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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171 PlazaRed [inre comment168] "...There was a 5.5 quake a bit to the southwest of the plant today about 3 hours ago and it was very close to what looks like another big installation or nuclear facility on the coast..."

~14miles(~22.5kilometres)south of SSW of TEPCO's FukushimaDaiichi nuclear disaster
~7miles(~11.3kilometres)SSW of TEPCO's FukushimaDaini nuclear powerplant
FukushimaDaini is located ~11kilometres south of FukushimaDaiichi

Yesterday there was a magnitude5.7quake epicentered
~20miles(~32.2kilometres)ENE from FukushimaDaiichi and
~24miles(~38.6kilometres)NE from FukushimaDaini.
The lone red dot represents centralTokyo.
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Quoting emcf30:
Have you seen the GFS NCEP.?...If it were to pan out (and there is a fair chance that it will) it could mean serious flooding and severe weather issues for a large portion of the U.S....Link
Member Since: September 27, 2007 Posts: 1 Comments: 22604

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I have a feeling that if it were October instead of April, 91L would be called a subtropical storm. Definitely looks like one now to me. Will be interesting to see what the NHC says. I think they wont start issuing advisories since it will probably be dead by tomorrow.
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Hello everyone,
A Blessed Good Friday afternoon
and Happy Earth Day to you all!

Nothing like a little invest out there to bring back all the hurricane watchers!

Doc, my Leo/Snake/Bro also here!!! along with a few others that have not been around much lately.


So while I have been lurking a little this week I think I may be popping in and out a little more until this system does something... We could sure use a good tropical rainfall here in South Florida!

Have a great afternoon.
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Wasn't it the GFS the other day that showed 91L splitting into two and not amounting to much? It was heavily discounted however, at the end of the day not to far off from the current situation.
Member Since: January 30, 2010 Posts: 0 Comments: 3259
199. IKE
Designate it! Now.
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Winds back up:

AL, 91, 2011042218, , BEST, 0, 265N, 640W, 35, 1007, LO, 34, NEQ, 0, 0, 0, 60, 1013, 200, 60, 0, 0, L, 0, , 0, 0, INVEST, M,
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... duplicate
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At this point, given the recent improvement in organization and slightly higher winds shown with the most recent ASCAT pass, I would now give this a medium chance for development into a tropical/subtropical cyclone.
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BBL... dinner time.

No hot cross buns this year... lol
Member Since: October 25, 2005 Posts: 19 Comments: 22727
91L-2 is about to be absorbed, loosing it's distinction on Satellite.
Member Since: January 30, 2010 Posts: 0 Comments: 3259
145.

Nrl site has been down for almost a week now. Pretty lame
Member Since: August 24, 2010 Posts: 19 Comments: 4358
Quoting washingtonian115:
It affected Mexico....So don't be surprised to see it not retired...Just like Alex of last year.
Not surprised.... just amazed....
Member Since: October 25, 2005 Posts: 19 Comments: 22727
Quoting alfabob:


It already is subtropical. The first phase of development is increased convection away from the center of the storm, next a ULL or trough comes in and if temperatures are high enough then convection starts at the core (23C+ SST). It has had convection at the core for a while now, thus it is subtropical. Only thing left for it to do now is to go tropical, which most likely wont happen.
Key word for me in that post was "significant"....

Meanwhile, I'm still hoping we get enough SWward drift with this to give us some rain soon.
Member Since: October 25, 2005 Posts: 19 Comments: 22727
Quoting BahaHurican:
Still amazes me that Emily that year wasn't retired....
It affected Mexico....So don't be surprised to see it not retired...Just like Alex of last year.
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Member Since: August 7, 2010 Posts: 0 Comments: 1957
Quoting AllStar17:
The names for this year:
Still amazes me that Emily that year wasn't retired....
Member Since: October 25, 2005 Posts: 19 Comments: 22727
Quoting aspectre:
New EvacuationZone contains areas more 40kilometres from FukushimaDaiichi.
And the old 20kilometre EvacuationZone is now officially a 20kilometre ExclusionZone:
no entry allowed without official escorts.

Radiation in the new EvacuationZone exceeds 20millisieverts per year. By how much, officials won't say.
A typical nuclear worker receives 2millisieverts of excess radiation in a year. 20millisieverts per year over 5years is the maximum allowed for nuclear workers before they're barred from entering a nuclear facility. (TEPCO and the Japanese government bumped up the limit for this disaster)
In little over a month, people living in the new EvacuationZone have already received a greater dose of excess radiation than typical nuclear workers receive in a year.

yeah, it seems many people are suffering from "The-nuclear-fiasco-is-yesterday's-news-say-what's -Charlie-Sheen-doing-now" disease, so they're tired of talking about the ongoing situation at Fukushima. But the fact that 600 square kilometers or so of once-prime agricultural land is about to be indefinitely/permanently closed to anyone but Hazmat-suited nuke workers should bother folks.

It was announced yesterday that readings of 100 microsieverts per hour are being detected up to three kilometers from the plant. That means a person sitting in his or her livingroom inside that limit can exceed the standard nuke worker annual dose of radiation in under a day. Nice, huh?
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I'm very impressed with the organization 91L pulled off over night into this morning.However I still don't see the NHC naming this at all.It's time is almost up.
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184. xcool
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Quoting PlazaRed:
Quoteing:-168. aspectre

As an interesting note to this post.
There was a 5.5 quake a bit to the south west of the plant today about 3 hours ago and it was very close to what looks like another big installation or nuclear facility on the coast, probably only a mile or so away from it.
Judging by the exclusion zone this plant will also now be inside the 20Km zone!



State school. Part of the "Non establishment of religion". Works out OK, means no changes in schedule for Ramadan or Rosh Hashanah.
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Tropical Weather Discussion

Excerpt:

...SPECIAL FEATURE...

AT 1500 UTC...A 1008 MB LOW IS CENTERED ABOUT 510 NM NNE OF
PUERTO RICO AT 26.6N 63.6W WITH NEAR GALE FORCE WINDS N OF THE
CENTER. A SECONDARY SURFACE SWIRL IS LOCATED 100 NM SW OF THE
LOW CENTER NEAR 25.3N 64.7W INTERACTING WITH THE PRIMARY CENTER.
A SURFACE TROUGH EXTENDS S FROM THE LOW CENTER TOWARDS PUERTO
RICO ALONG 26N61W 23N61W 19N66W. WIDELY SCATTERED MODERATE
CONVECTION IN BANDS IS N OF THE CENTER FROM 26N-30N BETWEEN
60W-65W. A 1014 UTC WINDSAT PASS...AND A 1424 UTC ASCAT PASS
CONFIRM 30 KT WINDS N OF THE CENTER. AN UPPER LEVEL LOW IS
CENTERED DIRECTLY OVER THE SECONDARY SURFACE SWIRL. UPPER LEVEL
DRY AIR IS WRAPPING AROUND THE WESTERN AND SOUTHERN PORTIONS OF
THE SYSTEM. EXPECT THE SURFACE LOW CENTER TO TRACK SW TOWARDS
HISPANIOLA AND WEAKEN OVER THE NEXT 24-48 HOURS WITH CONVECTION
AND STRONGER WINDS N OF THE CENTER.
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Orlando is always a decent bet for any kind of conference.
Dr. Masters could sell out his stock of WU wear.
Member Since: July 11, 2006 Posts: 14 Comments: 11423

Quoting nrtiwlnvragn:


That secondary spin-off shows up somewhat in the higher resolution gif from OSI SAF.
Hi-resolution from NESDIS


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Quoting AussieStorm:
Anyone else have this problem?
NRL Monterey web pages and data are currently inaccessible due to a technical outage. This home page will be updated as information becomes available.

Any other Navy site available?
Link

I also get that message but you can go here.
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Thanks Nrt,
Yes, it sure does...
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Quoting Patrap:
We are tossing around the idea of a wunderground members conference come August,,time and place TBD.

If interested in attending or have input as to the format and all,,wu mail me.
Sounds interesting. While we wouldn't want to be stranded due to a passing TC, it would make sense to do something in FL. [central location]

Member Since: October 25, 2005 Posts: 19 Comments: 22727
Hey Levi,
Yes agree, the tightest isobars / isotachs are sharply around 91L... and good point in #165, also might doubt ASCAT has the resolution to define the secondary spin-off...
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Just before I go... just came through.

Region: TONGA REGION
Geographic coordinates: 22.703S, 174.630W
Magnitude: 5.7 Mw
Depth: 1 km
Universal Time (UTC): 22 Apr 2011 17:14:48
Time near the Epicenter: 23 Apr 2011 05:14:48

Location with respect to nearby cities:
184 km (114 miles) SSE (160 degrees) of NUKU'ALOFA, Tonga
456 km (283 miles) S (188 degrees) of Neiafu, Tonga
2676 km (1663 miles) WSW (253 degrees) of PAPEETE, Tahiti, French Polynesia

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Quoting DocNDswamp:
#144
Indeed, interesting to also note the secondary spin-off is not evident in the ASCAT pass... had been wondering if was a bit more aloft, even though vis-RGB interpretation appeared to reflect at the sfc...

#150,
True enough, but also notice where those highest winds are - on NW side where we likely have highest gradient winds, right between the 91L low-mid circ and low-mid ridge anchored over the SE CONUS...


That secondary spin-off shows up somewhat in the higher resolution gif from OSI SAF.
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Quoting Levi32:
In other news, the Loop Current may be getting ready to close off an eddy? It will be interesting to see how the Loop Current behaves if it does release an eddy.



Out for class, back later.

Class??? on Good Friday??? WOW
Goodnight all... Stay safe
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Quoteing:-168. aspectre

As an interesting note to this post.
There was a 5.5 quake a bit to the south west of the plant today about 3 hours ago and it was very close to what looks like another big installation or nuclear facility on the coast, probably only a mile or so away from it.
Judging by the exclusion zone this plant will also now be inside the 20Km zone!

Member Since: January 21, 2011 Posts: 0 Comments: 2179
In other news, the Loop Current may be getting ready to close off an eddy? It will be interesting to see how the Loop Current behaves if it does release an eddy.



Out for class, back later.
Member Since: Posts: Comments:
New EvacuationZone contains areas more than 40kilometres from FukushimaDaiichi.
And the old 20kilometre EvacuationZone is now officially a 20kilometre ExclusionZone:
no entry allowed without official escorts.

Radiation in the new EvacuationZone exceeds 20millisieverts per year. By how much, officials won't say.
A typical nuclear worker receives 2millisieverts of excess radiation in a year. 20millisieverts per year over 5years is the maximum allowed for nuclear workers before they're barred from entering a nuclear facility. (TEPCO and the Japanese government bumped up the limit for this disaster)
In little over a month, people living in the new EvacuationZone have already received a greater dose of excess radiation than typical nuclear workers receive in a year.

The Japanese government is allowing folks to stay in the new EvacuationZone up to another month to encourage an orderly migration. ie They'll be exposed to more excess radiation than a typical nuclear worker receives in two years before the government takes its responsibility toward citizens seriously.
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Quoting AussieStorm:

In that song by Dexys Midnight Runners, they spell is Eileen.

lol...That does bring back a few memories....Some good news for Texas. Some really bad news for the eastern half....Link.....East U.S. link...Link
Member Since: September 27, 2007 Posts: 1 Comments: 22604
Quoting DocNDswamp:
#144
Indeed, interesting to also note the secondary spin-off is not evident in the ASCAT pass... had been wondering if was a bit more aloft, even though vis-RGB interpretation appeared to reflect at the sfc...


It is at the surface, quite obvious by the low-level cloud field on visible. I think the reason it shows up as so blatently open and unimpressive on the ASCAT is because it is rotating around the main center at quite a rate. Vector addition of the winds around that would give nothing but westerly net components, making it more of a closed vortex in reference to itself but not in reference to the Earth's surface.
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Over the next day or more, the surf will increase more in this Grace Bay Webcam at the Regent Grand.

Link
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Quoting cchsweatherman:


Very interesting indeed. Shows a well defined circulation center (no competing lows evident), no more trough associated with this low, and winds at about minimal tropical storm force very near the circulation center. Would appear more tropical based upon the wind distribution than subtropical.


There is a little wiggle associated with the other SW center though.
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Quoting DocNDswamp:
#150,
True enough, but also notice where those highest winds are - on NW side where we likely have highest gradient winds, right between the 91L low-mid circ and low-mid ridge anchored over the SE CONUS...


True enough, but think about what that implies if the strongest pressure gradient is located closest to the center of low pressure. Typically the gradient would be strongest out >100 miles away from the low center at some baroclinic boundary.
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Quoting DestinJeff:
Come on Arlene, well I swear what NHC means
At this moment, you mean not-a-thing
With you in that mess my thoughts I confess
Verge on dirty
Ah come on Arlene


In that song by Dexys Midnight Runners, they spell is Eileen.

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Quoting Drakoen:
Interesting:




Very interesting indeed. Shows a well defined circulation center (no competing lows evident), no more trough associated with this low, and winds at about minimal tropical storm force very near the circulation center. Would appear more tropical based upon the wind distribution than subtropical.
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Quoting Levi32:
The GFS is still chasing ghosts. However, the Caribbean is likely to be an active place this May, so pre-season activity will have to be watched for down there.



I just hope that high they show there is in a very different position come hurricane season. Yikes!
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#144
Indeed, interesting to also note the secondary spin-off is not evident in the ASCAT pass... had been wondering if was a bit more aloft, even though vis-RGB interpretation appeared to reflect at the sfc...

#150,
True enough, but also notice where those highest winds are - on NW side where we likely have highest gradient winds, right between the 91L low-mid circ and low-mid ridge anchored over the SE CONUS...
Member Since: Posts: Comments:
The GFS is still chasing ghosts. However, the Caribbean is likely to be an active place this May, so pre-season activity will have to be watched for down there.

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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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