Can't Count on EC Trough for Recurvature if 91L Develops

[MWatkins]

If…if…if…we see development from 91L…I would not immediately count on the upper system…forecast to develop in the east…to turn 91l out to sea.

Global models are in pretty good agreement about the development of the upper air pattern in the next 5 days. The models are suggesting a mid-layer area of lower pressure will develop and drop down the eastern seaboard. Usually, this would correspond with lowering heights in the Midwest and a trough sweeping across the Atlantic…or at least parking off of the east coast and creating southwesterly flow along it’s axis.

But the modeling is wanting to hold more of the ridge in the Midwest…and this could become a big deal later on…because rather than creating southwesterly flow in the steering levels…and thus allowing a cyclone to turn away…it may not do enough work…instead of a sweeping trough it could cause a dent in the pattern…perhaps weakening the upper flow in the western Atlantic (slowing the steering currents)…but not enough to turn something out. Here are a couple of examples from the 12Z GFS.

http://www.nco.ncep.noaa.gov/pmb/nwprod ... 0_072m.gif

http://www.nco.ncep.noaa.gov/pmb/nwprod ... 0_120m.gif

Before the GFS bash fest starts…NOGAPS is leaving plenty of 588DM ridging in place in the western Atlantic. The ridge is skinny…but is a significant departure from yesterdays run at the same verify time:

At 96 hours yesterday:

https://www.fnmoc.navy.mil/CGI/PUBLIC/w ... 00&tau=096

versus today’s 72 hour forecast (same verify time):

https://www.fnmoc.navy.mil/CGI/PUBLIC/w ... 00&tau=072

Note the skinny ridge holding instead of allowing the western Atlantic to open up.

And yesterday’s big open trough at 144 hrs

https://www.fnmoc.navy.mil/CGI/PUBLIC/w ... 00&tau=144

Vs today’s 126 (same v-time)…the ridge is already building back in:

https://www.fnmoc.navy.mil/CGI/PUBLIC/w ... 00&tau=120

So with this new deep burst of convection over 91L…this is becoming an interesting thing to watch. I would not automatically count on a recurve here…looks like the ridging may hold. The big question is…will we see development?

MW

[GeneratorPower]

Great analysis Mike. Thoughts on the convective flareup we're watching?

[Dean4Storms]

I agree Mike. Looks like enough ridging stays in place. Plus a deeper system would prefer riding more westward in the short term and this would make it miss the trough.

[SouthFloridawx]

Mike I was looking at that GFS run and even posted in another thread about possible TC development from the tail end of the front as a result of the short wave coming down. GFS indicated a fairly quick motion with this front and low pressure areas associated with it. I do not think it's gonna stick around very long.

I think with 91L if it can get it's act going we'll see it start to turn more WNW and then as the the shortwave moves down towards the southeast. This shortwave will cause enough weakness to weaken the ridge for a little while but, as I said GFS is not indicating for this feature to stick around long.

By the time 91L is possibly in the Northeastern Caribbean and possibly end up in the Southern Bahamas.

If the the ridge holds up enough this may end up in the gulf eventually.

This is gonna be a hard forecast for this one but, I think a general WNW motion at first and possibly ... depending on how much lattitude it gains we could see a jont off to the NW but, then back to the W as monday rolls around.

[MWatkins]

Great analysis Mike. Thoughts on the convective flareup we're watching?

The fact this is a concentrated burst...and the fact that the axis has crossed the 27C isotherm are both development indicators.

If the low clouds to the south continue to become better defined...and if the system is able to sustain the convection...we will likely see a TD in the next 12 to 18 hours.

MW

[Hybridstorm_November2001]

The models have all performed quite poorly this Summer, thus far. As such I'll wait and see what exactly happen. Chris was a prime example of this, even the NHC thought he would become a hurricane for a time, and look what happened. It is way too far out to make any call on eventual track.

[x-y-no]

Great analysis Mike. Thoughts on the convective flareup we're watching?

The fact this is a concentrated burst...and the fact that the axis has crossed the 27C isotherm are both development indicators.

If the low clouds to the south continue to become better defined...and if the system is able to sustain the convection...we will likely see a TD in the next 12 to 18 hours.

MW

Aye, there's the rub ...

How many times do we see these systems pulse their convection but never sustain it?

[sevenleft]

Great analysis Mike. Thoughts on the convective flareup we're watching?

The fact this is a concentrated burst...and the fact that the axis has crossed the 27C isotherm are both development indicators.

If the low clouds to the south continue to become better defined...and if the system is able to sustain the convection...we will likely see a TD in the next 12 to 18 hours.

MW

Aye, there's the rub ...

How many times do we see these systems pulse their convection but never sustain it?

Every single day.

[Weatherfreak14]

I agree Mike. Looks like enough ridging stays in place. Plus a deeper system would prefer riding more westward in the short term and this would make it miss the trough.

I agree also if this ridge holds in plce EC may have to watch out.

[Bailey1777]

Sounds more like Florida and the GOM to me.

[jabber]

I thought the models did pretty good with Chris. They all pretty much had him dying right about when he did.

The models have all performed quite poorly this Summer, thus far. As such I'll wait and see what exactly happen. Chris was a prime example of this, even the NHC thought he would become a hurricane for a time, and look what happened. It is way too far out to make any call on eventual track.

[WeatherEmperor]

Wouldnt this certainly be true IF the 91L system goes north of the islands? There is no guarantee that it will go north of the islands. It could just end up going straight into the Caribbean and stay south of hispanola. Then there would be no need to worry about recurvature. Any thoughts on this scenario?

<RICKY>

[hurricanetrack]

Since the typical model suite of global models show very little development with this system, I will have to say that 91L is not destined to become much more than a depression- if that. I mean, come on, NONE of the major models show development with this system. That's saying a lot. If it does develop and becomes a tropical storm and eventually a hurricane then ALL of the major global models, the ones I use from the FSU site are broken. So, what's more likely, all of the global models are not working or that 91L will not develop much because it is still too early? The Atlantic is just not ready yet. When that upward motion pulse reaches the Basin, then I'll get excited about seeing prolific development. Until then, I think the models are working fine and are seeing what's out there- a whole lot of nothing.

[Pearl River]

There's still a lot of dry air for it to fight thru.

http://www.ssd.noaa.gov/goes/east/catl/wv-l.jpg

[willjnewton]

can someone explain to me what does mike watkins in the statement above in this thread means???and also what does 91L mean???and what does recurvature mean??

[BayouVenteux]

The Atlantic is just not ready yet. When that upward motion pulse reaches the Basin, then I'll get excited about seeing prolific development..

Yep. And the MJO positive /upward motion pulse is steadily creeping eastward. While it hasn't been consistently distinct this summer in terms of easily detectable oscillation, it's clearly in positive phase right now in the western and central pacific judging by the ongoing tropical activity. In a few weeks, that pulse should be into the Atlantic basin just as we enter into the climatological peak weeks of the hurricane season.

[MWatkins]

Hey this system has all sorts of issues to work through:

1. It's moving about 20 knots. Going to be hard for a 25 knot system to close off a southern side of a circulation moving at 20 knots.

2. There is some sourtherly shear pretty clearly impacting the system

3. The BAM guidance is still all sorts of spread out but at least they are on the same trajectory

THe point of this thread was more to discuss the steering pattern than to deal with the prospects of imminent development. It does not look like the trough will be as deep or last as long as some were thinking. Once again...iff...iff...iff...this develops...it's not a done deal it's gone fishing.

MW

[Stephanie]

can someone explain to me what does mike watkins in the statement above in this thread means???and also what does 91L mean???and what does recurvature mean??

What Mike is saying is that the new "investment" 91L or potential tropical system to the east of the Virgin Islands may not be affected by the normal East Coast trough that usually sets up and tends to sweep the tropical systems out to sea. That's the "recurvature". The storms generally follow the air patterns that are prominent at the time in the area they are in. If a trough does appear, kind of like what we were discussing yesterday will, it would have the tendency to sweep it out to sea. However, if doesn't develop and the High pressure hangs around a while on the East Coast, the clockwise flow around the High pressure MAY help to direct it closer to the East Coast. HOWEVER, that's a BIG IF has Mike said.

Here's the website to the National Hurricane Center. This can give you explanations of the different terms that are used; http://www.nhc.noaa.gov/