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

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

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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1440. will45
Quoting kmanislander:


I posted a short while back that it was odd to see what appeared to be a very weak system still being pulled up to the WNW. The stacking we are seeing explains why.

92L is down but not out.


yes i think we started seeing it last night. Remember when it started to begin looking smaller with the consoliation? i think that helped the stacking
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1439. Levi32
Quoting MiamiHurricanes09:
WOW, it might have a chance. I noticed that but didn't give much care for it.


The entire pattern favors these things coming north instead of running into South America. Lowering pressures across the tropical basin over the next 2 weeks means trouble is possible as the MJO starts moving in again. I continue to say the real kick-off is approaching near the end of the month into early July.
Member Since: November 24, 2005 Posts: 635 Comments: 26780
Quoting StormW:
18Z GFS forecast shear map looks a little more optimistic...not optimal, but somewhat better.
Agree.
Member Since: September 2, 2009 Posts: 130 Comments: 21375
Quoting Levi32:


Even if it doesn't, the same would be true.

Agree
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1435. Levi32
Quoting Seflhurricane:

that is very disturbing looks like something strong near the bahamas approching the east coast ???


How astute.
Member Since: November 24, 2005 Posts: 635 Comments: 26780
Quoting Levi32:
Big changes on the GFS in only 48 hours as the upper ridge associated with 92L pushes the TUTT to the north, resulting in mostly ridging and light winds over 92L by 48 hours. You can already see the upper ridge busting right into the TUTT on water vapor imagery, forcing the air northwest of 92L to curve north.

18z GFS 200mb 48 hours:



WOW, it might have a chance. I noticed that but didn't give much care for it.
Member Since: September 2, 2009 Posts: 130 Comments: 21375
1433. Levi32
Quoting Seflhurricane:
if this develops into TS Alex this would be a bad warning sign of a precurser of things to come in aug-oct


Even if it doesn't, the same would be true.
Member Since: November 24, 2005 Posts: 635 Comments: 26780
Quoting Levi32:
Scary huh....should be taken with a grain of salt because it's obviously 384-hours but notice the tendencies we have here for these waves to try to develop early and the models catching on. This is scary stuff to have possibly more than one concern east of 60W in June.

18z GFS Day 15:


that is very disturbing looks like something strong near the bahamas approching the east coast ???
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1431. Drakoen
Quoting ElConando:


I assume you mean for it.


Yes
Member Since: October 28, 2006 Posts: 57 Comments: 32488
Ugh those awful tails they're like leeches to tropical storms and waves. Phet had this problem that's why it wasn't a 5
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Quoting Drakoen:



LOL. Going to be a long...long night.


I assume you mean for it.
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Quoting Weather456:
1378. Baltimorebirds 6:35 PM AST on June 14, 2010 Hide this comment.

Quoting Weather456:
I'm not feeling so well guys so I will be in and out throughout the night.

What's wrong??


I ate something bad so its messing with me.
I can just imagine... LOL. Hope you feel better man.
Member Since: September 2, 2009 Posts: 130 Comments: 21375
if this develops into TS Alex this would be a bad warning sign of a precurser of things to come in aug-oct
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As for 92L, I'll check a little later

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1424. Levi32
Scary huh....should be taken with a grain of salt because it's obviously 384-hours but notice the tendencies we have here for these waves to try to develop early and the models catching on. This is scary stuff to have possibly more than one concern east of 60W in June. Even the next one behind this one looks suspicious on the model.

18z GFS Day 15:

Member Since: November 24, 2005 Posts: 635 Comments: 26780
1423. xcool
dam <<< caps lock
Member Since: September 26, 2009 Posts: 2 Comments: 15707
Quoting Levi32:
18z GFS is bullish on the wave behind 92L.

Day 7:



Day 11:





Looks decent enough atm.
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1421. txjac
Get better weather456 ...I love reading your posts.
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1420. xcool
ROB .YOU SEE WHAT I MEAN ??
Member Since: September 26, 2009 Posts: 2 Comments: 15707
1419. Drakoen



LOL. Going to be a long...long night.
Member Since: October 28, 2006 Posts: 57 Comments: 32488
Quoting Drakoen:
Better aligned up through 700mb with some signs up to 500mb.


I posted a short while back that it was odd to see what appeared to be a very weak system still being pulled up to the WNW. The stacking we are seeing explains why.

92L is down but not out.
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Quoting Weather456:
I'm not feeling so well guys so I will be in and out throughout the night.


take care of yourself 456, we are going to need you in the comming months
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Quoting StormW:


Same here...get better!


I just got over that bad upper respiratory infection going around. I was in bed for 3 days. And if you knew me personally you would know that I hate laying in bed.
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1415. xcool
456 .GET BETTER...
Member Since: September 26, 2009 Posts: 2 Comments: 15707
92L beginning to look a bit better but let me remind everyone that last season we had the same problem all the conditions were there for this system to get cranked and collapsed. lets wait and see but it needs convection real soon
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1378. Baltimorebirds 6:35 PM AST on June 14, 2010 Hide this comment.

Quoting Weather456:
I'm not feeling so well guys so I will be in and out throughout the night.

What's wrong??


I ate something bad so its messing with me.
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Wow... I go on vacation for 3 days and I miss 92L? That's just my luck...
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1411. Levi32
18z GFS is bullish on the wave behind 92L.

Day 7:



Day 11:



Member Since: November 24, 2005 Posts: 635 Comments: 26780
1409. Drakoen
Better aligned up through 700mb with some signs up to 500mb.
Member Since: October 28, 2006 Posts: 57 Comments: 32488
shout out to 456 feel better!
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I think 92L might just pull it off after all!
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1405. xcool
Baltimorebirds Quoting Baltimorebirds:
.92L only has a couple of hours to go before getting ripped to shreads by shear. LOL
Member Since: September 26, 2009 Posts: 2 Comments: 15707
1404. Levi32
Quoting Weather456:
I'm not feeling so well guys so I will be in and out throughout the night.


Sorry to hear....hope you feel better.
Member Since: November 24, 2005 Posts: 635 Comments: 26780
Quoting wunderkidcayman:
wow 92L is starting to make a comeback


I believe the COC is still to the south.
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Quoting Seflhurricane:
yes lacks thunderstorms but circulation is getting tighter.


One thing can lead to another.
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1400. will45
Quoting Weather456:
I'm not feeling so well guys so I will be in and out throughout the night.


Hope you feel better soon 456
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1399. Levi32
Big changes on the GFS in only 48 hours as the upper ridge associated with 92L pushes the TUTT to the north, resulting in mostly ridging and light winds over 92L by 48 hours. You can already see the upper ridge busting right into the TUTT on water vapor imagery, forcing the air northwest of 92L to curve north.

18z GFS 200mb 48 hours:



Member Since: November 24, 2005 Posts: 635 Comments: 26780
wow 92L is starting to make a comeback
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Quoting Levi32:
Circulation is tightening in the last 3 hours....a good sign.

That is the strongest and most circular vortics i have seen on the system
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Quoting Levi32:
Circulation is tightening in the last 3 hours....a good sign.



Surface convergence still weak but better aligned with the 850 mb vorticity. 92L may be trying to right the ship.

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92L is quickly becoming better organized this afternoon, and I am becoming increasingly concerned that we will have a td by morning. its getting healthy outflow again and a new ball of convection right on top the the coc, ALSO, models are now all pretty much developing this system and strengthening it.
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1392. IKE
Monitoring Tropical Waves in the Central Atlantic
Jun 14, 2010 5:49 PM



As of Monday evening, EDT, a tropical wave is located about 1,375 miles east of the Windward Islands, near 11 north and 43 west. Satellite imagery earlier in the day showed impressive convection sparked by low-level convergence, but this convection has since waned into the evening. These concentrated thunderstorms interacted with southerly wind shear aloft, and the remaining storms are being pushed well away from the low-level circulation. The low-level circulation is moving west-northwestward around 17 mph. A tropical depression is possible over the next couple of days as conditions remain generally favorable for further development over the next 48 hours. However, a harsh wind-shear environment lies ahead after the midweek period.


By AccuWeather Senior Meteorologist Brian Wimer and Meteorologist Andy Mussoline
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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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Dr. Masters co-founded wunderground in 1995. He flew with the NOAA Hurricane Hunters from 1986-1990. Co-blogging with him: Bob Henson, @bhensonweather

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