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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Quoting tropicfreak:


we'll see what happens. If convection flares up tomorrow mornig and it continues to look organized like it has been then it will survive the shear. Again you are talking 15-30 kt shear so it could have a 50/50 chance of surviving the shear. Whan it does survive, it will head into very favorable area (GOM) with hot SST's and low wind shear and a very moist environment then this baby will fire up into a TS, perhaps a cat 1 at strongest at landfall.


First off none of the three of us said the shear would kill it

Second, anyting over 20 knots of shear can definitely kill a tropical system

Third, dont assume where this system is going and where it will find favorable conditions when we dont really know if it will survive the next 24 hours or how shear will be like the next few days.
1714. WxLogic
Hmm... based on the latest 00Z Shear charts... seems that shear is starting to break up into 2 pieces... might be the start of a less influential trough.
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Gfs 12 hour shear forecast:


Gfs 24 Hours:



Gfs 36 Hours:



Gfs 48 Hours:
Member Since: May 16, 2009 Posts: 1 Comments: 1231
Is there a synonym for shear in a thesaurus I think the word is getting worn out on the blog today lol.
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Quoting BurnedAfterPosting:


you seem to be denying it too, look at the shear map and then look at the visible, shear is not becoming move favorable in the short term

As I said if it can survive the shear in the Eastern Caribbean, I think we will see Ana with 97L in the Central Caribbean


we'll see what happens. If convection flares up tomorrow mornig and it continues to look organized like it has been then it will survive the shear. Again you are talking 15-30 kt shear so it could have a 50/50 chance of surviving the shear. When it does survive, it will head into very favorable area (GOM) with hot SST's and low wind shear and a very moist environment then this baby will fire up into a TS, perhaps a cat 1 at strongest at landfall.
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Quoting HurricaneKing:


The cimss map shows the shear which is going to be there for a couple of days. The WU forecast map doesn't show shear. The WU forecast map really hasn't been correct since I can remember. It almost always shows good conditions when what actually could be occuring is 100kts of shear.


and I want to thank you and SJ for backing me up on this one lol
Quoting StormJunkie:
1701. Very kindly put ¿~) It is showing one element of shear or something...But it does not relate well to shear impacting tropical systems.

Waiting to see if an ESE wind shows up here.


exactly, CIMSS is much more in depth in terms of shear and how it impacts tropical systems
Quoting tropicfreak:


That is the info he got. It shows favorable shear and unfavorable shear. What the heck are you talking about. Favorable and unfavorable shear isn't separated into 2 maps. You don't make any sense.


The cimss map shows the shear which is going to be there for a couple of days. The WU forecast map doesn't show shear. The WU forecast map really hasn't been correct since I can remember. It almost always shows good conditions when what actually could be occuring is 100kts of shear.
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1701. Very kindly put ¿~) It is showing one element of shear or something...But it does not relate well to shear impacting tropical systems.

Waiting to see if an ESE wind shows up here.
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1706. Vero1
~
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Feeling rather nice outside right now. Finally feeling the effects of the front.

Updated: 58 min 33 sec ago
Clear
79 °F
Clear
Humidity: 56%
Dew Point: 62 °F
Wind: 5 mph from the North
Pressure: 30.06 in (Rising)
Visibility: 10.0 miles
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1704. pottery
post 1700, TexasGulf.
The calm before the storm ?LOL
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Quoting tropicfreak:


That is the info he got. It shows favorable shear and unfavorable shear. What the heck are you talking about. Favorable and unfavorable shear isn't separated into 2 maps. You don't make any sense.


um take a look at the two maps

The one from WU shows red, which on that map is favorable shear throughout the Caribbean for the entire forecast period

The one from CIMSS also shows red by the islands, but that red is unfavorable shear with white lines of inceasing shear of upwards of 20 knots in the last 24 hours.

Same colors on the two maps, two totally different meanings
I never did get an answer to this question earlier...Maybe one of you can help...

Will the GHCC site be the first imagery site that gets a view of 97 in rapid scan mode (update every 15min)?
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Quoting weatherwatcher12:

I looked and I said the same thing as you until I saw the forecast for tomorrow.


that map from WU has favorable shear in about 80% of the Atlantic about 95% of the time lol, I have found that it isnt very trustworthy

Just got back from 7-day cruise from Galveston to Key West, Bahamas & back.

Weather was beautiful all week. Seas only 1-2 feet at most. I have never seen the gulf and Atlantic that calm ever. The seas were as calm as a small lake all the way through Florida straits, around the Bahamas & back into the gulf. The only rain and "slight" seas were on Saturday mid-gulf returning to Galveston.

SST's around bahamas were definitely 86-88 deg.F. The water temps felt like a warm backyard swimming pool.

That was a very good week out, but even the cruise crew were commenting about how abnormally calm the ocean was.

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Quoting BurnedAfterPosting:


look at the map you posted from CIMSS, you seem to only consider the maps that show favorable shear and are ignoring the maps that show unfavorable shear



That is the info he got. It shows favorable shear and unfavorable shear. What the heck are you talking about. Favorable and unfavorable shear isn't separated into 2 maps. You don't make any sense.
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1698. KEEPEROFTHEGATE (Mod)
Quoting surfmom:


welll, yeaaa -- you're next door to the Klondike dude!!!
i know i may have to break out the yak coat
Member Since: July 15, 2006 Posts: 169 Comments: 53296
Quoting tropicfreak:


Burned please I don't know how many times I have to say this but shear will decrease ahead of it.


you seem to be denying it too, look at the shear map and then look at the visible, shear is not becoming move favorable in the short term

As I said if it can survive the shear in the Eastern Caribbean, I think we will see Ana with 97L in the Central Caribbean
1696. Dakster
Melwerle - I can only empathize with you. At least I have A/C...
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Quoting StormW:

...not to be that conducive over the GOMEX.



I so enjoy seeing things like your quote above.. Thanx StormW
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Quoting BurnedAfterPosting:


look at the map you posted from CIMSS, you seem to only consider the maps that show favorable shear and are ignoring the maps that show unfavorable shear


I looked and I said the same thing as you until I saw the forecast for tomorrow.
Member Since: May 16, 2009 Posts: 1 Comments: 1231
Quoting BurnedAfterPosting:


shear continues to increase, doesnt look promising for 97L in the short term


Burned please I don't know how many times I have to say this but shear will decrease ahead of it.
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Quoting weatherwatcher12:

Look at the forecast I posted


look at the map you posted from CIMSS, you seem to only consider the maps that show favorable shear and are ignoring the maps that show unfavorable shear

I realize I shouldn't complain but it's HOT here...go figure. I think I brought the GA heat with us. It's 90, 67% humidity. The heat is supposed to break at some point this week. Not good though when you have no a/c.
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Quoting BurnedAfterPosting:


shear continues to increase, doesnt look promising for 97L in the short term

Look at the forecast I posted
Member Since: May 16, 2009 Posts: 1 Comments: 1231
Quoting IKE:


For the record....

We are through 49 days of the tropical season.
We have 134 to go and.....it's over.
27% of the season is behind us.

If you are counting days, then I suppose that's true.
However, I once went back through historical accounts and found that in the South Carolina Lowcountry, the vast majority of storms hit somewhere between the last 2 weeks of August and the month of September. (I am sorry that I do not remember exactly, but I think it was about 80%).
Since June and July have historically had not much impact, I will be waiting until August 15 to start my count down

Hey there, SJ.
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Quoting weatherwatcher12:


shear continues to increase, doesnt look promising for 97L in the short term
Evening Tsapp

The easy answer to that is it is way to far out to tell where it may be, and what would happen.

Hypothetically...even if it were in the Bahamas, it is certainly to far out to tell where edge of the high pressure will be and therefore where it would go. Depends on strength of the system as well.

Wait and see as always...
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Interesting from the wunderground site:


Beginning July 20 and ending July 22
Member Since: May 16, 2009 Posts: 1 Comments: 1231
1685. Dakster
Feels like July here... Albeit hotter than I can remember. (and apparently since records were kept as well, as South Florida keeps breaking heat records)

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1683. IKE
Quoting surfmom:


Ike, I live for the groundswell, but I'm not stupid either --I like knowing we're 27 percent through-- all it takes is one.

for example your namesake.


Junior was a beast.

Plenty of convection over Florida.....

Member Since: June 9, 2005 Posts: 23 Comments: 37858
Member Since: May 16, 2009 Posts: 1 Comments: 1231
1681. surfmom
Quoting KEEPEROFTHEGATE:


evening storm

feels like october where iam


welll, yeaaa -- you're next door to the Klondike dude!!!
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1680. IKE
Quoting sporteguy03:


There is always 6z tomorrow Ike quieter peaceful blog lol.


I'll be on here looking at 97L....
Member Since: June 9, 2005 Posts: 23 Comments: 37858
hey guys even if it does what StormW says and goes to the bahamas wouldn't the trough pick it up and move it out
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1677. surfmom
Hey MON, I am going to win Ossqss's contest....

Quoting sporteguy03:


There is always 6z tomorrow Ike quieter peaceful blog lol.
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1676. KEEPEROFTHEGATE (Mod)
Quoting RufusBaker:
Looks like a new burst of convection firing near the center of 97.
from nothing it comes
Member Since: July 15, 2006 Posts: 169 Comments: 53296
1675. surfmom
Quoting IKE:


You see it a few times in the winter. I'm in the panhandle of Florida. Just got a beneficial quarter inch of rain.

Who needs 97L?

For the record....

We are through 49 days of the tropical season.
We have 134 to go and.....it's over.
27% of the season is behind us.


Ike, I live for the groundswell, but I'm not stupid either --I like knowing we're 27 percent through-- all it takes is one.

for example your namesake.
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1674. KEEPEROFTHEGATE (Mod)


pop up convection begining to occur in 97l small areas at the moment
Member Since: July 15, 2006 Posts: 169 Comments: 53296
Quoting IKE:


LOL....

My prediction was no named storm through July. I still may be right.


There is always 6z tomorrow Ike quieter peaceful blog lol.
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1671. Middy83
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Quoting StormW:


I think right now (until I perform analysis tomorrow), the only concern I would have is if low pressure did start, and made its way over to the Bahamas in a few days. (fairly favorable upper level in a few)

Time to sign off. Have a great evening all!


why storm wouldn't the trought pick it up and move it out to see
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Night Storm, See ya tomorrow.
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Looks like a new burst of convection firing near the center of 97.
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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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