Major Hurricane Irma

[e46and2]

  On 9/3/2017 at 10:36 PM, TPAwx said:

The pressure outputs from this GFS run are inconceivable.

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with recon finding impressively low pressure, but less impressive winds, i wonder if the gfs could be correct?  i know winds take some time to react to pressure falls, but the gfs has consistently advertised these historic low pressures, while the wind speeds by the GFS, while certainly intense, do not line up with the projected pressure.  Is it possible to have a storm of such depth but have ""only"" cat 3-4 wind speeds?

[LakeEffectKing]

  On 9/3/2017 at 10:36 PM, TPAwx said:

The pressure outputs from this GFS run are inconceivable.

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No sh!t!  PW has 879 at 198....TT has it at 880....

And of course we know the issues with the GFS upgrade....but still, the consistency with all the models and their robust low pressure outputs are truly amazing...

[bdgwx]

  On 9/3/2017 at 10:36 PM, TPAwx said:

The pressure outputs from this GFS run are inconceivable.

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Which is exactly why I don't think they're realistic. We've already seen an extreme intensity bias since the update earlier this year with Typhoon Noru.

[downeastnc]

  On 9/3/2017 at 10:39 PM, LakeEffectKing said:

No sh!t!  PW has 879 at 198....TT has it at 880....

And of course we know the issues with the GFS upgrade....but still, the consistency with all the models and their robust low pressure outputs are truly amazing...

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Yeah even if they are overdone by 50mb you still looking at a 930ish cane thats 400 miles across.....

[bdgwx]

I will say that the GFS isn't the only model showing a very intense cyclone in the Bahamas. So it's not going to be unexpected if we see a low 900's cyclone once it gets there. Afterall, the Euro was showing it deepening into the 910's.

[Radtechwxman]

A large hurricane can have real low pressures and not winds you would expect with those pressures. The larger the hurricane the harder it is for it to really tighten up that inner core. Just like the ice skater effect. You put your arms out more and don't spin as fast. I remember Ike had really low pressure but with its extreme size it didn't have as intense winds as it could

[SnowGoose69]

The bad news is even if this misses the US its now evident someone is getting hit hard

[Buddy1987]

  On 9/3/2017 at 10:39 PM, LakeEffectKing said:

No sh!t!  PW has 879 at 198....TT has it at 880....

And of course we know the issues with the GFS upgrade....but still, the consistency with all the models and their robust low pressure outputs are truly amazing...

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What kind of sustained winds do you think we could see while it's potentially down at 900 or below in your opinion? 

[tim123]

  On 9/3/2017 at 10:38 PM, RU4Real said:

Once she gets into central Virginia it looks like the pressure kicks up pretty quickly (showing 979 at 222 hours) and the 10m winds are basically a strong breeze. Still some tropical storm force indicated over the Chesapeake, but the winds inland are all under 35 kts. This run has a really weird look to it.

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Not buying this track one bit. May hit where it shows but what it does after is nuts

[Hoosier]

  On 9/3/2017 at 10:38 PM, RU4Real said:

Once she gets into central Virginia it looks like the pressure kicks up pretty quickly (showing 979 at 222 hours) and the 10m winds are basically a strong breeze. Still some tropical storm force indicated over the Chesapeake, but the winds inland are all under 35 kts. This run has a really weird look to it.

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The inland decay rate will be interesting to watch.  I know there was some work done like 20 some years ago to model inland winds for a given storm intensity and speed (I think those maps can be found on NHC site) but I'm not sure if anything newer has come out.  A bigger storm tends to take longer to weaken than a smaller one but there's multiple factors that can modulate, including interaction with other mid latitude systems/baroclinic enhancement.  Fortunately we also have some historic examples to look at if necessary (Hugo, Fran, etc.)

[TPAwx]

  On 9/3/2017 at 10:45 PM, SnowGoose69 said:

The bad news is even if this misses the US its now evident someone is getting hit hard

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Various island communities are going to be facing potential catastrophe based on where they are in the track.  Even with an OTS the FLA and SE coast is going to get pounded for days by swells.  Can't even begin to think what this is going to mean if it makes landfall is the US anywhere near the projected strength.  The surge would be beyond belief.

[LakeEffectKing]

  On 9/3/2017 at 10:46 PM, Buddy1987 said:

What kind of sustained winds do you think we could see while it's potentially down at 900 or below in your opinion? 

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As stated earlier by others, a large established storm with a large wind field will most likely have winds relatively "lighter" than you'd expect from a storm with such low pressures (low 900's) especially at the higher latitudes...this will inevitably have a rather large eye, (not a pinhole eye which can really tighten the windspeeds... ie increase max winds).

I'd wager that even if Irma gets to near 900mb north of the Bahamas...she may "only" have winds in the upper Cat 4 range...(140's)

[Windspeed]

  On 9/3/2017 at 10:44 PM, StormChaser4Life said:

A large hurricane can have real low pressures and not winds you would expect with those pressures. The larger the hurricane the harder it is for it to really tighten up that inner core. Just like the ice skater effect. You put your arms out more and don't spin as fast. I remember Ike had really low pressure but with its extreme size it didn't have as intense winds as it could

They're definitely not all the same. Hugo was a large hurricane as was Floyd. It really depends on the organization of the eyewall and that surrounding pressure gradient. I am still hesitant about sub 910 pressures being achieved because it is so difficult. However, if Irma moves through the Bahamas sub 920s with high enough surface background pressures against the ridge, the gradient could remain tight and she could definitely be a high end 4 or even a 5.

 

[bdgwx]

  On 9/3/2017 at 10:46 PM, Buddy1987 said:

What kind of sustained winds do you think we could see while it's potentially down at 900 or below in your opinion? 

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They might not be as high as you'd think if it's a large hurricane. However, large low pressure cyclones typically have very high IKE (integrated kinetic energy) values. If Irma really does get favorably positioned for right entrance region jet dynamics I could see Irma expanding some while holding a low pressure. If so it might rank among cyclones with extreme IKE values (Isabel, Sandy, Katrina, etc.). That's still a big IF though.

[RU4Real]

  On 9/3/2017 at 10:49 PM, Hoosier said:

The inland decay rate will be interesting to watch.  I know there was some work done like 20 some years ago to model inland winds for a given storm intensity and speed (I think those maps can be found on NHC site) but I'm not sure if anything newer has come out.  A bigger storm tends to take longer to weaken than a smaller one but there's multiple factors that can modulate, including interaction with other mid latitude systems/baroclinic enhancement.  Fortunately we also have some historic examples to look at if necessary (Hugo, Fran, etc.)

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When I saw the decay on this model run it made sense, intuitively. Irma would start to have her circulation disrupted by the Appalachians. What I don't know is whether the models account for terrain variables.

[Tatamy]

  On 9/3/2017 at 10:39 PM, LakeEffectKing said:

No sh!t!  PW has 879 at 198....TT has it at 880....

And of course we know the issues with the GFS upgrade....but still, the consistency with all the models and their robust low pressure outputs are truly amazing...

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12z Euro has it at 923 MB while 200 miles east of Daytona at 192 hours

[bdgwx]

Just think about how ridiculous and unrealistic the GFS intensity forecast is. It is a sub-900mb cyclone for 60+ hours.

[downeastnc]

  On 9/3/2017 at 10:52 PM, Windspeed said:

They're definitely not all the same. Hugo was a large hurricane as was Floyd. It really depends on the organization of the eyewall and that surrounding pressure gradient. I am still hesitant about sub 910 pressures being achieved because it is so difficult. However, if Irma moves through the Bahamas sub 920s with high enough surface background pressures against the ridge, the gradient could remain tight and she could definitely be a high end 4 or even a 5.

 

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Another issue is going to be a massive system like that with a really low pressures and huge wind field is gonna push one hell of a surge in with it...probably record high where ever it makes landfall assuming of course it does actually come ashore. 

[wxmx]

  On 9/3/2017 at 10:51 PM, LakeEffectKing said:

As stated earlier by others, a large established storm with a large wind field will most likely have winds relatively "lighter" than you'd expect from a storm with such low pressures (low 900's) especially at the higher latitudes...this will inevitably have a rather large eye, (not a pinhole eye which can really tighten the windspeeds... ie increase max winds).

I'd wager that even if Irma gets to near 900mb north of the Bahamas...she may "only" have winds in the upper Cat 4 range...(140's)

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All previous Atlantic hurricanes with pressures below 910mb have been cat 5. 

[Hoosier]

fwiw, operational 18z GFS is east of almost all ensemble members.

[Tatamy]

Latest Vortex Data Message from recon

VORTEX DATA MESSAGE  AL112017
A. 03/22:45:27Z
B. 17 deg 21 min N
  050 deg 06 min W
C. 700 mb 2770 m
D. 82 kt
E. 315 deg 12 nm
F. 048 deg 99 kt
G. 318 deg 16 nm
H. 960 mb
I. 11 C / 3052 m
J. 17 C / 3049 m
K. 12 C / NA
L. OPEN W
M. C20
N. 1234 / 7
O. 0.02 / 2 nm
P. NOAA2 0111A IRMA OB 14
MAX FL WIND 99 KT 318 / 16 NM 22:41:38Z
MAX FL TEMP 18 C 317 / 6 NM FROM FL CNTR
CNTR DROPSONDE SFC WIND 180 / 16 KTS

 

[NJwx85]

  On 9/3/2017 at 10:29 PM, andyhb said:

That's not eastern NC if we're talking potential coastal landfall locations.

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Yes you're correct, ended up a bit West of where I projected.

[packfan98]

  On 9/3/2017 at 11:12 PM, Hoosier said:

fwiw, operational 18z GFS is east of almost all ensemble members.

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Yes.  Here is the mean.  The pressure is much lower than previous runs indicating to me a tighter cluster of ensemble members.  The mean basically rides the FL coastline comes ashore in GA and up through the mountains of NC.

[yoda]

18z HMON is nuts.... 882mb in Bahamas at 108

[Ser Pounce]

  On 9/3/2017 at 9:01 PM, UpstateSCBud said:

Hurricane magnet? You realize high odds means something is unlikley to happen right?

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Yeah you're correct... had to google it. I need to take my statistician hat off and put on a horse racing one.

[NJwx85]

18z HMON has Irma down to 911mb by hr 87.

[LakeEffectKing]

  On 9/3/2017 at 11:05 PM, wxmx said:

All previous Atlantic hurricanes with pressures below 910mb have been cat 5. 

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  On 9/3/2017 at 11:05 PM, wxmx said:

All previous Atlantic hurricanes with pressures below 910mb have been cat 5. 

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Nice stat.  I think Irma will have some special characteristics wrt pressure/wind relationship.  (If current modeling of "long duration" low pressures through the Bahamas occur)

All models show Irma gaining significant size, thus creating a larger, lower pressure environment, wrt the core....thus with pressures substantially lower than that a normal hurricane (say 100-200 miles from the center) the pressure change over distance from there to the core may not be quite as tight as you'd get with a cane in a higher pressure environment, or a cane that has explosively developed (ie Wilma), thus the wind speeds may be a tad lower than the traditional/normal pressure/wind relationship.

 

Edit:  And I'm talking about Irma when she is north of the Bahamas.....as she approaches them and enters them, I think CAT 5 winds are certainly possible (again, assuming the model outputs of low 900's verify)

[wxmx]

HMON and HWRF both make Irma a cat 5

[Voyager]

  On 9/3/2017 at 10:38 PM, RU4Real said:

Once she gets into central Virginia it looks like the pressure kicks up pretty quickly (showing 979 at 222 hours) and the 10m winds are basically a strong breeze. Still some tropical storm force indicated over the Chesapeake, but the winds inland are all under 35 kts. This run has a really weird look to it.

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I only looked at it in the car in my phone, but it looks like stalls in VA and dissipates. PA's total qpf is only about 1-3 inches

[yoda]