This is the one-Well Defined Wave in East Atlantic

[philnyc]

If everything else holds together, this is the wave you should worry about, the one in west central Africa, which will move offshore in two or three days. OK, I'm sticking my neck out, but the first wave that causes heavy thunderstorms and very heavy rain at Dakar (http://weather.noaa.gov/weather/current/GOOY.html) is the one to watch. We shall see..



It has plenty of mid-level water vapor to work with:



and the GFS has warmed up to the idea that this could be a significant low as it moves away from the African coast... (see upper right panel):



This has classic wave formation; anyone with a pencil could draw the outline, and it has no SAL or mid-level dry air to entrain. It will undoubtedly lose some oomph as it hits the marginal SSTs off the African coast, but it won't have to go far (a few hundered miles at most) before it moves over favorable SSTs. In addition, the unusually strong MLAEJ is quite favorable right now in sustaining the convection ahead of the wave rather than behind it. This will give it a much better chance of survivng the first few hundred miles off of the African coast.

[wxmann_91]

I respectfully disagree, Phil. There's a huge field of stratocu to the northwest. Also, it just has the outflowish look to it, IMO. There've been so many waves with all the strong convection on the west side, and right when the wave hits the water, the convection poofs.

[philnyc]

I respectfully disagree, Phil. There's a huge field of stratocu to the northwest. Also, it just has the outflowish look to it, IMO. There've been so many waves with all the strong convection on the west side, and right when the wave hits the water, the convection poofs.

Are we looking at the same wave, Jim? I'm talking about the easterly wave that is a few hundred miles EAST of Dakar. It will not move off of the coast until Sunday or Monday. It has no stratocu to its northwest. The one that has just come off the African coast has the stratocu - it is a classic easterly wave losing its convergence ahead of its axis. It will suck in and take care of the subsidence as it moves westward. The one I'm talking about will not have much, if any, subsidence in front of its axis - it looks like it will keep its convergence ahead of it, making it a much better candidate for development. Here is the IR sat:



Do you see what I'm saying, or am I missing something? I highly respect your opinion.

Phil

[wxmann_91]

Yep, we're looking at the same wave. Once it gets near the coast of Africa, it will start feeling the effects of the stratocu. Not sure the convection can put a strong enough dent on the subsidence - there's a lot of stability in the area and below-average SST's aren't helping.

The thing about the convection in front, it was just an observation I've made in the past year, watching many waves have intense convection over Africa, but go poof as the reach the stable realms of the eastern Atlantic. But it makes sense, since if the system has convection all around, the initial convection (the convection in front of the wave axis) acts as a buffer in a way.

Lower level convergence isn't all that strong, either. I've used the CIMSS maps for those and they have rarely failed me.
http://cimss.ssec.wisc.edu/tropic/real- ... 7conv.html
That leads me to believe this is diurnal maximum enhanced convection and not much more.

BTW, regarding the last line, thanks. I really appreciate that and I highly respect your opinion as well. This is a good discussion.

[Jam151]

I respectfully disagree, Phil. There's a huge field of stratocu to the northwest. Also, it just has the outflowish look to it, IMO. There've been so many waves with all the strong convection on the west side, and right when the wave hits the water, the convection poofs.

And such is the case nearly every season before the CV storms takeoff. Waves aren't supposed to "maintain" as they exit Africa in June and July....and only rarely do they do it even during August (the actual TCs).

[philnyc]

I respectfully disagree, Phil. There's a huge field of stratocu to the northwest. Also, it just has the outflowish look to it, IMO. There've been so many waves with all the strong convection on the west side, and right when the wave hits the water, the convection poofs.

And such is the case nearly every season before the CV storms takeoff. Waves aren't supposed to "maintain" as they exit Africa in June and July....and only rarely do they do it even during August (the actual TCs).

Absolutely right! It depends on what lays out ahead of it atmospherically. If conditions are right, it will maintain. If not, "poof". You can't just look at an easterly wave moving acorss Africa and say bcause it "looks good" that it will maintain and intensify as it moves off the African coast. That would be very unscientific. My contention here is that it has very favorable conditions developing in front of it.
And Jim has made a very good observation that the CIMSS analysis doesn't show very good convergence currently along the front edge of the wave axis. Very good observation Jim! But CIMSS often has the conv/diverg off by a few hundred miles because they are trying to match the satellite images with the surface obs by computer, and miss by a few hundred miles due to timing differences. Really, you would have to admit that there must be REALLY good convergence below and divergence aloft for that wave to look that healthy. So I'd be careful about where that convergence zone is really matched with. These waves are packed unusually tightly together.

[philnyc]

OK. Let's watch this one. I think it has a better than 30% chance...

[Meso]

Strong looking wave

Moist enviroment ahead of it


Gfs still developing a low with it in 78 hours

[WmE]

There may not be a moist environment. The SAL is very hard to dedect on water vapor pics.

[Meso]

SAL is quite spread but not as intense as it has been of late,the wave infront should help it a bit

[wxman57]

I'm afraid the latest GFS runs are a sign that the season is about to really start. Generally, it develops dozens of spurious hurricanes each year, but this is the first time in 2007 that it's forecast one. Long-range GFS is notoriously bad, but it may be picking up on a change in the eastern Atlantic, a signal that it won't be long before they start developing. Let's see if this wave can maintain its convection after moving offshore.

[wjs3]

Phil & Jim:

Nice analysis.

Couple of questions/comments:

1) The 0z GFS (I think this is posted elsewhere) is all over this wave...other models, including the UKMET (6z) and Euro (0z) that I looked at are not. I'd like to see a little bit more model agreement...though Phil, I think that's why you call it "sticking your neck out, and good for you!

The GFS seems a little suspiciously aggressive to me. Look, long track CV storms that form right west of the CV Islands happen, but are not common. As you all know, there's usually lower SSTs, SAL, TUTTs, etc for them to deal with and taking some time to organize and getting it together nearer to the Carib. is more common... Conditions have to be pretty spot on for "right off Africa" development like the GFS is suggesting. I think conditions are getting close...but not quite there yet!

2) Jim, I think you are right on about the stability. I always get leery when I see the stratocu extending really far south like it is now.

3) I think that one thing that would make me a little more bearish aobut Phil's wave is if the wave in front of it were a bit more impressive. We've all seen this over the years...big wave #1 comes through and sort of changes the pattern...busts up the SAL, helps moisten things up...then big wave #2 has really, really good conditions to form in. The leading wave here showed a little life, but never had much going. should it flare more, then maybe a better chance for wave #2--just an opinion.

4) Phil--great comment about the MLAEJ. Are you up for posting some stuff about the MLAEJ and tropical wave formation? I also think that informing people about the relative wind (and why these waves can/do go "poof" when they exit Africa) would be cool if you're up for it!

Great discussion!

WJS3

[flwxwatcher]

I'm afraid the latest GFS runs are a sign that the season is about to really start. Generally, it develops dozens of spurious hurricanes each year, but this is the first time in 2007 that it's forecast one. Long-range GFS is notoriously bad, but it may be picking up on a change in the eastern Atlantic, a signal that it won't be long before they start developing. Let's see if this wave can maintain its convection after moving offshore.

WXMAN57. Yes, in previous years the GFS seemed to jump the gun with Cape Verde Systems and spurious lows in the Atlantic Basin. So far this year it hasn't had that problem , the CMC seems to have taken that crown. It will be interetsing to see how the changes to the GFS affects its performance this season..

[CourierPR]

57, thank you for your post. I know that when you say that something might happen, you have good data to back up your opinion.

[ronjon]

I have to say that this is a massive wave rolling off the African coast. Is this the one that the GFS model is picking up on?

http://www.ssd.noaa.gov/met8/eatl/loop-rb.html

[Meso]

Yeah it's the one that the GFS has moving off the coast and then develops a closed low after 78 hours with it



The GFS is still showing this wave developing a closed low in 66 hours..see what the other models say soon

[philnyc]

Phil & Jim:

Nice analysis.

Couple of questions/comments:

1) The 0z GFS (I think this is posted elsewhere) is all over this wave...other models, including the UKMET (6z) and Euro (0z) that I looked at are not. I'd like to see a little bit more model agreement...though Phil, I think that's why you call it "sticking your neck out, and good for you!

The GFS seems a little suspiciously aggressive to me. Look, long track CV storms that form right west of the CV Islands happen, but are not common. As you all know, there's usually lower SSTs, SAL, TUTTs, etc for them to deal with and taking some time to organize and getting it together nearer to the Carib. is more common... Conditions have to be pretty spot on for "right off Africa" development like the GFS is suggesting. I think conditions are getting close...but not quite there yet!

2) Jim, I think you are right on about the stability. I always get leery when I see the stratocu extending really far south like it is now.

3) I think that one thing that would make me a little more bearish aobut Phil's wave is if the wave in front of it were a bit more impressive. We've all seen this over the years...big wave #1 comes through and sort of changes the pattern...busts up the SAL, helps moisten things up...then big wave #2 has really, really good conditions to form in. The leading wave here showed a little life, but never had much going. should it flare more, then maybe a better chance for wave #2--just an opinion.

4) Phil--great comment about the MLAEJ. Are you up for posting some stuff about the MLAEJ and tropical wave formation? I also think that informing people about the relative wind (and why these waves can/do go "poof" when they exit Africa) would be cool if you're up for it!

Great discussion!

WJS3

Thanks, Winn. As far as what you said:
1. Go back and check the models again. The UKMET still has an open wave but the GFS, NOGAPS, CMC and ECMWF all now have a closed low between Sunday and Tuesday. However, they are all over the place as to the position, but seem to be gradually consolidating around 35 degrees west by Tuesday.
2. That stratocu is problematic, but it seems to be diminishing somewhat at the moment.
3. I totally agree with your analysis there. Well said. Although right now it appears that wave number 1 is flaring up a little.
4. Eventually I will out up more on the MLAEJ. I'm waiting for the end of the month so I can look at July overall.

Having said all of that, I only give it a 30% chance right now, because I totally agree that the GFS is often too agressive and although the SAL is diminishing quite a bit now, there is still plenty of dust out there. But it does have positives that prior waves didn't, such as very good mid-level moisture, a strong MLAEJ and no shear.
I'm also well aware, as I'm sure you know, that waves, even strong ones very rarely roll off the African coast and become a hurricane in two days like Isabel did! I was careful in my posts to say that if it stayed fairly together, it still wouldn't develop into anything until a few hundred miles off of the African coast, like around Sunday or Monday.
We shall see soon enough. Thanks for the great comments and analysis Winn.

[philnyc]

Look at this "true color zoom" satellite from CIMSS. Wow!



Their new site is great, although I haven't explored it very well yet. It's obviously going to replace the old one fairly soon - it's just too good.

[cycloneye]

ITCZ AXIS IS CENTERED ALONG 10N13W 9N18W 14N27W 13N40W 9N54W
10N62W. A LARGE TROPICAL WAVE MOVING THROUGH W AFRICA NEAR 10W
IS PRODUCING STRONG LOW-LEVEL CONVERGENCE ALONG THE AFRICAN
COAST...AND RESULTING IN SCATTERED MODERATE CONVECTION WITHIN
120 NM OF THE COAST BETWEEN THE IVORY COAST AND GUINEA-BISSAU.


THE LARGE CIRCULATION OF A VIGOROUS TROPICAL WAVE OVER
W AFRICA APPEARS TO BE CHANGING THIS PATTERN WITH STRONGER
NORTHERLIES DEVELOPING OFF THE COAST...AND THE ITCZ IS PLUNGING
S TO ABOUT 8N INTO SIERRA LEONE AND LIBERIA.


8 PM Discussion by TPC.

Will this be the wave that some models develop?

[HurricaneMaster_PR]

Interesting..lets see tomorrow morning how it behaves as it hits the Atlantic waters..