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 eddye:
cchs weatherman go on facebookdude


Just to let you know, I've been on Facebook.
Member Since: April 14, 2007 Posts: 8 Comments: 5163
So Drak...in your opinion, should this be classified as a T.D.?
Member Since: September 10, 2007 Posts: 0 Comments: 10986
Bouys indicating proximity to invest?
41101

41040
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Quoting BaltOCane:
that Edith track is nuts


that one isnt Edith, that one with the loop by the Bahamas is Betsy
Quoting Weather456:
A well-define tropical system



Hehe... can't wait for DMAX to see what will happen with this one under this complex environment.
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859. beell
Quoting cchsweatherman:


Could be wrong, but wouldn't that cause the TUTT lift out faster than expected thus creating more favorable conditions to develop in the Caribbean sooner than expected? If thats the case, then it would suggest more promise for Invest 97L's future. But yet again, we'll just have to wait and see how things develop.


Only if the ULL pulls away. If it drifts west the base of the trough may be slow to lift.
Member Since: September 11, 2007 Posts: 141 Comments: 16239
that Edith track is nuts
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Quoting beell:


We'll see, WS.
After I invented the internet, I joined WU and turned my crap filter up to high, payed attention and finally learned what it meant to really follow the tropics.

LOL, "crap filter!" Too funny!
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856. eddye
cchs weatherman go on facebookdude
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855. eye
I am not downcasting, I am obviouscasting (along with the NHC)...there is a wall of shear right ahead of it...the shear is not moving much...this system is tiny...not like a Floyd that can deal with shear....
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Quoting AllStar17:


Why are you trying to downcast this system? Shear is clearly NOT affecting the system now. You can clearly see the system wrapping the "feeder band" to the north around, and increasing organization. This invest has excellent structure, and is continuing to organize as we speak. Also, model guidance is extremely spread out, so there is no way you can jump to conclusions about a track now. The most likely scenario is that the system tracks west, then WNW or NW as the trough moves north.


Allstar, spot-on, again! ;)
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Quoting Weather456:
AllStar17,

it's called troll bait. Don't risk being ban cuz he does it all the time. Since the infamous 2007.


Alright, I will put him on ignore. Thanks!
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the process of system to form is very complex, i am amazed how many of you are already saying the system will be gone by tomorrow,in weather nothing is certain and when it comes to tropical systems,is a lot more complex, wind shear is very hard to predict,i think it is better to wait before saying the system will be gone by tomorrow, which can happen,but really don't know
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Quoting jeffs713:


I just pulled the NOGAPS, and I don't see a closed low at all.

NOGAPS MSLP & Precip

I was talking about the NOGAPS shear forecast
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New microwave imagery confirms low level spirals bands in addition to the development of a LLC:
Member Since: October 28, 2006 Posts: 57 Comments: 29904
848. beell
Quoting WeatherStudent:


Bell, you're awfully good when it comes to making these types of observation. May Ia sk you, how did you learn about these types of things.


We'll see, WS.
After I invented the internet, I joined WU and turned my crap filter up to high, payed attention and finally learned what it meant to really follow the tropics.
Member Since: September 11, 2007 Posts: 141 Comments: 16239
Quoting Weather456:
A well-define tropical system



456, do you think this is a TD....or should be a TD??? It looks as good as the Tropical Depression we had of the Carolina coast in May. Very confusing why the NHC is forecasting conservatively.
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AllStar17,

it's called troll bait. Don't risk being ban cuz he does it all the time. Since the infamous 2007.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
845. IKE
Quoting AllStar17:


Why are you trying to downcast this system? Shear is clearly NOT affecting the system now. You can clearly see the system wrapping the "feeder band" to the north around, and increasing organization. This invest has excellent structure, and is continuing to organize as we speak. Also, model guidance is extremely spread out, so there is no way you can jump to conclusions about a track now. The most likely scenario is that the system tracks west, then WNW or NW as the trough moves north.


He always down-casts.
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Upper divergence is great with 97L. Convergence is non existent.
Member Since: June 9, 2007 Posts: 4 Comments: 15788
Quoting eye:
Probably this time Monday the focus will be the blob in the ITCZ (if it is still there).


oh I have heard stories about you from 2005 and 2006

You are the absolute kind of the downcasters, even with some of the biggest storms of the season you downcasted them to death

Your credibility is ZERO, actually its lower than ZERO
Quoting weatherwatcher12:

The NOGAPS disagrees


I just pulled the NOGAPS, and I don't see a closed low at all.

NOGAPS MSLP & Precip
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Interesting too is looking at all the sat pictures throughout the day if this was falling apart why does convection still keep firing, so if shear is effecting it what should we be looking for?
Member Since: July 7, 2005 Posts: 0 Comments: 5160
839. eye
Probably this time Monday the focus will be the blob in the ITCZ (if it is still there).
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A well-define tropical system

Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting eye:
even if it somehow survives the shear, it looks more and more like a Central America system.


Why are you trying to downcast this system? Shear is clearly NOT affecting the system now. You can clearly see the system wrapping the "feeder band" to the north around, and increasing organization. This invest has excellent structure, and is continuing to organize as we speak. Also, model guidance is extremely spread out, so there is no way you can jump to conclusions about a track now. The most likely scenario is that the system tracks west, then WNW or NW as the trough moves north.
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Quoting jeffs713:
Reading over everything here, I don't think this is a TD yet, as it is well-organized, but persistence is somewhat lacking. Remember at this time yesterday, it looked nothing like this. I think the NHC is spot-on in not designating this a TD, based on its current appearance and "age". If it looks like this late tonight, or early tomorrow, possible TD designation.

Also, the yellow circle is absolutely correct, as it has some very nasty shear ahead of it that can easily rip it apart within 48 hours. (200-300 miles at 20 mph = 10-15 hours)

The NOGAPS disagrees about 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.


Could be wrong, but wouldn't that cause the TUTT lift out faster than expected thus creating more favorable conditions to develop in the Caribbean sooner than expected? If thats the case, then it would suggest more promise for Invest 97L's future. But yet again, we'll just have to wait and see how things develop.
Member Since: April 14, 2007 Posts: 8 Comments: 5163
Top 10 analog track for 97L.
Closer view.
Member Since: June 9, 2007 Posts: 4 Comments: 15788
Reading over everything here, I don't think this is a TD yet, as it is well-organized, but persistence is somewhat lacking. Remember at this time yesterday, it looked nothing like this. I think the NHC is spot-on in not designating this a TD, based on its current appearance and "age". If it looks like this late tonight, or early tomorrow, possible TD designation.

Also, the yellow circle is absolutely correct, as it has some very nasty shear ahead of it that can easily rip it apart within 48 hours. (200-300 miles at 20 mph = 10-15 hours)
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Quoting eye:
even if it somehow survives the shear, it looks more and more like a Central America system.


That is absolutely false, most models keep it away from Central America
830. beell
Quoting Drakoen:



Yea i've been watching that.


But really, I gotta change that-should be the "trough tied to the ULL"

Dsylexic's UNTIE!

sorry, UNITE!
Member Since: September 11, 2007 Posts: 141 Comments: 16239
Just a tat of shear in the outskirts of the system ,tonight is the big encounter between the "shear" vs. 97L. Maybe a knockout? time will tell.
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Floater 1 AL97 - Funktop Color Infrared Loop
Member Since: July 3, 2005 Posts: 421 Comments: 127592
826. eye
even if it somehow survives the shear, it looks more and more like a Central America system.
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Quoting beell:


I'm not certain about huge yet but I agree it may affect shear. We're on the same page!


well you see how small of a distance it is between the 15 knots and 40 knots of shear, so I think it could have a huge impact

but hey what do I know, man these chicken nuggets are AWESOME!!! lol
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.
Member Since: June 9, 2007 Posts: 4 Comments: 15788
Quoting Drakoen:
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.



Shear map time lapse might not show that shear is retreating fast... but it is retreating nonetheless and with the TUTT N of PR retreating... conditions should be marginal enough to continue as a TD or minimal TS at best.
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Latest Funktop Image

Member Since: July 3, 2005 Posts: 421 Comments: 127592
Quoting eye:
by this time Monday it will be severely affected by shear, actually late tonight...it is almost there.

That is a perfectly normal shape for a cyclone
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Look at the clouds to the northwest of the center of the system they are trying to wrap around. Indication of further organization.
Member Since: October 28, 2006 Posts: 57 Comments: 29904
Quoting eye:
Storm, but on the flip side of that...small systems can get affected by even mild shear far greater than bigger systems.


That is true, but so far that isnt happening.
Member Since: June 9, 2007 Posts: 4 Comments: 15788
816. beell
Quoting BurnedAfterPosting:


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


I'm not certain about huge yet but I agree it may affect shear. We're on the same page!
Member Since: September 11, 2007 Posts: 141 Comments: 16239

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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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