Unusually well-organized 92L disturbance may become a tropical depression

By: Dr. Jeff Masters , 2:14 PM GMT on June 14, 2010

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Invest 92L, a remarkably well-developed African tropical wave for so early in the season, is midway between Africa and the Lesser Antilles Islands. Infrared satellite loops show a modest area of heavy thunderstorms along the north side of 92L's center of circulation, and the storm's heavy thunderstorms activity appears to be slowly increasing in intensity and areal coverage. Upper-level outflow is apparent to the west and north of 92L, and the outflow has been gradually improving this morning. Visible satellite loops do not show much in the way of low-level spiral bands, and my current take from the satellite imagery is that 92L is slowly organizing, and will not become a tropical depression any earlier than 11pm EDT tonight (Monday.) A 4:27 am EDT pass from the WINDSAT satellite saw a partially closed circulation at the surface (open on the south side), with top surface winds of 25 - 30 mph north of the center.


Figure 1. Morning satellite image of Invest 92L (left side of image) and a vigorous new tropical wave that has moved off the coast of Africa (right side.) None of models develop the new tropical wave, but it bears watching.

Sea surface temperatures
Climatology argues against development of 92L, since only one named storm has ever formed between Africa and the Lesser Antilles Islands in the month of June--Tropical Storm Ana of 1979 (Figure 2). However, sea surface temperatures (SSTs) underneath 92L are an extremely high 28°C, and will increase to 29°C by Thursday. In fact, with summer not even here, and three more months of heating remaining until we reach peak SSTs in the Atlantic, ocean temperatures across the entire Caribbean and waters between Africa and the Lesser Antilles are about the same as they were during the peak week for water temperatures in 2009 (mid-September.)

Dry air not a problem for 92L until Wednesday
The disturbance doesn't have to worry about dry air today or Tuesday--Total Precipitable Water (TPW) loops show a very moist plume of air accompanies 92L, and water vapor satellite loops show that the center of 92L is at least 200 - 300 miles from any substantial areas of dry air. As 92L continues to push northwest, though, the SHIPS model is predicting that relative humidity at middle levels of the atmosphere will fall from the current value of about 70%, to 60% on Wednesday. This dry air may begin to cause problems for 92L on Wednesday, especially since wind shear will be increasing at the same time. Tropical cyclones are more vulnerable to dry air when there is substantial wind shear, since the strong winds causing the shear are able to inject the dry air deep into the core of the storm.

Madden-Julian Oscillation
The 60-day cycle of enhanced thunderstorm activity called the Madden-Julian Oscillation is currently favoring upward motion over eastern tropical Atlantic, and this enhanced upward motion helps create stronger updrafts and higher chances of tropical cyclone development.


Figure 2. Tropical Storm Ana of 1979 was the only June named storm on record to form between Africa and the Lesser Antilles Islands.

Wind shear
A major issue for 92L, like it is for most June disturbances, is wind shear. The subtropical jet stream has a branch flowing through the Caribbean and tropical Atlantic north of 10° N that is bringing 20 - 40 knots of wind shear to the region. Our disturbance was located near 10°N, 40°W at 8am EDT this morning, a few hundred miles south of this band of high shear, and is currently only experiencing 5 - 10 knots of shear. This low amount of shear should allow for some steady development of 92L over the next two days as it tracks west-northwest or northwest at 15 mph. The latest run of the SHIPS model is predicting the shear will rise to 20 knots on Wednesday, which may start to cause problems for 92L.

The forecast for 92L
The National Hurricane Center is giving 92L a high (60% chance) of developing into a tropical depression by Wednesday morning, which is a reasonable forecast. The odds of development have increased since yesterday, as the storm has moved considerably to the northwest, away from the Equator. Now it can leverage the Earth's spin to a much greater degree to help get it get spinning. It is quite unusual for a tropical depression to form south of 8°N latitude.

I expect that 92L's best chance to become a tropical depression will come on Tuesday, and the storm could strengthen enough by Wednesday to be named Tropical Storm Alex. The farther south 92L stays, the better chance it has at survival. With the system's steady west-northwest movement this week, 92L will probably begin encountering hostile wind shear in excess of 20 knots by Wednesday, which should interfere with continued development. Several of our reliable models do develop 92L into a tropical storm with 40 - 55 mph winds, but all of the models foresee weakening by Thursday or Friday as 92L approaches the Lesser Antilles Islands and encounters high shear and dry air. I doubt 92L will be anything stronger than a 45 mph tropical storm when it moves through the northern Lesser Antilles Islands on Friday and Saturday, and it would be no surprise if wind shear has destroyed the storm by then. However, as usual, surprises can happen, and the GFS and the SHIPS model (which is based upon the GFS) do indicate that more modest levels of wind shear in the 15 - 20 mph range late this week may allow 92L to stay stronger than I'm expecting. Residents of the islands--particularly the northern Lesser Antilles--should follow the progress of 92L closely, and anticipate heavy rains and high winds moving through the islands as early as Thursday night.

Oil spill wind forecast
There is little change to the oil spill wind forecast for the coming two weeks. Light winds of 5 - 10 knots mostly out of the south or southeast will blow in the northern Gulf of Mexico all week, according to the latest marine forecast from NOAA. These winds will keep oil near the coast of Louisiana, Alabama, Mississippi, and the extreme western Florida Panhandle, according to the latest trajectory forecasts from NOAA and the State of Louisiana. The long range 8 - 16 day forecast from the GFS model indicates a typical summertime light wind regime, with winds mostly blowing out of the south or southeast. This wind regime will likely keep oil close to the coastal areas that have already seen oil impacts over the past two weeks.

Jeff Masters

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you would think that the National Hurricane Center would have a much better system then naming systems in Pacific and Atlantic the same thing. 92L what has happen to creative minds so mix ups dont happen. Just my thought of the day..

Good evening everyone!!
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1390. xcool
Baltimorebirds .48HR
Member Since: September 26, 2009 Posts: 2 Comments: 15684
Quoting Levi32:
Circulation is tightening in the last 3 hours....a good sign.

yes lacks thunderstorms but circulation is getting tighter.
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Quoting Weather456:
I'm not feeling so well guys so I will be in and out throughout the night.
Hope you feel better.
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1385. Levi32
Circulation is tightening in the last 3 hours....a good sign.

Member Since: November 24, 2005 Posts: 635 Comments: 26698
1383. IKE
Quoting scott39:
your not far from me Ike, I will drink anybodys who cant show.


LOL.
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1382. xcool
DO I SEE POPOP ON 92L .
Member Since: September 26, 2009 Posts: 2 Comments: 15684
1381. scott39
Quoting IKE:


If the NHC gives that anything higher then 30%, a round of drinks on me!
your not far from me Ike, I will drink anybodys who cant show.
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I also see all models still taking this to a tropical depression strength in the next 12 hours Link
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1379. Drakoen
Member Since: October 28, 2006 Posts: 57 Comments: 30717
Quoting Baltimorebirds:
Dammit I was typing to fast.I mean to say disturbences.


You really meant to say disturbances.
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Quoting IKE:


If the NHC gives that anything higher then 30%, a round of drinks on me!
Ok, I'll take sprite, lol!
Member Since: September 2, 2009 Posts: 130 Comments: 21194


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I'm not feeling so well guys so I will be in and out throughout the night.
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BLOG UPDATE!

Hurricane Season Blog #25: 92L Overlook
Member Since: September 2, 2009 Posts: 130 Comments: 21194
1371. IKE
Quoting MiamiHurricanes09:
It's sticking out its little arm:



If the NHC gives that anything higher then 30%, a round of drinks on me!
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Hmm, convection may be starting to flare again, and over the center at that. The flash loop suggests as much. From the storm's point of view, better to use energy for that than for blowing up the convection that is just being sheared. I'm not going to write this system off until I see what becomes of this new ball of convection.
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1369. Drakoen
The SHIPS still gives it 48 more hours of <20 knot wind shear. The RH looks to decrease so 92L has to do something overnight with the war waters it is going to be under if it wants to survive both short and long term. If it can develop then I assume it can handle a transient period marginal shear based on the SHIPS (*GFS based) forecast.
Member Since: October 28, 2006 Posts: 57 Comments: 30717
Good Evening I have been out all day and wonder why everyone is calling doom . This system has finally gotten itself out of the itz and is now ready to slowly develop as it moves to the wnw the reason it lost its convection is because the itz is not involved anymore and this should let the system loose its angular looks
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1364. xcool
AL, 92, 2010061418, , BEST, 0, 104N, 409W, 25, 1011,
Member Since: September 26, 2009 Posts: 2 Comments: 15684
Quoting DestinJeff:
also looks like some minor banding evident in the southern semi-circle ...?


The Southern side of 92L is beginning to "round out" somewhat and is looking more symmetrical.This is giving it a more upright appearance overall.
Member Since: August 19, 2006 Posts: 0 Comments: 15948
It's sticking out its little arm:

Member Since: September 2, 2009 Posts: 130 Comments: 21194
1359. xcool


Member Since: September 26, 2009 Posts: 2 Comments: 15684
well JLPR2 that is if the shear can take its toll which I expect it not to shear is dying so I don't think I will be a problem
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i am back what is new with 92L any changes
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Ladies and gents..........92L is kicking again
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Quoting HaboobsRsweet:
Ok so here is why I thought 92L wouldnt make it and why I am a little more concerned with the next wave. 92L was the wedge buster like the first player down a football field for kickoff. There were unfavorable conditions in front of it and sure enough it got eaten alive however it made its dent just like the wedge buster. Now the tutt many shift slightly north while the new wave is just a hair south of 92L Things may open up just enough for the next wave to form. Depends how much the shear relaxes.


Which is my concern as well. That wave behind 92L is not falling apart and it's been off the coast for awhile.
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1351. xcool



SHEAR lifting UP..
Member Since: September 26, 2009 Posts: 2 Comments: 15684
1350. Drakoen
Quoting Baltimorebirds:
Drakeon what are your feelings on the wave behind 92L.


Something to watch. Nothing imminent.
Member Since: October 28, 2006 Posts: 57 Comments: 30717
Quoting ssmate:

Teasecaster.....jk


LOL. Now everyone will be watching for the next ASCAT pass to see where it went.
Member Since: August 19, 2006 Posts: 0 Comments: 15948
Ok so here is why I thought 92L wouldnt make it and why I am a little more concerned with the next wave. 92L was the wedge buster like the first player down a football field for kickoff. There were unfavorable conditions in front of it and sure enough it got eaten alive however it made its dent just like the wedge buster. Now the tutt many shift slightly north while the new wave is just a hair south of 92L Things may open up just enough for the next wave to form. Depends how much the shear relaxes.
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1346. xcool
btwntx08 :0
Member Since: September 26, 2009 Posts: 2 Comments: 15684
1345. ssmate
Quoting kmanislander:
There was a nice surface low in the S. Caribbean this morning but probably moved inland by now.


Teasecaster.....jk
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1343. eddye
xcoolgo totropics chat and everybody else2
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the system behind 92L looks pretty good too and should have better overall conditions

also 92L looks to be fighting back at a time you would think it wouldn't

I found in my years of tracking developing systems that the minute you write them off, they try to come back. 92L isnt done yet
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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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