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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Quoting MississippiWx:
All of the salivating over where the GFS sends 93L in 300+ hours is a little ridiculous. It's no surprise that one run shows landfall, the next out to sea since it's so far out in the run.

We should be more worried about development of the actual system first, then trying to see if the models can lock down on a particular upper level pattern for steering. For now, they are going to take complete 180 degree turns each run.
Hey, we r just having fun with it for now.... lol ... while waiting slowly....
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Quoting TomTaylor:

hah. How long does it take for the script to do that?

I should time myself and see how long it takes me to do it. I use GIMP now, so it's faster than Paint, but still not a very quick process.


Don't talk about Grothar that way...

Just because he's old and can't walk very well doesn't mean he's a GIMP.
Member Since: July 15, 2006 Posts: 17 Comments: 10284
Quoting TomTaylor:

hah. How long does it take for the script to do that?

I should time myself and see how long it takes me to do it. I use GIMP now, so it's faster than Paint, but still not a very quick process.


~10 seconds, perhaps longer if the files are large and numerous.
Member Since: November 24, 2005 Posts: 635 Comments: 26654
Quoting Levi32:


Hopefully they are fully prepared for a potential disaster already, as they should be every season, and not need 13 days to board up.


it never ceases to amaze, or amuse, me the number of people who live on the coast and still have to rush out at the lst minute for plywood and the like.
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Quoting Levi32:


If you ever want a loop like that give me a shout lol.

hah. How long does it take for the script to do that?

I should time myself and see how long it takes me to do it. I use GIMP now, so it's faster than Paint, but still not a very quick process.
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Quoting TomTaylor:
93L
Oh ok thanks, just got back on & see some reference to Hugo, plus I'm on my phone so I can't see the date on the bottom for when that storm makes landfall.
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GFS MJO forecast has been very consistent, for a change:

Member Since: July 15, 2006 Posts: 17 Comments: 10284

585. KEEPEROFTHEGATE
Not wanting to appear crazy or out on a limb with this as I don't really understand the exact geographical layout of the lower US states but if the US can build a pipeline to bring oil from Alaska and across deserts and oil is a nasty thing to transport, surly their engineers can build a pipeline to transport water from a river like the Mississippi to the drought stricken areas even if it takes some time, it will be there for the future.

Keeper: In the 1960s Texas had this huge plan with the Missisippi River. It was going to cost I think $2 billion. Texans went to the polls and voted it down by a very narrow margin.

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Quoting P451:


92L





93L





They are both undergoing "SLOW ORGANIZATION" just as analyzed.








yes but 93L is looking better
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Quoting USAFwxguy:


Looking at long-range should definitely be undertaken with an understanding of the probabilities of change.

However, if you see similar solutions work their way down the scale of the out-hours, then that reinforces the solutions of medium range (perhaps).

I would hope nobody is boarding up on the SC coast based on the 18Z from today for a storm 13 days away. Hopefully they have friends that would look them in the eye and tell them they are crazy for doing so.


That's just the issue I'm getting across, though. Models have not locked onto one solution yet, simply because it's 4 or 5 days before we can talk medium range.
Member Since: July 15, 2006 Posts: 17 Comments: 10284
Quoting GTcooliebai:
92L or 93?
93L
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Quoting TomTaylor:
Thanks for making that loop. I was thinking about making one just a minute ago, you just saved me a good 5 minutes lol


If you ever want a loop like that give me a shout lol.
Member Since: November 24, 2005 Posts: 635 Comments: 26654
Quoting USAFwxguy:


Looking at long-range should definitely be undertaken with an understanding of the probabilities of change.

However, if you see similar solutions work their way down the scale of the out-hours, then that reinforces the solutions of medium range (perhaps).

I would hope nobody is boarding up on the SC coast based on the 18Z from today for a storm 13 days away. Hopefully they have friends that would look them in the eye and tell them they are crazy for doing so.


Hopefully they are fully prepared for a potential disaster already, as they should be every season, and not need 13 days to board up.
Member Since: November 24, 2005 Posts: 635 Comments: 26654
Quoting Levi32:
Some mid-level rotation is evident with 93L due to the MCS which just dissipated in the middle. Surface winds remain rather linearly convergent along the monsoon trough, with little circulation noted. The system has a ways to go yet before developing.

Thanks for making that loop. I was thinking about making one just a minute ago, you just saved me a good 5 minutes lol
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Quoting floodzonenc:
Private Idaho lives in Idaho.  LOL... I always thought you were just a big B-52s fan...  :)



That too!
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Quoting PrivateIdaho:


When looking at the GFS 2 weeks out, I recommend 2 of these......



....40 lb each....lol.


Thanks for the recommendation lol. I concur.
Member Since: November 24, 2005 Posts: 635 Comments: 26654
Quoting USAFwxguy:
Shades of Hugo... landfall wise.

92L or 93?
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Quoting Neapolitan:

I suppose you're right; the June Gloom gets very tiring, especially when it runs into September and longer. And those endless days from April until November without a drop of rain can be boring. But, still, the heaviest hailstorm I've ever seen in my life was in Orange County--it dropped about 4" of grape-sized stones in 10 or 15 minutes--and I've lived in Hail Alley. And the most rainfall, too; though I've been in very wet hurricanes and tropical storms, 2005's Pineapple Express event dumped 26" of rain in just three days at a station just a few miles from my house.


I guess I should be a little more specific-whether along coastal Southern California can be pretty boring. If you go inland a little, the marine layer becomes much less of an issue. You also get much more rain during the winter's and a better chance of some monsoonal action coming off the mountains to the East. Right along the coast, the marine layer is here just about everyday by nighttime. Only exception is when we get really strong ridging in our area or just to the east like we see during Santa Ana events.

Sounds like you must have lived a little ways away from the coast in some higher elevation if you got that kind of hail and rain during one rain event. I remember 2005 as well, we got about 21 or 22 inches of rain at my house for the entire season, not one rain event lol. Still was more than double our average, so it was neat getting all the rain and seeing everything so green.
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Quoting USAFwxguy:


Yeah.... but Idaho? I think it is great either way!


He misunderstood. Thought he was going to an island home. When the GPS said "You have arrived at your destination" he was still looking for the bridge to get to the tropical island.
;)
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Quoting Levi32:
Despite being two weeks out, and thus taken with big grains of salt, some of these recent GFS runs are illustrating what is a possibility of happening with the coming upper-air pattern. The trough that is likely to pick up 92L lifts out in a hurry, just like all of the other western Atlantic troughs this year, leaving the Atlantic ridge to build westward and try to bridge the gap with the U.S. ridge. The weakness along the eastern seaboard makes for some tough forecasts, like we had with Emily, but such a pattern is capable of bringing storms to the coast. We'll have to watch the pattern closely if 93L does develop.


When looking at the GFS 2 weeks out, I recommend 2 of these......



....40 lb each....lol.
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683. JLPR2
At this rate the ITCZ convection that was related to 92L is going to be stolen by 93L.
Member Since: September 4, 2007 Posts: 7 Comments: 8735
Quoting TropicalAnalystwx13:


When's your best guess of when this will become a TD/TS, if it ever does?


If either of these features develop, it may not be for a few days. 93L might try to beat 92L to development if it improves over the next day or so.
Member Since: November 24, 2005 Posts: 635 Comments: 26654
Quoting Levi32:
Some mid-level rotation is evident with 93L due to the MCS which just dissipated in the middle. Surface winds remain rather linearly convergent along the monsoon trough, with little circulation noted. The system has a ways to go yet before developing.



When's your best guess of when this will become a TD/TS, if it ever does?
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Quoting PlazaRed:


We have had hurricane type weather here in Europe but its few and far between, massive storms in the late 80s destroyed a lot of southern England and a couple of years ago a few million trees got downed in France along with a lot of damage.
I have seen 10 inches of rain in southern Spain in a morning and 2 years ago we had winds of about 140MPH in Spain.
Sooner or later our lucks going to run out and the damage will be unbelievable, possibly even by the Americas standards.

Look at comment 666
Cursed comment.
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678. JLPR2
Quoting MississippiWx:
All of the salivating over where the GFS sends 93L in 300+ hours is a little ridiculous. It's no surprise that one run shows landfall, the next out to sea since it's so far out in the run.

We should be more worried about development of the actual system first, then trying to see if the models can lock down on a particular upper level pattern for steering. For now, they are going to take complete 180 degree turns each run.


+10
Thank you! :D
Watch the 00z run send it somewhere else.
Member Since: September 4, 2007 Posts: 7 Comments: 8735
Some mid-level rotation is evident with 93L due to the MCS which just dissipated in the middle. Surface winds remain rather linearly convergent along the monsoon trough, with little circulation noted. The system has a ways to go yet before developing.

Member Since: November 24, 2005 Posts: 635 Comments: 26654
Quoting JLPR2:


No, Emily's remnants kept moving NE and is somewhere in this general area, that area was left behind by Emily, it is somewhat related to our notorious storm.
I can't believe it.Still talking about Emily.
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Quoting BahaHurican:
I do know in warmer periods England / Eire have been impacted by hurricane style storms. And there are tracks of storms from the 1890s [IIRC] which fetch up near Iceland.... so such activity is not completely unprecedented. And didn't we have Muifa up near Korea?


The issue with those storms like Faith and Debbie was that it was pre-satellite.

There was no real way to tell whether they had become extratropical prior to landfall. It was a guess. Hurricane style storms in the form of windstorms happen commonly enough and sometimes unseasonably (i.e. aside the typical October to March period). Until one becomes (uncomfortably) close in the present, we won't know for absolutely sure it's possible (Vince and Grace fell apart prior to any landfall with doubts on the latter of any tropical credentials whatsoever) to keep itself intact.

As for South Korea, Seoul is on 37N - same as Richmond, Virginia. Pyongyang of North Korea is 39N, same as Baltimore. Of course, the Gulf Streams aids storms off the Eastern Seaboard. The waters are still plenty warm enough in Asia until perhaps the island of Hokkaido, Japan (according to Wunderground).
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All of the salivating over where the GFS sends 93L in 300+ hours is a little ridiculous. It's no surprise that one run shows landfall, the next out to sea since it's so far out in the run.

We should be more worried about development of the actual system first, then trying to see if the models can lock down on a particular upper level pattern for steering. For now, they are going to take complete 180 degree turns each run.
Member Since: July 15, 2006 Posts: 17 Comments: 10284
Quoting Stormchaser2007:


Ouch! A SC hit, the ridge has clearly built in.
Member Since: September 2, 2006 Posts: 110 Comments: 6878
Quoting BahaHurican:
I do know in warmer periods England / Eire have been impacted by hurricane style storms. And there are tracks of storms from the 1890s [IIRC] which fetch up near Iceland.... so such activity is not completely unprecedented. And didn't we have Muifa up near Korea?


We have had hurricane type weather here in Europe but its few and far between, massive storms in the late 80s destroyed a lot of southern England and a couple of years ago a few million trees got downed in France along with a lot of damage.
I have seen 10 inches of rain in southern Spain in a morning and 2 years ago we had winds of about 140MPH in Spain.
Sooner or later our lucks going to run out and the damage will be unbelievable, possibly even by the Americas standards.
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Quoting USAFwxguy:


Sir, you have that right.

Over time, modelling that is "too far out" to be trustworthy becomes more so if it continues to be the solution into the medium range and sooner.


Which is why forecasts are currently limited to 5 days by the NHC. However, clues can be derived long before then, using both the models and knowledge of the global pattern thus far in the current summer season. This is what makes long-range forecasting both a challenge and a relatively new field that we may make leaps and bounds in during the coming decades.
Member Since: November 24, 2005 Posts: 635 Comments: 26654
Quoting USAFwxguy:


Thank you. Are you really in ID, and on a tropics forum?

Mt Home AFB.... like the nearby mountains. The national forest there are great.


I'm about 2.5 hours east of there in Blackfoot.
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Quoting TomTaylor:
cool vid

I don't live in Texas, but I wish we got that kind of weather here in Southern California. All we get is dreary, gloomy, marine layer. Which is basically a low level blanket of clouds that provides no rain and keeps us cool and cloudy. Blankets us every night, burns off slightly during the afternoon, but still hangs along the coast.

Lame weather for sure

I suppose you're right; the June Gloom gets very tiring, especially when it runs into September and longer. And those endless days from April until November without a drop of rain can be boring. But, still, the heaviest hailstorm I've ever seen in my life was in Orange County--it dropped about 4" of grape-sized stones in 10 or 15 minutes--and I've lived in Hail Alley. And the most rainfall, too; though I've been in very wet hurricanes and tropical storms, 2005's Pineapple Express event dumped 26" of rain in just three days at a station just a few miles from my house.
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Quoting USAFwxguy:


Yeah.... but Idaho? I think it is great either way!


Australia, too.
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Quoting BahaHurican:
I do know in warmer periods England / Eire have been impacted by hurricane style storms. And there are tracks of storms from the 1890s [IIRC] which fetch up near Iceland.... so such activity is not completely unprecedented. And didn't we have Muifa up near Korea?

Last time that happened was last year by Extratropical Storm "Xynthia" (weirdest name ever).
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all so the nhc may have tools that we cant ues at all
Member Since: May 21, 2006 Posts: 5091 Comments: 115241
Look at 18z NAM !!!
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Despite being two weeks out, and thus taken with big grains of salt, some of these recent GFS runs are illustrating what is a possibility of happening with the coming upper-air pattern. The trough that is likely to pick up 92L lifts out in a hurry, just like all of the other western Atlantic troughs this year, leaving the Atlantic ridge to build westward and try to bridge the gap with the U.S. ridge. The weakness along the eastern seaboard makes for some tough forecasts, like we had with Emily, but such a pattern is capable of bringing storms to the coast. We'll have to watch the pattern closely if 93L does develop.
Member Since: November 24, 2005 Posts: 635 Comments: 26654
Quoting USAFwxguy:


Thank you. Are you really in ID, and on a tropics forum?


yup. I was born in La and grew up in central Fl so got lots of peeps and family scattered along the coast from Texas to NC....Plus I like weather watching. BTW...

Pocatello, Pocatello Regional Airport (KPIH)
Lat: 42.92028 Lon: -112.57111 Elev: 4449
Last Update on 11 Aug 15:53 MDT


Fair

85F
(29C) Humidity: 17 %
Wind Speed: WSW 17 G 28 MPH

Barometer: 30.01 in (1011.80 mb)
Dewpoint: 35F (2C)
Heat Index: 82F (28C)
Visibility: 10.00 Miles

bit breezy today.



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Quoting USAFwxguy:


Thank you. Are you really in ID, and on a tropics forum?


Some of us are in Canada (and not on the coast) in this forum. Storms in the Gulf tend to greatly affect our weather, only a week or so later.
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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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