ATL : INVEST 90L - DISCUSSION

[Ptarmigan]

I think 90L could develop, especially as it heads towards the Caribbean.

[Aric Dunn]

90L will be a tropical wave at 00z surface analysis

Interesting ITCZ discussion that clears more the features.

http://www.nhc.noaa.gov/text/refresh/MI ... 0004.shtml?

...THE ITCZ...
THE ITCZ AXIS IS ANALYZED ALONG 11N18W 9N25W 8N29W 8N33W 13N53W
11N64W. A SURFACE TROUGH AND ASSOCIATED 1010 MB LOW PRES
IS CURRENTLY EMBEDDED WITHIN THE ITCZ NEAR 9N31W IS GENERATING
SCATTERED MODERATE ISOLATED STRONG OF CONVECTION WITHIN 120 NM S
OF THE AXIS BETWEEN 31W AND 41W. HOVMOELLER DIAGRAMS...LONG
TERM SATELLITE IMAGERY AND SPECTRAL ANALYSIS SUGGEST THAT THIS
TROUGH IS ACTUALLY A TROPICAL WAVE AND WILL THEREFORE BE
INTRODUCED ON THE 00 UTC SURFACE ANALYSIS. SCATTERED MODERATE TO
STRONG CONVECTION IS NOTED WITHIN 120-180 NM N OF THE AXIS
BETWEEN 45W AND 57W.
[/quote]

that is extremely important to know... that means the models will initialize it as such rather than just a ITCZ trough.... this may change the forecast of the two merging ... i do believe the two systems will continue to interact and likely transfer some energy.. we will see whats going to happen but watch for the 00z models to change slightly..

[cycloneye]

watch for the 00z models to change slightly..

What do you mean when you say change slightly?

[Aric Dunn]

watch for the 00z models to change slightly..

What do you mean when you say change slightly?

in there initialization of the system... before they were merging the two systems since one was not a tropical wave and now they both are and 90L will have a surface low. that may change how the two interact initially. also the speed may change a little..

[cycloneye]

00z Best Track

AL, 90, 2010073000, , BEST, 0, 82N, 313W, 20, 1010, DB

ftp://ftp.tpc.ncep.noaa.gov/atcf/tcweb/ ... 010.invest


Makes sense Aric about the models.

[KWT]

Its a very complicated set-up thats for sure, the waves are fairly far apart really considering but the gap will likely close. I'd imagine this one will be slow to get going but once the wave to the east gets closer it probably will add the extra spark.

Shear could be a possible issue down stream looking at the 12z ECM, which shows an upper low dropping down towards the C.Atlantic.

[Macrocane]

Well that just makes things even more complicated, now we could possibly end up having two waves trying to interact, just gotta wonder whether they will mess up each others mid level turning?

That's interesting I read today the TCR of 2006 Hurricane Florence and it says that it developed in a similar way, this is what it says:

Florence had a complex genesis tied to the interaction between two tropical waves. A tropical wave moved westward across the coast of Africa on 29 August. The wave moved slowly westward and first showed signs of convective organization on 31 August. On that day another wave moved westward from Africa at a faster forward speed than its predecessor. By 2 September, these two waves combined to form a large area of disturbed weather over the eastern tropical Atlantic.

[Aric Dunn]

Well that just makes things even more complicated, now we could possibly end up having two waves trying to interact, just gotta wonder whether they will mess up each others mid level turning?

That's interesting I read today the TCR of 2006 Hurricane Florence and it says that it developed in a similar way, this is what it says:

Florence had a complex genesis tied to the interaction between two tropical waves. A tropical wave moved westward across the coast of Africa on 29 August. The wave moved slowly westward and first showed signs of convective organization on 31 August. On that day another wave moved westward from Africa at a faster forward speed than its predecessor. By 2 September, these two waves combined to form a large area of disturbed weather over the eastern tropical Atlantic.

yep its going to be very similar..at least it seems that way..

[CalmBeforeStorm]

I think the structure is there for something to form around 10.0 and 33.0 There is a bit of an upper level high forming there and there is that popcorn convection you see before development. Also, the surrounding convection has eased off.

[cycloneye]

SSD dvorak at 00z.

30/0000 UTC 8.0N 31.5W T1.0/1.0 90L -- Atlantic

http://www.ssd.noaa.gov/PS/TROP/tdpositions.html

[cycloneye]

Here is Dr Rob Carver's discussion about 90l who is filling for Dr Jeff Masters.

Hi everybody, Dr. Rob Carver filling in for Dr. Masters while he's on vacation.

NHC has designated an area of thunderstorms in the tropical Atlantic as Invest 90L (8.5 N, 30.0 W). Microwave remote sensing suggests there are some decent storms in 90L, peak rain rates were around 1-2 inches/hours. According to CIMMS wind-shear analyses 90L is under 10-15 knots of shear with positive divergence aloft. The former isn't quite favorable for further development as it will ventilate the system, but the latter is favorable because it will aid in removing outflow from the storms. There's also a broad area of weak shear to the west and northwest of 90L's current position. Looking at the 500 mb height patterns, the steering currents for 90L are to the WNW, which will move it into the area of weaker shear and get it further away from the equator. This is important because if 90L stays south, it will have trouble developing a circulation. It will have a better chance of becoming a tropical cyclone once it goes north of 10N. The Saharan Air Layer is lurking just to the north of 90L. A WNW track would keep 90L out of the SAL, which is good for development.

Model Forecasts and Climatology
The 12Z Canadian model moves 90L to the WNW and develops tropical-storm force winds at the surface. The 12Z and 18Z GFS runs are less aggressive in intensifying 90L and adjusts the track so that 90L is moving to the WNW. Based on the run-to-run consistency, previous model verification (i.e. the Canadian model's tendency to overdo intensification), general synoptic pattern, I favor the GFS solution for now. Looking at climatology based on research done by Dr. Bob Hart at Florida State University, none of the tropical cyclones that passed within 1 degree of 90L's current position has ever made landfall. We'll have to keep an eye on this storm, but I don't think it's likely to be a major threat to the Caribbean or US.

[cycloneye]

Tony, you think is still early to say anything about any threat to the NE Caribbean?

[gatorcane]

I wouldn't let the fact it is at such a low lattitude fool you. There are many a storm that have formed at that low of lattitude that have missed the NE Caribbean to the NE by a comfortable margin. One system that comes to mind is Bill from last year. That said, I'm not saying it will take the same path though. This one looks to develop more gradually.

[Dean4Storms]

I wouldn't base a forecast saying I don't think it's likely to be a major threat to the Carib or US off Climatology. The global models all seem to take it toward a landfall and I've not seen any showing a fish!

[Cyclone1]

90L is about 5-7 degrees lower than even Bill. Not saying that means anything, just noting a fact. In fact, hypothetically, if Colin were named tonight, right now, we'd probably have a latitude record on our hands.

[Blown Away]

I wouldn't let the fact it is at such a low lattitude fool you. There are many a storm that have formed at that low of lattitude that have missed the NE Caribbean to the NE by a comfortable margin. One system that comes to mind is Bill from last year. That said, I'm not saying it will take the same path though. This one looks to develop more gradually.

Bill's starting point is a good 4-5 degrees north of 90L.

[Extremeweatherguy]

The problem with Rob Carver's discussion is that he says tropical cyclones passing near 90L's position have never made landfall. 90L is not yet an established tropical cyclone though, and likely will not be for days, so that climatology tidbit at the end of the Weatherunderground discussion doesn't really apply to this particular system right now. If it did, then that would mean every tropical wave passing through the eastern Atlantic would go on to miss land..which we know isn't the case.

[cycloneye]

As they said on the ITCZ discussion earlier, is now officially a tropical wave at the 00z surface analysis. Interesting to note the kink northward of the ITCZ west of 50W up to 14N.

[Aric Dunn]

been doing a little tracking this afternoon and evening looking for any signs of a low level circ... and well there is some evidence that one exists I would not say at the surface, but in the low and especially in the mid levels is a good possibility. the arrows in the image below depict the different layers of clouds by the different shades of gray. if you run a long loop you can see some good low level turning while the convection and the sun was still up and since then the convection as weakened and the decent low to mid level rotation is evident. there is also some convection beginning to fire nearby this low to mid level feature and it is just about where it should be according to the best track. I do believe it needs about another 24 hours before we see any real development but it seems farther along than I thought it would get too today. If convection builds again tonight I would have to bring up the percent chance of development tomorrow. right now though it is just an interesting feature on satellite.

http://www.ssd.noaa.gov/goes/flt/t1/loop-rgb.html

[Blown Away]

Climatology is just a tool and it gives us an idea what to expect in August.