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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1209. Levi32
Quoting atmoaggie:
gifsicle is easier to use for resizing/scaling/optimizing (smaller file size), IMO.


It would be nice if I could get my animations a bit smaller in size. By the way, I don't know what your file size was, but tinypic seems to have the largeset limit that I know of (5mb).
Member Since: November 24, 2005 Posts: 635 Comments: 26701
1208. JLPR2
Quoting MississippiWx:
Emily's ghost has a decent amount of 850mb vorticity associated with it as well...Should definitely be watched:



The interesting thing is that it is stronger than 92L's.

If it manages to get a burst of convection it may even become 94L eventually.
Member Since: September 4, 2007 Posts: 7 Comments: 8747
Quoting MississippiWx:
Emily's ghost has a decent amount of 850mb vorticity associated with it as well...Should definitely be watched:



Better than frick and frack to the east, priceless.
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Quoting Levi32:


Well I use such commands on a daily basis so I like having them in a script. I have a generic one that can process almost any set of images that I give it from URLs, including the NCEP GFS runs.

I have not come across gifsicle though. I might have to see how it compares to imagemagick.

gifsicle is easier to use for resizing/scaling/optimizing (smaller file size), IMO.
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Quoting tropicfreak:


Will probably have to be mentioned in the 2am TWO.


Maybe...I doubt it though. It really doesn't have any model support, other than the NAM. It's in an unfavorable environment currently, being on the SE periphery of the Bermuda High.
Member Since: July 15, 2006 Posts: 17 Comments: 10284
You guys that cannot see that GFS loop, someone try this URL: http://s2.postimage.org/bpqufcrmb/gifanim.gif

I see no reason why...
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Quoting MississippiWx:
Emily's ghost has a decent amount of 850mb vorticity associated with it as well...Should definitely be watched:



Will probably have to be mentioned in the 2am TWO.
Member Since: September 2, 2006 Posts: 110 Comments: 6878
1202. Levi32
Quoting atmoaggie:
LOL. Levi posted yesterday's 18 Z GFS a long time ago...

And we both used Linux, but used totaly different tools and programs.

No script, just 3 commands.

for i in `seq 0 3 192`; do paddednum=`printf "%03d" $i`; wget http://mag.ncep.noaa.gov/GemPakTier/MagGemPakImage s/gfs/20110810/18/gfs_atlantic_${paddednum}_10m_wn d_precip.gif; done
for i in `seq 204 12 384`; do paddednum=`printf "%03d" $i`; wget http://mag.ncep.noaa.gov/GemPakTier/MagGemPakImage s/gfs/20110810/18/gfs_atlantic_${paddednum}_10m_wn d_precip.gif; done

gifsicle --delay 30 --loopcount=0 --scale 0.75 -O2 gfs_atlantic_*.gif > gifanim.gif


Well I use such commands on a daily basis so I like having them in a script. I have a generic one that can process almost any set of images that I give it from URLs, including the NCEP GFS runs.

I have not come across gifsicle though. I might have to see how it compares to imagemagick.

Member Since: November 24, 2005 Posts: 635 Comments: 26701
Emily's ghost has a decent amount of 850mb vorticity associated with it as well...Should definitely be watched:

Member Since: July 15, 2006 Posts: 17 Comments: 10284
Quoting Stormchaser2007:


Can't see it, but this is what I have.



That was insane last night, and still hasn't changed that much.... Sheesh.
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1199. emcf30
Quoting Grothar:
The GFDL and GFDI still want to move 93L west. The others are taking a more NW bias.



Hey Gro, Why do you think the models are not wanting the trough to take 93L more NW. You would think since the intensity forecast are increasing with each run it would have a tensity to be pulled towards any weakness in the High created by any trough like they do with 92L.
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1198. ncstorm
Quoting JLPR2:


I think it will change, besides I tend to trust the 00z run more than the 18z one. No idea why. xD


we havent had any consistent runs from the GFS on 93L..will be interesting to see if this will be a first..
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Whole Lot of Shaking Going On!

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Quoting MississippiWx:


I think you're right...I hope at least.

Emily's ghost:




Don't make me look at her, she's the most annoying woman I've ever met!
Member Since: September 2, 2006 Posts: 110 Comments: 6878
1195. JLPR2
Quoting ncstorm:
Does anyone think the 00Z run will be consistent and still show the same track as 18Z?


I think it will change, besides I tend to trust the 00z run more than the 18z one. No idea why. xD
Member Since: September 4, 2007 Posts: 7 Comments: 8747
Quoting JLPR2:


LOL! If something similar to the NAM does happen it would leave me speechless, but I guess it would gain a new name since Emily's original circulation went NE and this is just a piece of her. Right?


I think you're right...I hope at least.

Emily's ghost:

Member Since: July 15, 2006 Posts: 17 Comments: 10284
Cool & wet in Jupiter (SEFL) tonight, loving the 77 degrees however.

Temperature
77.2 °F

Humidity
94%

Heat Index
78 °F

Dew Point
75 °F
Member Since: Posts: Comments:
Quoting navarch:


Houma, LA
Temp 85.5F
Dewpoint 78F
Humidity 79%
Heat Index 98F

Moist Heat




Daphne, AL
Now Clear
Temperature
87.4 °F
Feels Like 102 °F

My dogs won't even go outside....the cat loves it.


Member Since: Posts: Comments:
1191. ncstorm
Does anyone think the 00Z run will be consistent and still show the same track as 18Z?
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1190. JLPR2
Quoting MississippiWx:


Lol...She's taking everyone's dignity.


LOL! If something similar to the NAM does happen it would leave me speechless, but I guess it would gain a new name since Emily's original circulation went NE and this is just a piece of her. Right?
Member Since: September 4, 2007 Posts: 7 Comments: 8747
Quoting ProgressivePulse:



Would be rather interesting to see the remnants of Emily come back around and develop. I really think that I would need some counseling if that happened.



I know I would need that too. She's been driving me friggen insane!!
Member Since: September 2, 2006 Posts: 110 Comments: 6878
1188. angiest
Quoting ProgressivePulse:



Would be rather interesting to see the remnants of Emily come back around and develop. I really think that I would need some counseling if that happened.



Remember Ivan.
Member Since: August 26, 2006 Posts: 16 Comments: 4766
Quoting Levi32:


What? Web browser? When I have command-line? I wrote a BASH script for it that invokes "curl" to download files, and imagemagick to create GIF animations with the data that is downloaded.
LOL. Levi posted yesterday's 18 Z GFS a long time ago...

And we both used Linux, but used totaly different tools and programs.

No script, just 3 commands.

for i in `seq 0 3 192`; do paddednum=`printf "%03d" $i`; wget http://mag.ncep.noaa.gov/GemPakTier/MagGemPakImage s/gfs/20110810/18/gfs_atlantic_${paddednum}_10m_wn d_precip.gif; done
for i in `seq 204 12 384`; do paddednum=`printf "%03d" $i`; wget http://mag.ncep.noaa.gov/GemPakTier/MagGemPakImage s/gfs/20110810/18/gfs_atlantic_${paddednum}_10m_wn d_precip.gif; done

gifsicle --delay 30 --loopcount=0 --scale 0.75 -O2 gfs_atlantic_*.gif > gifanim.gif
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1186. Grothar
The GFDL and GFDI still want to move 93L west. The others are taking a more NW bias.

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Quoting ProgressivePulse:



Would be rather interesting to see the remnants of Emily come back around and develop. I really think that I would need some counseling if that happened.



Lol...She's taking everyone's dignity.
Member Since: July 15, 2006 Posts: 17 Comments: 10284
Quoting MississippiWx:
In 84 hours, the 00z NAM tries to develop the part that split off Emily and headed south around the Eastern periphery of the Bermuda Ridge. Just something to humor you while waiting on the 00z GFS:




Would be rather interesting to see the remnants of Emily come back around and develop. I really think that I would need some counseling if that happened.

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1183. navarch
Quoting outofdablue:

summerdale alabama

current temp 83.3
heat index 94
Humidity 83%
dew point 78


Houma, LA
Temp 85.5F
Dewpoint 78F
Humidity 79%
Heat Index 98F

Moist Heat
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1182. dearmas
Tampa Fl
83.6F
Feels like 97
humidity 90%

and it's 11:07pm

Just saying ugh :)
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1181. Grothar
Quoting atmoaggie:
Umm, dunno what to say. Works fine for me. Anyone else actually see a gif animated loop in post 1147?


Now you know I wouldn't tease you. All I see is a red X. But I have seen that image enough. I posted it myself the other night.
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Quoting atmoaggie:
After a fight over the file size on the image hosting sites...

I think someone was hoping to see a loop of yesterday's 18 Z GFS posted.



I did have truncate off the first 178 hours and resample to get it under the hosting services' file size limits.


Can't see it, but this is what I have.

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Quoting MississippiWx:
In 84 hours, the 00z NAM tries to develop the part that split off Emily and headed south around the Eastern periphery of the Bermuda Ridge. Just something to humor you while waiting on the 00z GFS:



Oh god not again, SHE WON'T GIVE UP!!
Member Since: September 2, 2006 Posts: 110 Comments: 6878
Quoting atmoaggie:
Umm, dunno what to say. Works fine for me. Anyone else actually see a gif animated loop in post 1147?


Nope (FF)
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Quoting Grothar:
You think 92L will be renamed 9.2L




Should be renamed "93L's b**ch".
Member Since: July 15, 2006 Posts: 17 Comments: 10284
1176. JLPR2
Quoting Stormchaser2007:


Sure.

Just needs to escape the easterly shear and it should develop by this weekend.
FULL

Thank you!

Quoting emcf30:


SHIPS Intensity Text

I posted a portion on post 1050

Thank you as well!
Member Since: September 4, 2007 Posts: 7 Comments: 8747
1175. emcf30
Quoting JLPR2:


Could you post it? I never saved a link to see the Ships text.


SHIPS Intensity Text

I posted a portion on post 1050
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Quoting Grothar:


I think you shrunk your link too much. All I see is a red X.
Umm, dunno what to say. Works fine for me. Anyone else actually see a gif animated loop in post 1147?
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Quoting JLPR2:


Could you post it? I never saved a link to see the Ships text.


Sure.

Just needs to escape the easterly shear and it should develop by this weekend.
FULL
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1172. Grothar
You think 92L will be renamed 9.2L


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1170. JLPR2
Quoting Stormchaser2007:
00z Consensus (red line) brings 93L into PR's area.

SHIPS and LGEM range from 95-100 knots.



Thank goodness that has time to change; I like using my air conditioner. :\
Member Since: September 4, 2007 Posts: 7 Comments: 8747
Quoting Stormchaser2007:
00z Consensus (red line) brings 93L into PR's area.

SHIPS and LGEM range from 95-100 knots.





ouch
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00z Consensus (red line) brings 93L into PR's area.

SHIPS and LGEM range from 95-100 knots.

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1167. yoboi
where is emily at is it 93l?
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Quoting Stormchaser2007:
00z SHIPS has a pretty dangerous track. Really beefed up the intensity as well.


Been saying all along that 93L is going to be the one to watch and I still believe it. 92L is going to have a decent chance to develop down the road if it can fight off the dry air. Shear looks to be almost a non-factor for a while.
Member Since: July 15, 2006 Posts: 17 Comments: 10284
Quoting Thrawst:


I Live in Nassau, Bahamas. Beat this haha :P -

Temperature: 82 F
Dew Point: 81 F
Humidity: 94%
Heat Index: 94
Wind: Calm

... THAT is miserable :P

summerdale alabama

current temp 83.3
heat index 94
Humidity 83%
dew point 78
Member Since: Posts: Comments:
1164. JLPR2
Quoting MississippiWx:


No, no mice, unless you count the one in my computer. The cats around here do a pretty good job rounding up the real ones.


:)

Also, Africa has the next ones ready to go.
Member Since: September 4, 2007 Posts: 7 Comments: 8747
Quoting Stormchaser2007:
00z SHIPS has a pretty dangerous track. Really beefed up the intensity as well.


how strong do it make 93L?
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Quoting JLPR2:


You have a mouse there? Need a cat to catch it? XD


No, no mice, unless you count the one in my computer. The cats around here do a pretty good job rounding up the real ones.
Member Since: July 15, 2006 Posts: 17 Comments: 10284
1161. JLPR2
Quoting Stormchaser2007:
00z SHIPS has a pretty dangerous track. Really beefed up the intensity as well.


Could you post it? I never saved a link to see the Ships text.
Member Since: September 4, 2007 Posts: 7 Comments: 8747
00z SHIPS has a pretty dangerous track. Really beefed up the intensity as well.
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1159. JLPR2
Quoting MississippiWx:


Eh, you just took the words right out of my mouse. :-p I was about to post the same thing.


You have a mouse there? Need a cat to catch it? XD
Member Since: September 4, 2007 Posts: 7 Comments: 8747

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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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