Huge outflow boundary surging west away from Emily

[Wthrman13]

It's far enough away from the core that I doubt it's affecting the strength of the system too much, athough it is probably cutting down on the inflow into the system from the west side. Generally, if you see outflow boundaries racing away from the cores of developing systems, it's a bad sign for development or intensification. However, I have seen outflow boundaries (though not quite this big) on the outskirts of strong hurricanes, and those hurricanes showed no ill effects.

It appears that SW shear is still the culprit in weakening the storm right now.

[Lowpressure]

Dennis had that outflow explosion right before intensification phase. Dennis was not this strong at that point however. Interesting to look at.

[joseph01]

Is that long, curved, spiralling cloud what you're refering to? If so, what altitude would that thing be?

[Derecho]

Dennis had that outflow explosion right before intensification phase. Dennis was not this strong at that point however. Interesting to look at.

You're confused about the use of the term outflow (understandable.)

Outflow at 200 mb (upper level) is GOOD for a hurricane.

What Wthrman13 is talking about is a huge SURFACE outflow boundary shooting west from Emily; it's the big obvious curved cloud racing away from Emily.

It's never good for a tropical system for air at the surface to be racing AWAY from the center; you want air coming IN at the bottom and shooting out of the top.

[Thunder44]

I see an eye starting to show up in latest visble images again.

[GalvestonDuck]

Dennis had that outflow explosion right before intensification phase. Dennis was not this strong at that point however. Interesting to look at.

You're confused about the use of the term outflow (understandable.)

Outflow at 200 mb (upper level) is GOOD for a hurricane.

What Wthrman13 is talking about is a huge SURFACE outflow boundary shooting west from Emily; it's the big obvious curved cloud racing away from Emily.

It's never good for a tropical system for air at the surface to be racing AWAY from the center; you want air coming IN at the bottom and shooting out of the top.

Great explanation, Der! Thanks!

[joseph01]

Yes, thank you, Derecho!

[Wthrman13]

Yes, sorry, I should have clarified that. Surface outflow boundaries form when convective downdrafts hit the surface and spread out horizontally. The advancing curve of clouds racing away to the west is the boundary of this advancing surface outflow, probably as a result of collapsing convection on the west side of the system (you can see this convection form and die on the west side in an IR loop). Perhaps some drier air got entrained in the downdrafts associated with this convection, making the downdrafts cooler (by evaporative cooling), and thus more negatively buoyant, and thus stronger, leading to the development of a particularly large and well defined outflow boundary.

[Patrick99]

It's almost funny-looking - she really burped that one out. I seem to remember the developing Charley doing the same thing on a couple of occasions, at practically the same location.

How fast is that boundary moving? 40 mph?

[joseph01]

It's almost funny-looking - she really burped that one out. I seem to remember the developing Charley doing the same thing on a couple of occasions, at practically the same location.

How fast is that boundary moving? 40 mph?

It did seem to be moving at a pretty good clip. I'm curious what the weather would be like under it, as it passed over you.

[Pebbles]

Yes, sorry, I should have clarified that. Surface outflow boundaries form when convective downdrafts hit the surface and spread out horizontally. The advancing curve of clouds racing away to the west is the boundary of this advancing surface outflow, probably as a result of collapsing convection on the west side of the system (you can see this convection form and die on the west side in an IR loop). Perhaps some drier air got entrained in the downdrafts associated with this convection, making the downdrafts cooler (by evaporative cooling), and thus more negatively buoyant, and thus stronger, leading to the development of a particularly large and well defined outflow boundary.

Nice explaination... could an outflow boundary be started by the collapse of an inner eyewall during an eye wall replacement cycle?

[jax]

It's far enough away from the core that I doubt it's affecting the strength of the system too much, athough it is probably cutting down on the inflow into the system from the west side. Generally, if you see outflow boundaries racing away from the cores of developing systems, it's a bad sign for development or intensification. However, I have seen outflow boundaries (though not quite this big) on the outskirts of strong hurricanes, and those hurricanes showed no ill effects.

It appears that SW shear is still the culprit in weakening the storm right now.

it did the same thing yesterday with an outflow boundry... about this
time yesterday... it was followed by rapid intensifiation... the outflow,
yesterday, was moving to the Northwest...

[Lowpressure]

Thanks, I stand corrected. Should have clarified outflow from outflow boundry. Thanks Derecho.

[Wthrman13]

Yes, sorry, I should have clarified that. Surface outflow boundaries form when convective downdrafts hit the surface and spread out horizontally. The advancing curve of clouds racing away to the west is the boundary of this advancing surface outflow, probably as a result of collapsing convection on the west side of the system (you can see this convection form and die on the west side in an IR loop). Perhaps some drier air got entrained in the downdrafts associated with this convection, making the downdrafts cooler (by evaporative cooling), and thus more negatively buoyant, and thus stronger, leading to the development of a particularly large and well defined outflow boundary.

Nice explaination... could an outflow boundary be started by the collapse of an inner eyewall during an eye wall replacement cycle?

Good question.

In the inner core of a mature hurricane, the air is close to saturated throughout the column (except for in the eye itself). Thus, convective downdrafts in the inner core are weak to begin with and are superimposed on large scale rising motion. The collapse of the inner eye therefore would be unlikely to produce downdrafts of enough intensity to create a significant outflow boundary, unless entrainment from dry air in the eye becomes significant. Furthermore, any outflow boundaries that were created would be superimposed on the strong vortical inflow and would quickly be mixed out and lose their definition. If dry air were entrained into the core, this might enhance downdraft potential and produce stronger outflow boundaries, but again, these would be constrained by the very strong inflow present in the inner core. But, your question is a good one. I'm not sure to what extent convective downdrafts actually affect inner core dynamics of hurricanes and how much (if any) role they have to play in ERC's. A lot of this stuff is still not well understood, even by top researchers in the field.