Two African waves worth mentioning

By: Dr. Jeff Masters , 3:51 PM GMT on July 18, 2009

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There are two African tropical waves worth mentioning today, though neither looks particularly threatening. A tropical wave near 12N 45W, about 1200 miles east of the Lesser Antilles Islands (97 L), is moving west at 15 - 20 mph. This wave is now surrounded by an area of very dry air from the Sahara Desert. The dry air has disrupted most of the wave's heavy thunderstorm activity, and will continue to make it difficult for this system to develop over the next 2 - 3 days. Wind shear is a modest 10 knots over the disturbance, and should remain in the moderate 10 - 15 knot range over the next 2 - 3 days. Thereafter, shear is expected to rise to 20 - 30 knots. This morning's QuikSCAT pass showed no evidence of a surface circulation, and only a modest wind shift associated with 97L. The National Hurricane Center is giving this system a low (less than 30% chance) of developing into a tropical depression in the next 48 hours.

A second tropical wave now approaching the northern Lesser Antilles Islands is under 30 knots of wind shear, and has little prospect of development due to the high shear. However, the wave will bring heavy rain to the islands over the next two days.

None of the computer models are forecasting tropical storm development over the next seven days, and I don't expect either of the two African waves mentioned today to develop over at least the next three days.


Figure 1. Current satellite image of African wave 97L, 1200 miles east of the Lesser Antilles Islands.

I'll have an update Sunday afternoon.
Jeff Masters

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Quoting IKE:


What is unfavorable to him? Is he saying?
He says once it moves further west winds aloft are to fast.But every day they have been weakening.I think the thing is that twc copys everything the nhc says.
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Quoting Weather456:
There is probably no doubt this system is organizing before us, but I want to hold out another 6-12 hrs before I can be sure this will become Td 2.


you think we will see the NHC bump the chances up from yellow to orange?
What I am most supprised about is the turning at the lower levels...

In the RGB loop the lower clouds are turning at a a pretty good clip.
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Quoting HurricaneSwirl:


yeah, well the system is def getting better organized and the llc could be developing right now. dont meant to hype it but every frame has a better turning to it.


I agree that's why I said it was getting better organized. I'm thinking that if the shear to the west moves out like forecasted then a td by tomorrow.
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There is probably no doubt this system is organizing before us, but I want to hold out another 6-12 hrs before I can be sure this will become Td 2.
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I don't want to sound stupid, but I can't help but notice what looks like banding, or is it just the way the storms have setup around it?
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2044. IKE
Quoting STORMMASTERG:
Here we go again lyons saying you don't have to worry about 97l condtions not favorable.I think its the last time i will ever watch the twc.


What is unfavorable to him? Is he saying?
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ASCAT got part of the circulation
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2042. Drakoen
97L needs to moisten it's environment before it can expand convection. There is still a fair amount of black around the system.
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2041. MZV
97L looks decent for a small system - I think the NHC's interest in it will pick up. I suspect there will be recon to it around the 55W mark. Cost savings is one thing, but they need a pressure reading to decide what it is. I would presume the budget is built around the assumption of some recon in July.
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Quoting HurricaneKing:


The mid level circulation is but the lower level circulation is still getting organized. I think this could be Ana in the making.


yeah, well the system is def getting better organized and the llc could be developing right now. dont meant to hype it but every frame has a better turning to it.
Member Since: July 7, 2008 Posts: 2 Comments: 3237
The band of upper winds north of the system can actually benefit this storm, as it can form a focal point for a poleward outflow channel.

This was also seen for Andres with a band of upper wind sretching across the caribbean at that time.
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Quoting STORMMASTERG:
Here we go again lyons saying you don't have to worry about 97l condtions not favorable.I think its the last time i will ever watch the twc.


Steve is a good forecaster, but he is just saying what is happening currently, he is not looking at models, which are saying favorable conditions. He will change his tune if the NHC ups the probability of development. I think they should put them at medium at 2 pm.
Member Since: June 29, 2009 Posts: 13 Comments: 5238
2029... 12.1N 51.0W ???
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also if this thing does develop it could get things going quickly - its about as small as carlos!
Member Since: July 7, 2008 Posts: 2 Comments: 3237
Quoting HurricaneSwirl:


yeah i dont know much whats gonna happen with the highs.. i think the track it takes is gonna rely more on strength. anyway i honestly am now thinking this could be ana. the circulation is very well defined.


The mid level circulation is but the lower level circulation is still getting organized. I think this could be Ana in the making.
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Here we go again lyons saying you don't have to worry about 97l condtions not favorable.I think its the last time i will ever watch the twc.
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Quoting BurnedAfterPosting:
not to get ahead of ourselves, but look at the last two frames of the visible loop, I am starting to see more of a rolling motion

start of a more pronounced circulation?


I agree BAP. this thing is showing signs of building. thank you and everyone for the great post and graphics. they help people like me to understand what is happening and also gives us here a bit of heads up for things to come.
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Thunderstorm coverge needs to expand but BAP I'm seeing what you seeing, some turning evident, also premature outflow N of the system.
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Quoting BurnedAfterPosting:


the strength of a high determines the speed in which these systems move, it doesnt mean the high is going to erode away though



yeah i dont know much whats gonna happen with the highs.. i think the track it takes is gonna rely more on strength. anyway i honestly am now thinking this could be ana. the circulation is very well defined.
Member Since: July 7, 2008 Posts: 2 Comments: 3237
2030. IKE
Quoting BurnedAfterPosting:
not to get ahead of ourselves, but look at the last two frames of the visible loop, I am starting to see more of a rolling motion

start of a more pronounced circulation?


It does look better.

I think they need to up the odds.
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not to get ahead of ourselves, but look at the last two frames of the visible loop, I am starting to see more of a rolling motion

start of a more pronounced circulation?
Quoting BurnedAfterPosting:


maybe that is the "shear" tampaspin was seeing


Well it is moving at a fair whack, occasionally you see storms struggling to sort themselves out when they're moving that quickly.

Been a couple of examples in the last couple of years. (I want to say Dolly, but the reason for that might be something else, don't remember too well.)
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I give this 97l a high chance of developing,its looking really good right now.Tstms erupting/and very cold too.Signs of an organizing system.
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Actually Reedzone was calling this the whole time and received some major flak for it. But he said this system would make a comebak on the past night and it did... Props to Reedzone for being strong... and BAP
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Quoting HurricaneSwirl:


yeah i think its slowed from 23 mph to at least below 19 mph. but could that also be a sign of a weakening high? which would indicate more nw movement once it gets in the caribbean. maybe too early to tell though.


the strength of a high determines the speed in which these systems move, it doesnt mean the high is going to erode away though

Here is something interesting

The SOI has been in positive territory since July 3rd
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97L has a little structure to it. Looking for that rolling motion and outflow channels. Maybe Bill Gates better get his barges ready?? Inflow and outflow is the name of the game*****
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2021. Drakoen
Nice they got the floater up. SSD has been working fast this season in get everything ready.
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Quoting BurnedAfterPosting:


Based on the visible loop I do believe it has slowed down some though


yeah i think its slowed from 23 mph to at least below 19 mph. but could that also be a sign of a weakening high? which would indicate more nw movement once it gets in the caribbean. maybe too early to tell though.
Member Since: July 7, 2008 Posts: 2 Comments: 3237
Sorry, just noticed NHC has the floater back on 97L and re-designated. Looking extremely healthy on wv too.
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Quoting StormJunkie:


I agree BAP, and that likely has something to do with it's ability to organize imvho...Even during the convective bursts last night it seemed that it was moving so fast it was creating self induced shear.


maybe that is the "shear" tampaspin was seeing
Quoting BurnedAfterPosting:


Based on the visible loop I do believe it has slowed down some though


I agree BAP, and that likely has something to do with it's ability to organize imvho...Even during the convective bursts last night it seemed that it was moving so fast it was creating self induced shear.
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Thanks 456
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Lets not forget the wave 1,0000 miles east of the current Invest..Looks interesting NHC has moved the satellite over former 97l
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Floater is back on 97L
2013. IKE
Quoting Weather456:
Another round of convective bursts



Nice frame...and one of the best frames for any invest this season in the Atlantic...low shear helps....
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Quoting StormJunkie:
Thanks nrti and good morning

Not what I wanted to hear...I am not a big fan of data latency... :~)


Morning SJ. Worse than I originally stated:

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Wowza @ 97L... I should check in more often...
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97L is getting its act together... Alot of you called it. Def a fighter.
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Quoting claimsadjuster:
good to see you back 456. i know it is early but what direction do you think this thing will take? what i am asking is there a good chance it will find it's way into the gulf?


Its not too early to get an idea on track since it pretty much at all levels. W then WNW.

Though development is pretty much 50/50, track is a bit more evident. The storm is currently moving west and has slowed down some since about 24 hrs ago. On this current path, it should bring it near the Windward Islands and Barbados by Monday morning. Regardless of development increase in showers expected for the region. Beyond that is pretty much anyone’s guess. The subtropical ridge is well established across the subtropical Atlantic but there is weakness on its western end that may help ease the disturbance more towards the WNW, then NW in the Caribbean Sea. Now I cannot guarantee we will have a tropical storm from this, so I think areas like Jamaica, the Caymans and Cuba should monitor the system since conditions are forecasted to be conducive for development.

More
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Quoting HurricaneSwirl:


IMO it all depends on how fast its going. right now its going pretty fast so we'll see..


Based on the visible loop I do believe it has slowed down some though
Quoting Weather456:
Another round of convective bursts

Starting to look a lot more organized even than earlier this morning.
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2006. Drakoen
I see a well-defined inverted V signature on satellite imagery. That's the most I can find at the surface given the frames we have.
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Quoting Dr3w:
what do you guys think about 97l?

do you think it will become TD #2 or will it stay a Tropical Wave


IMO it all depends on how fast its going. right now its going pretty fast so we'll see..
Member Since: July 7, 2008 Posts: 2 Comments: 3237
Another round of convective bursts

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2003. IKE
SAL just about gone....

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2002. Dr3w
what do you guys think about 97L?

do you think it will become TD #2 or will it stay a Tropical Wave
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Quoting jurakantaino:
"Burnedafterpoiting" is the only person here that have forecast this system correctly so far. Even when they were driving him crazy!


Thank you for the props, but I am not the only one who got it right.

I felt it was very important yesterday for it to be noted the difference between 97L and the wave at 60W. Many seemed in awe of the pretty colors on satellite with the wave at 60W, tropical systems are much more complicated than just pretty colors lol

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About JeffMasters

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.