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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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.
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Florida could get some beneficial rain from this....144 hours out..
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Quoting CyclonicVoyage:



I see the big H is making it's way down for the May bedding. Man, it's been 6 years since the last neutral, have to do some studying this year. Factoring in climate change, is it really worth it though?


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.
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Quoting hydrus:
This is just off the press(so to speak) This is a large and slow moving system. Which means a flooding event is almost a certainty. And to top it off, it will spark 3 full days of tornadoes and severe thunderstorms.


Lawdy, Lawdy.....but thanks for the reply :) You keep safe, I'll do the same..
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Quoting TampaSpin:


Most would if they was smart.........LOL........hey Grothar!


Yo, big T! Things are starting off interesting. Just feel bad so many people have to suffer. Any one of us could be in their shoes. I always think that when I see these things. Hope you doing well.
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Quoting CyclonicVoyage:



I see the big H is making it's way down for the May bedding. Man, it's been 6 years since the last neutral, have to do some studying this year. Factoring in climate change, is it really worth it though?
I noticed that. It reminds me of 1995 very much. The rainy season kicked in with a lot of severe thunderstorms right away.
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Oh Yeah, some great visuals for sure!!
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Quoting EYEStoSEA:


Hydrus, I've been out of touch today....is that system suppose to move SE thru TN and Ms ?
This is just off the press(so to speak) This is a large and slow moving system. Which means a flooding event is almost a certainty. And to top it off, it will spark 3 full days of tornadoes and severe thunderstorms.
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Quoting Grothar:


He's been avoiding me lately. Must have been something I said.


Most would if they was smart.........LOL........hey Grothar!
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Quoting sunlinepr:


Look, sun. Mine moves.

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Quoting emcf30:


I need to scan and post so pics one day. I was responding to the first touch down reports in Campbell city at the Good Samaritan Village then I saw the Tornado hit the fair grounds and then the RV park. It was about 11:30 or so at night. Pulled up on the scene could not believe my eyes
You see these disasters up close and in detail..Some people would not be able to handle that...You have to be of strong character for that type of work..jmo
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Quoting hydrus:
If this system becomes even more negatively tilted than the models are hinting at, there will be some very strong tornadoes. I do not like the little "L" at the end of the squall line either. It seems like every time that happens we get almost double the rain...



I see the big H is making it's way down for the May bedding. Man, it's been 6 years since the last neutral, have to do some studying this year. Factoring in climate change, is it really worth it though?
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Quoting hydrus:
If this system becomes even more negatively tilted than the models are hinting at, there will be some very strong tornadoes. I do not like the little "L" at the end of the squall line either. It seems like every time that happens we get almost double the rain...


Hydrus, I've been out of touch today....is that system suppose to move SE thru TN and Ms ?
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Quoting emcf30:


I need to scan and post so pics one day. I was responding to the first touch down reports in Campbell city at the Good Samaritan Village then I saw the Tornado hit the fair grounds and then the RV park. It was about 11:30 or so at night. Pulled up on the scene could not believe my eyes


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Quoting IFuSAYso:
Atoka county, OK may be FEMA declared for individual assistance soon. It is declared a major.
That is another area that could use a breather from severe weather..
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Al is about to get declared for Indev assistance, currently its on standby for PB.
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Quoting IFuSAYso:
Atoka county, OK may be FEMA declared for individual assistance soon. It is declared a major.


Several counties in Ms are still waiting, also...many need it...hopefully will hear soon..
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If this system becomes even more negatively tilted than the models are hinting at, there will be some very strong tornadoes. I do not like the little "L" at the end of the squall line either. It seems like every time that happens we get almost double the rain...
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Quoting Grothar:


I still think that was one of the worst outbreaks we ever had. It really was tragic. One of my cousins daughter was badly injured during that. Still has a large scar on her forehead.


I need to scan and post so pics one day. I was responding to the first touch down reports in Campbell city at the Good Samaritan Village then I saw the Tornado hit the fair grounds and then the RV park. It was about 11:30 or so at night. Pulled up on the scene could not believe my eyes
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Tornado causes injuries at St. Louis airport
By JIM SALTER, Associated Press 26 mins ago

ST. LOUIS- Authorities say at least five people have been treated for minor injuries after an apparent tornado ripped through Lambert Field in St. Louis.

The storm lifted a roof off the terminal and sent plate glass flying everywhere. Airport spokesman Jeff Lea says four people were taken to the hospital with minor injuries, and another person was treated at the scene.

Lea said the airport was shut down Friday night and planes were diverted to other locations.

Lea said passengers from at least two planes were stranded briefly on the Lambert tarmac because of debris. They were eventually taken away by buses.

Several people at Lambert Airport in St. Louis were injured Friday after an apparent tornado touched down, spewing debris over the airfield, bursting glass in the concourse and damaging cars atop a parking garage.

The tornado was part of a series of strong storms that struck central and eastern Missouri. Unconfirmed tornadoes were reported in several counties in the St. Louis area.

Link
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Atoka county, OK may be FEMA declared for individual assistance soon. It is declared a major.
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Quoting Grothar:


A lot of schools alternate. There will be tons down here next week.


Gotcha. For the kids up in PBC, it was this week.
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Quoting hydrus:
1998 was the year of those deadly tornadoes..Killed over 40 people in and around the Kissimee area. I still have the newspaper from that day.


I still think that was one of the worst outbreaks we ever had. It really was tragic. One of my cousins daughter was badly injured during that. Still has a large scar on her forehead.
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Quoting hydrus:
1998 was the year of those deadly tornadoes..Killed over 40 people in and around the Kissimee area. I still have the newspaper from that day.


Yep, Feb 1998. Then a couple of months latter, we were on fire. That was a weird year flooding from Dec - March then in about 1 to 2 months we were bone dry. One of the worst fire outbreaks in Fl history.
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Quoting caneswatch:


Uhhh........Wasn't that this week?


A lot of schools alternate. There will be tons down here next week.
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Quoting emcf30:


Reminds me of 1998 here.
1998 was the year of those deadly tornadoes..Killed over 40 people in and around the Kissimee area. I still have the newspaper from that day.
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Quoting emcf30:


Glad I can make you laugh.


Bet you're good at math, too! As long as you remember the hospital rule. LOL
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Has anyone heard of any damage reports to the hotels to the South of the airport. These areas should have been impacted more than Lambert.
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Quoting Grothar:


Ha. Have the storms been going around you? Poor hydrus has been getting banged left and right for weeks. We haven't had so much as a breeze. Looking forward to a rainy week. Too bad in a way, because a lot of people here for Easter Week.


Uhhh........Wasn't that this week?
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Quoting Grothar:


Ha. Have the storms been going around you? Poor hydrus has been getting banged left and right for weeks. We haven't had so much as a breeze. Looking forward to a rainy week. Too bad in a way, because a lot of people here for Easter Week.


Been dodging tornadoes and storms for a while now, I've been lucky, other family members, not so good. In Ms , we learn young that in order to get sufficient rainfall in the spring and summer, you must take the bad with the good.....problem is , as I'm getting older, I dont dodge as well, ya know...
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Quoting Grothar:


Alive. Thanks for asking. And you? Chuckled at a few of your comments today.


Glad I can make you laugh.
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Quoting emcf30:
Hey Grothar, how you doing tonight?


Alive. Thanks for asking. And you? Chuckled at a few of your comments today.
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Quoting hydrus:
...Check dis out....Link


Reminds me of 1998 here.
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Quoting hydrus:
Redecorated.lol... In 1983 I was visiting Melbourne when T.S.Barry was suppose to cause a ruckus but fizzled before moving ashore.


I knew I was screwed when I was watching Cooper Anderson
broadcasting live from the Intracoastal Marina about 1/2 mile from my house. That place was destroyed. I lived on the water on Crane Creek and the Indian River. Glad I sent my family to Jax to my sisters house. We lived in the camper for a long time.
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91L's dead, Jim.
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Quoting emcf30:
Ref: 506 Hydrus. We could only pray that Tx gets some much need rail without the severe stuff
...Check dis out....Link
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Quoting EYEStoSEA:


It is...it is...how are ya there , somebody mad at you? When that day comes, I'm just gonna go hide under the bed....lol...


Ha. Have the storms been going around you? Poor hydrus has been getting banged left and right for weeks. We haven't had so much as a breeze. Looking forward to a rainy week. Too bad in a way, because a lot of people here for Easter Week.
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thanks, mech.

dramatic video for sure, stormx.

hydrus- a little too well-defined for my taste, that outlook. Don't like it when they're already that comfortable with the forecast, esp days 5-7.

Go in peace, carry on. G'nite m'friends.
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Hey Grothar, how you doing tonight?
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Quoting Grothar:


Darla, is that you! LOL


It is...it is...how are ya there , somebody mad at you? When that day comes, I'm just gonna go hide under the bed....lol...
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Ref: 506 Hydrus. We could only pray that Tx gets some much need rail without the severe stuff
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Testing. Vorticity map.

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Quoting KrippleCreekFerry:
Me and my friend Elway.


Ohh okay :)
Not trying to interrogate you, just curious.
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Quoting Grothar:


He's been avoiding me lately. Must have been something I said.
Yeah, He is avoiding you and taking it out on us...jk.....really....jk...Next week is making a lot of people nervous...And I do mean alot..
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Quoting EYEStoSEA:
Well, just read back through the blog, actually saw some glints of humor, here and there....thank goodness !....It's all gonna be Otay....as for as the weather....here in Ms the humidity is smothering, makes me wanna move north for the summer......naaah......lol


Darla, is that you! LOL
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Quoting emcf30:


Looks like the next round is going to be further south
And with this event will come a more serious flood threat......DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0355 AM CDT FRI APR 22 2011

VALID 251200Z - 301200Z

...DISCUSSION...
MEDIUM-RANGE MODELS IN FAIRLY GOOD AGREEMENT THROUGH DAY 7 /THU.
4-28/...WITH RESPECT TO A LARGE TROUGH NOW MOVING INTO/DEVELOPING
ACROSS THE WRN CONUS. THE TROUGH IS FORECAST TO EJECT/EVOLVE SLOWLY
EWD ACROSS THE CENTRAL AND ERN U.S. THROUGH DAY 7...AND AS IT
DOES...AN ASSOCIATED SURFACE COLD FRONT WILL ALSO SHIFT SLOWLY EWD
ACROSS THIS REGION.

WITH PERSISTENT SLY LOW-LEVEL FLOW AHEAD OF THIS SYSTEM ADVECTING
GULF MOISTURE NWD...AMPLE INSTABILITY SHOULD BE AVAILABLE -- BEING
ENHANCED EACH AFTERNOON IN CONJUNCTION WITH THE DIURNAL HEATING
CYCLE. WITH STRONG MID-LEVEL FLOW ACCOMPANYING THE ADVANCING
SYSTEM...SHEAR WILL ALSO BE FAVORABLE FOR
ORGANIZED/POTENTIALLY-SEVERE CONVECTION. AS A RESULT...A
MULTIPLE-DAY PERIOD OF SEVERE WEATHER IS EXPECTED...WITH THE MAIN
THREAT AREA SHIFTING SLOWLY EWD WITH TIME.

WILL HIGHLIGHT A THREAT AREA FROM E TX NWD ACROSS THE ARKLATEX TO
ERN OK/WRN AR/SWRN MO FOR DAY 4 /MON. 4-25/...WHERE RELATIVELY
SUBSTANTIAL SEVERE WEATHER POTENTIAL IS EVIDENT INCLUDING SUPERCELLS
AND SOME THREAT FOR TORNADOES.

A SIMILAR THREAT APPEARS POSSIBLE DAY 5...AS THE INITIAL SHORT-WAVE
TROUGH EJECTS NNEWD AND A SECOND SHORT-WAVE FEATURE DIGS SEWD
TOWARD/INTO THE BASE OF THE LARGER-SCALE TROUGH.

ATTM...SPECIFICS OF THE SEVERE WEATHER THREAT GET MORE DIFFICULT TO
DISCERN DAY 6 /WED. 4-27/ AND BEYOND...AS THE FRONT SHIFTS E OF THE
MS VALLEY.

..GOSS.. 04/22/2011

CLICK TO GET WUUS48 PTSD48 PRODUCT
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Quoting hydrus:
Yes it is..Would you please tell him to cut it out.


He's been avoiding me lately. Must have been something I said.
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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.

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