97L growing more organized, will bring heavy rain to the Lesser Antilles

By: Dr. Jeff Masters , 3:55 PM GMT on July 19, 2009

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The tropical wave near 12N 52W, about 600 miles east of the Lesser Antilles Islands (97 L), has grown more organized this morning as it tracks west at about 20 mph. This wave is surrounded by an area of very dry air from the Sahara Desert, but 97L has been able to steadily moisten a large region of the atmosphere over the past day, insulating itself from the dry air. This moistening process has been aided by sea surface temperatures (SSTs) that have steadily increased from 26.5°C to 27.5°C, plus the presence of only 10 knots of wind shear. The system now has a small area of intense thunderstorms near its center, with some rotation of the cloud pattern evident at mid-levels of the atmosphere. An upper-level outflow channel has opened to the north, and there is evidence that surface spiral bands are beginning to form. This morning's QuikSCAT pass missed 97L, so we don't know what is happening at the surface.

Wind shear is a modest 10 knots over the disturbance, and is forecast to remain in the moderate 10 - 15 knot range through Monday morning. This should allow further development to occur today, and 97L could be approaching tropical depression strength on Monday as it moves through the central Lesser Antilles Islands. Monday night, shear is expected to rise to 20 - 30 knots, thanks to the presence of a trough of low pressure at upper levels of the atmosphere over the eastern Caribbean. Since 97L is a relatively small system, it is very vulnerable to wind shear. This shear may be able to drive some of the dry air west of 97L deep into its interior, significantly disrupting the disturbance. Shear will remain high along 97L's path through Thursday, when the storm should be in the western Caribbean near Cuba. If there is anything left of 97L by then, some development is possible. The National Hurricane Center gave 97L a low (less than 30% chance) of developing into a tropical depression in the next 48 hours in their 8am Tropical Weather Outlook. However, I'd say the odds are now in the medium range (30 - 50%).

None of the computer models are forecasting tropical storm development over the next seven days.


Figure 1. Current satellite image of African wave 97L.

I'll have an update Monday morning. As 97L approaches the islands, you may want to follow local observations there using our wundermap for 97L.

Jeff Masters

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814. eye
by this time Monday it will be severely affected by shear, actually late tonight...it is almost there.
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Quoting eye:
the shear has already begun to affect it...look at its shape...it is easy to see to the west of the system where the shear is at it is fast approaching the shear.

I think it is perfectly normal for a cyclone to look like this. Isn't it?
Member Since: May 16, 2009 Posts: 1 Comments: 1231
Quoting eye:
the shear has already begun to affect it...look at its shape...it is easy to see to the west of the system where the shear is at it is fast approaching the shear.
No shear effecting at at all/5kt.
809. eye
Storm, but on the flip side of that...small systems can get affected by even mild shear far greater than bigger systems.
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Quoting beell:


The ULL at 29N 53W tied to the trough near 97L appears to be headed off to the NW per WV. Lift or de-amplify-either option. The GFS might be a tad incorrect with its more westward drift of the ULL.



Yea i've been watching that.
Member Since: October 28, 2006 Posts: 57 Comments: 30615
Quoting eye:
the shear has already begun to affect it...look at its shape...it is easy to see to the west of the system where the shear is at it is fast approaching the shear.

Right now shear is not affecting it. Shear is near 5-10 knots.
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804. eye
the shear has already begun to affect it...look at its shape...it is easy to see to the west of the system where the shear is at it is fast approaching the shear.
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Quoting beell:


The ULL at 29N 53W tied to the trough near 97L appears to be headed off to the NW per WV. Lift or de-amplify-either option. The GFS might be a tad incorrect with its more westward drift of the ULL.


great point, GFS is incorrect about the movement of the ULL, could have a huge impact on the impending shear 97L would have to deal with
burneafterposting,,"listen to him he is right where the money is",,by the way is just a saying, just to say he is right.
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Now if it were to take the track of the NOGAPS or CLIP than it would have some help for a potential anti cyclone.

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799. beell
Quoting Drakoen:


Yes slowing down would definitely help. Give more time to the trough to lift out.


The ULL at 29N 53W tied to the trough near 97L appears to be headed off to the NW per WV. Lift or de-amplify-either option. The GFS might be a tad incorrect with its more westward drift of the ULL.
Member Since: September 11, 2007 Posts: 144 Comments: 16876
I apologize for just asking questions and not being able to contribute more. Just heard that a tropical system may be able to create its own high-pressure above it. How strong must the system be; and would this affect any wind shear which may be in front of it? I infer this is the problem that 97L may encounter due to the 20kt wind shear I see on the maps. It appears to be a well-formed system at the moment; noticing a more comma shape than before.
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Floater 1 AL97 AVN Color Imagery Loop
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Calm down and watch the radar
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Quoting Patrap:

ESL Hurricane Page


nice link
Member Since: May 19, 2009 Posts: 0 Comments: 484
794. eye
bigger systems might be able to handle it...but this is a tiny system and just a lil shear could easily kill it.
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Quoting weatherwatcher12:

They should at least issue a TCFA

Yup!
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Quoting howarjo1943:
The NHC has many smart and levelheaded guys, but they are being a little too cavalier with this wave. Shear is still a couple hundred miles ahead of this system & it is approaching the 29 degree isotherm. It appears to be heading W or WSW toward the weaker shear. There are still many ?'s on how the shear patterns will evolve over the next couple of days according to the models. It is nearly a depression now, and it should be classified as such by tomorrow morning IF it maintains that convection near its center through this evening and especially overnight. That being said, convection has waned a bit this afternoon, but it is a very well formed wave with banding evident. The high wind shear to its north is also aiding in outflow. They should at least schedule a recon for tomorrow morning.

They should at least issue a TCFA just for the safety of the people
Member Since: May 16, 2009 Posts: 1 Comments: 1231
Quoting Drakoen:
This blog is so bipolar...


LOL
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790. eye
It is so depressing watching a developing system heading right to its death.....this time Monday it will be a weak sheared wave....its head will be blasted off tonight.
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The NHC has many smart and levelheaded guys, but they are being a little too cavalier with this wave. Shear is still a couple hundred miles ahead of this system & it is approaching the 29 degree isotherm. It appears to be heading W or WSW toward the weaker shear. There are still many ?'s on how the shear patterns will evolve over the next couple of days according to the models. It is nearly a depression now, and it should be classified as such by tomorrow morning IF it maintains that convection near its center through this evening and especially overnight. That being said, convection has waned a bit this afternoon, but it is a very well formed wave with banding evident. The high wind shear to its north is also aiding in outflow. They should at least schedule a recon for tomorrow morning.
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Well right now the clouds over the southern Lesser Antilles aren't racing off to the east like the clouds south of Hispaniola a sign that the upper trough isn't affecting it.
Member Since: October 28, 2006 Posts: 57 Comments: 30615
Quoting GeoffreyWPB:
Closer to home..a number of Severe T-Storm Warnings issued for So. Fla...



Some strong storms.
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Quoting weatherwatcher12:

If it makes it through it has a chance in the Carib because the TUTT is slowly lifting up


agreed

ESL Hurricane Page
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Quoting BurnedAfterPosting:


just seems to me everyone is ignoring the increasing shear that is occuring east of the Islands, that shear is dipping southward

If it makes it through it has a chance in the Carib because the TUTT is slowly lifting up
Member Since: May 16, 2009 Posts: 1 Comments: 1231
g'afternoon folks. I hear we have a storm a-brewin'


hiya, w-witch. Some folks here aren't overly conversational, others are. Your caps signify yelling and, in general, most people don't react well to being yelled at. Your choice, of course, as you said... but, if last year started out on a sour note, why not try a different approach this year? I hope you get the answers to your questions and I hope you settle in and find this a nice place to watch and learn (as the rest of us have).
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Quoting Drakoen:


46


Oh I get it now lol.
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Quoting Patrap:
Afternoon Chief,..looks like a lil sumthing to track.



Afternoon...

you're right about that one...
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Quoting StormW:

I've never researched where this website gets its model info from, but here are 2 that I use:


PSU e-Wall

FSU Experimental forecast Tropical Cyclone Genesis Potential Fields


I subscribe to the Accuweather Pro Site for model analysis too.


storm w or patrap you guys are awesome
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Quoting Spartan117:


HAHA! Drak is so funny isn't he guys!?


46
Member Since: October 28, 2006 Posts: 57 Comments: 30615
Quoting BurnedAfterPosting:


just seems to me everyone is ignoring the increasing shear that is occuring east of the Islands, that shear is dipping southward

Exactly. Shear looks rather unfavorable at best in its path. Although right now its near 5-10 knots.
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Quoting Drakoen:
I want to take it home with me and pet it lol!


HAHA! Drak is so funny isn't he guys!?
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FNMOC WXMAP
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Quoting WaterWitch11:


YOUR RIGHT AND I DIDN'T LAST THE PREVIOUS YEAR! BECAUSE THE WAY YOU GUYS TREAT PEOPLE WHEN THEY ARE JUST TRYING TO LEARN.


Using CAPS makes it look like you are yelling. Undo the CAPS lock and I'm sure that will ease the tension up a bit.
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Quoting Drakoen:
This blog is so bipolar...


LOL

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Quoting Stormchaser2007:


Rofl...starting to sound like me. Welcome to the dark side.


just seems to me everyone is ignoring the increasing shear that is occuring east of the Islands, that shear is dipping southward
Closer to home..a number of Severe T-Storm Warnings issued for So. Fla...

Member Since: September 10, 2007 Posts: 0 Comments: 11425
Quoting Drakoen:
This blog is so bipolar...


LOL! :-)
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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.