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: 655 - 605

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

655. bohonkweatherman
12:58 AM GMT on April 24, 2011
Hello Weather Lovers, First time I have been on in months, Happy Easter
Member Since: July 5, 2009 Posts: 0 Comments: 1348
654. Zack1
3:41 PM GMT on April 23, 2011
Here, Here!
Member Since: March 24, 2008 Posts: 0 Comments: 0
653. aspectre
3:29 PM GMT on April 23, 2011
NEW BLOG
Member Since: August 21, 2007 Posts: 0 Comments: 4860
651. washingtonian115
3:18 PM GMT on April 23, 2011
Generally though 91L looked more decent than the most ugliest storms that I've seen in the past......does Danny come to mind.I don't even....know what that was...
Member Since: August 14, 2010 Posts: 10 Comments: 17095
650. ycd0108
3:12 PM GMT on April 23, 2011
637 Aussie: (The quote function is one PIA)
I'm a builder as well and very interested in disaster proofing. We get H force winds here occassionaly, heavy snow loads and, once every half millenium or so, a megathrust earthquake (january, 1700 was the last one).
I was being flippant about the design you posted but Shen's point still stands - any structure can be destroyed by an overwhelming natural event.
"The Harder they come
The harder they fall"
Member Since: January 1, 2008 Posts: 179 Comments: 4634
649. Jedkins01
3:11 PM GMT on April 23, 2011
Quoting Grothar:


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?


LOL, well its not that we have never had cold fronts moves through in May, its just that this year everything is ahead of schedule, I mean heck we haven't had a cold front clear through in a very long time. The strong Bermuda high has already taken shape, which always marks the end of cold fronts, well not completely. I am have seen fronts come down and stall near the area or over South Florida in the wet season, often times in June. However they quickly lift back north as a warm front with a return of higher moisture and rainfall. I would imagine any front will crawl through the area before quickly lifting north again.
Member Since: August 21, 2008 Posts: 0 Comments: 7605
648. washingtonian115
3:09 PM GMT on April 23, 2011
91L was nothing but good eye candy,and a pratice as you will for the real stuff that's ahead.Don't worry tropical weather fans.We'll get action soon enough.
Member Since: August 14, 2010 Posts: 10 Comments: 17095
647. Jedkins01
3:07 PM GMT on April 23, 2011
Quoting hydrus:
I did type "could" in there for a reason smart ass..Good evening Jed...Hope you are doing good...:)



hahaha I am doing great! You? I just finished my last Calculus test of the semester, now I only have the final exam left!
Member Since: August 21, 2008 Posts: 0 Comments: 7605
646. hydrus
3:03 PM GMT on April 23, 2011
This will turn out to be a large and severe event.... DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0350 AM CDT SAT APR 23 2011

VALID 261200Z - 011200Z

...DISCUSSION...
SUBSTANTIAL SEVERE WEATHER POTENTIAL IS EXPECTED TO SHIFT SLOWLY EWD
ACROSS THE ERN U.S. DAYS 4-6 /TUE. 4-26 THROUGH THU. 4-28/...AS A
LARGE UPPER TROUGH PROGRESSES FROM THE CENTRAL U.S. DAY 4 ACROSS THE
MS VALLEY DAY 5...AND THEN ON EWD THROUGH DAYS 6/7. MODEL
DIFFERENCES WITH RESPECT TO TIMING OF THIS FEATURE BEGIN TO EMERGE
DAY 5...BUT BECOME INCREASINGLY PRONOUNCED THROUGH DAYS 6 AND 7 AS
THE TROUGH APPROACHES THE E COAST STATES/ERN ATLANTIC.

THE PRIMARY SEVERE THREAT DAY 4 IS PROGGED FROM E TX NEWD ACROSS THE
ARKLATEX INTO THE MID MS VALLEY...AS A SHORT-WAVE TROUGH DIGS ESEWD
INTO THIS REGION...WITHIN THE LARGER-SCALE TROUGH. UNSTABLE AIRMASS
COMBINED WITH THE ENERGETIC SHORT-WAVE FEATURE AND ASSOCIATED/STRONG
FLOW FIELD SUGGESTS WIDESPREAD SEVERE WEATHER POTENTIAL -- INCLUDING
RISKS FOR LARGE HAIL...DAMAGING WINDS...AND ISOLATED TORNADOES.

THE THREAT SHOULD SHIFT E OF THE MS VALLEY INTO THE MID
SOUTH/SOUTHEAST DAY 5...AS THE SHORT-WAVE FEATURE TAKES ON A NEUTRAL
TO EVEN NEGATIVE TILT AS IT CROSSES THIS REGION. AGAIN -- AMPLY
UNSTABLE AIRMASS COMBINED WITH THE STRENGTH OF THE UPPER SYSTEM AND
ASSOCIATED FLOW FIELD SUGGESTS WIDESPREAD SEVERE WEATHER CAN BE
EXPECTED...INCLUDING THE POTENTIAL FOR TORNADOES.

AS MODELS BEGIN DIVERGING SOMEWHAT WITH RESPECT TO TIMING AND
SMALLER-SCALE DETAILS...DEGREE OF THREAT SHIFTING ACROSS THE
APPALACHIANS LATE DAY 5 AND INTO DAY 6 BECOMES LESS CERTAIN. WHILE
SEVERE WEATHER WILL BE LIKELY WITH THE FRONT EXPECTED TO REACH THE
ATLANTIC COAST BY THE END OF THE PERIOD...WILL REFRAIN FROM
HIGHLIGHTING A THREAT AREA THIS FORECAST.

WITH THE FRONT LIKELY OFFSHORE BY THE START OF DAY 7... SEVERE
WEATHER POTENTIAL ACROSS THE U.S. APPEARS LESS
WIDESPREAD/SIGNIFICANT AND MUCH MORE UNCERTAIN THROUGH THE END OF
THE PERIOD.

..GOSS.. 04/23/2011
Member Since: September 27, 2007 Posts: 1 Comments: 21424
645. Hurricanes101
3:01 PM GMT on April 23, 2011
Quoting jasonweatherman2010:
good news!!


I dont see where 91L was deactivated, not on the atcf site
Member Since: March 10, 2010 Posts: 1 Comments: 7824
644. KEEPEROFTHEGATE (Mod)
2:48 PM GMT on April 23, 2011
Member Since: July 15, 2006 Posts: 174 Comments: 54449
642. KEEPEROFTHEGATE (Mod)
2:31 PM GMT on April 23, 2011
XX/INV/91L
MARK
deactivate
Member Since: July 15, 2006 Posts: 174 Comments: 54449
640. dave4321
2:20 PM GMT on April 23, 2011
Quoting AussieStorm:

Would this type of construction be good for Hurricane prone area's in the ATL/EPAC??
This is the draft plan for new houses to be built after TC Yasi. More here


I agree with the other comment. Hip Roofs are the best for strength, and reducing the wind drag. A home built on Piers is great for a coastal / storm surge prone areas. Walls and Truss / Rafters should be secured to each other with metal plates or straps and nailed with non-shearing fasteners.
All sheathing and roofing fasteners should be ring shank when possible.

Not sure if you have any systems like this over there, but for energy efficiency and strength this is the best system I've seen for the shell construction on a concrete slab:
http://omnicrete.net/Omnicrete_Home_Page.html

I'm a Florida General Contractor, and have worked most of the latest land-falling hurricanes in the Continental US, and I'm familiar with the latest coastal codes in the US and Miami-Dade, FL (Our most strict)
Member Since: October 22, 2010 Posts: 0 Comments: 15
639. AussieStorm
2:17 PM GMT on April 23, 2011
Quoting RandomText:


People stay because everyone is full of themselves and actually believe they won't be the one when it happens.

But if it is proven there house is not structurally safe to stay, would people evac or stay and lose there house and life?
Member Since: September 30, 2007 Posts: 9 Comments: 15940
637. AussieStorm
2:01 PM GMT on April 23, 2011
Quoting ycd0108:
I have to agree with Shen (by the way: we sang "Shannendoa")and if you can stand another opinion: that structure is ugly

pst, its only a draft, but would you rather stay in a house that will save your life or just looks good and blows away in a cat 1 or 2 hurricane?
Member Since: September 30, 2007 Posts: 9 Comments: 15940
636. AussieStorm
1:57 PM GMT on April 23, 2011
Quoting ShenValleyFlyFish:
I have a somewhat counter intuitive take on this. Think "perminant"shelters should not be built in Hurricane/surg prone areas. Go back to the build it as cheep as you can fishing shack. In the end loss of life and damage totals might go down as folks would be more prone to evacuate and clean-up replacement costs would decline. Case in point would be H-Ike. Folks would have been less likely to chose to try to ride it out if they knew they were living in a structure with only H-2 capabilities.

How much would it cost for structural engineers to go from house to house and put a cat number on houses in hurricane prone areas. would that then make people think. ok. i live in a house that's cat 1 rated, there is a cat 2 or 3 hurricane approaching, would people stay if they know there house is not rated to withstand the approaching hurricane.
Member Since: September 30, 2007 Posts: 9 Comments: 15940
635. ycd0108
1:54 PM GMT on April 23, 2011
I have to agree with Shen (by the way: we sang "Shannendoa")and if you can stand another opinion: that structure is ugly
Member Since: January 1, 2008 Posts: 179 Comments: 4634
634. ShenValleyFlyFish
1:47 PM GMT on April 23, 2011
Quoting AussieStorm:

Would this type of construction be good for Hurricane prone area's in the ATL/EPAC??
This is the draft plan for new houses to be built after TC Yasi. More here
I have a somewhat counter intuitive take on this. Think "perminant"shelters should not be built in Hurricane/surg prone areas. Go back to the build it as cheep as you can fishing shack. In the end loss of life and damage totals might go down as folks would be more prone to evacuate and clean-up replacement costs would decline. Case in point would be H-Ike. Folks would have been less likely to chose to try to ride it out if they knew they were living in a structure with only H-2 capabilities.
Member Since: September 9, 2007 Posts: 36 Comments: 4687
633. emcf30
1:41 PM GMT on April 23, 2011
Quoting AussieStorm:

it's just a void. it's time is over


As some people say on this blog often,
Poof
Member Since: August 7, 2010 Posts: 0 Comments: 1937
632. AussieStorm
1:38 PM GMT on April 23, 2011
Quoting stormpetrol:
91L though void of convection has a very vigorous low level spin

it's just a void. it's time is over
Member Since: September 30, 2007 Posts: 9 Comments: 15940
631. stormpetrol
1:14 PM GMT on April 23, 2011
91L though void of convection has a very vigorous low level spin
Member Since: April 29, 2007 Posts: 0 Comments: 7932
630. emcf30
1:07 PM GMT on April 23, 2011
Member Since: August 7, 2010 Posts: 0 Comments: 1937
629. emcf30
1:03 PM GMT on April 23, 2011
Member Since: August 7, 2010 Posts: 0 Comments: 1937
628. islander101010
12:54 PM GMT on April 23, 2011
interesting little note umphreys mcgee (one of our top jam bands) concert is already sold out for their 2012 mexican mayan festival near cancun. 2012 is stacking up to be one of the best yrs to party of all of them. if we dont blow up there will be alot of people running around with hangovers.
Member Since: September 11, 2010 Posts: 1 Comments: 4734
627. emcf30
12:52 PM GMT on April 23, 2011
Member Since: August 7, 2010 Posts: 0 Comments: 1937
626. GeoffreyWPB
12:41 PM GMT on April 23, 2011
...SPECIAL FEATURES...

A 1011 MB NON-TROPICAL LOW CONTINUES TO SPIN ABOUT 500 NM S OF
BERMUDA NEAR 24N65W MOVING S NEAR 10 KT. THIS IS A DEEP LAYERED
LOW WITH THE UPPER LEVEL LOW NEAR 26N62W. WATER VAPOR SATELLITE
IMAGERY SHOWS DRY AIR ALOFT NEARLY SURROUNDS THE UPPER LOW
EXCEPT TO THE NE. A SURFACE TROUGH EXTENDS FROM THE SURFACE LOW
E TO 24N57W. SCATTERED SHOWERS AND POSSIBLE ISOLATED
THUNDERSTORMS ARE FROM 22N-25N BETWEEN 61W-65W. UPPER LEVEL
WINDS ARE INCREASINGLY LESS CONDUCIVE FOR DEVELOPMENT AND ARE
FORECAST TO BECOME HIGHLY UNFAVORABLE FOR DEVELOPMENT DURING THE
NEXT 48 HOURS. THE DRY AIR ALOFT ALONG WITH UNFAVORABLE UPPER
LEVEL WINDS ARE EXPECTED TO HINDER FURTHER DEVELOPMENT.
Member Since: September 10, 2007 Posts: 0 Comments: 11279
624. AussieStorm
12:29 PM GMT on April 23, 2011
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. This info will only be used in an emergency. If we know where you are then we can look out for you.

Just go here
Thanks
Member Since: September 30, 2007 Posts: 9 Comments: 15940
623. emcf30
12:26 PM GMT on April 23, 2011
Good morning everyone. Looks like the residents made it out last night without fatalities and only a few injuries. CNN has good coverage from the air. There are a lot of people praising the early warning from the NWS of saving their lives. Did not realize that everyone had basements there. Some of the damage looks to be at least EF3 maybe a isolated 4. There are several homes with no walls standing
Member Since: August 7, 2010 Posts: 0 Comments: 1937
622. aquak9
11:40 AM GMT on April 23, 2011
g'morning all

Tampaspin- took me a good ten minutes to figure out where that 6.9 was, I shoulda just come here first. Solomon Islands. My eyes just don't see the USGS site as good as they used to.

At least I can still see the spikes on the seismos.

Senorpescado _ dreamed I was in a fish market last night, fresh fish white meat around the lower jaws. It was delicious.

The flooding along the Miss seems to be coming later this year than I had expected. Flow, baby, flow.
Member Since: August 13, 2005 Posts: 168 Comments: 26072
621. Vincent4989
11:16 AM GMT on April 23, 2011
Japanese aftershocks activity still occurring.


Member Since: November 13, 2009 Posts: 2 Comments: 728
620. TampaSpin
11:02 AM GMT on April 23, 2011
HAPPY EASTER EVERYONE! HAVE A BLESSED DAY!
Member Since: September 2, 2007 Posts: 178 Comments: 20443
619. TampaSpin
10:57 AM GMT on April 23, 2011
618. TampaSpin
10:48 AM GMT on April 23, 2011

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
Time of Earthquake in other Time Zones
Location
10.349S, 161.233E
Depth
81.6 km (50.7 miles)
Region
SOLOMON ISLANDS
Member Since: September 2, 2007 Posts: 178 Comments: 20443
617. TampaSpin
10:45 AM GMT on April 23, 2011


Magnitude
6.0
Date-Time
Saturday, April 23, 2011 at 10:12:48 UTC
Saturday, April 23, 2011 at 07:12:48 PM at epicenter
Time of Earthquake in other Time Zones
Location
39.164°N, 142.892°E
Depth
38.9 km (24.2 miles)
Region
NEAR THE EAST COAST OF HONSHU, JAPAN
Member Since: September 2, 2007 Posts: 178 Comments: 20443
616. TampaSpin
10:42 AM GMT on April 23, 2011
Member Since: September 2, 2007 Posts: 178 Comments: 20443
615. AussieStorm
7:55 AM GMT on April 23, 2011

Would this type of construction be good for Hurricane prone area's in the ATL/EPAC??
This is the draft plan for new houses to be built after TC Yasi. More here
Member Since: September 30, 2007 Posts: 9 Comments: 15940
614. KoritheMan
6:56 AM GMT on April 23, 2011
Quoting senorpescador:

who cares about cars

I'm assuming you drive one, so obviously you.
Member Since: March 7, 2007 Posts: 585 Comments: 20854
612. WatchingThisOne
6:35 AM GMT on April 23, 2011
"Apparent" tornado hits concourse C at Lambert St. Louis international. Injuries from shattered glass. Looks like no loss of life, no planes thrown around. Major says airport will be shut down "indefinitely," but I bet he wishes he had chosen a better word.

msnbc.msn.com

Edit: apparently I did not read far enough back. St. Louis is hurting tonight.
Member Since: July 15, 2005 Posts: 3 Comments: 1269
606. sunlinepr
5:36 AM GMT on April 23, 2011
Member Since: August 2, 2010 Posts: 21 Comments: 9821
605. PolishHurrMaster
5:32 AM GMT on April 23, 2011
Foreca update:COC near 24.8N 64.8W,strongest winds near 42-44mph(what?)
Member Since: May 19, 2010 Posts: 0 Comments: 351

Viewing: 655 - 605

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.