ATL: Ex COLIN - Discussion

[Wthrman13]

If I recall correctly, the NHC mentioned in the Advisories that a slow down was expected as this feature neared the Leewards.

A slowdown almost always occurs as a TC enters a recurve. Due to conservation of angular momentum, it slows down going into a curve and accelerates out of it. So yeah, it should be slowing down if it hasn't already.

Sorry, but conservation of angular momentum doesn't work that way for a tropical cyclone's translational motion. Remember, a tropical cyclone is not an object, it's a vortex, which itself is a dynamic pattern within a fluid -- in this case, the atmosphere. The laws governing the motion of a vortex in a fluid are indeed derived from Newton's laws of motion, but they are not applied in the same way as if you were applying them to a solid object like a car driving around a bend in a road: it's quite a bit more complicated than that.

The consequences of this are that tropical cyclones can change speed and direction much more rapidly than they would if they were solid objects of a comparable size and mass. It all depends on the dynamic nature of the steering currents they are embedded in, and the highly nonlinear interaction of the vortex with these steering currents.

[SoldMayor]

Wow it looks now like a tropical storm

[KWT]

Judging from what is happening right now Ivanhater its possibly redeveloping a good deal faster then most were expecting, I'd have to agree its certainly got a shot once it lifts out to the north.

I'd still be surprised to see it have a LLC just yet but its well on its way for sure I think...I'd have personally have gone to Code Red myself but I suppose the fact it'll probably struggle for a little while in this sheared conditions is why they've stayed at 40%.

[Gustywind]

[Aric Dunn]

If I recall correctly, the NHC mentioned in the Advisories that a slow down was expected as this feature neared the Leewards.

A slowdown almost always occurs as a TC enters a recurve. Due to conservation of angular momentum, it slows down going into a curve and accelerates out of it. So yeah, it should be slowing down if it hasn't already.

Sorry, but conservation of angular momentum doesn't work that way for a tropical cyclone's translational motion. Remember, a tropical cyclone is not an object, it's a vortex, which itself is a dynamic pattern within a fluid -- in this case, the atmosphere. The laws governing the motion of a vortex in a fluid are indeed derived from Newton's laws of motion, but they are not applied in the same way as if you were applying them to a solid object like a car driving around a bend in a road: it's quite a bit more complicated than that.

The consequences of this are that tropical cyclones can change speed and direction much more rapidly than they would if they were solid objects of a comparable size and mass. It all depends on the dynamic nature of the steering currents they are embedded in, and the highly nonlinear interaction of the vortex with these steering currents.

well having taken many fluids and physics classes I understand this process quite well and it is very difficult to model something that is not "an object" as you say in a fluid as we all know from our various weather models...

[ConvergenceZone]

Now that we know this won't affect the USA, hopefully it won't effect Bermuda either, that way we can hope for a quick ramp up...Although if it is going to split the middle between Bermuda and the USA, it would be nice to see a cat 3 or cat 4, which I know, isn't going to happen, but at least we have something to track now that may turn into something decent without any threat to USA. Hopefully it will be west of Bermuda.

[ozonepete]

If I recall correctly, the NHC mentioned in the Advisories that a slow down was expected as this feature neared the Leewards.

A slowdown almost always occurs as a TC enters a recurve. Due to conservation of angular momentum, it slows down going into a curve and accelerates out of it. So yeah, it should be slowing down if it hasn't already.

Sorry, but conservation of angular momentum doesn't work that way for a tropical cyclone's translational motion. Remember, a tropical cyclone is not an object, it's a vortex, which itself is a dynamic pattern within a fluid -- in this case, the atmosphere. The laws governing the motion of a vortex in a fluid are indeed derived from Newton's laws of motion, but they are not applied in the same way as if you were applying them to a solid object like a car driving around a bend in a road: it's quite a bit more complicated than that.

The consequences of this are that tropical cyclones can change speed and direction much more rapidly than they would if they were solid objects of a comparable size and mass. It all depends on the dynamic nature of the steering currents they are embedded in, and the highly nonlinear interaction of the vortex with these steering currents.

Thanks for pointing that out. I wasn't clear enough. I wasn't talking about conservation of angular momentum within its own fluid envelope. And you are certainly right that there are other forces involved - I didn’t want to get into it too heavily here. However, I wasn’t applying the laws of motion to it as if it were a solid object. I fully understand that a hurricane is not a solid object like a ball or a car (I would hope!). But even though a TC is not a solid object, but indeed a rotating fluid, it still has angular momentum with respect to the earth’s axis. The conservation of that momentum causes a westward moving cyclone to experience an acceleration to the east as it move’s northward. That’s what I was talking about.
I also totally agree that many aspects of the interaction of the vortex with its steering currents is highly non-linear. But non-linear doesn’t exclude angular momentum.

[ozonepete]

well having taken many fluids and physics classes I understand this process quite well and it is very difficult to model something that is not "an object" as you say in a fluid as we all know from our various weather models...

Great point.

[ozonepete]

Now that we know this won't affect the USA, hopefully it won't effect Bermuda either, that way we can hope for a quick ramp up...Although if it is going to split the middle between Bermuda and the USA, it would be nice to see a cat 3 or cat 4, which I know, isn't going to happen, but at least we have something to track now that may turn into something decent without any threat to USA. Hopefully it will be west of Bermuda.

Wow! Hold on! Who said it won't affect the U.S.? It still has a lot of westward momentum, and I would say it's a little early to write it off. Just being cautious.

[wjs3]

Thanks for pointing that out. I wasn't clear enough. I wasn't talking about conservation of angular momentum within its own fluid envelope. And you are certainly right that there are other forces involved - I didn’t want to get into it too heavily here. However, I wasn’t applying the laws of motion to it as if it were a solid object. I fully understand that a hurricane is not a solid object like a ball or a car (I would hope!). But even though a TC is not a solid object, but indeed a rotating fluid, it still has angular momentum with respect to the earth’s axis. The conservation of that momentum causes a westward moving cyclone to experience an acceleration to the east as it move’s northward. That’s what I was talking about.
I also totally agree that many aspects of the interaction of the vortex with its steering currents is highly non-linear. But non-linear doesn’t exclude angular momentum.

Hey, um, Pete--

You lost me on the highlighted part. If a TC is moving westward, how does it accelerate to the east as it moves northward? It's gotta be doing one or the other--westward OR northward, right? I think (?) what you mean is that as a westward moving cyclone turns northward, there's an eastward component?

Wouldn't that element be tiny compared to the effect of steering currents, BTW? In this case in particular, the ridge got crushed, right?

WJS3

[cycloneye]

00z Best Track

AL, 04, 2010080500, , BEST, 0, 202N, 628W, 35, 1009, WV

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

[Wthrman13]

Thanks for pointing that out. I wasn't clear enough. I wasn't talking about conservation of angular momentum within its own fluid envelope. And you are certainly right that there are other forces involved - I didn’t want to get into it too heavily here. However, I wasn’t applying the laws of motion to it as if it were a solid object. I fully understand that a hurricane is not a solid object like a ball or a car (I would hope!). But even though a TC is not a solid object, but indeed a rotating fluid, it still has angular momentum with respect to the earth’s axis. The conservation of that momentum causes a westward moving cyclone to experience an acceleration to the east as it move’s northward. That’s what I was talking about.
I also totally agree that many aspects of the interaction of the vortex with its steering currents is highly non-linear. But non-linear doesn’t exclude angular momentum.

Thanks for clarifying. I just see the misconception of "hurricane as huge lumbering freight train" quite often, and I erred in assuming you were propagating that.

[hurricaneCW]

One of the few times where the Herbert Box doesn't apply. The storm crossed 60W south of 20N, and even now is near 20N and 63W. Also, kind of unusual to see a storm curve out like that in early August where the Bermuda Ridge should be at its strongest.

[wjs3]

Ozonepete--

Question retracted. I reread it and I'm "picking up what you're laying down"--just got wrapped up in the language.

Apologies

WJS3

[ConvergenceZone]

Wow! Hold on! Who said it won't affect the U.S.? It still has a lot of westward momentum, and I would say it's a little early to write it off. Just being cautious.

I've been reading posts from the Mets on this. There isn't anything to force it westward towards the US.....In order for it to move westward and effect the USA as opposed to out to sea, there has to be something to force in that direction. What would that be?

[KWT]

You've got quite a strong upper trough trying to dig down and whilst its not amazingly strong its enough and inportantly sticks round long enough to slowly lift up the system...orginally it looked like it might take several bites of the cherry.

CZ, it'd be nice if we could get a hurricane out of this one as it starts to race to the north towards the weakness...I wouldn't rule it out either though personally I'd go a little lower with strength.

[TheBurn]

[ozonepete]

Wow! Hold on! Who said it won't affect the U.S.? It still has a lot of westward momentum, and I would say it's a little early to write it off. Just being cautious.

I've been reading posts from the Mets on this. There isn't anything to force it westward towards the US.....In order for it to move westward and effect the USA as opposed to out to sea, there has to be something to force in that direction. What would that be?

Mostly caution. But seriously, the SubTropicalRidge to its east and northeast is still pushing it west to northwestward, especially as it remains weak. There's a lot of confusion as to its movement because the low level center keeps reforming (or better said, trying to reform) and there's a number of convective blowups going on. As usual (and I'm as guilty as everone else here) we're all trying to judge its present and future motion by looking at cloud formations. Right now a good deal of the convection is getting blown off to the north so it gives the optical illusion that the low itself is moving that way. That's just not the case. Until it gels into a strong identifiable LLC stacked under a MLC we can't be sure how far west it will get. If it gets far enough west before it turns, it could even catch Cape Hatteras, let alone Bermuda. That's not out of the question at this still early stage.

[HURAKAN]

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[hurricaneCW]

Something insane would have to happen to allow it to come further west than forecast. According to the model suite, it's still moving between wnw and nw at 21 knots. The track looks to be very Bill-ish.