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Hurricane Irene Model and Forecast Discussion


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I've yet to see any good answer on any of the threads on this site that tells me WHY most, if not all, of the models have pressure so low at 40N latitude. They can't all have the same bias can they?? I understand that the upper levels are ideal and shear is low, yada, yada, yada. But, these pressure forecasts are unreal. What are we missing here, or is the atmosphere in such a rare setup for a once a generation storm at these latitudes?

I don't know that anyone has a good answer here. I've not seen anything in the literature addressing this issue, but I've noticed it in the WPAC too. It's only started since the resolution of the Euro and GFS were increased last summer, so I'd guess it is somehow tied to that. Maybe an unrealistic representation of the inertial stability of systems at high latitudes?

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It can't get much worse than that. Or that bad either. It picks up some forward speed after the Delmarva.

slp17.png

If someone could answer this, b/c that would be UNREAL if it were to verify: Is the GFDL wind forecast on this map underdone? I would have thought the winds would be much stronger than just 20-35kts over NJ w/ this track? Thanks in advance

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I am very pleased to hear about the 6 hour balloon launches in Montana... this should help sample the kicker shortwave that is still over the pacific better when it comes in.

Good because with we had all the sondes yesterday to determine if the ridge off the southeast coast was 589 or 590DM. Meanwhile a northern stream shortwave over the lakes 00z run over EMontana completely disappeared on the 18z!!! However that system is still over the Pacific and will be for days.

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I don't know that anyone has a good answer here. I've not seen anything in the literature addressing this issue, but I've noticed it in the WPAC too. It's only started since the resolution of the Euro and GFS were increased last summer, so I'd guess it is somehow tied to that. Maybe an unrealistic representation of the inertial stability of systems at high latitudes?

Thanks. If you'll recall, this atypical pressure trend started before Irene even formed. Everyone was marveling about the rapid intensification even after crossing Hispaniola (models showed a hit at the time). Maybe you are correct that there is a systemic issue at play here. I would expect a hurricane taking the Euro 12z track to be 975-980 at 40N.

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If someone could answer this, b/c that would be UNREAL if it were to verify: Is the GFDL wind forecast on this map underdone? I would have thought the winds would be much stronger than just 20-35kts over NJ w/ this track? Thanks in advance

The pressure gradient in the inner core is weakening as the storm starts extratropical transition, despite the MSLP still being quite low. Notice how all the isobars are spaced out, instead of tightly packed like we normally see in the Tropics.

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If someone could answer this, b/c that would be UNREAL if it were to verify: Is the GFDL wind forecast on this map underdone? I would have thought the winds would be much stronger than just 20-35kts over NJ w/ this track? Thanks in advance

Here is the GFDL wind swath.

irene09l2011082418nest3.png

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If someone could answer this, b/c that would be UNREAL if it were to verify: Is the GFDL wind forecast on this map underdone? I would have thought the winds would be much stronger than just 20-35kts over NJ w/ this track? Thanks in advance

No the pressure is underdone. Few SUB 930MB storms have ever hit the US, let alone NJ with cool water wind shear, and dry air I doubt you see 955MB. And I doubt it tracks that far west.

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Right, the EnKF based forecasts that they are running are using the exact same model as the current operational GFS (though, it's being run on a different machine architecture, used a different compiler, etc.). This isn't quite the same configuration as we plan to implement in spring, as this is a pure EnKF that is being used for the initialization (the model is started from the mean of the ensemble of analyses).

For our spring implementation, the hybrid EnKF-3DVAR will be somewhere in between, where we still run the varational algorithm, but will be incorporating something like 75% of the information from an ensemble-based increment.

From our experience, the EnKF and hybrid-based GFS forecasts have been superior to 3DVAR based runs (well beyond any statistical significance test).

If you don't mind, when you get chance can you explain exactly how this is done? I'm sure most folks on here understand exactly what you mean, but I just don't understand how this is done. Thx.

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The interesting thing about that pic is that the GFDL doesn't bend NE after a NYC hit. It goes up the Hudson. Most guidance has Irene veering NE near NYC. Any synoptic basis in that representation?

A stronger negative tilt to the shortwave moving across the Great Lakes... probably incorrect since the GFDL doesn't handle synoptic features particularly well

kCnvZ.png

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A stronger negative tilt to the shortwave moving across the Great Lakes... probably incorrect since the GFDL doesn't handle synoptic features particularly well

kCnvZ.png

If the GFDL doesnt handle synoptic features well, why do we believe what the gfdl is showing/?I,m not trying to be insolent, but by your statement I,m really wondering why the model is relied upon on this storm?? Thanks

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Hmm wow, this is amazing especially considering most offices are chronically short on sondes. In fact we just got an email today talking about conserving ALL upper air data as their is hardly any left. Interesting. Here at LBF we are low on sondes like most offices. I am the upper air focal point here responsible for ordering/inventory on supplies. I guess I will be hearing about this tomorrow.arrowheadsmiley.png

I just got called in to do the 06Z flight. Kinda exciting. laugh.gif

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If the GFDL doesnt handle synoptic features well, why do we believe what the gfdl is showing/?I,m not trying to be insolent, but by your statement I,m really wondering why the model is relied upon on this storm?? Thanks

I don't believe what the GFDL is showing. I rarely factor it into my forecast.

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I don't believe what the GFDL is showing. I rarely factor it into my forecast.

final question, is the gfdl showing a big hit with Irene, especially in the mid atlantic?? The last time I saw the 4 models they were showing a coastal runner. Is the gfdl now showing what the ec is indicating. Is what the ec is showing believable. Thanks in advance.

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final question, is the gfdl showing a big hit with Irene, especially in the mid atlantic?? The last time I saw the 4 models they were showing a coastal runner. Is the gfdl now showing what the ec is indicating. Is what the ec is showing believable. Thanks in advance.

I haven't inspected the GFDL run that closely (see previous post), but yes, the 12z Euro is believable, though an extreme scenario.

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A stronger negative tilt to the shortwave moving across the Great Lakes... probably incorrect since the GFDL doesn't handle synoptic features particularly well

kCnvZ.png

Didn't the Euro come in with a more negative tilt than previous runs??? I didn't check...but to just add another piece of guidance (albeit of much lessr value)

18z DGEX:

f114.gif

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Didn't the Euro come in with a more negative tilt than previous runs???

Yeah, but I give it credence when the Euro comes in with it. I mean, I was expecting the s/w to trend stronger/more tilted, but I couldn't really care less what the depiction of it is in the GFDL.

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Yeah, but I give it credence when the Euro comes in with it. I mean, I was expecting the s/w to trend stronger/more tilted, but I couldn't really care less what the depiction of it is in the GFDL.

Fair enough. When do the 18z GFS-KF runs come out?? I've checked the site a bit ago and 12z was still the last run...

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Didn't the Euro come in with a more negative tilt than previous runs??? I didn't check...but to just add another piece of guidance (albeit of much lessr value)

18z DGEX:

f114.gif

That isn't a negative tilt wave per se, but actually the hurricane being "captured" by the westerly flow and undergoing baroclinic transition. It is deceiving but isn't the same as a negative tilt baroclinic wave in terms of the baroclinic westerlies.

Edit: I see it is you LE, but I don't think this can be compared with a negative tilt wave in the "normal" sense.

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