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 weatherman566:


Hey everyone-

I think it's worth noting the 4th area of storms circled by the NHC. This is moving west/southwestward and the NAM has something forming in 84 hours pretty close to home. NAM has done an excellent job this year finding these smaller systems that the GFS and EURO have problems finding.
Puts it just north of Haiti again.
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Hey everyone-

I think it's worth noting the 4th area of storms circled by the NHC. This is moving west/southwestward and the NAM has something forming in 84 hours pretty close to home. NAM has done an excellent job this year finding these smaller systems that the GFS and EURO have problems finding.
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Quoting Neapolitan:
And a new one, 94L:

BEGIN
NHC_ATCF
invest_al942011.invest
FSTDA
R
U
040
010
0000
201108121132
NONE
NOTIFY=ATRP
END
INVEST, AL, L, , , , , 94, 2011, DB, O, 2011081212, 9999999999, , , , , , METWATCH, , AL942011
AL, 94, 2011081212, , BEST, 0, 249N, 545W, 25, 0, DB, 0, , 0, 0, 0, 0,



i wounder where 94L is
Member Since: May 21, 2006 Posts: 5091 Comments: 115243
1506. ncstorm
Accuweather..

We are not saying the models have a 100 percent right idea on the storms and their supposed tracks, but we are relaying concerns we have in this matter.

On a personal note, I am not a fan of long-range computer model forecasts in the tropics. However, my 28 years of professional forecasting experience tell me that when two commonly used models are essentially predicting the same outcome with minor variances, the situation is worth watching.

If either of the two or both tropical waves slowly organize and become legitimate named tropical systems, they could become strong enough and large enough to have impact on populated areas.

Size, intensity and exact track of the systems will matter as far as local impacts. Even a weak system could bring a period of disruptive, heavy, gusty squalls to island areas such as the Leewards and Virgin Islands.

Both systems will pass nearby the Leeward Islands first. The first system is on track to approach and pass the Leewards spanning Sunday into Monday (Aug. 14 and 15). The second system is due to pass days later; Thursday into Friday of next week (Aug. 18 and 19).

Bermuda may have to deal with the first system spanning Tuesday into Wednesday. The second system would pass near Bermuda the weekend of Aug. 20 and 21.

Part of Atlantic Canada sticks out to the east hundreds of miles relative to the U.S. coast. As a result, at this early stage, people and interests from New Brunswick to Nova Scotia will need to monitor storm development in the tropical Atlantic. The first system would make its run at the region Thursday into Friday of next week (Aug. 18 and 19). The second system would be of concern for the region the week of Aug. 22.

Additionally, shipping and cruising interests will want to watch the situation closely, as the outcome currently most certain is for at least periods of rough seas in the western Atlantic.

Even if both storms were to stay east of the U.S., one or more episodes of rough surf and dangerous rip currents could occur.

Interestingly, it would not take much for an approaching dip in the jet stream to capture one or both systems in such a way as to pull them closer to the East Coast of the U.S.



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Member Since: May 21, 2006 Posts: 5091 Comments: 115243
And a new one, 94L:

BEGIN
NHC_ATCF
invest_al942011.invest
FSTDA
R
U
040
010
0000
201108121132
NONE
NOTIFY=ATRP
END
INVEST, AL, L, , , , , 94, 2011, DB, O, 2011081212, 9999999999, , , , , , METWATCH, , AL942011
AL, 94, 2011081212, , BEST, 0, 249N, 545W, 25, 0, DB, 0, , 0, 0, 0, 0,
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Quoting Tazmanian:



the most up too date





92 and 93L
I know Taz but I wondered why he said 93L is falling apart when the most up to date image is from 4 or 5 hours ago. Need to see what the morning brings.
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Quoting stormwatcherCI:
Why ? The only images I can find were from 0600 UTC which is over 4 hours old.



the most up too date





92 and 93L
Member Since: May 21, 2006 Posts: 5091 Comments: 115243
1501. ackee
I think EURO models SEEM to be best models in figure out 93L unltimate track the EURO has been hinting all along that system would be weak unlike the GFS track further west and south seem possblie I 92L will stall 93L devlopment as well
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Waiting for the 8 AM update since I got up at 440 AM
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Quoting RukusBoondocks:
93 is falling all to pieces
Why ? The only images I can find were from 0600 UTC which is over 4 hours old.
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And ATCF's 1200Z update for 93L:

AL, 93, 2011081206, , BEST, 0, 112N, 284W, 25, 1011, LO, 34, NEQ, 0, 0, 0, 0, 1014, 180, 60, 0, 0, L, 0, , 0, 0, INVEST, M,
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1497. ncstorm
HPC Extended Discussion..

DAYS 3-4 START WITH A 60/40 BLEND OF THE 00Z ECMWF/00Z GFS TO
REPRESENT THE BEST CONSENSUS WITH THE SYSTEMS NEAR THE EAST COAST
AND OVER THE HIGH PLAINS/WEST COAST... WITH SHORT RANGE
PREFERENCES LEANING A LITTLE MORE TOWARD THE ECMWF THAN GFS.
AFOREMENTIONED ISSUES THEN FAVOR A BLEND OF 00Z GEFS/12Z ECMWF
ENSEMBLE MEANS FOR DAYS 5-7 WED-FRI. THIS SOLN ALSO DOWNPLAYS
LOWER CONFIDENCE OPERATIONAL DETAILS WITH THE SLOW MOVING WAVY
FRONT NEAR THE EAST COAST.

RAUSCH
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93 is falling all to pieces
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1495. ncstorm
CMC


GFDL..southern route..barely develops it
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Click for larger image:

Appropriate tropical weather-related image.
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ATCF's 1200Z update for 92L:

AL, 92, 2011081212, , BEST, 0, 168N, 437W, 25, 1011, LO, 34, NEQ, 0, 0, 0, 0, 1014, 175, 75, 0, 0, L, 0, , 0, 0, INVEST, S,
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NAO forecast to change positive by next week.
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Quoting ncstorm:


thats a big change in the model run though..GFS has become the freddy Krueger of every state, slashing and dicing..next run will be south america..lol..


Lol. Yeah. No tellin'.
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Two more waves to exit in the next 5 days
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Quoting stormwatcherCI:
Crownweather says he thinks 92L will absorb the southern part of 92L and also read that on another site. This would just serve to give 93L more energy to work with.


That is strange. Probably would slow down development and more westerly course then. I haven't really seen much about these two or now 4 areas the NHC has marked. I need to get on my other computer that has all my links. Lol.
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93L dos not look so good this AM
Member Since: May 21, 2006 Posts: 5091 Comments: 115243
1486. ncstorm
Quoting AtHomeInTX:


Nah. Just one model run. Seems like gfs is going scary strong into the east coast. Still a long way out.


thats a big change in the model run though..GFS has become the freddy Krueger of every state, slashing and dicing..next run will be south america..lol..
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Quoting AtHomeInTX:


I hope nothing like that again ever! Although that model Tig posted is a scary sight for the east coast! I hope if they get really nasty that they all go out to sea. Seems to be a question of development of 93l and where it goes.
Crownweather says he thinks 92L will absorb the southern part of 92L and also read that on another site. This would just serve to give 93L more energy to work with.
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Quoting ncstorm:
this is a texas storm now?


Nah. Just one model run. Seems like gfs is going scary strong into the east coast. Still a long way out.
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Quoting bohonkweatherman:
Del rio got 4.5 inches, great for them, Rain got within 200 miles of my house, not bad. Unfortunately the High Pressure is moving back over Texas for awhile


I'm glad for Del Rio. Hopefully it's a sign of things to come. Looks like we may get some rain around here before the ridge builds back too strong.
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1482. ncstorm
this is a texas storm now?
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From National Weather Service: ON SATURDAY...THE UPPER RIDGE OF HIGH PRESSURE MOVES EASTWARD AND
MARKS AND END TO CHANCES OF RAIN OVER TEXAS FOR THE MOST PARTS.
THERE IS A SLIGHT CHANCE OF SHOWERS AND THUNDERSTORMS JUST FOR
PORTIONS OF VAL VERDE COUNTY LATE SATURDAY AFTERNOON/EVENING.
OTHER THAN THAT...DRY AND HOT CONDITIONS RETURN FOR THE NEXT
SEVERAL DAYS.

MODEL GUIDANCE ARE IN GOOD AGREEMENT OF THE UPPER RIDGE OF HIGH
PRESSURE AND ESTABLISHING IT OVER TEXAS THROUGH THE UPCOMING WEEK
WITH LIMITED TO NO CHANCES OF RAIN.

ABOVE NORMAL TEMPERATURES ARE EXPECTED FOR THE NEXT SEVERAL DAYS
WITH HIGHS AVERAGING 96 TO 99 DEGREES OVER THE HILL COUNTRY AND
100 TO 105 DEGREES ACROSS THE REMAINDER OF SOUTH CENTRAL TEXAS.

A HEAT ADVISORY CONTINUES IN EFFECT FOR SOUTH CENTRAL TEXAS
EXCLUDING THE HILL COUNTY THROUGH THIS EVENING DUE TO HEAT INDEX
VALUES EXPECTED TO REACH THE 105 TO 110 DEGREES MARK
THIS AFTERNOON/EARLY EVENING

I hope Texas gets and day or 2 of rain
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Quoting stormwatcherCI:
The current position reminds me of where Ivan was born. Just pray it is not a re-run.


I hope nothing like that again ever! Although that model Tig posted is a scary sight for the east coast! I hope if they get really nasty that they all go out to sea. Seems to be a question of development of 93l and where it goes.
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Quoting aislinnpaps:
Good morning, all. I see TX is getting rain! I don't know that it's enough to make much of a dent, if any, in the drought, but it's needed pyschologically for them just as much.
Del rio got 4.5 inches, great for them, Rain got within 200 miles of my house, not bad. Unfortunately the High Pressure is moving back over Texas for awhile
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ugh...ok...been at work for a little more than an hour, got some stuff done but guess i should go do more lol...bbl tho, pop in and out today...later baha, ais, aquak...i sooooooo tired lol but yes, it is friday n if i am lucky my little one will sleep in tomorrow...later taters
Member Since: September 16, 2007 Posts: 0 Comments: 3650
Quoting AtHomeInTX:


Morning all. You beat me to it. Lol. Just read it. Noticed that model run. Hopefully it'll stay weak and bring rain. Sorry broken record strikes again. :)
The current position reminds me of where Ivan was born. Just pray it is not a re-run.
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Quoting stormwatcherCI:
Good morning. Not liking this at all.


Link


Morning all. You beat me to it. Lol. Just read it. Noticed that model run. Hopefully it'll stay weak and bring rain. Sorry broken record strikes again. :)
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Morning, Aqua,
LOL, you'll be weaving baskets and still checking in. Curiousity will keep you looking.
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hmmm, blog must have liked my post, it sent it twice.
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Quoting tiggeriffic:


yeah...being on the east coast this time of year is not the most enjoyable thing when there are storms pending lol...esp since Hugo anyway...that one was enuf for me to last a life time...i went n got coffee too so "CHEERS n G'morning" lol...let my dog out over an hour ago...at work now...gonna be a long day


I leave for work in about forty minutes. I should be home in about ten hours. But it's FRIDAY! LOL I shouldn't complain, just went back to work on Tuesday. I'm a teacher.
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Quoting tiggeriffic:


yeah...being on the east coast this time of year is not the most enjoyable thing when there are storms pending lol...esp since Hugo anyway...that one was enuf for me to last a life time...i went n got coffee too so "CHEERS n G'morning" lol...let my dog out over an hour ago...at work now...gonna be a long day


I leave for work in about forty minutes. I should be home in about ten hours. But it's FRIDAY! LOL I shouldn't complain, just went back to work on Tuesday. I'm a teacher.
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1471. aquak9
g'morning ais n tig- ya'll aren't alone, just still folks stirrin' coffee.

I ain't even watching for another 4-6 days. Model shmodel...might as well try to weave baskets outta spiderwebs.

zoomz-
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1470. MahFL
Quoting JLPR2:
Each circle is to the NW of the other.

Lots of disturbances out there.


No its not, one is WNW.
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Good morning. Not liking this at all.


Link
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hey, tig... got up abt 3 hrs ago, now getting back into bed... glad I don't have an early start today... lol

So far so good with our two Twaves... 92 look like it's got a bit further N... dunno if it'll do much before the weekend is over....

Anyway, u all enjoy your day....
Member Since: October 25, 2005 Posts: 19 Comments: 22322
0805 AM
..SPECIAL FEATURES...

A 1010 MB LOW IS CENTERED ABOUT 1000 NM W OF THE CAPE VERDE
ISLANDS NEAR 13N40W WITH A TROPICAL WAVE EXTENDING NW FROM THE
LOW TO 20N44W. THE SYSTEM IS MOVING W AT 13 KT. SCATTERED
MODERATE TO ISOLATED STRONG CONVECTION IS FROM 16N-19N BETWEEN
41W-46W. SATELLITE IMAGERY SUGGESTS THE SYSTEM MAY BE
ENCOUNTERING A DRIER AND MORE STABLE AIR MASS...HOWEVER
ENVIRONMENTAL CONDITIONS STILL APPEAR FAVORABLE FOR GRADUAL
DEVELOPMENT OVER THE NEXT SEVERAL DAYS. THIS SYSTEM HAS A MEDIUM
CHANCE OF BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS.

A 1010 MB LOW IS CENTERED ABOUT 275 NM SSW OF THE CAPE VERDE
ISLANDS NEAR 11N27W WITH A TROPICAL WAVE EXTENDING N ACROSS THE
CAPE VERDE ISLANDS TO 17N25W. HE SYSTEM IS MOVING W AT 13-17 KT.
WIDELY SCATTERED MODERATE CONVECTION IS NEAR THE LOW CENTER FROM
8N-14N BETWEEN 27W-33W. ENVIRONMENTAL CONDITIONS ARE EXPECTED TO
GRADUALLY BECOME MORE CONDUCIVE FOR DEVELOPMENT OVER THE NEXT
SEVERAL DAYS. THIS SYSTEM HAS A MEDIUM CHANCE OF BECOMING A
TROPICAL CYCLONE DURING THE NEXT 48 HOURS.


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1466. WxLogic
Good Morning...

Glad that NHC agreed with INVEST#4 as it could develop some as it moves underneath the Bermuda High:

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Quoting aislinnpaps:
Morning Tig,
Went to get coffee and put dogs out. I am also waiting and watching. I'm out of worrying about them so far as I'm not on the East Coast, but I know things can change.


yeah...being on the east coast this time of year is not the most enjoyable thing when there are storms pending lol...esp since Hugo anyway...that one was enuf for me to last a life time...i went n got coffee too so "CHEERS n G'morning" lol...let my dog out over an hour ago...at work now...gonna be a long day
Member Since: September 16, 2007 Posts: 0 Comments: 3650
Morning Tig,
Went to get coffee and put dogs out. I am also waiting and watching. I'm out of worrying about them so far as I'm not on the East Coast, but I know things can change.
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93L

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i am waiting to see what this model says tonight... 1st run had both 92 and 93 slamming east coast... this one is 92 turning out and 93 hitting...a little more than 13 hours to go lol...

Link
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oh, morning aislinnpapas
Member Since: September 16, 2007 Posts: 0 Comments: 3650
apparently no one is awake lol...will pop back in after a while...g'nite to those going to bed after a long nite watching and g'mornin to those just getting up...it is gonna be a LONG LONG day...
Member Since: September 16, 2007 Posts: 0 Comments: 3650

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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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