New African disturbance 96L likely to develop

By: Dr. Jeff Masters , 2:55 PM GMT on September 07, 2009

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A tropical wave (96L) that emerged off the coast of Africa yesterday has organized rather quickly, and will likely become a tropical depression by Tuesday night. Satellite imagery from the European satellite shows a well-organized circulation, but not enough heavy thunderstorm activity near the center of circulation to be considered a tropical depression. The storm is far enough south that the dry air of the Saharan Air Layer is not a major impediment to development. Wind shear is moderate, 10 - 15 knots, and ocean temperatures are 1 - 2°C above the threshold needed for tropical cyclone formation.


Figure 1. Morning satellite image of 96L, off the coast of Africa. The remains of disturbance 95L, which are under 30 - 40 knots of wind shear, can be seen at upper left.

The forecast for 96L
Most of the models develop 96L, and the chances are that this disturbance will become Tropical Storm Fred later this week. The system will initially move west-northwest, but by Thursday, a strong trough of low pressure passing to 96L's north will pull the storm to the northwest, and may be capable of fully recurving the storm to the northeast. However, most of the models foresee that 96L will not move far enough north for this to happen, and that the storm will have to wait for the next trough of low pressure. With the steering pattern for this year continuing to feature plenty of deep troughs of low pressure moving off the U.S. East Coast, the odds of 96L making it all the way across the Atlantic to threaten land areas appear low. Still, much that is unexpected can and does happen in the world of tropical meteorology, and 96L bears watching.

North Carolina low
An area of concentrated thunderstorms has developed off the North Carolina coast in association with the remains of an old cold front. This system is under about 20 - 30 knots of shear, and is not tropical. However, it will bring heavy rain to eastern North Carolina today and Tuesday, as the storm slides north-northeastward along the coast.

I'll have an update Tuesday.

Jeff Masters

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One thing I've learn is that Tropical Forecasting is very difficult becuz you are trying to forecast the state of an atmosphere that is uniform in structure or composition throughout. As compared to mid-latitude weather where the atmosphere is contrasting.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Just ignore SyKid, just a wishcaster who is upset that a Hurricane isn't coming to his house so he'll downcast the season. I'm sure if a hurricane threatens the US he'll be all 'Category 5 shortly'.
Member Since: July 8, 2005 Posts: 259 Comments: 23501
Fred BUST

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Almost the peak of the season and we have one depression and two tropical waves to watch!
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Quoting VAbeachhurricanes:


so according to this its been moving at about 260 degrees since moving off the coast right?


yea, due the Azores side the subtropical ridge
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting StormW:


It's the same principal as just sinking air, like from the MJO downward motion. As air sinks, it warms at the DAR of 5.5F/1,000ft. As the sinking air warms, it has the tendency to dry out the atmosphere.


Dry Adiabatic Lapse Rate right?
Member Since: July 24, 2005 Posts: 407 Comments: 19076


so according to this its been moving at about 260 degrees since moving off the coast right?
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No one is right 100% of the time. The models are definetly not right 100% of the time either.

One thing the NHC always seem to sy is that we do not know that much about intensity. Once there is an established system, they are decent at track - but not whether it will fall apart or strengthen, or rapidly intensify.

Just my .02. Saying that I wouldn't be suprised if "fred" fell apart or became a Cat 3 Hurricane - just the same.
Member Since: March 10, 2006 Posts: 0 Comments: 10028
Quoting StormW:


Outflow from a system will also stifle a system that is close enough, as the outflow, being anticyclonic, begins to sink away from the storm. This sort of puts a "cap" on a system near enough, as the sinknig motion doesn't allow for an outflow to establish with a second system that is too close to a developed system.


Learn something new everyday. Thanks!
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Quoting SykKid:


It's not forcasted to become a Hurricane....Once it dies....there is nothing.


It's okay to go above the pros sometimes. In this case, that's what 456 and I are doing. The anticyclone should persist for at least three and a half days.
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I am going slightly above the NHC intensity guidance, I think TD 7 could come close to be Hurricane Fred briefly.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting BurnedAfterPosting:
I disagree about all that shear, I think we will see close to home activity at the end of September and into October

It is definitely possible
also not possible
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Quoting SykKid:


It's not forcasted to become a Hurricane....Once it dies....there is nothing.


And we know all forecast are set in stone, right ST?
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07L would be more interesting if he drifted his way into the Central Atlantic. I know there are alternatives, but I prefer the satellite on the NHC page.
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Quoting Hurricane009:
What is TD 7 's T#


SAB = 2.0
TAFB = 2.5
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Holy macrel it's wet here in eastern NC. Some guy flipped a boat in the middle of US70 this afternoon. Maybe he was just preparing for these conditions....
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Quoting SykKid:


I want a Hurricane to track....Dont recall saying anything about lives being ruined?


You have TD7. It will probably become a hurricane due to that anticyclone. Isn't that enough?
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963. IKE
Quoting justmehouston:
Thanks Ike and thanks to Patrap for answering my earlier questions


You're welcome.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Quoting KoritheMan:


To add to this in order to help serial out some more, along with any others, outflow aloft flows anticyclonically, so remember that if you are ever making a forecast of which direction the shear will come from when upper-level outflow shears another system.


I'm trying to get my head around that!
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Quoting KoritheMan:


Upper-level outflow does have shearing within it, so you are somewhat correct. But outflow in itself does not shear the TC that is producing the outflow.

Outflow will, however, shear other developing disturbances, as was the case with Hurricane Fran's outflow destroying Tropical Storm Gustav in 1996. Had it not been for that, Gustav would've probably been a major hurricane.


Thanks 456 and kori for answering... Those were pretty active seasons! I was looking back to the 1995 days ago where Luis, Jeane, Humberto, Iris were simultaneous.
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something interesting

Finally, around midday on September 1, the NHC initiated advisories on Tropical Storm Erika, skipping depression status; the second storm of the year to do so.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Thanks Ike and thanks to Patrap for answering my earlier questions
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Quoting SykKid:
boring


Lives are not being ruined, though with that comment, perhaps... Nevermind.
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956. IKE
Quoting justmehouston:
Hey Ike, got a question for you. I just looked at the shear map that you posted for the GOM. Here's the question ...everytime that I push the +1 what does that equal in time?


6 hours.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
954. IKE
Looks like the cooler/fall like weather comes into the SE USA after that low makes landfall and heads NE according to the 18Z GFS....

Member Since: June 9, 2005 Posts: 23 Comments: 37858
953. JLPR
Quoting Hurricane009:
It is not a Tropical Wave, it is a tropical depression. :)


oh yeah whoops sorry xD
my brain died for a minute there lol xD
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Quoting KoritheMan:


Upper-level outflow does have shearing within it, so you are somewhat correct. But outflow in itself does not shear the TC that is producing the outflow.

Outflow will, however, shear other developing disturbances, as was the case with Hurricane Fran's outflow destroying Tropical Storm Gustav in 1996. Had it not been for that, Gustav would've probably been a major hurricane.


To add to this in order to help serial out some more, along with any others, outflow aloft flows anticyclonically, so remember that if you are ever making a forecast of which direction the shear will come from when upper-level outflow shears another system.
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Hey Ike, got a question for you. I just looked at the shear map that you posted for the GOM. Here's the question ...everytime that I push the +1 what does that equal in time?
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949. JLPR
Quoting Weather456:


Actually, the cirrus clouds out head of TD 7 is outflow, shear is about 5-10 knots over the depression due to an upper anticyclone.



that's one of the nicest anticlones I have seen this year with a TC
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Quoting serialteg:


i know about the a/c, i thought that when you saw clouds like that in a TC it was shear


in this case, the outflow cirrus indicate a well ventilated system. Signs of sheared TC usual is indicated when convection is removed from the COC.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting serialteg:


i know about the a/c, i thought that when you saw clouds like that in a TC it was shear


Upper-level outflow does have shearing within it, so you are somewhat correct. But outflow in itself does not shear the TC that is producing the outflow.

Outflow will, however, shear other developing disturbances, as was the case with Hurricane Fran's outflow destroying Tropical Storm Gustav in 1996. Had it not been for that, Gustav would've probably been a major hurricane.
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946. IKE
18Z GFS......shows the shear in the GOM lifting out.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Quoting Weather456:


Actually, the cirrus clouds out head of TD 7 is outflow, shear is about 5-10 knots over the depression due to an upper anticyclone.



i know about the a/c, i thought that when you saw clouds like that in a TC it was shear
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Quoting serialteg:


very nice, some shear on it hmm


No shear, TD7 has an anticyclone aloft, hence the outflow observed in that satellite photo.
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943. IKE
Quoting CybrTeddy:
@924, your also about to hit everyones ignore list if you haven't already.


I don't understand his post. When people post like that it's like their looking for responses.

And the GFS is calling for a western GOM system!


Quoting fldude99:


What are you talking about? Nothing mentioned at all anywhere about any GOM activity AFAIK


Houston,Texas afternoon discussion....

"THINGS GET REAL MESSY BY THE END OF THE WEEK. THE GFS DEVELOPS A
WEAK SURFACE LOW OVER THE WESTERN GULF WITH A SLUG OF PW AIR
APPROACHING 2.6 INCHES. THE GFS ACTUALLY DEVELOPS A WEAK SURFACE
LOW AND TRACKS IT N-NE TOWARD SOUTHERN LOUISIANA. THE CAN AND
ECMWF KEEP AN OPEN WAVE OVER THE GULF BUT BOTH MODELS STILL BRING
A SURGE OF MOISTURE NORTHWARD TOWARD THE UPPER COAST. UPPER LEVEL
WIND SHEAR LOOKS RATHER STRONG SO PREFER THE OPEN WAVE SOLUTION AS
SUGGESTED BY THE CAN/ECMWF."......


Lake Charles afternoon discussion...

"FOR THU INTO NEXT WEEKEND...CHANGE WILL BEGIN TO TAKE PLACE
ALOFT...AS THE FLOW BECOMES MORE SOUTHWESTERLY...ALLOWING THE
MOISTURE AND LIFT ACROSS MOST OF THE GULF OF MEXICO TO ADVANCE
NORTHWARD. ALSO...BOTH THE ECMWF AND GFS SUGGEST EITHER A COASTAL
SFC TROF OR LOW TO DEVELOP OFF THE MEXICAN AND TX COAST...AND LIFT
NE OVER THE COURSE OF THE WEEKEND. THIS TYPE OF SCENARIO HAS
HAPPENED IN THE PAST...AND HAS LED TO SIGNIFICANT RAINFALL FOR THE
REGION. FOR NOW...RAISED POPS IN THE 40-50% RANGE FOR THE DAYTIME
DURING SAT & SUN. POPS SHOULD DIMINISH BY MON AND TUE AS MOISTURE
GRADUALLY DIMINISHES."
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Quoting serialteg:


very nice, some shear on it hmm


Actually, the cirrus clouds out head of TD 7 is outflow, shear is about 5-10 knots over the depression due to an upper anticyclone.

Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting hurricanetracker:
All, Interesting GOM AOI possibly gearing up for development? A hint of a low level swirl now evident on visible satellite over the extreme southwestern BOC (very near the coast off Vera Cruz).

The wind sheer over the GOM is now between 30-40KT! Except over the BOC, where sheer is around 5-10KT! IF anything developed NOW and moved into the central GOM sheer would eat it alive!! There is an anti-cyclone just W of the AOI, IF the AOI joined forces, it may be interesting! They say sheer over the GOM is supposed to decrease over the next few days! Just watch and see!!
Member Since: August 25, 2009 Posts: 20 Comments: 6785
about to make landfall near jacksonville. Tropical or not, its the end for [possible development of] this storm.

Member Since: July 29, 2006 Posts: 28 Comments: 1776
Quoting Weather456:
Solid curve band is developing with TD 7 - Fred soon



very nice, some shear on it hmm
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Quoting BurnedAfterPosting:


you must not have been paying attention, 456 nailed it from the beginning. While everyone yelled fish, he said he thought it was going to the caribbean
Must have missed that, sorry 456. It was lonely on the west team.
Member Since: August 10, 2007 Posts: 0 Comments: 3221
Quoting BurnedAfterPosting:


you must not have been paying attention, 456 nailed it from the beginning. While everyone yelled fish, he said he thought it was going to the caribbean


not everyone...
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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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