Can an ULL couple up with a LLC?

[Stormavoider]

I asked this question in the Mmmm.. thread. I thought it might need some visibility. It seems the opportunity is presenting itself off the Mississippi delta.

[sevenleft]

The last time Chris got too close to an ULL...what happened?

[JonathanBelles]

i think it could happen but it would be a difficult process

[Stormavoider]

The last time Chris got too close to an ULL...what happened?

It decoupled! Can the reverse happen????????????

[sevenleft]

If an ULL got close to "Chris" now, it would shear the convection apart, just like before....and a surface low without convection will spin down and dissipate.

[Normandy]

I guess an LLC can move under a ULL since they are at different levels, but I really don't know u have to ask a pro met.

[Stormavoider]

If an ULL got close to "Chris" now, it would shear the convection apart, just like before....and a surface low without convection will spin down and dissipate.

As you can tell from my topic post I am not writing about Chris. I am writing about what is currently playing out in the northern Gulf.

[sevenleft]

Oh. Sorry, I thought this post was geared at the Chris LLC coupling with the ULL in the northern gulf....

[Stormavoider]

I referenced the Mmmmm thread.

[MWatkins]

Usually when this happens 2 things will occur...

1. No tropical development at all
2. The development of a subtropical cyclone or extratropical cyclone

Warm-core tropical cyclones by definition cannot exist when a cold-core upper low is sitting right on top of them. If you think of the mechanics it makes sense.

In order for a tropical cyclone to intensify...it must lower pressures at the surface. Condensation and release of latent heat are big parts of the deal...but the leftover cold, dried out air has to go somewhere. That's where the anticyclone aloft does it's job. It transports the exhaust away from the surface low. An upper low on top of the surface low basically shuts down this process.

Over time the upper low can produce lowering pressures at the surface by creating an area of strong upper winds over the surface low...if they line up right. But this...again...would create a subtropical system with lots of dry....sinking air in the mix.

hope this helps...

MW

[Derek Ortt]

the 1991 unnamed hurricane and Olga formed directly underneath UL's, but they were not purely tropical cyclones

[Stormavoider]

Thank you, Thank you. Great explanation!

[AJC3]

I am assuming that you're talking about the case where there is already a pre-existing LLC and ULL to begin with.

The problem here is that while a TC is in the development process, it is going to try to build upper level heights and improve anticyclonic outflow aloft via convective processes (i.e. latent heat release form thunderstorms). The presence of an ULL moving over the top of a LLC will inhibit that process.

If the TC is already developed, then it already has an anticyclone aloft and encountering an ULL is not going to be at all healthy at all either.

What you're more likely to see is an extratropical cyclone captured by an ULL and becoming vertically stacked. This often occurs when a trough is digging SE-ward across the eastern U.S. and a cutoff ULL forms, then captures a developing nor'easter along or just offshore the eastern U.S. seaboard.

[sevenleft]

And someone gets a TON of snow.

[Stormavoider]

I am assuming that you're talking about the case where there is already a pre-existing LLC and ULL to begin with.

The problem here is that while a TC is in the development process, it is going to try to build upper level heights and improve anticyclonic outflow aloft via convective processes (i.e. latent heat release form thunderstorms). The presence of an ULL moving over the top of a LLC will inhibit that process.

If the TC is already developed, then it already has an anticyclone aloft and encountering an ULL is not going to be at all healthy at all either.

What you're more likely to see is an extratropical cyclone captured by an ULL and becoming vertically stacked. This often occurs when a trough is digging SE-ward across the eastern U.S. and a cutoff ULL forms, then captures a developing nor'easter along or just offshore the eastern U.S. seaboard.

Thank you another great explanation. What I am specifically talking about is described here:

From 8:05 pm TWD
...DISCUSSION...
GULF OF MEXICO...
BROAD MID/UPPER LOW IS OVER THE E GULF NEAR 27N86W WITH AN UPPER
TROUGH EXTENDING S TO THE YUCATAN CHANNEL. A 1013 MB SURFACE LOW
HAS DEVELOPED AT 05/2100 UTC OFF THE COAST OF THE MISSISSIPPI
DELTA NEAR 29N88W WITH A DEVELOPING UPPER LEVEL HIGH TO THE S
NEAR 27N90W DIFFLUENCE BETWEEN THESE FEATURES IS DEVELOPING A
RATHER LARGE AREA OF SCATTERED SHOWERS/THUNDERSTORMS OVER THE
CENTRAL GULF FROM 22N-28N BETWEEN 85W-97W. A SURFACE TROUGH
REMAINS OVER THE SW GULF AND THE BAY OF CAMPECHE FROM 23N97W TO
THE COAST OF MEXICO NEAR 18N94W. SCATTERED MODERATE/ISOLATED
STRONG CONVECTION IS WITHIN 120 NM E OF THE SURFACE TROUGH.
AFTERNOON THUNDERSTORMS DEVELOPING OVER THE FLORIDA PENINSULA
FROM THE SE SEA BREEZE ARE MOVING INTO THE FAR E GULF BUT
WILL BE RAPIDLY DISSIPATING AS THE LEAVE LAND.

hmm.. that's an interesting new development. That is only 1mb higher than when Chris was considered a TS.

And looking at the WV http://www.ssd.noaa.gov/goes/east/gmex/loop-wv.html
The ULL is moving in fast on this surface low.

[HurricaneBill]

Sometimes an ULL itself can develop into a TC.

[Jim Cantore]

Didnt the perfect storm occur with Hurricane Grace and a ULL?

[HurricaneBill]

An example of a ULL becoming a TC was TS Beryl in 1994. A ULL moved into the Gulf of Mexico and developed into a tropical depression, which went on to become TS Beryl.

[Jim Cantore]

Danny in 1997 formed from a stalled front

[Aslkahuna]

An even more recent example of a ULL developing into a Tropical Cyclone is the current TS Maria off the coast of Japan which developed from a TUTT ULL this past week. Actually, the outflow of a hurricane does not immediately become anticyclonic as it leaves the eyewall region for it takes some time for the oroiginal cyclonic flow to completely reverse sign.