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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Foreca update:COC near 24.8N 64.8W,strongest winds near 42-44mph(what?)
Member Since: May 19, 2010 Posts: 0 Comments: 351
Quoting hydrus:
My Dads first car was a Desoto (not sure of the year ). Mine was a 1967 Cutlass Supreme. 330 Jetfire engine, 2 speed PowerGlide transmission. 320 Horses off da show room floor...I wish I had that one back.


You could probably retire. I will tell you my first new car off the blog.
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Quoting EYEStoSEA:


Yeah, and I'd be a rich ole belle, if I had that Hornet....oh well.....:)
My Dads first car was a Desoto (not sure of the year ). Mine was a 1967 Cutlass Supreme. 330 Jetfire engine, 2 speed PowerGlide transmission. 320 Horses off da show room floor...I wish I had that one back.
Member Since: September 27, 2007 Posts: 1 Comments: 19501
Quoting Grothar:


Sad thing was, they weren't bad cars. The few still around are worth a fortune.


Yeah, and I'd be a rich ole belle, if I had that Hornet....oh well.....:)
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Quoting Grothar:


Sad thing was, they weren't bad cars. The few still around are worth a fortune.
they sold a Tucker last night for over a million dollars..I heard that the Edsel,s were exceptional cars.
Member Since: September 27, 2007 Posts: 1 Comments: 19501
Quoting Grothar:


Ok, see you in about two weeks.
Ouch.Poor T.S......That graph has almost 10 inches of rain over a large part of the Mississippi Valley...No matter what, there will be flooding along with the adverse weather..
Member Since: September 27, 2007 Posts: 1 Comments: 19501
Quoting hydrus:
Dad told me..I thought to myself being Henry Ford,s son would have been more than enough to keep Edsel,s flying off the showroom floor...Guess not.


Sad thing was, they weren't bad cars. The few still around are worth a fortune.
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Quoting TampaSpin:
Need my lots of beauty sleep! Good nite all!


Ok, see you in about two weeks.
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Pray for instability, she's dry as a bone.


Member Since: January 30, 2010 Posts: 0 Comments: 3259
Need my lots of beauty sleep! Good nite all!
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Quoting TampaSpin:


Now that is really serious. I hope hydrus doesn't see it.
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Big Time Flooding Problems coming to the Mississippi Valley.......this might get very ugly!
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Quoting TampaSpin:





I didn't ask for color blind test.
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Quoting RastaSteve:
To do that type of damage in their neighborhood I would say this was an EF-3 or EF-4.


I was actually watching the velocities at that time of the KO cell. It will probably be rated an EF2. Not much can withstand a direct hit, even from a weak tornado.
Member Since: January 30, 2010 Posts: 0 Comments: 3259
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Quoting RastaSteve:
Just ot give you an idea of how strong this tornado was these houses are brick homes that are destroyed in a ritzy area of suburban STL.


Brick homes are one of the worst types of structures in tornado prone areas. Brick is not that strong; unless it is hurled in one's direction.
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Heart goes out to those in St Louis.
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Quoting EYEStoSEA:


We had a Hudson Hornet......lol...gotcha


My goodness, and you are still able to type? LOL My father had a Model A. I can remember riding in it.
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Quoting Grothar:


Tampa, we need a little more color variation. Blue as a center focus went out with Gainsborough.



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Quoting sunlinepr:


Hey, Make it move away from us...



If you insist. Just thought you guys would like a little rain in el Yunque.
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Quoting Grothar:


That happens a lot. It is not a waste of time. Pattern studies may imply many different scenarios, but does not necessarily mean that if the end result is not what you expected, it could be a different pattern. That is one of the exciting things about science. There is always another variable when you least expect it. You think they just designed a car the first time out. I am sure many plans have been scrubbed. Anyone here over 50 has to remember the Edsel. LOL
Dad told me..I thought to myself being Henry Ford,s son would have been more than enough to keep Edsel,s flying off the showroom floor...Guess not.
Member Since: September 27, 2007 Posts: 1 Comments: 19501
Quoting Grothar:


That happens a lot. It is not a waste of time. Pattern studies may imply many different scenarios, but does not necessarily mean that if the end result is not what you expected, it could be a different pattern. That is one of the exciting things about science. There is always another variable when you least expect it. You think they just designed a car the first time out. I am sure many plans have been scrubbed. Anyone here over 50 has to remember the Edsel. LOL


We had a Hudson Hornet......lol...gotcha
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Quoting CyclonicVoyage:


Really at a loss here. All the pattern studies I was doing in my spare time have all been scrubbed.

Last neutral was 2005. Actually a smooth neutral this year too, not a drastic change like the last 5 years.


That happens a lot. It is not a waste of time. Pattern studies may imply many different scenarios, but does not necessarily mean that if the end result is not what you expected, it could be a different pattern. That is one of the exciting things about science. There is always another variable when you least expect it. You think they just designed a car the first time out. I am sure many plans have been scrubbed. Anyone here over 50 has to remember the Edsel. LOL
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Quoting Grothar:


Tampa, we need a little more color variation. Blue as a center focus went out with Gainsborough.
This is what I am talking about when I say a major flooding event. Look at the chart at the bottom right of your screen. ( Watch the Mississippi River and surrounding areas)..Link
Member Since: September 27, 2007 Posts: 1 Comments: 19501
Magnitude 6.9 Quake - Solomon Islands

* This event has been reviewed by a seismologist.

Magnitude 6.9
Date-Time * Saturday, April 23, 2011 at 04:16:55 UTC
* Saturday, April 23, 2011 at 03:16:55 PM at epicenter

Location 10.349°S, 161.233°E
Depth 81.6 km (50.7 miles)
Region SOLOMON ISLANDS
Distances 76 km (47 miles) W of Kira Kira, San Cristobal, Solomon Isl.
173 km (107 miles) SE of HONIARA, Guadalcanal, Solomon Islands
184 km (114 miles) SSE of Auki, Malaita, Solomon Islands
2084 km (1294 miles) NNE of BRISBANE, Queensland, Australia
Location Uncertainty horizontal +/- 14.4 km (8.9 miles); depth +/- 7.9 km (4.9 miles)
Parameters NST=393, Nph=393, Dmin=173.7 km, Rmss=0.86 sec, Gp= 22°,
M-type=regional moment magnitude (Mw), Version=7
Source * USGS NEIC (WDCS-D)
Event ID usc0002xcx

No current Tsunami warning according to NOAA
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Quoting RastaSteve:


yeah I am sure these images of STL come daylight will be insane as they literally said half of there neighborhood is gone. Thank God they are fine!


Sad news coming out of STL tonight and other areas down stream I'm sure.
Member Since: January 30, 2010 Posts: 0 Comments: 3259
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Quoting TampaSpin:


Tampa, we need a little more color variation. Blue as a center focus went out with Gainsborough.
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Quoting RastaSteve:
My family lives where that tornado hit in chester county and the damage is devastating. Luckly my wife's side of the family is fine but a few blocks from them is complete devastation. Infact we were told it looked as if a BOMB went off. They actually heard the tornado and went for cover. No visuals of the tornado as it was dark but the area is pretty much a loss near them but luckily there side of the neighborhood did not get hit. I am stunned by what happened there as we were at dinner when we got the call from them of the extent of the damage in their area.
Tornadoes at night..That has to be terrifying.
Member Since: September 27, 2007 Posts: 1 Comments: 19501
Quoting TampaSpin:


That must be one of those $$$ visuals.....NICE ! Looking good on the "cycle"....how fun that must be :)
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Quoting Grothar:


Look, sun. Mine moves.



Hey, Make it move away from us...

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Quoting Grothar:


The entire year has been strange. I guess we forget all the ice storms and frigid temperatures that started the year. And now this constant barrage of storms. Very active pattern.


Really at a loss here. All the pattern studies I was doing in my spare time have all been scrubbed.

Last neutral was 2005. Actually a smooth neutral this year too, not a drastic change like the last 5 years.
Member Since: January 30, 2010 Posts: 0 Comments: 3259
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Quoting Jedkins01:
A cold front clearing through Central Florida this Thursday? Not sure if I'm buying that. The high in the Atlantic seems way too strong for that, I Mean, it might happen but a stalling front around here or to the north of here sounds like a more likely bet considering the last cold front hasn't clear through here in like 2 weeks.


We've had strong cold fronts come down in May. You are just too young to remember. LOL How you doing, Jed? Still being rambunctious?
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Quoting Jedkins01:


that doesn't look very beneficial to me, lol, and that's 144 hours out...
I did type "could" in there for a reason smart ass..Good evening Jed...Hope you are doing good...:)
Member Since: September 27, 2007 Posts: 1 Comments: 19501
Quoting Jedkins01:


that doesn't look very beneficial to me, lol, and that's 144 hours out...


We're thinking positive here, Jed...lol...:)
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Quoting flsky:


It already has been.
It already has been what?
Member Since: September 27, 2007 Posts: 1 Comments: 19501
Quoting hydrus:
Florida could get some beneficial rain from this....144 hours out..


that doesn't look very beneficial to me, lol, and that's 144 hours out...
Member Since: August 21, 2008 Posts: 0 Comments: 6832
Quoting EYEStoSEA:
Oh Yeah, some great visuals for sure!!
Great visuals.....:)
Member Since: September 27, 2007 Posts: 1 Comments: 19501
556. flsky
Quoting hydrus:
That is another area that could use a breather from severe weather..


It already has been.
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A cold front clearing through Central Florida this Thursday? Not sure if I'm buying that. The high in the Atlantic seems way too strong for that, I Mean, it might happen but a stalling front around here or to the north of here sounds like a more likely bet considering the last cold front hasn't clear through here in like 2 weeks.
Member Since: August 21, 2008 Posts: 0 Comments: 6832

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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.