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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Here's the deal. No matter what someone says on this blog, or what the computer models say; Mother nature will always decide what is going to happen. Everyone needs to just relax a little bit, and OBSERVE. How many times in the last hour or two has someone said that the invest is currently in the diurnal minimum? So isn't it expected that the system not look as good as it did several hours ago? Maybe I'm a little confused. I don't think that the shear has such swift swings from one hour to the next. It looks to me like a normal diurnal pattern is what is unfolding with 97 L right now. This will happen EVERY DAY with ANY tropical system. So why should someone say at one part of the day, "oh... this system looks great and is going to survivie", and then a few hours later, "oh... this system looks ragged and soon will go POOF"? why is that?
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Quoting Nolehead:
everyone wrote 97l off last night and WALLA today..so lets see what it does tonight and wait to see what the new models are saying..before you bash the daylights out of it...


Ahhem... not everyone ;)
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Quoting stormwatcherCI:
Sorry if I misunderstood.


not a problem, I probably shouldnt have said it anyway
Quoting HurricaneSwirl:


thanks much for clearing that up futuremet, helps to have an expert on when all this confusion is everywhere.. so as long as this system doesn't get to the antilles by mid tomorrow shear wont disrupt it much?


As long as it stays south of 17N, it will be okay.
Member Since: July 19, 2008 Posts: 43 Comments: 4051
Quoting HurricaneSwirl:


dang it! my memory blanked out on me. does an anticyclone aid or prevent development again? d'oh i used to know this lol.


Anticyclones are basically shields for tropical systems.
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I still think we will eventually get Ana out of 97L, but I think it will be in the long term and not the short term

this situation with the shear is very fickle and it could go either way, right now though it looks like shear will prevent 97L from organizing further in the short term

of course I could be wrong, we will see
Quoting StormW:


The TUTT movement is dictated by the upper level steering layer.

When a TUTT starts to lift out, or back away, it helps to "ventilate" the area that a storm is sitting in, for instance with 97L...if you look at a TUTT, on the east side of the axis, you'll notice how once the wind flow comes out of the axis, that it humps up into a ridge...it is this ridging that helps to produce some upper level outflow, or ventilation for the system.


Thanks Storm - appreciate the time
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Quoting BurnedAfterPosting:


LMAO you caught that huh? No ignorance means not admitting something that is right in front of you

shear maps and the visible clearly shows that there is shear in the immediate vicinity of 97L, yet he claims over and over there is no shear

that is being ignorant, it is taken out of context as being an insult
Sorry if I misunderstood.
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everyone wrote 97l off last night and WALLA today..so lets see what it does tonight and wait to see what the new models are saying..before you bash the daylights out of it...
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from what I am seeing the best chance for developement of any type will be tomorrow. it might get the orange color but if it doesnt it is going to be because of the shear. If the shear is reallyu at 50 then it does not matter what the thing is it will be killed. Stop the hyping and just let what happens happen Later Bye
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Quoting KoritheMan:


If the shear is westerly (coming from the west), and 97L is moving westward, then that will spell disaster for the tiny circulation. The NHC has even mentioned this before: if vertical shear is coming from the direction in which a storm is moving, then it is that much more detrimental to intensification, or in this case, tropical cyclogenesis.
It will be like hitting a brick wall,like what happened to the other disturbance as it entered the lesser antiles..
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A new AOI by the Cape Verde's?
Member Since: May 16, 2009 Posts: 1 Comments: 1231
HWRF looses the circulation after about 36 hours.

Link
Member Since: September 23, 2005 Posts: 14 Comments: 10873
Quoting stormwatcherCI:
You give it long. Looks like almost continuous bashing to me. BurnedafterPosting telling someone not to be ignorant. Everyone is not as highly educated as he seems to think he is. It doesn't mean you are ignorant if you ask questions when you don't know something.


LMAO you caught that huh? No ignorance means not admitting something that is right in front of you

shear maps and the visible clearly shows that there is shear in the immediate vicinity of 97L, yet he claims over and over there is no shear

that is being ignorant, it is taken out of context as being an insult
Quoting Dakster:
What's the latest? Anyone think 97L will go *poof* tonight like the other wave?

Or are we still in line to get an orange or red circle?


I do believe it will fire up overnight but will be less organize because of strong shear
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Quoting futuremet:
Mean shear is only averaging about 30Kts over the Antilles,and it should be averaging <15kts by tomorrow.



Albeit this map is accurate it self, it shows values taken in one time frame. It gives the the delusional impression that shear is blowing incessantly at 50kts.









thanks much for clearing that up futuremet, helps to have an expert on when all this confusion is everywhere.. so as long as this system doesn't get to the antilles by mid tomorrow shear wont disrupt it much?
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1298. 789
were is vote tally
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Quoting KEEPEROFTHEGATE:
in another hr or so the bashing will begin
You give it long. Looks like almost continuous bashing to me. BurnedafterPosting telling someone not to be ignorant. Everyone is not as highly educated as he seems to think he is. It doesn't mean you are ignorant if you ask questions when you don't know something.
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Ill be back for the midnight shift.
Member Since: June 9, 2007 Posts: 4 Comments: 15776
1295. WxLogic
Quoting nrtiwlnvragn:


Yes, they are running now.


Good news then... we'll see what these say about what possible changes we might see on the 00Z runs if any hehe...
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Quoting TerraNova:


An anticyclone can do both, depending on where it forms in relation to the disturbance. Systems need upper level ventilation to intensify, and if an anticyclone forms on top of a system, it can help it out.


oh, so its still a hit or miss type scenario for 97L. thanks for refreshing my memory
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1292. Dakster
Thanks CyberTeddy... So you would think this has a chance to develope?
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Mean shear is only averaging about 30Kts over the Antilles,and it should be averaging <15kts by tomorrow.



Albeit this map is accurate it self, it shows values taken in one time frame. It gives the the delusional impression that shear is blowing incessantly at 50kts.







Member Since: July 19, 2008 Posts: 43 Comments: 4051
Quoting HurricaneSwirl:


dang it! my memory blanked out on me. does an anticyclone aid or prevent development again? d'oh i used to know this lol.

It helps if it is over it
.
Member Since: May 16, 2009 Posts: 1 Comments: 1231
Quoting HurricaneSwirl:


dang it! my memory blanked out on me. does an anticyclone aid or prevent development again? d'oh i used to know this lol.


An anticyclone can do both, depending on where it forms in relation to the disturbance. Systems need upper level ventilation to intensify, and if an anticyclone forms on top of a system, it can help it out.
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1288. KEEPEROFTHEGATE (Mod)
all you bashers prepare your bashing sticks less than an hr from bashing time
Member Since: July 15, 2006 Posts: 169 Comments: 53296
Quoting KoritheMan:


If the shear is westerly (coming from the west), and 97L is moving westward, then that will spell disaster for the tiny circulation. The NHC has even mentioned this before: if vertical shear is coming from the direction in which a storm is moving, then it is that much more detrimental to intensification, or in this case, tropical cyclogenesis.


well that shear is coming right in towards 97L then, not good news for it
Quoting stormdude77:
gwadaman, I'm in Barbados as well. I'm located in St. Joseph....


Good Evening to ya Stormdude77 & all the Barbados Posse.......
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Quoting BurnedAfterPosting:
I will say this, the shear is now coming more from west to east, as supposed to earlier where the shear looked like it would come from the north

I think that kind of shear, as long as its not like 30 knots, 97L could at least survive it


If the shear is westerly (coming from the west), and 97L is moving westward, then that will spell disaster for the tiny circulation. The NHC has even mentioned this before: if vertical shear is coming from the direction in which a storm is moving, then it is that much more detrimental to intensification, or in this case, tropical cyclogenesis.
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Quoting TerraNova:


Exactly. As W456 said earlier, it's not so much that the shear map indicates higher shear as the actual effect the shear has on the storm's satellite presentation.


thats true
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97l will be traveling over 5 to 10kt shear tonight/wrf shows the shear/shifting and weakening.What do u trust more gfs and its ghost storms/not accurate predicitons or WRF model close to the HWRF model?
1281. K8eCane
Quoting K8eCane:



wind shear is only an issue if it becomes an issue with this storm


sorry but i've seen too many freaky things happen with storms out there in the atlantic over the years
Member Since: April 26, 2006 Posts: 5 Comments: 3075
Quoting K8eCane:



wind shear is only an issue if it becomes an issue with this storm


Exactly. As W456 said earlier, it's not so much that the shear map indicates higher shear as the actual effect the shear has on the storm's satellite presentation.
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Quoting reedzone:
I believe they will run the NHC models (GFDL and HWRF) tonight, there's really no reason not to, the invest isn't falling apart.. yet.


Yes, they are running now.
Member Since: September 23, 2005 Posts: 14 Comments: 10873
Quoting Dakster:
What's the latest? Anyone think 97L will go *poof* tonight like the other wave?

Or are we still in line to get an orange or red circle?


The other wave was embedded within the TUTT, this isn't. I don't think it will.
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Quoting reedzone:


Depends on that Anticyclone forming near Costa Rica, could be a huge player for 97L


dang it! my memory blanked out on me. does an anticyclone aid or prevent development again? d'oh i used to know this lol.
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Quoting STORMMASTERG:
Cape along 97l path is right now at 1,500 to 2,000 will increase to 3,000 later on.


that instability to me is what will save 97L from dying out completely
1275. Dakster
What's the latest? Anyone think 97L will go *poof* tonight like the other wave?

Or are we still in line to get an orange or red circle?
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Cape along 97l path is right now at 1,500 to 2,000 will increase to 3,000 later on.
1273. K8eCane
Quoting BurnedAfterPosting:


wind shear is a huge issue becuase it can prevent 97L from forming that closed LLC

the loop confirms the increase in shear in the immediate vicinity of 97L



wind shear is only an issue if it becomes an issue with this storm
Member Since: April 26, 2006 Posts: 5 Comments: 3075
Quoting WeatherStudent:



I see it, but it'll be going bye-bye soon enough.


Depends on that Anticyclone forming near Costa Rica, could be a huge player for 97L
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Quoting BurnedAfterPosting:


wind shear is a huge issue becuase it can prevent 97L from forming that closed LLC

the loop confirms the increase in shear in the immediate vicinity of 97L


agree. that patch of extreme shear probably wont kill it but will set 97L quite a few steps backwards.
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I will say this, the shear is now coming more from west to east, as supposed to earlier where the shear looked like it would come from the north

I think that kind of shear, as long as its not like 30 knots, 97L could at least survive it
Closest buoy

41101 29.91 in Pressure Tendency (PTDY): -0.01 in ( Falling )



Member Since: July 9, 2006 Posts: 184 Comments: 29594
Quoting barbadosjulie:
gwadaman, where are you located in Barbados? Which Parish?


I'm in St. Phillip in the East
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Lol….Everyone here is looking at the same shear maps and data and coming up with diametrically-opposed opinions. I think I will trust the experts at the NHC.
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gwadaman, I'm in Barbados as well. I'm located in St. Joseph....

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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.