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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288. j2008
12:40 AM GMT on April 22, 2011
Its too early for a named storm, but 91 sure does look good enough to become a subtropical deppresion.
Member Since: December 19, 2008 Posts: 1 Comments: 224
287. Levi32
12:39 AM GMT on April 22, 2011
Quoting sammywammybamy:


Levi, why wont they classify it as a TD at least? It certainly looks like it has enough convection , circulation, and satelite appeal to be declared one?



Based on the written criteria it is a subtropical cyclone, but the NHC likes to see other "hidden" requirements before naming stuff. It is usually convective organization, which is almost never great for subtropical storms anyway. It would certainly be easier if they laid it out more clearly in the written criteria, but as it is there is no way to know what the NHC will name and what they won't, though their tropical outlooks are usually a good indicator.
Member Since: November 24, 2005 Posts: 635 Comments: 26647
285. hydrus
12:37 AM GMT on April 22, 2011
Quoting Grothar:
TEST

Failed
.
Member Since: September 27, 2007 Posts: 1 Comments: 21249
283. plywoodstatenative
12:35 AM GMT on April 22, 2011
because I work in the business of marine supply, is if it hits the Bahamas we are talking about a massive loss of business as well as one other item. The Bahamas have been hit over and over in recent years and can not use another hit by even a sub tropical system.
Member Since: November 15, 2005 Posts: 16 Comments: 4189
282. TomTaylor
12:35 AM GMT on April 22, 2011
Quoting flsky:
Just wondering - how did readers/posters on this blog first come across it?

I first found wu when I was looking for info on Hurricane Ivan in 04. I returned again to get the updates on a few big ones in 2005, but I never signed up. When 2010 came around and things got active, I returned here to find hurricane info, but also ran across Jeff's blog, and decided to finally sign up.
Member Since: August 24, 2010 Posts: 19 Comments: 4357
281. KoritheMan
12:35 AM GMT on April 22, 2011
Quoting sammywammybamy:


Levi, why wont they classify it as a TD at least? It certainly looks like it has enough convection , circulation, and satelite appeal to be declared one?



Because classification by way of organized convection is inherently arbitrary, being subject entirely to the forecaster's discretion.
Member Since: March 7, 2007 Posts: 576 Comments: 20612
278. MrstormX
12:32 AM GMT on April 22, 2011
Quoting sammywammybamy:


Most Models take it into the Southern Bahamas



I imagine it would recurve before it gets there but who knows right now.
Member Since: May 27, 2009 Posts: 0 Comments: 4438
276. Levi32
12:30 AM GMT on April 22, 2011
Quoting washingtonian115:
What now.Those things confuse me.


00z 4-22-11 position: 25.3N 63.0W; 35 knots; 1009mb; Low (in other words, not a classified tropical/subtropical storm)
Member Since: November 24, 2005 Posts: 635 Comments: 26647
275. MrstormX
12:30 AM GMT on April 22, 2011
Still extra-tropical but decent convection.
Member Since: May 27, 2009 Posts: 0 Comments: 4438
274. washingtonian115
12:29 AM GMT on April 22, 2011
Quoting GeoffreyWPB:
AL, 91, 2011042200, 253N, 630W, 35,1009, LO
What now.Those things confuse me.
Member Since: August 14, 2010 Posts: 10 Comments: 16979
272. GeoffreyWPB
12:25 AM GMT on April 22, 2011
AL, 91, 2011042200, 253N, 630W, 35,1009, LO
Member Since: September 10, 2007 Posts: 0 Comments: 11159
269. KoritheMan
12:22 AM GMT on April 22, 2011
Quoting sammywammybamy:


KoritheMan,

How are you, ready for another hurricane season?


Prepped and ready. I'm actually considering writing a blog on 91L in a couple hours, so keep a lookout.
Member Since: March 7, 2007 Posts: 576 Comments: 20612
268. hydrus
12:21 AM GMT on April 22, 2011
Quoting beell:


Ain't it hydrus? Every time I see this picture I'm reminded of the photos taken after the A-Bomb was dropped on Hiroshima. Silhouettes flash burned onto sidewalks and buildings during the final seconds of life.
I have seen those pictures you speak of. There was a program that was uncensored and uninterrupted by PBS showing the injuries people received by the atomic blast. There was one man, you could see in between his ribs and view the lungs and organs through the paper thin skin. He was so fragile. They said there was nothing to apply a skin graph to. He is still alive, and there are many like him.
Member Since: September 27, 2007 Posts: 1 Comments: 21249
267. oceanbug
12:20 AM GMT on April 22, 2011
Quoting flsky:
Just wondering - how did readers/posters on this blog first come across it?


Several years ago a writer friend posted a link to one of Dr. Master's blogs on climate change. I was hooked by his knowledge and even-handed way of explaining a controversial topic. Lurked a while, then finally signed up. :)
Member Since: February 2, 2011 Posts: 0 Comments: 72
266. Levi32
12:19 AM GMT on April 22, 2011
Quoting snotly:
Is that visualization software? did you ever try running the weather models under Linux. I thought that it was possible to compile the WRF, ARPS and/or MM5 with the G95 compiler and get it to spit out Visual5d or GRIB formatted data sets. I tried once to get it to work on Linux but gave up at about the 90% completed point because I just didn't know enough about compiling and setting up the software packages.




I would imagine that task would be too large for a personal computer. I'm only a novice linux user myself (something I need to remedy). That screenshot is from the Integrated Data Viewer from UCAR Unidata. It's a great data visualization program. In fact Unidata has a whole lot of data processing tools available for playing with, though I don't know how to properly use them all. Computer programming is something I'm still catching up on.
Member Since: November 24, 2005 Posts: 635 Comments: 26647
265. Grothar
12:19 AM GMT on April 22, 2011
TEST

Failed
Member Since: July 17, 2009 Posts: 71 Comments: 26153
264. Jedkins01
12:19 AM GMT on April 22, 2011
Quoting sammywammybamy:
wouldnt this pattern also allow for 1 or 2 tropical storms or hurricanes to hit Florida and enter the gulf later in the season?


It would be easy to assume so, but you can't for sure make that connection. The wet season had a nice early start in 2009 with a very wet May in Central Florida, and all summer into fall was very wet. However, it didn't increase the threat of tropical cyclone landfalls that year.
So does an early start to the wet season mean land falling tropical cyclones? As far as I know there's no way to make any correlation.
Member Since: August 21, 2008 Posts: 0 Comments: 7449
262. snotly
12:16 AM GMT on April 22, 2011
Is that visualization software? did you ever try running the weather models under Linux. I thought that it was possible to compile the WRF, ARPS and/or MM5 with the G95 compiler and get it to spit out Visual5d or GRIB formatted data sets. I tried once to get it to work on Linux but gave up at about the 90% completed point because I just didn't know enough about compiling and setting up the software packages.


Quoting Levi32:
Here's a shot I took in IDV of the 18z GFS initialization of 20C isosurface with 950mb wind streamlines cutting through. This view is looking towards the center of 91L from the west. Notice the hump in the 20C isosurface at the center, perhaps supporting evidence of a shallow warm-core structure.

Member Since: August 27, 2005 Posts: 0 Comments: 685
261. sunlinepr
12:15 AM GMT on April 22, 2011
Member Since: August 2, 2010 Posts: 21 Comments: 9814
260. KoritheMan
12:15 AM GMT on April 22, 2011
Quoting KrippleCreekFerry:
New Season. Same idiots!


Because comments like that really help matters...
Member Since: March 7, 2007 Posts: 576 Comments: 20612
259. Skyepony (Mod)
12:14 AM GMT on April 22, 2011
Heavy rains and risks of mudslides have kept most of Colombia on high alert. On Wednesday, President Juan Manuel Santos toured the affected areas and asked the residents to take preventive measures. In Honda, many homes were almost completely submerged by the overflowing Magdalena river. Santos visited the town of Utica where a mudslide caused damages to at least 120 houses. The government says 80 people have died in different incidents related to the rains this year.
Member Since: August 10, 2005 Posts: 164 Comments: 37855
258. beell
12:12 AM GMT on April 22, 2011
Quoting hydrus:
Kind of an eerie picture...


Ain't it hydrus? Every time I see this picture I'm reminded of the photos taken after the A-Bomb was dropped on Hiroshima. Silhouettes flash burned onto sidewalks and buildings during the final seconds of life.
Member Since: September 11, 2007 Posts: 143 Comments: 16651
256. Grothar
12:11 AM GMT on April 22, 2011
Quoting SQUAWK:


Gro, I can't run fast. So I will be driving at approx. 90 knots southeast or northwest, whichever give me a reasonably clear path. I drive a big truck -- get the heck outta the way!


Roger, that!
Member Since: July 17, 2009 Posts: 71 Comments: 26153
253. washingtonian115
12:07 AM GMT on April 22, 2011
Maybe if this was May I don't think the idea of 91L turning into a sub-tropical storm will be out of the question.However as I stated before this is good eye-candypractice for the real season that's coming up.
Member Since: August 14, 2010 Posts: 10 Comments: 16979
252. Levi32
12:03 AM GMT on April 22, 2011
Here's a shot I took in IDV of the 18z GFS initialization of 20C isosurface with 950mb wind streamlines cutting through. This view is looking towards the center of 91L from the west. Notice the hump in the 20C isosurface at the center, perhaps supporting evidence of a shallow warm-core structure.

Member Since: November 24, 2005 Posts: 635 Comments: 26647
251. flsky
12:02 AM GMT on April 22, 2011
Just wondering - how did readers/posters on this blog first come across it?
Member Since: October 24, 2006 Posts: 0 Comments: 1958
Quoting beell:
Seeking shelter from a tornado underneath an overpass is still considered an extremely bad idea also. Lower is always better. Hiding under an overpass puts you 10-20' up in the stronger above-ground tornadic winds. An overpass can also serve to focus/increase the winds. A Venturi Effect.

The photo below is from the May 3rd, 1999 Oklahoma Tornado Outbreak. This is the 16th St. bridge crossing I-44 near Newcastle, OK.

The lighter colored cement areas under this overpass are actually silhouettes left behind from individuals crouching under the bridge as the tornado scoured/splattered this area with mud, dirt and debris. There was one fatality here.

Photobucket
Image Credit: Norman, OK NWS
Kind of an eerie picture...
Member Since: September 27, 2007 Posts: 1 Comments: 21249
Quoting RastaSteve:


Yeah I hate when people act like I made that up. I couldn't make that up even if I tried. I bet Jedkins still doen't believe it. By the way thanks man!


I'm not trying to make you upset, I'm just careful to believe something unless I'm pretty sure its true, its not personal I just always do that. I'm not stubbornly skeptical of everything. I just don't like spreading around rumors and gossip.

I'm not saying what you said was a rumor, you probably were right. I just am careful about what I hear.
Member Since: August 21, 2008 Posts: 0 Comments: 7449
00Z BAMs update


Member Since: Posts: Comments:
247. beell
Seeking shelter from a tornado underneath an overpass is still considered an extremely bad idea also. Lower is always better. Hiding under an overpass puts you 10-20' up in the stronger above-ground tornadic winds. An overpass can also serve to focus/increase the winds. A Venturi Effect.

The photo below is from the May 3rd, 1999 Oklahoma Tornado Outbreak. This is the 16th St. bridge crossing I-44 near Newcastle, OK.

The lighter colored cement areas under this overpass are actually silhouettes left behind from individuals crouching under the bridge as the tornado scoured/splattered this area with mud, dirt and debris. There was one fatality here.

Photobucket
Image Credit: Norman, OK NWS
Member Since: September 11, 2007 Posts: 143 Comments: 16651
Quoting GeoffreyWPB:


I don't know about that canes. The models are really spread out. Plus who knows what is going to be left of this four or five days out?



Well, it doesn't really matter where the low pressure center goes cause its not gonna become much, what really matters for Florida is that the bermuda high is coming into place and now a tropical pattern is beginning to replace the dry season frontal pattern. Soon the wet season will be cranking up, the models are all saying an inverted trough will cross Florida at some point next week and bring a tropical air mass into the area allowing daily buildup of afternoon sea breeze storms over Florida.

How much thunderstorm activity will there be and when it will come, its hard to say, the models are not in agreement in terms of how much and when. But the models are showing the early stages of the tropical wet season regime moving into Florida.
Member Since: August 21, 2008 Posts: 0 Comments: 7449
242. Skyepony (Mod)
All this talk of staying in your car for a tornado.. Someone happened to send me this today.
Member Since: August 10, 2005 Posts: 164 Comments: 37855
91L's opportunity is tomorrow. If it doesn't become Arlene tomorrow then its not happening.
Member Since: Posts: Comments:
Quoting Grothar:
QUOTING KEEPEROFTHEGATE:

Just to clarify, I was not advocating staying in one's car. I was just showing the link as to why the question was asked. I believe the advice given by the Red Cross was bad information, as the article explained. I would never stay in a car during a tornado. I would be running faster than the car could drive anyway. Bet you didn't know I can run and scream at the same time.


Gro, I can't run fast. So I will be driving at approx. 90 knots southeast or northwest, whichever give me a reasonably clear path. I drive a big truck -- get the heck outta the way!
Member Since: Posts: Comments:

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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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