of the Atlantic tropical disturbance 91L.

Jeff Masters

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Quoting hurricane23:


Hey mike!! Loving that WV view on GR earth..Wish I could afford it.


Hey Adrian!

Congratulations on your daughter!
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Quoting Levi32:


Keep in mind that most convection associated with subtropical storms is a direct result of instability/divergence from the ULL. You can't ask for fully tropically supported convection.


Exactly...
Member Since: August 21, 2008 Posts: 0 Comments: 7278
Quoting Levi32:


Keep in mind that most tropical convection associated with subtropical storms is a direct result of instability/divergence from the ULL. You can't ask for fully tropically supported convection.


Agree... From my view there's been no warm convective process going just purely baroclinic as I expressed earlier. Just hoping for some precip here
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437. JLPR2
I hope 91L slides a little to the south, we need a little rain here. :\
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Quoting aspectre:
Computer programming is as necessary and as basic a skill to the modern meteorologist as using a grease-pencil was to previous generations.
If ya can't write programs, ya gotta get someone else to do it for ya. And it's usually harder to use words to precisely describe what ya want an algorithm to do than it is to write that algorithm yourself.


if you say so....... lol
Member Since: August 21, 2008 Posts: 0 Comments: 7278
Quoting hurricane23:


Hey mike!! Loving that WV view on GR earth..Wish I could afford it.


Wait that was on Google Earth? What weather program is that?
Member Since: November 24, 2005 Posts: 635 Comments: 26547
Quoting Drakoen:

Ah no. I have never programmed beyond a very elementary level, though I certainly do not object to it. They don't just throw courses for the degree just for the heck of it. They want to make sure that we are well-rounded in the event that we may need to use it. It is only one class is programming that you will have to take, I wouldn't panic...too much about it.


Yeah, I know they do it so we will be well rounded, but I figure since I'm an adult and its college I should have the choice when it comes to things like that. I mean yeah most classes in the program should be covered, I just know that those who work with computer programming is not universally a meteorologist's job. Whereas all meteorologists work with, meteorology things, which need a lot of physics and calculus.
Although I don't like math, it is a very important part of the science. But I see computer programming as well, good for computer programmers but not for someone like me who plans to never use it.

Whatever though, that's just my prospective. Whenever I end up taking it I'll hate it but I don't let anything stop me from reaching my goal.
Member Since: August 21, 2008 Posts: 0 Comments: 7278
Quoting Stormchaser2007:
Dry air is not nearly as big of a problem for the circulation as it was last night.







Hey mike!! Loving that WV view on GR earth..Wish I could afford it.
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Quoting hurricane23:
Chances of this developing are slim to none... The convection seen on satellite is being induced by the interaction of the ULL in it's vicinity.All in all everything looks very baroclinic and SST's in the area are barely 26C. Hopefully this will enhance precipitation across SFL but I wouldn't get my hopes up.


Keep in mind that most convection associated with subtropical storms is a direct result of instability/divergence from the ULL. You can't ask for fully tropically supported convection.
Member Since: November 24, 2005 Posts: 635 Comments: 26547
Computer programming is as necessary and as basic a skill to the modern meteorologist as using a grease-pencil was to previous generations.
If ya can't write programs, ya gotta get someone else to do it for ya. And it's usually harder to use words to precisely describe what ya want an algorithm to do than it is to write that algorithm yourself.
Member Since: August 21, 2007 Posts: 0 Comments: 4860
Quoting KoritheMan:


Most global models barely show a discernible cyclonic signature at 850 mb when it reaches Florida. So yes.

Hey kori! The ECMWF has been wanting to carry a nice moisture surge into SFL early next week. You can see it on TPW.
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Quoting Jedkins01:



Only because you like computer programming... lol
I would beg do differ, there are plenty of meteorologists who don't use computer programming whatsoever. But that is how college is, there are going to be classes you have to take but will never actually use on your job. Computer programming has its usage of course but there are some scientific people like me who don't find any interest in it at all and don't plan on using it.

Therefore, it should be a grad program option if you ask me.
Ah no. I have never programmed beyond a very elementary level, though I certainly do not object to it. They don't just throw courses for the degree just for the heck of it. They want to make sure that we are well-rounded in the event that we may need to use it. It is only one class is programming that you will have to take, I wouldn't panic...too much about it.
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It's looking like maybe a near to above normal rainy season across SFL for those wondering. Based on past La Nina weakening to neutral summers, we could have some increase in southerly flow during parts of the rainy season, which could translate to wetter than normal. At least that's what the CFS and past years have shown.
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Quoting hurricane23:
Hopefully this will enhance precipitation across SFL but I wouldn't get my hopes up.


Most global models barely show a discernible cyclonic signature at 850 mb when it reaches Florida. So yes.
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426. JRRP


Member Since: August 16, 2007 Posts: 0 Comments: 5337
Quoting Drakoen:

I think it is important that all meteorologist have some understanding of computer programming at least as it pertains to meteorology. Fortran is good, even though it is old, at least from what I have heard from others.



Only because you like computer programming... lol
I would beg do differ, there are plenty of meteorologists who don't use computer programming whatsoever. But that is how college is, there are going to be classes you have to take but will never actually use on your job. Computer programming has its usage of course but there are some scientific people like me who don't find any interest in it at all and don't plan on using it.

Therefore, it should be a grad program option if you ask me, but what do I know, I'm just the fun loving guy with a passion for science caught in a nerds world :)
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Member Since: August 2, 2010 Posts: 21 Comments: 9695
423. JRRP
Quoting Stormchaser2007:
Olga 2007


91L:

that is what i said....!
Member Since: August 16, 2007 Posts: 0 Comments: 5337
Chances of this developing are slim to none... The convection seen on satellite is being induced by the interaction of the ULL in it's vicinity.All in all everything looks very baroclinic and SST's in the area are barely 26C. Hopefully this will enhance precipitation across SFL but I wouldn't get my hopes up.
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Quoting Drakoen:

That is incorrect. You are going to Florida State University and i'm assuming you have seen the FSU Meteorology Handbook. You will be required to take Meterological Computations (MET3220C): "This course covers the solution of meteorological problems using
computer and statistical programs; distributions of meteorological
variables; meteorological programming." You will be introduced to Fortran.


Oh God help me then, I guess I didn't look into that class much because FSU is the meteorology program I am going for... Dang. That will be the one class I am going to hate.... That is gonna suck, I hate working with anything beyond normal computer usage, and hell if I know what Fortan is, yuck.
Member Since: August 21, 2008 Posts: 0 Comments: 7278
check my new tropical blog page

Link
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Quoting alfabob:
I don't think the LLC is elongated, it is just in a broad counter-clockwise circulation. Still looks good on RGB, and structure is steadily improving. It's already developed, what would be the point of raising the chance?



The latest ASCAT pass shows otherwise. Note the defined trough extending from the circulation to the southwest and very little westerly winds in the southern half.


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Quoting Stormchaser2007:
Dry air is not nearly as big of a problem for the circulation as it was last night.







Sure there may be less dry air around shown in water vapor imagery, but note that with the flow around the upper level low, dry air now getting pumped directly into the core of the elongated circulation unlike last night where the upper level low was not driving dry air into the disturbance.
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Olga 2007


91L:
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Member Since: August 2, 2010 Posts: 21 Comments: 9695
Dry air is not nearly as big of a problem for the circulation as it was last night.





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Quoting cchsweatherman:


Keep in mind that the circulation is rather elongated and not well defined at this moment as shown with the most recent ASCAT pass posted earlier.


Im not saying that they should classify it, I just think that they should upgrade its chances of development to at least 30%.

Just needs to tighten up and maintain convection. Still has about 24 hours.
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Quoting 7544:


looking above dry air seems to be less also


Note the dry slot circulating around the upper low to the west and impinging on the disturbance. Dry air continues to be a major hindrance for this.
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407. 7544
Quoting sunlinepr:


looking above dry air seems to be less also
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Yep, quakes continue....
Link
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navy still conducting exercises

NMFC Norfolk Tropical Feed
Tropical Storm 82L (ZULU) Warning #06 - EXERCISE
By Maritime.CDO@navy.mil (NMFC CDO) from Fleet Weather Center Norfolk Virginia. Published on Fri, Apr 22, 2011.

Issued: Fri 22 Apr 2011 00:00Z
TC Warning Graphic
TC Warning Text
TC JMV Data
TC Gold Ovly
TC Warning Shapefile (zip format)
TC Google Earth (KMZ format)
FNMOC Satellite Data Tropical Cyclone Page
Tropical Storm 81L (XRAY) Warning #07 - EXERCISE
By Maritime.CDO@navy.mil (NMFC CDO) from Fleet Weather Center Norfolk Virginia. Published on Fri, Apr 22, 2011.

Issued: Fri 22 Apr 2011 00:00Z
TC Warning Graphic
TC Warning Text
TC JMV Data
TC Gold Ovly
TC Warning Shapefile (zip format)
TC Google Earth (KMZ format)
FNMOC Satellite Data Tropical Cyclone Page
Member Since: July 15, 2006 Posts: 169 Comments: 53296
Member Since: August 2, 2010 Posts: 21 Comments: 9695
Quoting Stormchaser2007:
Convection getting rather close to the center...

NHC might need a new TWO soon.



Keep in mind that the circulation is rather elongated and not well defined at this moment as shown with the most recent ASCAT pass posted earlier.
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Quoting altesticstorm011:
Looking at the SOI's it's amazing how weak the kelvin waves have been this winter and spring. I guess it's the negative-PDO at work?

And can anyone tell me how many AEW's that we've had now, including the one that just came off the coast? I haven't kept track.


None. They aren't AEWs.
Member Since: November 24, 2005 Posts: 635 Comments: 26547
401. 7544
Quoting Levi32:


It has the look of a sheared subtropical storm. Certainly better than a few others I've seen with names.


agree
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GOES E sounder winds still reveal a rather elongated trough to the south.

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Quoting Stormchaser2007:
Convection getting rather close to the center...

NHC might need a new TWO soon.



It has the look of a sheared subtropical storm. Certainly better than a few others I've seen with names.
Member Since: November 24, 2005 Posts: 635 Comments: 26547
Looking at the SOI's it's amazing how weak the kelvin waves have been this winter and spring. I guess it's the negative-PDO at work?

And can anyone tell me how many AEW's that we've had now, including the one that just came off the coast? I haven't kept track.
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Quoting Stormchaser2007:
Convection getting rather close to the center...

NHC might need a new TWO soon.



I'd agree. I don't understand why they don't just issue a new Special TWO every six hours as long as the disturbance exists.
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all so early season storms dos not mean it will be a busy year it be a bust year or a vary busy year we this have too wait and see
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A magnitude5.6quake struck 65.5degrees(ENE) and 14miles from FukushimaDaiichi

Earlier a magnitude6.1quake struck 97.6degrees(E) and 42miles from centralTokyo
Member Since: August 21, 2007 Posts: 0 Comments: 4860
Convection getting rather close to the center...

NHC might need a new TWO soon.

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392. 7544
cmc says rain for fla too from 91l

Link
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FYI, here in Naples,FL, we are actually 5 degrees above normal. Should be 77 but it's 82.
Quoting wxwonder1:
It looks like there are some above normal SSTs present around and in front of 91Ls potential forecast track. The most notable just south of the Florida peninsula.
Quoting wxwonder1:
It looks like there are some above normal SSTs present around and in front of 91Ls potential forecast track. The most notable just south of the Florida peninsula.
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Invest 91L

Based upon the latest RGB imagery, the center of this disturbance exists around 25.6 N and 63.0W. The disturbance appears to be undergoing gradual organization as thunderstorms have developed and becoming more co-located with the somewhat elongated circulation. Some decent low level inflow into the disturbance is noted to the southeast of the circulation center with a notable band with diffuse showers.

Recent enhanced IR imagery shows that convection has deepened within the past few hours in a tight cluster very near the circulation center. Also, you can clearly see that the circulation remains somewhat elongated in a near north-south orientation.

Water vapor imagery shows very well the struggles the disturbance continues to encounter in attempts to develop further. An upper level low can be clearly seen very near to the west. This upper level low has been imparting some hostile wind shear as noted by the immense cloud debris spreading northward. In addition, dry air continues to get pumped into the disturbance from the south by the clockwise flow around the upper low. The disturbance has been able to sustain some due to its connection with deeper moisture well to the south as explained earlier with a notable inflow band.

All in all, Invest 91L has been and continues to attempt slow organization and may have a chance, albeit not high, to become something more in the next 24 hours.
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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.