Two African waves, 92L and 93L, worth watching

By: Dr. Jeff Masters , 2:59 PM GMT on August 11, 2011

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An African wave is near 13°N 35°W, about 700 miles west-southwest of the Cape Verde Islands. This system, (Invest 92L), is moving west to west-northwest at 10 - 15 mph, and has the potential to develop into a tropical depression or tropical storm before arriving near the northern Lesser Antilles Islands early next week. Recent visible satellite loops show that 92L has less heavy thunderstorm activity near where it is trying to develop its circulation center than yesterday. Water vapor satellite loops that a large area of dry air lies just to the west of 92L, but the atmosphere in the immediate vicinity of 92L is moist. Even so, the decline of heavy thunderstorm activity since yesterday implies that dry air is probably working its way into 92L. The SHIPS model and University of Wisconsin CIMSS wind shear analysis are showing moderate wind shear of 10 - 15 knots affecting 92L. Sea surface temperatures are 26.5° - 27°C, which is very close to the 26.5°C threshold usually needed to support a tropical storm.


Figure 1. Morning satellite photo of Invest 92L and Invest 93L.

Forecast for 92L
Low to moderate wind shear of 5 - 15 knots is predicted along 92L's path over the coming three days, which should allow the storm to organize, assuming it can shut out any incursions of dry air that might intrude. The latest 00Z and 06Z model runs of the four best models for predicting tropical storm formation (GFS, ECMWF, NOGAPS, and UKMET) show weak development or no development of 92L, and NHC gave 92L a 30% chance of developing into a tropical depression by Saturday morning in their 8am outlook. A steady west to west-northwest motion for 92L is predicted by all of the models, which would put the storm in the vicinity of the northern Lesser Antilles Islands by Sunday. On Saturday and Sunday, 92L is expected to enter a region where an upper-level low pressure system will bring high wind shear of 20 knots to the storm, which should slow development. This upper-level low is also expected to turn 92L more to the northwest, so the storm is likely to pass north of the Lesser Antilles, though may pass close enough to give heavy rains to the northernmost islands. It is too early to know if 92L will recurve out to sea and potentially threaten Bermuda, or continue to the northwest towards the U.S. East Coast.

93L
An African wave that emerged off the coast of Africa is near 10°N 22°W, a few hundred miles south of the Cape Verde Islands. This system, (Invest 93L), is also moving west at 10 - 15 mph, and has the potential to develop into a tropical depression or tropical storm before arriving near the northern Lesser Antilles Islands near the middle of next week. Recent visible satellite loops show that 93L has a decent amount of heavy thunderstorms, but this activity is not well organized. There is not much spin associated with 93L yet. 93L is fairly well-protected from dry air to its north and west. The SHIPS model and University of Wisconsin CIMSS wind shear analysis are showing moderate wind shear of 10 - 20 knots affecting 93L. Sea surface temperatures are 27.5°C, which is one degree above the 26.5°C threshold usually needed to support a tropical storm.

Forecast for 93L
Moderate wind shear below 20 knots is predicted along 93L's path over the coming five days, which should allow the storm to steadily organize. 93L is about 600 miles east of 92L, which is close enough that the two systems may interfere with each others' organization. The latest 00Z and 06Z model runs of the four best models for predicting tropical storm formation (GFS, ECMWF, NOGAPS, and UKMET), have only one model, the GFS, that is indicating significant development of 93L. This model brings 93L near the northern Lesser Antilles Islands by Wednesday. NHC gave 93L a 20% chance of developing into a tropical depression by Saturday morning in their 8am outlook. Due to moister air, the potential for less wind shear, and a more southerly track, 93L is probably a greater threat to the Lesser Antilles than 92L.

Jeff Masters

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Have to head back to work now so will catch up later.
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Quoting USAFwxguy:


Some good advice is simply to make general preperations for evacuation (or shelter in place, as applicable). If a storm does approach your area, local officials will offer guidance. Otherwise, enjoy the nice weather and maintain your own awareness. If it becomes increasingly likely that the storm may threaten directly, then you begin more specific actions as you deem necessary, or follow instruction of local authorities.
FINALLY! A calm, sane demeanor. Must be all that military training. Welcome Aboard!
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Quoting reedzone:


Trough is too strong, will likely be weaker in reality.. It's not October, it's August.

I agree most models seem to be overdoing the troughs a bit this year i think we might be surprised by how far west 92L gets and really surprised by 93L should it develop!!!IMO
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Quoting beell:


It does. As well as the short wave induced weakness between them. Betting money is on 92L to find it-along with some of the driest air in the Atlantic. 93L may stay within the monsoon for a while longer. But just to make things perfectly unclear...92L could keep a piece of energy south also, lol.


All agreed there LOL. 92L looks like a feature that could become a split personality.
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Quoting Ivanhater:


92L is likely to develop before 93L...Canadian, GFS and Euro all develop 92L in the next couple of days

12z Euro 96 hours



Trough is too strong, will likely be weaker in reality.. It's not October, it's August.
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Quoting Ivanhater:


92L is likely to develop before 93L...Canadian, GFS and Euro all develop 92L in the next couple of days

12z Euro 96 hours



We'll see. The center is displaced from any sort of convection and is very broad in nature. 92L also has to fight the dry air effects. 93L is still in the development stages of its low level center, but I'm starting to notice a nice turn in the clouds in the middle of the convection:

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252. beell
Quoting kmanislander:


That shows the two high centers very nicely


It does. As well as the short wave induced weakness between them. Betting money is on 92L to find it-along with some of the driest air in the Atlantic. 93L may stay within the monsoon for a while longer. But just to make things perfectly unclear...92L could keep a piece of energy south also, lol.
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Who thinks 93L can be a threat to the U.S.?
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Quoting MississippiWx:
Wow, both areas at 40% I see. I believe that's a little too generous for 92L, but seems very reasonable for 93L.


Eh they must see something.
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Quoting MississippiWx:
Wow, both areas at 40% I see. I believe that's a little too generous for 92L, but seems very reasonable for 93L.


92L is likely to develop before 93L...Canadian, GFS and Euro all develop 92L in the next couple of days

12z Euro 96 hours

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248. JRRP

GFDL
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center of 92L becoming better defined around 12.5N/35W, looks to be moving west now to me.
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Hey guys. Just jumping in out of lurk mode to say hello for the first time this season. Looks like 93L could be a player. Not liking the latest GFDL track. Maybe a good time to fill up the gas cans while oil is down. Keep up the good work. Back to lurk mode.
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Wow, both areas at 40% I see. I believe that's a little too generous for 92L, but seems very reasonable for 93L.
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Quoting Matt74:
I'm no expert just an observer but people have been saying since last year that the pattern will change in the next 10 days and it still hasn't happened. I'll believe it if and when it ever happens.

It's going to change in about 10 days.....
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243. beell
Quoting USAFwxguy:


That is certainly the case. I should have been more clear in stating a tight cyclonic spin.

Thanks for pointing that out.


No problem. Still easier for something to develop in the monsoon circulation as opposed to the confluent flow found in the ITCZ.
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Quoting beell:
12Z 850mb streamlines
click to enlarge



That shows the two high centers very nicely
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Quoting Jebekarue:


LOL, ok how bout the theme of Jaws to go with it? or should it be the background music to some slasher flick? Or maybe some tchaikovsky :)


Khatchurian's Sabre Dance is a good option.
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I'm no expert just an observer but people have been saying since last year that the pattern will change in the next 10 days and it still hasn't happened. I'll believe it if and when it ever happens.
Member Since: June 21, 2011 Posts: 0 Comments: 329
239. beell
12Z 850mb streamlines
click to enlarge

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Wonder where Presslord is ? LOL




3. DISORGANIZED SHOWERS AND A FEW THUNDERSTORMS LOCATED OVER THE
ATLANTIC ABOUT MIDWAY BETWEEN THE CAROLINAS AND BERMUDA ARE
ASSOCIATED WITH A BROAD TROUGH OF LOW PRESSURE. ANY DEVELOPMENT OF
THIS AREA OF DISTURBED WEATHER SHOULD BE SLOW TO OCCUR AS IT MOVES
NORTHEASTWARD AT 15 TO 20 MPH. THIS SYSTEM HAS A LOW CHANCE...10
PERCENT...OF BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS.
Member Since: October 9, 2008 Posts: 0 Comments: 8399
Quoting Cotillion:


Channel your inner Gene Kelly. ;)

LOL
It lasted 2 minutes.
Just enough to raise the Humidity to "Dread"....
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Quoting Stormchaser2007:
Would be funny if the ECMWF was right again and these invests stayed weak with little development occurring.

It's been pretty great so far this year.


Actually, it has done pretty poorly compared to other years when it comes to development, its excellent on track however.

Didn't pick up on Arlene until a day or so before.
Didn't pick up on Bret.
Didn't pick up on Cindy.
Got Don right, but never indicated it would be a TS.
Didn't pick up on Emily, though it could be argued it got Emily right as it never showed a closed low.. when the recon found one.
Member Since: July 8, 2005 Posts: 259 Comments: 24254
Quoting kmanislander:


Before I answer the question about the high, you will have seen from the surface map that the monsoon trough gives way to the ITCZ which then dives off to the South. If that pattern holds then 92L will escape to do what it will, but still no guarantee of development. We will need to wait and see where 93L is farther out in time.

Regarding the high East of the Bahamas, the forecast steering by the GFS, Navy and CMC hold that high there through this Sunday along with a high in the N Atl and separating the two by a weakness near 60W. After Sunday the Bahamas high breaks down some which should allow for anything coming that way next week early to recurve. Still long range though and could change as we well know.

Nice!
Thanks.
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Quoting pottery:
AAAAHHHhh!
It's RAINING !!!!
(first time in over a week.......)


Channel your inner Gene Kelly. ;)
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Quoting pottery:

Also...

Looking at the ITCZ, and the sharp "dog-leg" to the south, just west of both systems.
It would be expected that both the systems will escape the ITCZ as they go west.


Before I answer the question about the high, you will have seen from the surface map that the monsoon trough gives way to the ITCZ which then dives off to the South. If that pattern holds then 92L will escape to do what it will, but still no guarantee of development. We will need to wait and see where 93L is farther out in time.

Regarding the high East of the Bahamas, the forecast steering by the GFS, Navy and CMC hold that high there through this Sunday along with a high in the N Atl and separating the two by a weakness near 60W. After Sunday the Bahamas high breaks down some which should allow for anything coming that way next week early to recurve. Still long range though and could change as we well know.
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Quoting CarolinaHurricanes87:
Some if the posts I've seen today worry me. I am a Wilmington, nc resident, and love weather and am very interested in TC's, but also realize the amazing damage they cause. I am "enthusiast", but know very little compared to most on this
Board. Some models suggest 92 and 93 will recurve, which is good for my location. But others say these model runs could drastically shift westward , like earl... Which had it's intense ball of convection literally 20 miles off my coast.

If these do not recurve, or recurve much further west than it currently looks, I feel Wilmington, nc could be directly in the path. I kno it's too early to worry, but......

What exact pattern should I be following to give me better insight as to why (and if) these potential storms could impact my area. With so much warm, open water this summer I fear if they do get directed towards NC that it could be a bad situation.
Thanks for any insight everyone


As for which pattern to watch for, I wouldn't watch any of them. They are all different both in set up and outcome. A series of identical setups and identical conditions often, nay always, brings different results.

With respect, to be sitting in Wilmington now and looking at 92 and 93 with more than passing interest is a complete waste of what I am sure is your valuable time.

Now, if the models point at your street 7 days from now, I would have a closer look, and in 10...well in ten I would show the concern that you have now...lol

Looooong way to go before anyone worries about where, if anywhere, these babies are going. Even the professionals are about two percentage points away from clueless right now.

Enjoy the watchful speculation though, lotta people here for just that purpose.
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Would be funny if the ECMWF was right again and these invests stayed weak with little development occurring.

It's been pretty great so far this year.
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227. beell
Quoting USAFwxguy:


You make an important distiction about the monsson trough. Those areas will be largely unable to aquire much of a cyclonic spin until separated from it.


A cyclonic spin over a large area is inherent with this monsoon trough.
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Quoting USAFwxguy:


Thanks. Glad I found this place.

I'm sure the antics can't get that bad.


So where are you located? I spent 10 years in the AF, last six at Eglin AFB where I decided to get out and stay in NW Florida!
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93L has a good chance of not being picked up by the trough due to the low latitude 93L will be having over the next few days. Won't be as prone to the weakness as 92L will be. A lot of 93L's fate and future will probably rely on 92L's fate and future as well.
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Quoting Stormchaser2007:
12z GFDL for 93L

Very far south


BAD.
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AAAAHHHhh!
It's RAINING !!!!
(first time in over a week.......)
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12z GFDL for 93L

Very far south

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221. JRRP
GFDL
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Quoting kmanislander:


Be right back. Note post edited to substitute monsoon trough for ITCZ

OK
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Dual 40%s, interesting. Could be a real race to TD6 first.
Member Since: July 8, 2005 Posts: 259 Comments: 24254
Quoting kmanislander:
Good afternoon

I have noted many posts that comment about the ragged look of 92L and how neither of the two invests seem to be doing much by way of organizing.

An important factor that is being overlooked is that both invests are still firmly in the grip of the monsoon trough. Until they separate out on a stand alone basis development will of necessity be slow. Of course, the longer they take to do so the greater the risk of a motion further West and South and the potential to threaten the NE Caribbean Islands.Once 92L reaches about 45W it should have outrun the trough so let's see what happens after that. Until then it will probably be slow going on the development front.

I have posted the surface map showing the ITCZ and the two lows.


Also...

Looking at the ITCZ, and the sharp "dog-leg" to the south, just west of both systems.
It would be expected that both the systems will escape the ITCZ/trough as they go west.
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Quoting tropicfreak:


It will most likely change.

Hurricane Protection Set to Expire August 17


When the first storm to do more than blow someone's hairdo out of whack lands on US soil, I will believe.

Until then, I am not buying the "pattern change."

I heard about it all last season, and it never materialized.

I want to believe, but I am having a difficult time.
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Quoting pottery:

What is the forecast for the high east of Bahamas?
Does it hang around?


Be right back. Note post edited to substitute monsoon trough for ITCZ
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Quoting pottery:

Wrong music.....


LOL, ok how bout the theme of Jaws to go with it? or should it be the background music to some slasher flick? Or maybe some tchaikovsky :)
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Quoting kmanislander:
Good afternoon

I have noted many posts that comment about the ragged look of 92L and how neither of the two invests seem to be doing much by way of organizing.

An important factor that is being overlooked is that both invests are still firmly in the grip of the ITCZ trough. Until they separate out on a stand alone basis development will of necessity be slow. Of course, the longer they take to do so the greater the risk of a motion further West and South and the potential to threaten the NE Caribbean Islands.Once 92L reaches about 45W it should have outrun the ITCZ so let's see what happens after that. Until then it will probably be slow going on the development front.

I have posted the surface map showing the ITCZ and the two lows.


What is the forecast for the high east of Bahamas?
Does it hang around?
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Some if the posts I've seen today worry me. I am a Wilmington, nc resident, and love weather and am very interested in TC's, but also realize the amazing damage they cause. I am "enthusiast", but know very little compared to most on this
Board. Some models suggest 92 and 93 will recurve, which is good for my location. But others say these model runs could drastically shift westward , like earl... Which had it's intense ball of convection literally 20 miles off my coast.

If these do not recurve, or recurve much further west than it currently looks, I feel Wilmington, nc could be directly in the path. I kno it's too early to worry, but......

What exact pattern should I be following to give me better insight as to why (and if) these potential storms could impact my area. With so much warm, open water this summer I fear if they do get directed towards NC that it could be a bad situation.
Thanks for any insight everyone
Member Since: Posts: Comments:

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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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