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


The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

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991. ryang
Is this the wave going through the Windwards that the Euro is developing? TIA

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mm
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Quoting MiamiHurricanes09:


cur blimey the kids got measles somebody call the Dr.
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Quoting WindDamage:
indeed, Met, I wonder why it's redeveloping ti, hmm, levi, thoughts?


I wouldn't be surprised if that was so. Pressures will be lowering across the entire tropical Atlantic over the next two weeks, and shear really won't be that bad in the Caribbean once 92L gets there. An upper-level ridge will be in place across most of the MDR by that time. If 92L has opened up into a wave before it reaches the islands, then it will have no chance in the eastern Caribbean. It is most likely to go north and interact with Hispaniola and Puerto Rico, but if it happens to make it farther west, it could possibly work some mischief. That, however, will be assessed when we get there. It's speculation at this point. The lowering pressures on the ECMWF, however, do point to the building energy that will need to be watched for as some of these things are really gonna want to pop over the next 2 weeks.
Member Since: December 31, 1969 Posts: Comments:
..."I saw a Werewolf drinking a Pina Colada at Trader Vic's"..


He was Glancing at the GFS..
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Quoting Gustavike:
A tropical wave interacting with an upper level low


It will not develop.
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Quoting Levi32:


I don't deal in statistical probabilities. I continue to technically give 92L a high chance to become a tropical depression, but that's because I believe it already is and has been. It has the look of a struggling tropical cyclone. The NHC will be the NHC....they are like this with events that take place outside of climatology. They will avoid classifying it if possible.

As for whether I think it will remain a significant and defined system as it approaches the islands, I'll give it a moderate chance.


Well said...
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The thing is, a couple hours ago when I saw the RIPs, and I thought, " If this thing develops tomorrow, everyone will be eating crow."
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968. Thanks StormW, although one who follows the weather would know things can change, weather is dynamic and not constant, but always appreciate your work.
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African waves very interesting, needs to be watched. 92L per the ECMWF has a shot in the Caribbean too.
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A tropical wave interacting with an upper level low
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Quoting scott39:
I worded my question wrong, with already having that convection, will it help it tonight at DMAX and help develope it faster?


Well, the convection is getting farther from the center, so that's not really helping it, but if it keeps producing convection throughout the day, even if it's removed from the center, will indicate that it has the ability to send up some more thunderstorms tonight, if it is allowed.
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RIP 92L. There, I said it. This thing doesn't have much of a window to organize and it is already pretty disorganized.
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92L is somewhat a fighter I see it's holding its weak convection near the coc
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Quoting jasoniscoolman09:
92E


Not looking too well.
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Quoting wunderkidcayman:
tonight 92L will look hot like fire when we go into DMAX and become TD1 tomrrow morn or midday and maybe TS ALEX
That's what everyone said yesterday.
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Quoting Levi32:


Keeping convection to the north is not a good thing.
I worded my question wrong, with already having that convection, will it help it tonight at DMAX and help develope it faster?
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tonight 92L will look hot like fire when we go into DMAX and become TD1 tomrrow morn or midday and maybe TS ALEX
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Hey Miami, do you think that 92L will ever become a TD?
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This place cracks me up. On one hand you have people hoping for storms, and on the other hand, people praying against them and smugly/happily rejoicing every time one doesn't develop, or dies. Frankly, I think this season is going to be quite interesting. I think I will be evacuating NOLA at least once. We shall see.
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Quoting futuremet:
Perhaps it is not the wave behind 92L the ECMWF is developing. It seems to be one of the detached waves from the ITCZ. The ECMWF redeveloping 92L in the western Caribbean.

Allan Huffman's 12Z ECMWF
Yup, just pointed that out.
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Member Since: December 31, 1969 Posts: Comments:
The ECMWF seems to be redeveloping 92L in the western Caribbean.

Allan Huffman's 12Z ECMWF
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Quoting CaribBoy:


This general area should get wet.. and i must say it is in agreement with the above-average rainfall forecast for this month.
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Quoting scott39:
Levi, Does it mean anything good short term for 92L , since it has kept the convection to the N all day?


Keeping convection to the north is not a good thing.
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You know what, I will RIP 92L because if the NHC didn't call it yesterday, they won't anymore, and it'll just get that it didworse from here on out. The kid that it did that
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Quoting MiamiHurricanes09:
12z ECMWF keeps 92L an open wave and takes it though the northern lesser Antilles, Puerto Rico, Hispanola, and then the Caribbean. In the Caribbean it develops a 1010 millibar low but then quickly dissipates in the western Caribbean. Very interesting run to say the least.


This general area should get wet.. and i must say it is in agreement with the above-average rainfall forecast for this month.
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Quoting Levi32:
On the ECMWF also notice the area of expanding low pressure in the western Caribbean. The entire Caribbean will be favorable for waves to move in and develop during the next couple weeks.

Agreed.
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What a shame-It would have been nice to have 91L & 92L upgraded to Tropical Storm Status before their demise. At least that way we would have been looking for the "C" storm with June not even half over.
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On the ECMWF also notice the area of expanding low pressure in the western Caribbean. The entire Caribbean will be favorable for waves to move in and develop during the next couple weeks. The 1009mb low near the windwards is the next wave behind 92L.

Member Since: December 31, 1969 Posts: Comments:
12z ECMWF keeps 92L an open wave and takes it though the northern lesser Antilles, Puerto Rico, Hispanola, and then the Caribbean. In the Caribbean it develops a 1010 millibar low but then quickly dissipates in the western Caribbean. Very interesting run to say the least.
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Levi, Does it mean anything good short term for 92L , since it has kept the convection to the N all day?
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Quoting futuremet:


The upcoming waves will have a much higher chance of developing. This is substantiated by the 12Z ECMWF.


I'm surprised to see the Euro taking a bite already.
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Quoting altesticstorm10:

The shear's going to continue to diminish ahead of 92L as it trucks westward?


It will increase to weak-moderate levels over the system as it approaches the TUTT but will then remain the same as the equatorial ridge begins to push the TUTT northward. By the time 92L gets to the islands, upper-level conditions overhead will be just as favorable as they have been for the last couple days. Upper ridging will be across the entire MDR by the end of this week.
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Quoting MiamiHurricanes09:
GFDL and HWRF have no idea what to do with 92L, intensity-wise.



Obviously
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Quoting Levi32:


Dang....look at these things wanting to pop one after another already.


The upcoming waves will have a much higher chance of developing. This is substantiated by the 12Z ECMWF.
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18z Early Cycle NHC model tracks
Invest92
Statistical/Simple Models (CLIPER,BAMs,LBAR,other Statistical Models)





Dynamic Models (More sophisticated models)



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Hi Relix, it's not over yet. 92L is still spinning, still over warm water. Looks like the southerly portion is getting into the act again.
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945. IKE
Quoting futuremet:
As I thought, 12Z ECMWF develops the wave behind 92L.


I saw that too. It looks sheared to me with all of the convection away from the center.
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Quoting futuremet:
As I thought, 12Z ECMWF develops the wave behind 92L.


Dang....look at these things wanting to pop one after another already.
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Quoting Levi32:


I don't deal in statistical probabilities. I continue to technically give 92L a high chance to become a tropical depression, but that's because I believe it already is and has been. It has the look of a struggling tropical cyclone. The NHC will be the NHC....they are like this with events that take place outside of climatology. They will avoid classifying it if possible.

As for whether I think it will remain a significant and defined system as it approaches the islands, I'll give it a moderate chance.
I think 92L was a tropical depression yesterday and possibly a tropical storm. I am pretty sure that the NHC will never classify 92L anymore, but was it a TD, yes.
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941. Relix
I am still impressed how a so good looking system turned to nothingness. Wow.
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Cat 6 lead authors: WU cofounder Dr. Jeff Masters (right), who flew w/NOAA Hurricane Hunters 1986-1990, & WU meteorologist Bob Henson, @bhensonweather

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