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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Whats TD1 doing tonight out there
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Quoting kmanislander:


If there was a closed low you would certainly see evidence of it in that ASCAT pass. Not a scintilla of empirical evidence to suggest a closed low
Satellite imagery would conclude otherwise.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
2288. MZV
I think closed circulation is pretty easily seen on the shortwave image.

One thing I've come to learn over the last few years is that reallllyy crummy looking systems can revive when the conditions merit it. And that shallow systems can slide right under shear.

That is plenty warm water that 92L is coming into contact with in a few days. If it's spinning, it can grow again.
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Quoting MiamiHurricanes09:
Circulation isn't there it's here:

113N, 421W


If there was a closed low you would certainly see evidence of it in that ASCAT pass. Not a scintilla of empirical evidence to suggest a closed low
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Quoting 7544:
92l gets dresss for the show tonight

and the blog is moving at a fast pace

now i really need caffine to keep up here hi bt xcool levi and all
yes I check my facebook page and come back in here and 200 pages later I get back up with everybody....

Taco :o)
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2285. xcool
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2283. OneDrop
Quoting Levi32:


I wish people would stop playing the NHC card. I could care less what they think. It is a fact that they are ultra-conservative with events that take place outside of climatology. This is a potentially historic storm that they will be epically hesitant to classify.

It's been a convection argument this whole time, not a matter of closed circulation. A TD doesn't need a CDO, which is a feature of a 50 knot TS and above. It had more than enough banded convective organization yesterday and certainly last night when it bursted. Try to forget the NHC's opinion and look at a satellite loop of the Atlantic, and tell me what you see doesn't look like a tropical cyclone out there.


Could be, only time will tell. Big swell for the carribean
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2282. Drakoen
Quoting Levi32:


I wish people would stop playing the NHC card. I could care less what they think. It is a fact that they are ultra-conservative with events that take place outside of climatology. This is a potentially historic storm that they will be epically hesitant to classify.

It's been a convection argument this whole time, not a matter of closed circulation. A TD doesn't need a CDO, which is a feature of a 50+ knot TS and above. It had more than enough banded convective organization yesterday and certainly last night when it bursted. Try to forget the NHC's opinion and look at a satellite loop of the Atlantic, and tell me what you see doesn't look like a tropical cyclone out there.


I don't think it is a tropical depression now, however I do think it was a td back when it was in the ITCZ.
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Quoting DestinJeff:
I am having flashbacks to 90L in the GOM last season ... I think that was the invest number "that should have been named" and "probably will be in post-season analysis" because "there is no way this isn't at least a TS, if not a CAT-1."
This blog goes through this "is it or isn't it" L after L, year after year. Some things will never change.
..
Though I did think my idea of just calling them WuWu's was a good one. Why fight. We're all friends with a common interest here. Why quibble about whooo killed whooo?
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Quoting kmanislander:
Not a single N, NW or W wind at 11N 43 W

Closed ?. I don't think so

Circulation isn't there it's here:

113N, 421W
Member Since: September 2, 2009 Posts: 130 Comments: 21194
2279. SLU
Quoting Levi32:
Loop this and think to yourself what your first guess would be as to what this feature is east of the islands if you had no prior knowledge of what the situation in the Atlantic was. First thing that comes to mind? For most experienced people that looks like a tropical cyclone that is struggling to maintain deep convection.


I'm with you on this issue. 92L is way past the "tropical wave" stage. It looks nothing like a wave or a disturbance. More like a TD or maybe even a weak TS trying hard to buy some thunderstorms. It looks very similar to tropical storm Debbie of 2006 when it moved over cooler waters near the Cape Verdes and struggled to generate convection. Maybe someone can post a pic of it.
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2278. 7544
92l gets dresss for the show tonight

and the blog is moving at a fast pace

now i really need caffine to keep up here hi bt xcool levi and all
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2277. Grothar
Rough crowd tonight!!!
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Quoting Levi32:


Well, I wouldn't have classified 90L and 91L.
I wouldn't have classified 91L but I would of called 90L an STS.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
Quoting Orcasystems:


couldn't resist could you? better watch that halo
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NHC arent gods, remember that. they make mistakes too.
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Quoting GTcooliebai:

Wow Miami you went wayy back in the post! As I understand they are scavengers and eat the remains of dead animals. So No way would I ever eat something that feeds off the dead, No way!
Lol, I quoted someone else that quoted you. And people don't really eat crows, just a form of speech when someone is wrong.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
Not a single N, NW or W wind at 11N 43 W

Closed ?. I don't think so

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2269. Levi32
Quoting MiamiHurricanes09:
Lol, yeah you wouldn't want me as chief of the NHC. 92L would of been a TS already, 90L would of been an STS, and 91L would've been a TD.


Well, I wouldn't have classified 90L and 91L.
Member Since: November 24, 2005 Posts: 635 Comments: 26661
Quoting Levi32:


I don't want a floor. You challenged me first so I'll speak my mind because you invited me to.


Cmon guys you both are good in this... The debate is always good especially in this blog!
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To me, it looks like this system has everything going for it tonight, its starting to move into warmer waters, its approaching dmax, AND for the moment it is still under low shear. Tomorrow and tomorrow night may be a different story but for now it looks like this thing has one more chance
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Quoting Levi32:


I wish people would stop playing the NHC card. I could care less what they think. It is a fact that they are ultra-conservative with events that take place outside of climatology. This is a potentially historic storm that they will be epically hesitant to classify.

It's been a convection argument this whole time, not a matter of closed circulation. A TD doesn't need a CDO, which is a feature of a 50+ knot TS and above. It had more than enough banded convective organization yesterday and certainly last night when it bursted. Try to forget the NHC's opinion and look at a satellite loop of the Atlantic, and tell me what you see doesn't look like a tropical cyclone out there.
I agree 100%. Virtual high five.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
Post season analysis....

Im out.
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Quoting OneDrop:
Whether it was or wasn't a depression isn't the argument. When a storm, especially the first storm is that far out to sea, does it really matter? The last thing the U.S. needs is the crazy, aggro media thinking a storm is even heading in this direction to start new "what if" scenarios into the Gulf and then a domino effect will start with rising gas prices, falling stock markets, uneasiness in the masses and an overall unstable population in the Southeast which is unneeded right now. I think the NHC knows what they are doing and when long range models were leaning towards 92L's demise anyways what is the difference? Let's start off 2010 in a peaceful fashion. Make waves not war or just go fishing and be thankful for the good weather when you have it and for all storms to head out to sea.

No, that won't do at all. Makes entirely too much sense. Let's have no more talk like that.
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2260. scott39
Quoting wfyweather:


I still see wnw but quickly transitioning west
Its definitely shifting more to the W.
Member Since: June 13, 2009 Posts: 0 Comments: 6871
Quoting MiamiHurricanes09:
You do understand that you called a crow more "intelligent" that yourself. At that pace you will be eating rocks let alone "intelligent" vegetables. LOL!

Wow Miami you went wayy back in the post! As I understand they are scavengers and eat the remains of dead animals. So No way would I ever eat something that feeds off the dead, No way!
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I think the public is safe without all those designations. When the time comes, I don't think the NHC can deny you.
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Member Since: September 2, 2009 Posts: 130 Comments: 21194
2254. Levi32
Quoting kmanislander:
Levi, the floor is yours.


I don't want a floor. You challenged me first so I'll speak my mind because you invited me to.
Member Since: November 24, 2005 Posts: 635 Comments: 26661
2253. leo305
is it just me or is it slowing just a bit
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2252. Grothar
Quoting Baltimorebirds:
Don't worry that should'nt amount to much.



Funny, that is the same thing that my Father told me when I was in high school.
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Quoting ElConando:


I see it moving SSW.


I still see wnw but quickly transitioning west
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2250. scott39
Quoting ElConando:


I see it moving SSW.
Its going to take its new convection and make a run for the Carribean!
Member Since: June 13, 2009 Posts: 0 Comments: 6871
hey guys if you look at the last surface map and now that tropical wave in BOC/E PAC it moving backwards/eastward
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2248. Levi32
Loop this and think to yourself what your first guess would be as to what this feature is east of the islands if you had no prior knowledge of what the situation in the Atlantic was. First thing that comes to mind? For most experienced people that looks like a tropical cyclone that is struggling to maintain deep convection.
Member Since: November 24, 2005 Posts: 635 Comments: 26661
Quoting tropicaltank:
Can somebody explain to me why the Blob entering th GOM is of no interest?
its a Upper Level Low just from what I'm seeing...

Taco :o)
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Quoting kmanislander:
Levi, the floor is yours.
Good night Kman!
Member Since: September 2, 2009 Posts: 130 Comments: 21194
2244. MZV
People are never satisfied. Complaints now are about NHC being too cautious. But I remember complaints in 2005 that they were too trigger-happy to name storms that barely qualified.... using up letters quickly and pushing into the "Greek Zone"
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Quoting Baltimorebirds:
Miami hurricanes work twards your futuer.Your the only one that can save the nch from all this conservative crap.
Lol, yeah you wouldn't want me as chief of the NHC. 92L would of been a TS already, 90L would of been an STS, and 91L would've been a TD.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
My first cell phone in 1990 came in a huge leather bag. It included a lead acid battery and a 4 foot whip antenna. Laugh all you want but that baby a Motorola Bag Phone could carry a signal for nearly 100 miles on a good day. Today I can't always connect to towers that I can see the phones are so weak. We called them car phones back then. We actually considered ourselves elite to have one back then. What a joke.



Quoting Baltimorebirds:
You mean cell phones??.Becuase when my grandmother showed me hers I laughed.
Link
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Levi, the floor is yours.
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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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