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

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

Share this Blog
2
+

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

Reader Comments

Comments will take a few seconds to appear.

Post Your Comments

Please sign in to post comments.

or Join

Not only will you be able to leave comments on this blog, but you'll also have the ability to upload and share your photos in our Wunder Photos section.

Display: 0, 50, 100, 200 Sort: Newest First - Order Posted

Viewing: 55 - 5

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14Blog Index

What was the last Hurricane to Strike the US Mainland?
Member Since: Posts: Comments:
Quoting RandomText:



Yeah, at the moment it does, but what is it going to look like in 3 or 4 days after it gets sheared and interacts with so much dry air?
It doesn't really matter, that may prevent it from developing into anything, but there is at least an inverted trough access, its not like its moving into the Saharan Desert. At some point surge of higher moisture will be drawn into Florida, regardless of what happens to the low. Well, at least that's what the models are telling me, nothing is for certain in weather though.

Member Since: August 21, 2008 Posts: 0 Comments: 7384
Quoting AussieStorm:

I wouldn't be surprised, maybe a twitter # tag

How do I change my Avatar?


Click on the Avatar,delete the image and upload another.Click the Primary Portrait thingee.

Member Since: Posts: Comments:
Quoting AussieStorm:

I wouldn't be surprised, maybe a twitter # tag


A search for 'Arlene' on twitter leads to Jim Cantore, quote, "I think we have a bonified sub-tropical low here!"

If Jim Cantore says it's a sub-tropical low, it must be....

...
Member Since: Posts: Comments:
I'm pretty sure that the northern center is gonna be the dominating center.
Member Since: Posts: Comments:
91L is beginning its move back to the southwest now, and that means that the window of opportunity is already closing, and fast. With a single center, this more than meets the written criteria to be named, and did so also when it had a single center yesterday. Right now as it has developed two vortices, it will need to get rid of the southern one to become a solid candidate again.

But of course, we all know that yellow on the TWO means the NHC will never name it.
Member Since: Posts: Comments:
Happy good friday to everyone here.
Member Since: Posts: Comments:
ughhhhh its bugging me to the core as to why this not being named a subtropical storm.....

Oh well, they have access to information about it that I don't. There must be something it lacks, even though to the eye it should easily be named.
Member Since: August 21, 2008 Posts: 0 Comments: 7384
Quoting Patrap:
Does 91L have a FB page yet?

I wouldn't be surprised, maybe a twitter # tag

How do I change my Avatar?
Member Since: September 30, 2007 Posts: 9 Comments: 15935
Quoting RandomText:
A dry, naked low level circulation remnant with 20mph to 30mph winds is definitely not what you want going to Florida right now. That would be potentially worse than a category 1 hurricane because of the fires.

They really need this system to get over there with some good moisture involved and fix this drought and fire problem.


No not really, the system has high PWAT, it would produce plenty of rain in Florida...
Member Since: August 21, 2008 Posts: 0 Comments: 7384
Does 91L have a FB page yet?
Member Since: Posts: Comments:
Quoting SQUAWK:


You really are Polish, aren't you.

Oczywiście,że jestem!(Of course I am!) And a question for you-can you speak Polish as good as I speak English?
Member Since: May 19, 2010 Posts: 0 Comments: 351
MESOSCALE DISCUSSION 0514
NWS STORM PREDICTION CENTER NORMAN OK
1009 AM CDT FRI APR 22 2011

AREAS AFFECTED...ECNTRL/SERN MO...SRN IL

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 221509Z - 221615Z

THREATS FOR LARGE HAIL AND DAMAGING WINDS WILL INCREASE THROUGH
EARLY AFTERNOON. A SEVERE THUNDERSTORM WATCH IS POSSIBLE...50
PERCENT PROBABILITY.

THUNDERSTORM INTENSITY HAS SLOWLY BEEN INCREASING NW-SW OF THE
ST.LOUIS METRO AREA SINCE 14Z WITH PREFERENTIAL DEVELOPMENT ALONG
SRN FLANKS COINCIDENT WITH THE LLJ. ACTIVITY WILL PROPAGATE ESE
ALONG THE LLVL THETA-E GRADIENT AND AFFECT ALL OF THE ST.
LOUIS/LAMBERT INTERNATIONAL AIRPORT AREA 1530-1630Z.

AS OF 15Z...STORMS WERE LIKELY ELEVATED...BUT AS HEATING CONTINUES
ACROSS ECNTRL MO AND SRN IL...THEY WILL BECOME MORE SURFACE-BASED
WITH DAMAGING WIND THREATS INCREASING. OTHERWISE...LARGE HAIL WILL
BE LIKELY OWING TO NEARLY 8 DEG C PER KM MID-LEVEL LAPSE RATES. IN
FACT...STRONGER STORMS MAY YIELD HAIL GREATER THAN HEN EGG SIZED.

..RACY.. 04/22/2011


ATTN...WFO...PAH...ILX...LSX...SGF...

LAT...LON 39459061 38448810 37378898 37058936 36998996 36979036
37079093 37199132 37449162 37819182 38449191 39459061

Member Since: Posts: Comments:
Today is do or die for 91L, if the NHC doesn't give it a designation here chances are it never will. Plus 91L should begin to disintegrate into a remnant low/open trough in a couple of days.
Member Since: Posts: Comments:
Happy Earth Day to all the wunderground members and staff.

Member Since: Posts: Comments:
Quoting hydrus:
You'd better tell the Captain we've got to land as soon as we can. This woman has to be gotten to a hospital.
A hospital? What is it?
It's a big building with patients, but that's not important right now.........:)


OMG! Classic stuff. Thanks for the laugh...I needed it! :-)
Member Since: Posts: Comments:
Just a reminder....

I've created a blog entry, If anyone is interested. Feel free to write your location on this blog. Just so as to keep track of where people are in the event of severe weather/hurricane.

Just go here
Thanks
Member Since: September 30, 2007 Posts: 9 Comments: 15935
How seriously possible is that BAMS???
Member Since: Posts: Comments:
31. IKE

Quoting hydrus:
You'd better tell the Captain we've got to land as soon as we can. This woman has to be gotten to a hospital.
A hospital? What is it?
It's a big building with patients, but that's not important right now.........:)
And don't call me Shirley.
Member Since: Posts: Comments:
Quoting fmbill:


LOL!! Airplane!
You'd better tell the Captain we've got to land as soon as we can. This woman has to be gotten to a hospital.
A hospital? What is it?
It's a big building with patients, but that's not important right now.........:)
Member Since: September 27, 2007 Posts: 1 Comments: 20927
Quoting IKE:
***Just wanted to tell 91L....good luck....we're all counting on you.***


LOL!! Airplane!
Member Since: Posts: Comments:
did someone say ingesting dry air?
Member Since: September 27, 2007 Posts: 1 Comments: 20927
Its the mighty Fujiwara babeeee..jk...really...jk..
Member Since: September 27, 2007 Posts: 1 Comments: 20927
23. IKE
Center looks near 26.7N and 63.5W....moving south of west.

Positive thinking....good thoughts for 91L.
Member Since: Posts: Comments:
Only bad thing about rain on Monday is that Easter Monday is the unofficial start of the beach season here in the Bahamas, and a lot of beach parties and cookouts would get rained out. This is not a good thing....
Member Since: Posts: Comments:
Actually, the Northern circulation is starting to look very well defined...
Member Since: Posts: Comments:
Quoting sammywammybamy:


Two Centers...

the southern one become prime then its done for after tonight
Member Since: July 15, 2006 Posts: 170 Comments: 53494
Name that thang!!!
Member Since: Posts: Comments:
Quoting sammywammybamy:


Baha... if your here.. it appears that most of the models take it in the direction of the Bahamas, however by that time it will just be a blob of tropical rain.

Yeah, that's the IDEAL solution... no genuine tropical characteristics, but a goodly amount of tropical rain to cut the drought conditions we've been experiencing late in April.
Member Since: Posts: Comments:
14. IKE
***Just wanted to tell 91L....good luck....we're all counting on you.***
Member Since: Posts: Comments:
thanks for update doc
91 got about 12 to 14 hrs to go then its gone
Member Since: July 15, 2006 Posts: 170 Comments: 53494
Wow. Wasn't expecting another refresh today.... lol

I was about to say in the old blog that it looks like shear is dropping to the west of 91L, especially towards the SW, where it's been forecasted to move. I still don't think we're going to get a named storm out of it, but if whatever circulation is there can hold together for another two-three days, we may actually get some rain out of it past 75W.

In August I might not be so excited by those prospects, but for now I'd be ok with it... lol





Member Since: Posts: Comments:
Quoting CyclonicVoyage:
From previous blog


Quoting PolishHurrMaster:

So let'em choose a dominant one!They are professionalists,should be able to do this.



They won't name it with 2 vortice. Should 91L acquire enough organization to be named 91L will eat that second center for lunch.

So I'll give you a merithorical situation:tropical system in August,gusting to 100mph,heading for Florida.But has two competing centers.Would you name it?
Member Since: May 19, 2010 Posts: 0 Comments: 351
Complete Update





Member Since: Posts: Comments:
If the North one becomes dominant in the next few hours, 91L still has a chance. If they keep competing, or the southern wins, it's doomed.
Member Since: Posts: Comments:
Thanks for the update Dr Masters
Member Since: Posts: Comments:

Viewing: 55 - 5

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14Blog Index

Top of Page

About

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

Local Weather

Scattered Clouds
79 °F
Scattered Clouds