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 AussieStorm:

August is our last month of winter, once we hit September temps start the very much welcome upward trend.
there is to be more cold yet
Member Since: July 15, 2006 Posts: 163 Comments: 52230
hey Levi. good morning. I read your blog and a good one as usual.

just curious but are you still as bullish on the potential upcoming pattern change coming up in approx two weeks?

reason I ask is because suddenly I am reading that the troughs will be stubborn and not make room for the Bermuda High to build stronger and westward

just wanted to get your insight, analysis and thoughts. thanks
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It's so bad in TX that the grass in the parks have the same color as concrete...and the ground is so hard it might as well be concrete
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92L and 93L Model Runs Link

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We need rain but not hurricane. I hope neither makes it to that.
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Quoting Neapolitan:
TIME has a worthwhile photo spread today titled "Picturing the American Drought".

An example: "'The Island,' a resort on Lake Travis, is normally a peninsula surrounded almost completely by water. The level of the Lake has dropped, and now it now sits on dry land, as do the neighboring boat docks."


A picture is worth a thousand words....
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anyone read what dr m. said, 93 is going to be much farther south....
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Quoting gatorman98:
Is 92L leftover Emily?

No, 92L came off Africa a few days ago.
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Is 92L leftover Emily?
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Quoting Neapolitan:
TIME has a worthwhile photo spread today titled "Picturing the American Drought".

An example: "'The Island,' a resort on Lake Travis, is normally a peninsula surrounded almost completely by water. The level of the Lake has dropped, and now it now sits on dry land, as do the neighboring boat docks."


that leaves me speechless.
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TIME has a worthwhile photo spread today titled "Picturing the American Drought".

An example: "'The Island,' a resort on Lake Travis, is normally a peninsula surrounded almost completely by water. The level of the Lake has dropped, and now it now sits on dry land, as do the neighboring boat docks."

Member Since: November 8, 2009 Posts: 4 Comments: 13263
sooooo... with Dr. Masters back in the saddle.. will the storms start behaving  less 'schizophrenic' than Emily??? (when the cat's away....)
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73F in Poland
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Quoting Levi32:


You guys are moving upward in temperature for spring now, right? Or not because August is technically the equivalent of our February?

August is our last month of winter, once we hit September temps start the very much welcome upward trend.
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Quoting AussieStorm:

52.2F here right now. getting down to 46F overnight.


You guys are moving upward in temperature for early spring now, right? Or not because August is technically the equivalent of our February?
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Quoting USAFwxguy:
12Z GFS images should be coming shortly, so we can see how it handles that same trough over the Eastern US/West Atlantic in the out-hours.

This is the current 7-day 500mb heights chart that shows the trough firmly in place:



EURO has a huge 500mb trough off east coast next 10 days. Hard to see a US impact from anything out of the deep tropics.
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Quoting Levi32:


Too cold lol. It's amazing how experiencing 85 degrees for the first time will spoil a person's tolerance of the cold that comes with autumn. I'll get back into it, but 40 degrees is chilly for me right now.

52.2°F here right now. getting down to 46°F overnight.
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Quoting hurricane23:


Not much hope in my view of any cv wave threatening the US over the next 1-2 weeks- the ridge in the Rockies and the eastern trough show no signs of shifting in the near future on the ensembles or op models. Unless it stays fairly weak its up and out.

Agreed!!
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92L seems a likely recurve at this time. The jury is still out on 93L. It could easily affect either the northeast Caribbean islands or the southeast U.S., or both, in the long term. It's too early to say for certain. That trough over the eastern seaboard is replaced by a zonal flow over southeastern Canada with a weakness underneath by all of the ensemble suites Days 8-12. That setup could easily bring something close to the coast if we have a storm approaching during that time frame. 93L could be that storm if it develops. Guarantees on its track would be unwise at this time.
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Quoting AussieStorm:

Morning Mate, How the weather in Alaska today?


Too cold lol. It's amazing how experiencing 85 degrees for the first time will spoil a person's tolerance of the cold that comes with autumn. I'll get back into it, but 40 degrees is chilly for me right now.
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33. wpb
Quoting hurricane23:


Not much hope in my view of any cv wave threatening the US over the next 1-2 weeks- the ridge in the Rockies and the eastern trough show no signs of shifting in the near future on the ensembles or op models. Unless it stays fairly weak its up and out.
agree good post
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Appears we might have a 4th area to watch in front of 92L (may be by this weekend):





If it pans out then this disturbance could become our 3rd possible TD/TS to develop.
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Quoting angiest:


That little patch east of Galveston Bay is in the D2-D3 range due to heavy rains that fell in July. It it already shrinking rapidly and being replaced with D3/D4 drought conditions.

Meanwhile, the town I live in west of Houston has officially recorded no rain, not even a trace, in the last two months.


Yea on the SW side of Galveston Bay were right back in it and getting worse by the day. Thank God for the rain we got or we would be in your situation
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Quoting Levi32:
Good morning.

Blog update:

Tropical Tidbit for Thursday, August 11th, with Video

Morning Mate, How the weather in Alaska today?
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Quoting RitaEvac:




That little patch east of Galveston Bay is in the D2-D3 range due to heavy rains that fell in July. It it already shrinking rapidly and being replaced with D3/D4 drought conditions.

Meanwhile, the town I live in west of Houston has officially recorded no rain, not even a trace, in the last two months.
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Dr Masters, What's the reason that the NHC is giving 92L 30% and 93L 20%, yet 93L is looking much better.
Also I was doing a mail out for UNICEF at work tonight. It's about the crisis in the Horn of Africa that you did a blog about a few weeks ago. It anyone would like a copy. WUmail me and I'll get you a pdf copy of it.
Cheers AussieStorm
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23. HCW


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Quoting Patrap:

12z Early Cycle NHC model tracks
Invest93
Statistical/Simple Models (CLIPER,BAMs,LBAR,other Statistical Models)





Dynamic Models (More sophisticated models)






Not much hope in my view of any cv wave threatening the US over the next 1-2 weeks- the ridge in the Rockies and the eastern trough show no signs of shifting in the near future on the ensembles or op models. Unless it stays fairly weak its up and out.
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Good morning.

Blog update:

Tropical Tidbit for Thursday, August 11th, with Video
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Blog update! Lengthy read, and read for my opinion.. enjoy!
Invest 92L and Invest 93L to watch 8/11/11
Member Since: July 8, 2005 Posts: 259 Comments: 23012
AL932011 - INVEST



Enhanced Infrared (IR) Imagery (4 km Mercator)

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BAD in Oklahoma and Texas and western Louisiana
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Post 11. It's nice that they were able to get a "group shot" of the invests.
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Thanks Doc...
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12z Early Cycle NHC model tracks
Invest93
Statistical/Simple Models (CLIPER,BAMs,LBAR,other Statistical Models)





Dynamic Models (More sophisticated models)




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12z Early Cycle NHC model tracks
Invest92
Statistical/Simple Models (CLIPER,BAMs,LBAR,other Statistical Models)




Dynamic Models (More sophisticated models)




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Thank you for the update Dr. Masters. I hope you had a good vacation.

The tropics are starting to get interesting. The next 60 days or so could be crazy, especially with the approach of the upward motion of the MJO.
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About JeffMasters

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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