Major Hurricane Irma

[No snow for you]

2 minutes ago, NWLinnCountyIA said:

No it wasnt, it had high CC and ZDR near one meaning it was a met phenomenon. Was probably some sort of weird mesovortex as others have said.

You have your theory I have mine. I have seen it happen before on large eyes. But ok 

[Hoosier]

Ah yes, the radar hallucination stage.

If you're going to definitively state that it has changed direction/is running north of NHC track, back it up with some evidence.

[jojo762]

Eye wall is starting to become wrapped entirely in deep convection again, evident on radar as well as satellite. Won't happen immediately though, as it is a process... Believe one of our red-tags mentioned this was probably going to happen earlier.

[OUGrad05]

1 minute ago, jojo762 said:

Eye wall is starting to become wrapped entirely in deep convection again, evident on radar as well as satellite. Won't happen immediately though, as it is a process... Believe one of our red-tags mentioned this was probably going to happen earlier.

Yeah the presentation is definitely down a couple notches from earlier, dry air I suspect combined with ERC.  We'll see how it ramps back up over night.

[LakeEffectKing]

Can't say that I differ too much from NHC...I think Irma will move a tad quicker initially, but, overall, the only subtle differences is wind speed at LF and a slightly western position at LF.

 

 

 

[USCG RS]

The ERC may have been disrupted due to some land interaction thanks to the close pass to PR. With that being said, it still has 3 more days over very warm water with nearly optimal atmospheric conditions to work with. All guidance shows Irma strengthening in the Southern Bahamas, so current intensity is irrelevant now that we temporarily don't have any threats to land.

OK.. So this has been bothering me the whole night. Therefore i spent the past three hours working and researching eyewall replacement cycle s (ERC) . I will preference with this: ERC are very poorly understood and research on them is just beginning. However, I found a theory about ERC which not only makes sense, but I was likewise able to extrapolate an answer for which I believe fits why these ERC are doing nothing to weaken Irma.

Terms:

ERC : Eyewall replacement cycle. HBL : Hurricane boundary layer. NRF : Net radial force. PGF : Pressure Gradient Force.

I will also preferance with the fact that I view weather as the earth's immune system and really all weather is is an attempt for the atmosphere to find an equilibrium (much like our immune system is to bring homeostasis to the body).

So let's get to it. ERC, in this theory, are believed to take place due to a set of complicated physics. As a hurricane is born, there are three main components, physics wise, which make up the storm (at least as it pertains to ERC). The first is the HBL which extends approximately 1 km into the atmosphere, from the surface. It interacts with most of the surface friction. The second is the PGF, which essentially forces particles from areas of higher density (pressure) to areas of lower pressure. The last is known as the NRF, which is essentially the force directed towards the center of a rotating mass.

As a hurricane develops, these forces work with each other and eventually, when the storm reaches a certain intensity, an excess of NRF creates a secondary wind maximum approximately 40-60km from the center of the hurricane. This secondary wind maximum is always believed to be because the HBL cannot properly maintain a balance of angular momentum (or the acceleration of particles/mass in a circulation motion), or in other words, the HBL cannot keep the particles separated in such a way that the pressure and buildup of particles remain uniform. This, combined with a positive NRF, creates convergence. This convergence creates an up welling which then leads to a secondary maximum. This secondary maximum, in turn, creates more PGF (the force of a particle over a given area. The higher the PGF, due to more particles in a smaller area, the higher the winds). Eventually, this leads to enough of a convergence that a secondary eyewall is formed and two wind maxima are thus created. As many know, during this time, the overall windspeed of the maximum sustained winds decrease due to the maximum winds being spread out over a larger area and thus the wind speed lowers (or.. The PGF is distributed over a larger area and therefore while the mass remains the same, because force equals mass times acceleration, acceleration is lower and therfore the force or net wind speed decreases). Eventually, the PGF, combined with angular momentum, will coerce the outer eyewall to contract, thus ending the ERC. At this time, the winds will increase as will the overall size of the wind field of the storm, while allowing the hurricane to likewise strengthen.

But the question that's plagues me today is why has Irma skipped this weakening phase of the ERC and likewise why has she been constantly cycling through them and having them take place in a rapid fashion? What I propose is this. Irma has been in essentially a perfect, or lab like environment, for her lifespan. This is what is allowing her to explosively deepen and shatter records. What I likewise propose is this. Irma is showing us that hurricanes create ERC of their own accord. In other words, an ERC has nothing to do with outside influences and is strictly because of the mechanism of the hurricane itself (and the strengthening mechanisms within). Likewise, because ERC are part of the hurricanes overall structure, in theory, it should not hurt the hurricane, but rather, help it. Left to its own devices, this is what Irma is doing. It's part of a necessary strengthening cycle for well developed hurricanes. The HBL, I propose, creates the issue for ERC as within this layer, there is friction. This friction slows the contraction of the secondary eyewall and forces the storm to balance itself out to preserve itself, while it deals with the friction and the effects of it. Because Irma is in a lab like environment, the friction of the ocean is essentially non existant as it is over flat and incredibly warm water. Likewise, there is no sheer or dry air to interfere with the Core and venting mechanisms of Irma. As such, these ERC can begin and complete without any interference and then, once the outer wind maxima are mature, the PGF and angular momentum can allow the outer wind maxima to contract, replacing the old eyewall and thus completing the ERC, in time for it to build and start once again. Therefore, she can bypass any weakening state that the friction within the HBL would cause, as, essentially, there isn't any to speak of.

This, of course, is strictly a theory

[Drz1111]

2 minutes ago, OUGrad05 said:

Yeah the presentation is definitely down a couple notches from earlier, dry air I suspect combined with ERC.  We'll see how it ramps back up over night.

Come on.  Dry air?  There's a bare bit on the SJU sounding but nothing that explains any dry air ingestion into the core.

[NJwx85]

3 minutes ago, LakeEffectKing said:

Can't say that I differ too much from NHC...I think Irma will move a tad quicker initially, but, overall, the only subtle differences is wind speed at LF and a slightly western position at LF.

 

Is that max winds of 145 at LF? 

[4waresnowcone]

1 minute ago, USCG RS said:

OK.. So this has been bothering me the whole night. Therefore i spent the past three hours working and researching eyewall replacement cycle s (ERC) . I will preference with this: ERC are very poorly understood and research on them is just beginning. However, I found a theory about ERC which not only makes sense, but I was likewise able to extrapolate an answer for which I believe fits why these ERC are doing nothing to weaken Irma.

Terms:

ERC : Eyewall replacement cycle. HBL : Hurricane boundary layer. NRF : Net radial force. PGF : Pressure Gradient Force.

I will also preferance with the fact that I view weather as the earth's immune system and really all weather is is an attempt for the atmosphere to find an equilibrium (much like our immune system is to bring homeostasis to the body).

So let's get to it. ERC, in this theory, are believed to take place due to a set of complicated physics. As a hurricane is born, there are three main components, physics wise, which make up the storm (at least as it pertains to ERC). The first is the HBL which extends approximately 1 km into the atmosphere, from the surface. It interacts with most of the surface friction. The second is the PGF, which essentially forces particles from areas of higher density (pressure) to areas of lower pressure. The last is known as the NRF, which is essentially the force directed towards the center of a rotating mass.

As a hurricane develops, these forces work with each other and eventually, when the storm reaches a certain intensity, an excess of NRF creates a secondary wind maximum approximately 40-60km from the center of the hurricane. This secondary wind maximum is always believed to be because the HBL cannot properly maintain a balance of angular momentum (or the acceleration of particles/mass in a circulation motion), or in other words, the HBL cannot keep the particles separated in such a way that the pressure and buildup of particles remain uniform. This, combined with a positive NRF, creates convergence. This convergence creates an up welling which then leads to a secondary maximum. This secondary maximum, in turn, creates more PGF (the force of a particle over a given area. The higher the PGF, due to more particles in a smaller area, the higher the winds). Eventually, this leads to enough of a convergence that a secondary eyewall is formed and two wind maxima are thus created. As many know, during this time, the overall windspeed of the maximum sustained winds decrease due to the maximum winds being spread out over a larger area and thus the wind speed lowers (or.. The PGF is distributed over a larger area and therefore while the mass remains the same, because force equals mass times acceleration, acceleration is lower and therfore the force or net wind speed decreases). Eventually, the PGF, combined with angular momentum, will coerce the outer eyewall to contract, thus ending the ERC. At this time, the winds will increase as will the overall size of the wind field of the storm, while allowing the hurricane to likewise strengthen.

But the question that's plagues me today is why has Irma skipped this weakening phase of the ERC and likewise why has she been constantly cycling through them and having them take place in a rapid fashion? What I propose is this. Irma has been in essentially a perfect, or lab like environment, for her lifespan. This is what is allowing her to explosively deepen and shatter records. What I likewise propose is this. Irma is showing us that hurricanes create ERC of their own accord. In other words, an ERC has nothing to do with outside influences and is strictly because of the mechanism of the hurricane itself (and the strengthening mechanisms within). Likewise, because ERC are part of the hurricanes overall structure, in theory, it should not hurt the hurricane, but rather, help it. Left to its own devices, this is what Irma is doing. It's part of a necessary strengthening cycle for well developed hurricanes. The HBL, I propose, creates the issue for ERC as within this layer, there is friction. This friction slows the contraction of the secondary eyewall and forces the storm to balance itself out to preserve itself, while it deals with the friction and the effects of it. Because Irma is in a lab like environment, the friction of the ocean is essentially non existant as it is over flat and incredibly warm water. Likewise, there is no sheer or dry air to interfere with the Core and venting mechanisms of Irma. As such, these ERC can begin and complete without any interference and then, once the outer wind maxima are mature, the PGF and angular momentum can allow the outer wind maxima to contract, replacing the old eyewall and thus completing the ERC, in time for it to build and start once again. Therefore, she can bypass any weakening state that the friction within the HBL would cause, as, essentially, there isn't any to speak of.

This, of course, is strictly a theory

You are a saint for the acronyms at the beginning. As a newbie, it really makes my life easier. Thanks for all of the hard work!

[LakeEffectKing]

Just now, NJwx85 said:

Is that max winds of 145 at LF? 

yes...should be mph, lol!

[yoda]

1 minute ago, NJwx85 said:

Is that max winds of 145 at LF? 

Um, yes

[hlcater]

2 minutes ago, LakeEffectKing said:

yes...should be mph, lol!

Based on pressure/wind relationship, I am assuming you have a very large hurricane at this point, in line with most guidance?

[NavarreDon]

Can't say that I differ too much from NHC...I think Irma will move a tad quicker initially, but, overall, the only subtle differences is wind speed at LF and a slightly western position at LF.

 

Thank you! That is not a good look for SE Florida! Just to give some of the posters an idea of Irma's size look at these pics.



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[harrisale]

8 minutes ago, LakeEffectKing said:

Can't say that I differ too much from NHC...I think Irma will move a tad quicker initially, but, overall, the only subtle differences is wind speed at LF and a slightly western position at LF.

 

Fully agree with your estimate of position of lowest pressure. I think we'll really see Irma go for the hail mary sub-900mb after the north turn begins, and she pulls just far enough away from Cuba to avoid any effects of land interaction and dry air ingestion. And the water between FL and Cuba is toasty enough to do it.

[NEG NAO]

0Z NAM for what its worth - out of its usable range - keeps Irma far enough off the FLA coast to spare it the worst

[the ghost of leroy]

1 minute ago, NavarreDon said:

Thank you! That is not a good look for SE Florida! Just to give some of the posters an idea of Irma's size look at these pics.



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Wish it was hitting west central tx

[Chinook]

In response to an earlier post, the hurricane has been heading at 294 degrees compass direction for the past few hours (according to my estimation by radar). NHC says it is moving 14 knots. It is 275 nautical miles to Grand Turk, at a compass heading of 298 degrees. So, if the hurricane moves at the same compass heading, it will get to Grand Turk in 19.6 hours, if the compass heading is exactly 298 degrees. There is a lot of time in there for the heading of the hurricane to change a bit, one way or the other. So it's not totally certain that it will track exactly to Grand Turk.

[MattPetrulli]

Wouldn't rule out a 160 MPH hurricane making landfall in South FL Sunday. Waters are just too warm to pass up.

[larrye]

6 minutes ago, Drz1111 said:

Come on.  Dry air?  There's a bare bit on the SJU sounding but nothing that explains any dry air ingestion into the core.

Am I the only one who thinks that it's looking a bit asymmetrical over the past few hours?

[LakeEffectKing]

1 minute ago, NWLinnCountyIA said:

Based on pressure/wind relationship, I am assuming you have a very large hurricane at this point, in line with most guidance?

Absolutely!  I think we have yet to see her "best", from a meteorological standpoint.

[jojo762]

6 minutes ago, Drz1111 said:

Come on.  Dry air?  There's a bare bit on the SJU sounding but nothing that explains any dry air ingestion into the core.

I'd call it more of a "less-moist" inflow into the core type scenario because of interaction with P.R. Likewise, some of the less-than earlier satellite presentation appears to be partially caused by some weird glitch tonight with GOES 16... Its color scheme on the east side of the cyclone is glitchy.

[NJwx85]

5 minutes ago, LakeEffectKing said:

yes...should be mph, lol!

What's your reasoning for that speed max given your forecasted pressures? They don't seem to correlate well.

[Hoosier]

As others have said, the NAM is fairly useless for tropical purposes, but I want to use it in this instance to point something out.  Look how far offshore it has the center and still manages to brush the coast with hurricane force winds.  

Anybody that gets any part of the core/eyewall of Irma is in serious danger, even if "only" the western side.

 

[MattPetrulli]

NHC keeps Irma at 185 MPH/ 916 MB at 11 PM.

[Hoosier]

4 minutes ago, NEG NAO said:

0Z NAM for what its worth - out of its usable range - keeps Irma far enough off the FLA coast to spare it the worst

It's trending west toward other prior models...

[NaoPos]

3 minutes ago, LakeEffectKing said:

Absolutely!  I think we have yet to see her "best", from a meteorological standpoint.

Scary to even fathom that. 

[NEG NAO]

3 minutes ago, MattPetrulli said:

Wouldn't rule out a 160 MPH hurricane making landfall in South FL Sunday. Waters are just too warm to pass up.

Also can't rule out what the 0Z NAM is showing - an off the coast solution - still within the current forecast "cone"

 

[Blue_Ridge_Escarpment]

1 minute ago, NEG NAO said:

Also can't rule out what the 0Z NAM is showing - an off the coast solution - still within the current forecast "cone"

 

That's well west of previous NAM runs. Look for it to correct even further 

[LakeEffectKing]

1 minute ago, NJwx85 said:

What's your reasoning for that speed max given your forecasted pressures? They don't seem to correlate well.

I think shear will start to impact it 6-8 hours before.  Plus, I do think it will have a bit larger eye.  I think when it is at 899mb a few hours before, it will probably have winds around 155-160.

[aperson]

Does NAM have any validity whatsoever at tracking the steering of a tropical system? When watching Harvey it seemed useful for synoptics and precipitation behavior, but it constantly missed the track of the system.