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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Why is Dr. Masters saying it will move toward Bermuda? That's not what the models say...
Member Since: August 21, 2008 Posts: 0 Comments: 7440
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137. Jax82
just cuz no one has yet

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135. xcool
Euro and ensembles are currently predicting lower pressures -i post 114
Member Since: September 26, 2009 Posts: 2 Comments: 15670
Quoting alfabob:
I'm just saying that it would be possible for a TS to form in the region off of the coast of Africa. SST are 2 - 3C over normal in that region and shear is 5 - 10 knots. NOAA had the 0.2-0.4% probability on this area and not the sub-tropical system that everyone else has been paying attention to (0z). I don't care what has happened historically, because we won't be seeing the historical patterns in the future. Also I guarantee that by the end of May that shear anomaly will be further north as the subtropical jets begin to pickup again.


NOAA doesn't draw that graphic. A computer spits out the probabilities.

Ignoring history is unwise. Although anything can happen, something that has never happened before can only be assumed to be unlikely to happen now if the circumstances are not extraordinary, which they aren't here.
Member Since: November 24, 2005 Posts: 635 Comments: 26647
We dont look exclusively to the Eastern Atl till later downstream,as the early threats usually to the CONUS develop in the BOC, Southern GOM and the Western Caribbean.

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Quoting alfabob:


It means we are about a month ahead of schedule. Shear up to about 10N is below 30 kt, that is considered borderline productive.



It also takes more than one day of wind shear anomalies to determine whether we are ahead of schedule.

Taking April thus far as a whole, 200mb winds if taken all together have been averaging about normal overall in the MDR. An interesting thing to note is the easterly anomalies over and west of South America, indicating above-normal upward motion in the central-eastern Atlantic between the equator and 10N, which we have been seeing evidence of in the African blobs of late.

200mb zonal wind anomaly April 1st-April 19th, 2011:

Member Since: November 24, 2005 Posts: 635 Comments: 26647
Quoting alfabob:


It means we are about a month ahead of schedule. Shear up to about 10N is below 30 kt, that is considered borderline productive.



Waves over Africa, although very intense, are still too low in latitude.. Still another 10 degrees N more to go... and the CV machine is ON
Member Since: August 2, 2010 Posts: 21 Comments: 9814
Quoting alfabob:


It means we are about a month ahead of schedule. Shear up to about 10N is below 30 kt, that is considered borderline productive.


10N is also generally regarded as the southern border of the MDR. As Levi32 mentioned, development off Africa early in the season (and especially preseason) is very unlikely.
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Quoting alfabob:
I think the first real development will be coming off of Africa in May; maybe even late April. Shear has been about 10 - 15 kts below normal and sst are above average.



It is highly unlikely that the first development of the season will be of African origin, especially in pre-season. To my knowledge that has never occurred.
Member Since: November 24, 2005 Posts: 635 Comments: 26647
Quoting alfabob:
I think the first real development will be coming off of Africa in May; maybe even late April. Shear has been about 10 - 15 kts below normal and sst are above average.

5-10 knots below normal does not mean "low", it just means it goes from "highly destructive" to "slightly less than highly destructive" at this time of year.
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Quoting xcool:
What is the blue and the red? :(
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I do not wish to see how this will continue to unfold, but it will not be good unless they get some decent widespread rainfall soon.

"Since January 1, the Texas Forest Service said, it has responded to more than 800 fires that have damaged some 5,000 structures across 1.4 million acres.

The state has seen fires in 252 of its 254 counties since December 21, 2010."

CNN...

Link
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Thanks Aussie. I like to see where everyone is located as well. LOL NOT that I am going to remember on the fly. I loved your crater pictures. I didn't realize Australia had so many. Now I know I want to go to Australia to visit all the craters. Nice poem too.
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121. JRRP


Member Since: August 16, 2007 Posts: 0 Comments: 5799
The Latest from Fukushima Daiichi and Daini nuclear accident.

The government declared the 20-kilometer evacuation zone as a "no-entry zone" -- that is, entry into this area shall be prohibited for all except those carrying out emergency response work. Local mayors have granted temporary entry for one person per household. This does not mean there is a higher risk in the area; rather, it is meant to ensure evacuation and to prohibit re-entry without permission.

Tokyo Electric Power Company (TEPCO) announced that the radiation levels -- measured by robots -- were 10-49 millisieverts per hour at unit 1 and 28-57 millisieverts per hour at unit 3; these levels are considered very dangerous for workers. The robots also measured oxygen levels and temperatures, which were both found to be acceptable.

TEPCO announced that the estimated total of contaminated water is more than 67,000 tons.

Tokyo Electric Power Company (TEPCO) released a "road map" for stabilization of the Fukushima nuclear plants. The first step (approximately three months) will be to build a cooling system and water treatment facility. The second step (approximately six to nine months) will be to get the reactor and spent fuel under control (cooled status) and to stop the release of radioactive materials (air and water) into the environment.

Water samples taken from unit 4's spent fuel pool suggest that the fuel damage could be minor (220 Becquerel (Bq) per cubic meter for iodine 131, and 88 Bq per cubic meter for cesium 134). Still, the water temperature seems to be high, and cooling must continue.

Tokyo Electric Power Company (TEPCO) tried to absorb radioactive materials by putting zeolite into the sea. We shall see how effective this will be.
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Member Since: August 2, 2010 Posts: 21 Comments: 9814
I've made a blog entry, If anyone is interested. Could Everyone write there location on this blog. Just so as to keep track of where people are in the event of severe weather/hurricane.


Ok, my new blog is up.
Just go here
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Member Since: August 2, 2010 Posts: 21 Comments: 9814


Member Since: August 2, 2010 Posts: 21 Comments: 9814
Quoting Neapolitan:
A quick catch-up on the Fukushima situation for those interested:

Thanks Nea!
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114. xcool
Member Since: September 26, 2009 Posts: 2 Comments: 15670
Quoting jeffs713:


Didn't the GFS constantly try to spin something up in that same general region last year? I remember several instances where the GFS would spin something up 7-10 days out, then it would disappear...


Yeah I remember last year. We were "supposed" to have the C or D storm by the season's start in June. And then everyone rage-quit when it didn't happen and started to call the season a bust before June was over XD. That was fun.
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57 RastaSteve "Lots of seismic energy off the coast of Japan is causing major concern for seismologist."

Recent discussions by earthquake experts on NHK (Japan's main television network) concerning the high probability of a LARGE aftershock yet to come (magnitude8 or greater) probably ain't helping the public to sleep easier at night either.

52 Neapolitan "TEPCO plans to cut all its employees' salaries by 20%."

Which along with layoffs, turnovers&retirements, a hiring freeze, and sales of assets such as stocks&bonds and real estate will raise ~400billion yen (~$5billion) or 1/20th of the expectable property&income loss compensation claims against the company.
And TEPC0 has ZERO insurance coverage to help out with the rest of the bill. The world's other nuclear plant operators ain't in much better shape inregards to the amount of liability insurance they carry.
Member Since: August 21, 2007 Posts: 0 Comments: 4860
109. xcool
Member Since: September 26, 2009 Posts: 2 Comments: 15670
Quoting wxgeek723:
Wait...when was there a 90L?


About March 13, near it's peak passed right over the Madeira Islands which recorded gusts of 38-46 mph in bands around it's center... a well organized subtropical to hybrid type low, however as it's primary hindrance was trekking over 63F-64F SST's...
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JW!

Weather is so much better with a soundtrack!
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Yikes, our NWS Office really blew our forecast today. Two hours ago, we had zero chance of rain today. Now, we have a 60% chance of rain today and tonight with heavy rain producing tstorms. Pretty nasty MCS working its way through MS at this time...
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105. xcool
Member Since: September 26, 2009 Posts: 2 Comments: 15670
Quoting DocNDswamp:
Hiya MS Wx!

LOL, thanks but not so sure about the expert stuff... just a blogger offering my opinion here...
Shhhhhhh, don't tell anybody I was here...
;)


Oh, I'll keep quiet! I enjoy reading your blogs without having the drama that goes on in here. Oh yeah...I'm supposed to be quiet about that...LOL.
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Quoting Levi32:
It's long-range model blob-watching season already?



Didn't the GFS constantly try to spin something up in that same general region last year? I remember several instances where the GFS would spin something up 7-10 days out, then it would disappear...
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Hiya MS Wx!

LOL, thanks but not so sure about the expert stuff... just a blogger offering my opinion here...
Shhhhhhh, don't tell anybody I was here...
;)
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Well, I guess the NHC have no intentions of naming it then.
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It seems like they are just being nice to folks suffering from BTSMS.
blank tropical storm map syndrome.

That much shear wouldn't have folks glance at it twice during the regular season. If waves are following it off Africa, then I get it.
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A LOW PRESSURE AREA LOCATED ABOUT 450 MILES NORTH-NORTHEAST OF SAN
JUAN PUERTO RICO IS PRODUCING POORLY ORGANIZED SHOWER AND
THUNDERSTORM ACTIVITY. UPPER-LEVEL WINDS ARE EXPECTED TO BECOME
LESS CONDUCIVE FOR DEVELOPMENT ON FRIDAY...AND DEVELOPMENT OF THE
SYSTEM...IF ANY...SHOULD BE SLOW TO OCCUR AS IT MOVES NORTHWESTWARD
TO NORTHWARD AT ABOUT 10 MPH DURING THE NEXT DAY OR TWO. THERE IS
A LOW CHANCE...10 PERCENT...OF THIS SYSTEM DEVELOPING INTO A
SUBTROPICAL OR TROPICAL CYCLONE DURING THE NEXT 48 HOURS.
ADDITIONAL INFORMATION ON THIS LOW CAN BE FOUND IN HIGH SEAS
FORECASTS ISSUED BY THE NHC/TROPICAL ANALYSIS AND FORECAST
BRANCH...UNDER AWIPS HEADER NFDHSFAT2 AND WMO HEADER FZNT02 KNHC.
ANOTHER SPECIAL OUTLOOK WILL BE ISSUED ON FRIDAY...OR SOONER IF
NECESSARY.
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Right on Levi, it's best chance at getting a lil better organized should be overnight tonight... the modeling I'm seeing on the GFS shows it closing off in the 06Z-09Z timeframe... guess that's about near the short period as it's LL steering influence shifts... a very brief window of opportunity before gets shredded...
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Nice to see you in here, DocNDSwamp! Wish it were always this quiet in here so you could offer your expert opinion to more people. You are the best kept secret on WU! LOL! Hope you're doing great, my friend!
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Quoting wxgeek723:
Wait...when was there a 90L?


A couple weeks ago in the far northeast Atlantic. It was one of those systems that sometimes randomly forms near the Azores directly from an old extratropical low center.
Member Since: November 24, 2005 Posts: 635 Comments: 26647
Quoting RastaSteve:


I don't think the NHC will classify 91L Arlene but I do think we will get something in the Caribbean before mid May and that will become Arlene.


I agree, 91L is unlikely to get Arlene. Still, it's very unusual that we have the potential for two before June.
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The 205 PM Tropical discussion from NHC says that the gales on the north of 91L should weaken to below gale force in the next 6 hours....
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Wait...when was there a 90L?
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The GFS ensembles are interesting, showing an early flux of tropical moisture into the Caribbean in early May. This is supported by the dynamical MJO forecasts.

Member Since: November 24, 2005 Posts: 635 Comments: 26647

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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.