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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465. amd
it looks like 15 degrees latitude is becoming the dividing line between favorable shear and very unfavorable shear in the Caribbean, at least in the short term.

If 97L stays below 15 degrees, it may develop. IMO.
Member Since: August 29, 2005 Posts: 0 Comments: 1024
press... I think you might be safe.
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19/1745 UTC 12.2N 52.1W T1.0/1.0 97L -- Atlantic
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LOL Press.
Sleep sound, man. We will wake you when your roof blows off, and the boat its in the gallery.
No probs.
Member Since: October 24, 2005 Posts: 0 Comments: 24776
Quoting presslord:
Any reason I can't take a nap without having to worry about shuttering up and evacuating?


Some of the model want to develop a coastal system and make it warm core. Something to keep an out out for Press.
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Quoting Drakoen:



Looks rather impressive.
Member Since: June 9, 2007 Posts: 4 Comments: 15947
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Any reason I can't take a nap without having to worry about shuttering up and evacuating?
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Quoting PensacolaDoug:
Thats a bad joke right, KOG?
nope tagged and bagged and forwarded to NHC for there response
Member Since: July 15, 2006 Posts: 176 Comments: 55462
:No but we have eyes and 3+ years at Weather Underground...oh wait.

And the waters over the Atlantic are still warm in spite of the shear. Seasonally, this storm should miss the trough.
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Quoting jasoniscoolman09:
its still a tropical wave.That map is 6 hours old.
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Nice microwave pass there SJ.
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Quoting extreme236:
I'd say its chances are 30-50% (medium) in my own opinion.


I'd have to agree with that.
Member Since: June 9, 2007 Posts: 4 Comments: 15947
its still a tropical wave.
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Quoting Vortex95:
Guys Drak is pulling your leg


I'd say he's more likely playing devil's advocate than pulling people's leg. He tells you one side of things and then the other side of things. Keeps it a bit more balanced usually.
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I'd say its chances are 30-50% (medium) in my own opinion.
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Latest microwave pass...
Member Since: August 17, 2005 Posts: 26 Comments: 16874
Quoting weatherwatcher12:

That map is 3 hours old. Things could change

That's not what that map says anyways. Shear is "decreasing" in front of 97L - the blue, perfed line is decreasing shear.
Member Since: July 9, 2006 Posts: 184 Comments: 29610
Quoting Weather456:


I'm In Saint Kitts, just to your ESE. 97L should dive to the south of us.


Thank you;the cistern's low;and,(carefully);we could use a wee drop.
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Doug, post 435
I hope it is.
But I fear it isn't.
Member Since: October 24, 2005 Posts: 0 Comments: 24776
Good deal Brian. I'll scope it in a few.
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Quoting Stormchaser2007:


Shear is increasing by 10 knots right in front of it. Also the lowering trend of the shear in the Caribbean has slowed to only 5 to 10 knots.


That map is 3 hours old. Things could change
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97L is still 420 miles away from the Upper trough.
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It would to be good to read the post for more information.
97L looks a lot like TS Marco!

Also, I think 97L has a 50-70% chance of becoming a TD by Monday.

Next, I think 97L has a 70-90% chance of becoming a TD.

Finally, I think 97L has a 60-80% chance of becoming a TS.
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Shear forecast is uncertain. All that needs to be said.
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Hey Doug!

John and I just launched it on the new site. We're working this afternoon to fine tune it, just in case this next week becomes important.
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Quoting BurnedAfterPosting:


First off it would not be unfortunate, we dont need systems developing

Second we dont know whether it will get sheared or not. Need I remind you that just last night at 8pm the NHC said conditions were unfavorable for development and then at 2am they said it was favorable again

Shear is incredibly hard to predict and we have all seen many many times the NHC change their tune on its favorability.


Shear is increasing by 10 knots right in front of it. Also the lowering trend of the shear in the Caribbean has slowed to only 5 to 10 knots. Right now it looks unfavorable. Whether it stays this way remains to be seen.

Member Since: June 9, 2007 Posts: 4 Comments: 15947
Quoting StormW:
Good afternoon!

Good afternoon
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97L reminds me of dolly when she was an invest.
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Thats a bad joke right, KOG?
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Wow big bursts of convection from the waves near panama and Puerto Rico. Also a busy GOM.
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Quoting STXpat:

W456:
Where are you in the Carib.I'm in St.Croix;
watching with a measure offear and amusement.


I'm In Saint Kitts, just to your ESE. 97L should dive to the south of us.
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It is kinda depressing when you see a nice wave that will get its head blown off in a couple days.....
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I have a question.

Right now, 97L is barreling along at 20 mph.

When it hits the shear later on, might the shear have the additional effect of perhaps slowing it down some?
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remember NHC dropped it last night, they are late to party.
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Quoting Stormchaser2007:


Im not writing it off. Its just unfortunate that it was developing nicely and has come back from virtually nothing just to get sheared apart.


First off it would not be unfortunate, we dont need systems developing

Second we dont know whether it will get sheared or not. Need I remind you that just last night at 8pm the NHC said conditions were unfavorable for development and then at 2am they said it was favorable again

Shear is incredibly hard to predict and we have all seen many many times the NHC change their tune on its favorability.
Good afternoon! Will admit that I may have written Invest 97L off too soon. It has really come together nicely and has become much better organized. Been noticing what seem like banding features developing around the disturbance indicating an increasingly better organized low-level structure. It will be interesting to watch and see how much an effect diurnal minimum will have on this disturbance as the day progresses. Overall, this is the best this feature has ever looked to this point. Its future will all depend upon what happens with the TUTT over the Northern Caribbean and how the upper-level high develops over the Caribbean.
Member Since: April 14, 2007 Posts: 8 Comments: 5169
Quoting Weather456:
lol, the NHC has been wrong before, 97L isn't going poof cuz they say so, nor isn't it going to develop becuz most others think so. 97L will do what it wants regardless of what anyone says no matter how official it is. I'm just patiently waiting for tonight.
Quoting Weather456:
lol, the NHC has been wrong before, 97L isn't going poof cuz they say so, nor isn't it going to develop becuz most others think so. 97L will do what it wants regardless of what anyone says no matter how official it is. I'm just patiently waiting for tonight.

Do you believe that we should watch it closely in Jamaicaa
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Old guys rule!
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Quoting nrtiwlnvragn:
I like sarcasm and jolking around, but a word of caution to thoses mimicking NHC content. The FEDS have been known to make mountains out of molehills.

NHC Disclaimer

The information on government servers are in the public domain, unless specifically annotated otherwise, and may be used freely by the public so long as you do not 1) claim it is your own (e.g. by claiming copyright for NWS information -- see below), 2) use it in a manner that implies an endorsement or affiliation with NOAA/NWS, or 3) modify it in content and then present it as official government material. You also cannot present information of your own in a way that makes it appear to be official government information..
its already been copied and sent to the NHC its not proper to add or change an official forecast it just should not be done
Member Since: July 15, 2006 Posts: 176 Comments: 55462
Quoting Weather456:
Well we all will know by 2night.

W456:
Where are you in the Carib.I'm in St.Croix;
watching with a measure offear and amusement.
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Go Tom!
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lol, the NHC has been wrong before, 97L isn't going poof cuz they say so, nor isn't it going to develop becuz most others think so. 97L will do what it wants regardless of what anyone says no matter how official it is. I'm just patiently waiting for tonight.
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420. beell
Quoting thermoclined:
Yeah, I posted that earlier, not sure what to make of it


Busy morning on the blog, yes? I missed your post. Just noting it is enough for now I guess!
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Quoting hurricane23:


Conditions are just fine were the disturbance is presently which (may) allow for this to reach TD intensity BUT the issue is what lies ahead the southerly jet is very much entrenched down there take a look at THIS MAP 50kt shear all over the caribbean this thing will suffer the same fate of the previous wave.This is what el nino will do for you.The islands could see some squally weather.


50 knots of shear all over the Caribbean? Um no, over a few of the Islands yes, but not in the Caribbean

Its going to be a close call, we just have to see how it goes.
LOL Drak.
People are so gullible. Some even believed your "could not care less".
I love it.
Member Since: October 24, 2005 Posts: 0 Comments: 24776
I don't see this "THERE IS AN EXTEMELY LOW CHANCE..." I don't think safe to use these kind of verbs in this situation. Maybe I would not take offense if they substituted possible and percentage. It's just sending the wrong message.
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Quoting BurnedAfterPosting:


ah well as in RIP?

Again writing it off too quickly, makes you lose all credibility


Im not writing it off. Its just unfortunate that it was developing nicely and has come back from virtually nothing just to get sheared apart.
Member Since: June 9, 2007 Posts: 4 Comments: 15947
Quoting Vortex95:
Guys Drak is pulling your leg


How?? No one is near me right now.
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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.