ATL: Ex INVEST 96L - Discussion

[Aric Dunn]

More westward track would keep in a lower shear environment until central carrib. Key to that would be if it can develop and drop a few MB to survive the faster low level flow in carrib.

Its not dead by any means yet.

[Hurricaneman]

No doubt, there's shear to the north of her.... shear to the south of her.... "here I am, stuck in the middle with you" (isn't that a Beatles song?? Anyway, I digress... )

So, your not thinking the present COC might narrowly be under any east/west upper COL extending eastward from the Caribbean? Based on today's earlier shear analysis it looked to me like it might just thread that needle. Then again, perhaps I was overestimating the relative area of lighter UL winds?

at 8pm i see % drop too 10 and 5% next five days 96l done

You may well be right That would certainly keep in character with this season so far. It certainly has good spin but in spite of the seemingly moist envelope it's riding west with, convection just continues to get choked off - not just "over center" but within the broader low latitude envelope around it. SST's seem to be a net zero factor. Not anomalously warm or cool, but adequate and around 28C. Funny, this was supposedly the year of the "wet Saheal". Perhaps, but something's seemingly awry with the air over much of the Atlantic. I'm not so sure that's something that'll just get fixed simply because Climo says so

It has to do with the Convectively suppressed kelvin wave causing sinking air over the Atlantic, things will improve when it moves on, it might have a chance in the western Caribbean

[floridasun78]

ZCZC MIATWOAT ALL
TTAA00 KNHC DDHHMM

Tropical Weather Outlook
NWS National Hurricane Center Miami FL
800 PM EDT Sat Aug 3 2019

For the North Atlantic...Caribbean Sea and the Gulf of Mexico:

1. A large area of disorganized showers and thunderstorms located
several hundred miles east of the Lesser Antilles is associated with
a tropical wave. Some slow development of this system is possible
over the next day or two as the disturbance moves west-northwestward
toward the Lesser Antilles. Upper-level winds are then expected to
become unfavorable for further development early next week.
* Formation chance through 48 hours...low...20 percent.
* Formation chance through 5 days...low...20 percent.

Forecaster Pasch

[chaser1]

Nope Hurricaneman, I've gotta take issue with that.
I dont buy into this decade's latest "revelation", the bandied Convectively suppressed kelvin wave. I'm not at all suggesting it's not real or not ever a factor. Just as "El Nino" once became the pre-eminant solution or force causing many to step up and pronounce how any given year would clearly be over-active or under-active based on what seemed like clear Nino/Nina signals, has seemingly morphed into broader scale and location of ENSO signals.... it seems as if many are latching on to convectively suppressing (or enhancing) kelvin waves. I've seen evidence of related broad scale uptick or downturn impact on regional convection over the tropics but in the form of an actual (large wave), not in terms of a semi-permanent cap covering a span or distance as broad as an entire ocean. I believe there are other less transient factors that play into why certain years' particular hemispheric areas seem "dryer" then other years. There's no doubt that during particilar ENSO events, there's a very clear and multi-month impact to regions around the world. I just dont think that either are always the go-to Answer A or Answer B solution to the puzzle. I think their may well be something suppressing 96L's convection. Perhaps you're right and it's feeling the 2 or 3 day impact of suppressed conditions? Maybe, but what about last week - or next week. Strong waves have moved off of Africa but convection fairly quickly turns anemic. Sometimes SAL plays a role, less often unusually cool SST's might, and varying levels of wind shear certainly are a big force here.
We've seen plenty of years where the tropics snapped into climotological symmetry. Hostile conditions quickly became less hostile. Sometimes conditions just find a way to buck historical norms though. I'm pretty sure we're still a ways off from knowing why though.

[Aric Dunn]

Nope Hurricaneman, I've gotta take issue with that.
I dont buy into this decade's latest "revelation", the bandied Convectively suppressed kelvin wave. I'm not at all suggesting it's not real or not ever a factor. Just as "El Nino" once became the pre-eminant solution or force causing many to step up and pronounce how any given year would clearly be over-active or under-active based on what seemed like clear Nino/Nina signals, has seemingly morphed into broader scale and location of ENSO signals.... it seems as if many are latching on to convectively suppressing (or enhancing) kelvin waves. I've seen evidence of related broad scale uptick or downturn impact on regional convection over the tropics but in the form of an actual (large wave), not in terms of a semi-permanent cap covering a span or distance as broad as an entire ocean. I believe there are other less transient factors that play into why certain years' particular hemispheric areas seem "dryer" then other years. There's no doubt that during particilar ENSO events, there's a very clear and multi-month impact to regions around the world. I just dont think that either are always the go-to Answer A or Answer B solution to the puzzle. I think their may well be something suppressing 96L's convection. Perhaps you're right and it's feeling the 2 or 3 day impact of suppressed conditions? Maybe, but what about last week - or next week. Strong waves have moved off of Africa but convection fairly quickly turns anemic. Sometimes SAL plays a role, less often unusually cool SST's might, and varying levels of wind shear certainly are a big force here.
We've seen plenty of years where the tropics snapped into climotological symmetry. Hostile conditions quickly became less hostile. Sometimes conditions just find a way to buck historical norms though. I'm pretty sure we're still a ways off from knowing why though.

Just like anything.. it plays a factor but it is not an end all be all. I have seen many many instances of very convectively active waves and TC under the suppressed side of the kelvin wave.

[abajan]

If nothing else, it certainly has a great satellite presentation (circulation-wise)!

[GCANE]

Good convection firing close to the CoC.
500mb and 700mb vorts are stacked.
No 200mb vort to push down on this.
Enough of a shear gradient around this to keep periphery convection firing.
Still has strong steering due west.

Still watching this as it heads into the Carib.
I think there maybe enough momentum with the mid-level vorts that it may fire once it lines up with Hispaniola.
All it takes is some long-duration vortical hot towers to fire off and drive the mid-level angular momentum down to the surface.

[GCANE]

Euro keeps the 500mb Vort intact just south of Hispaniola.
Pretty much ditto with GFS-Legacy.
This is were I estimate it will be.
At this point it all depends if convection can reignite.
Got to remember, global models are poor at forecasting small-scale convection development.
In terms of hot-tower development, they totally suck.
If it does reignite, forecast ridging is conducive for this to run thru the Yucatan Channel.

[abajan]

Good convection firing close to the CoC ...

Definitely.

[GCANE]

Good convection firing close to the CoC ...

Definitely.

Looks like a DMAX-induced tower is firing off now just south of the CoC.

[Aric Dunn]

And just like that.. it is 90 percent there now. Some sustained convection today and we will have a TD. Should be enough to close off a surface circ. If not already there.

Evidence of the circ is on the eastern edge of the convection. And the convective pattern around it is pretty telling.

If pressure can fall a few mb surface convergence will increase and it will be on its way.

[Aric Dunn]

Euro keeps the 500mb Vort intact just south of Hispaniola.
Pretty much ditto with GFS-Legacy.
This is were I estimate it will be.
At this point it all depends if convection can reignite.
Got to remember, global models are poor at forecasting small-scale convection development.
In terms of hot-tower development, they totally suck.
If it does reignite, forecast ridging is conducive for this to run thru the Yucatan Channel.

Yeah ridging looks to hold until at leat south if hispaniola if not all the way to the western carrib.

[Emmett_Brown]

Per the GFS, the shear for the next 48 hours won't be that strong, so there is a brief window for 96L to organize before shear increases Tuesday (assuming 96L remains below 15N before that time)

[wxman57]

While it certainly looks more impressive on satellite, an overnight ASCAT pass (last evening) did not indicate any LLC. Winds at Barbados continue to blow from the east. Any apparent rotation may be aloft. The disturbance is heading into ever-increasing wind shear, even if it stays south. NHC lowered development chances to 10% last hour, by the way.

[Aric Dunn]

While it certainly looks more impressive on satellite, an overnight ASCAT pass (last evening) did not indicate any LLC. Winds at Barbados continue to blow from the east. Any apparent rotation may be aloft. The disturbance is heading into ever-increasing wind shear, even if it stays south. NHC lowered development chances to 10% last hour, by the way.

http://wxman57.com/images/96Lb.JPG

Actually both the GFS and EURO show the shear axis shifting west to the central to western cariib. at least in terms of upper level winds. so staying south would keep it in a low upper level shear environment.

the big issue will be the forward speed causing decoupling

of course, this is contingent on convection sustaining today.. lol

[GCANE]

Chomping at the bit

Large but short duration hot tower at DMAX.
No associated lightning though.

[LarryWx]

The model consensus has had a weak surface low once it got to its current position for many days of runs. So, the current rather organized appearance is no surprise. However, is it moving more quickly WNW than model consensus has shown? I mean I thought many model runs til a couple of days ago didn’t have it reach the Lesser Antilles til Tuesday or so. Am I correct? At this rate, it may get there tonight.

[Aric Dunn]

Coming into radar range. At least we will have that.

http://www.meteofrance.gp/previsions-me ... r/antilles



Really wish they would change their color schema lol



Ok the other site is working now

http://www.barbadosweather.org/Composit ... 1564932610

[abajan]

It's been raining lightly at my location for the last hour or so. No thunder as yet.

[Siker]

The model consensus has had a weak surface low once it got to its current position for many days of runs. So, the current rather organized appearance is no surprise. However, is it moving more quickly WNW than model consensus has shown? I mean I thought many model runs til a couple of days ago didn’t have it reach the Lesser Antilles til Tuesday or so. Am I correct? At this rate, it may get there tonight.

This is mostly due to the current observed low not merging with the portion of vorticity to the east (seen at the end of the line of weak convection to the north), which would have resulted in Tuesday impacts to the Lesser Antilles. This separation was not fully picked up on by the EURO until last night’s 00z run. GFS showed it by its 00z run two nights ago, but has adjusted westward by maybe a few hours on subsequent runs.