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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Drak, no clue who the other piece of driftwood is in here.

My concern is the winds and shear values in the Caribbean. So far this system has beaten everything that has been posted about it, high shear, dry air and the such. I am concerned that in the end, it won't be us eating the crow but instead it would be the NHC.
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Quoting eddye:
where you live weatherwatcher 12

Jamaica
Member Since: May 16, 2009 Posts: 1 Comments: 1231
563. eddye
where you live weatherwatcher 12
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561. eye
yeah, it is easy to see the cloud tops being blown off just ahead of 97....it will hit that early AM Monday....
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SLU you are so right. the way things are looking i have already said TS ana through the cental windwards tomrrow
Member Since: August 22, 2006 Posts: 0 Comments: 2722
Quoting plywoodsale:
Look at the convection ahead of 97L....it just got smashed. That is what 97L is about to run into.


That thing was within the upper trough when it was mentioned lol
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Quoting SLU:


I can't agree with you more. Remember when invest 93L was entering the Gulf and they had a 50% chance of development for a cloudmass that looked like crap???? When I took the NHC to task some US bloggers were up in arms. The system dissipated hours later. Here you have a vigorous tropical wave close to the Windwards looking like perhaps the best organised system all season and its given almost no chance of developing. Who knows if those upper level winds they are talking about will actually materialise?? What if it doesn't and the system rapidly spins up into a storm over the Islands???

I don't agree with all the NHC's forecasts. I only use it as a guide. I have my own opinions about the weather and they are normally correct. As they were with 93L and as I expect to be with 97L.


Amen, Amen, Amen
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557. eye
NHC thinks shear will kill it Monday that is why....
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Satelite shows a lot of moister in that NE section of 97.
Nice high cloud tops
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TO: nrtwlnvragn
Could you please tell me how to get the link to the models which you posted. It appears interesting. By the way, thank you for your comment on my initial picture I posted on my blog.
Question: are these dynamic models or extrapolated information for possible projections. Again, thank you all for the information you have all provided. Quite educating.
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Quoting SLU:


I can't agree with you more. Remember when invest 93L was entering the Gulf and they had a 50% chance of development for a cloudmass that looked like crap???? When I took the NHC to task some US bloggers were up in arms. The system dissipated hours later. Here you have a vigorous tropical wave close to the Windwards looking like perhaps the best organised system all season and its given almost no chance of developing. Who knows if those upper level winds they are talking about will actually materialise?? What if it doesn't and the system rapidly spins up into a storm over the Islands???

I don't agree with all the NHC's forecasts. I only use it as a guide. I have my own opinions about the weather and they are normally correct. As they were with 93L and as I expect to be with 97L.


SLU, when I first ran into you this season, I thought you sounded a bit egotistical but then I saw your view point and have since enjoyed your post... keep up the good work.. also agree with you about the NHC this season
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Look at the convection ahead of 97L....it just got smashed. That is what 97L is about to run into.
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Looks decent. WAY better than yesterday at this same time.

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NHC seems afraid to stick their neck out.
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550. SLU
Quoting Weather456:
If it was in the GOM under the same circumstances and the threatening the US Gulf Coast, it would have an orange circle. However, I'm waiting for tonight on Monday, for this "increase in upper winds" but being so close to the islands, I hope they know what they are doing.


I can't agree with you more. Remember when invest 93L was entering the Gulf and they had a 50% chance of development for a cloudmass that looked like crap???? When I took the NHC to task some US bloggers were up in arms. The system dissipated hours later. Here you have a vigorous tropical wave close to the Windwards looking like perhaps the best organised system all season and its given almost no chance of developing. Who knows if those upper level winds they are talking about will actually materialise?? What if it doesn't and the system rapidly spins up into a storm over the Islands???

I don't agree with all the NHC's forecasts. I only use it as a guide. I have my own opinions about the weather and they are normally correct. As they were with 93L and as I expect to be with 97L.
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extreme, mail
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Damn these ice cream and cake commercial. So annoying
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Just talked to a friend of mine who is a met and he is more bullish on this than the NHC. He also says the GOM may need to keep an eye on this in about a week.
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Quoting Drakoen:


The NOGAPS may be right on with it's track. That's something that I am looking for it to end up in the central Caribbean.

Then I better keep an eye on it
Member Since: May 16, 2009 Posts: 1 Comments: 1231
Quoting StormW:
Afternoon 456!


Afternoon SW, what do you think of 97L?
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Quoting weatherwatcher12:


The NOGAPS may be right on with it's track. That's something that I am looking for it to end up in the central Caribbean.
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CMC is on the new tracks too, well a full line of the CMC lol
they say tropical meteorology is difficult . itreally is!!!
Member Since: August 22, 2006 Posts: 0 Comments: 2722
Quoting StSimonsIslandGAGuy:
It does look cute Drakoen :) How long does it take the computers to complete the processing for the XTRAP run?


Afternoon SSIG

It's already out for the 18z..Along with the BAM models.
Member Since: August 17, 2005 Posts: 26 Comments: 16874
This system has a long way to go before it would hit the shear, perhaps 18-24 hours and it is not too far from being a depression right now. It has a center of circulation with heavy convection. Trade winds in that area are normally 15-20kts anyway, so it doesn't take much of an increase in sustained winds to get a TD. I usually agree w/ the NHC since all of those guys have Master's degrees and PHD's, but they should be a little more bullish with this system(Orange or Red circle). Plus, there is uncertainty on how much shear there will actually be in the next 24-72 hours as models diverge on the evolution of the upper trough. Basically, they need to get their heads out of their...
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The nogaps brings it straight to me in favorable conditions
Member Since: May 16, 2009 Posts: 1 Comments: 1231
Quoting plywoodstatenative:
What are the water temps in the area that its heading into.


Rather warm...28C to eventually 29-30C
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532. eye
Based on the cloud movement ahead, I see some shear in that pic 456. Look closely....
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What are the water temps in the area that its heading into.
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Managed to get the NOGAPS (black line) in there. Perhaps they tracked the 850mb maxima on the model
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Might be useful later on.
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This thing looks really good.This should be at least at high risk or td by now.NHC are sleeping?
T1.0 rating indicates some primitive organization so far.
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Big big ups for Tom Watson though, a great performance regardless

Congrats to Stewart Cink
Hmmmmm, a little southward motion there ?
Excuse me, but that is NOT permitted.
Go away.../
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Quoting Drakoen:


1 second lol?


However long it takes to draw a straight line lol
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I'm here looking at the visible I'm baffled by the yellow circle. I'm looking at the clouds ahead and it does seem to be anything that would increase shear as early as tonight. Frankly, I have to disagree with the NHC.

Also:

19/1745 UTC 12.2N 52.1W T1.0/1.0 97L

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Quoting stormwatcherCI:
No thanks.

Not Ivan again
Member Since: May 16, 2009 Posts: 1 Comments: 1231
Stewart Cink is da man!
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Quoting StSimonsIslandGAGuy:
It does look cute Drakoen :) How long does it take the computers to complete the processing for the XTRAP run?


1 second lol?
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Quoting moonlightcowboy:


Agreed, and steering layers suggests that; but, sat appears to show it has moved about a degree more northwards since this early this morning - or am I not seeing this correctly?


If anything it has decreased in latitude. It went from 12.4N to 12.2N.
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Quoting extreme236:


Yes. Although for the time being it doesn't look like it is.


Yea. Its heading WSW right now...not really gaining much northward momentum.
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Quoting eye:
Since people like to compare invests with past major hurricanes here...how about a IVAN path?
No thanks.
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Can the Columbia low interfere with 97L development?
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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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