ATL : TROPICAL STORM GRACE

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CrazyC83
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#361 Postby CrazyC83 » Wed Oct 07, 2009 11:24 am

The basis for the 981mb pressure estimate is the general trend in pressure data, since there was a ship report of 986mb at about 6/0000 while the winds were definitely no more than 50 kt. Also the first hurricane period was when the eye was best defined and the pressure was around 984mb at the time. I went back through this thread to look at satellite images and other data while it was not being actively tracked.

I kept it as a tropical storm all the way to 7/0000 (while over central Great Britain) when it was clearly no had any real tropical characteristics, and the front clearly took over shortly after that. That meant I believe it was still a tropical storm when it hit Wales. The 35 kt winds are based on near-shore ship data, and the 995mb pressure is based on surface data (the lowest I could find was 997mb, but with breezes at the time).
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#362 Postby brunota2003 » Wed Oct 07, 2009 6:51 pm

You know, looking back on Grace and everyone asking about the eye...I think Grace was more like a polar low, they tend to form eyes and are small...just like Grace was. Could there be a connection between the high altitudes and systems having a clear eye?
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#363 Postby ozonepete » Wed Oct 07, 2009 7:26 pm

brunota2003 wrote:You know, looking back on Grace and everyone asking about the eye...I think Grace was more like a polar low, they tend to form eyes and are small...just like Grace was. Could there be a connection between the high altitudes and systems having a clear eye?


Wow, that's a really great observation and question. I was taught "arctic hurricane" is better than polar low because a lot of people confuse the latter term with the larger common polar low pressure areas. They are still not that well understood and neither are systems such as Grace. Artic hurricanes have a specific configuration and are closer to the mid-latitude low pressure model called the 'Shapiro-Keyser' model than the standard Norwegian model.

Anyway, there have to be some similar aerodynamics going on in both, since both are the result of very cold upper air over relatively warm water. All I can say is that I'll keep looking for research on both of these pretty rare events and I'll post them here when I find them. I was also thinking of doing an article on arctic hurricanes for my Penn State website, so if I do I promise to let you know.

BTW, that's why this thread was so much fun - there was a lot of arguing about exactly what Grace was and whether a system that small could be "legitimate" TS or hurricane.
Last edited by ozonepete on Wed Oct 07, 2009 7:50 pm, edited 1 time in total.
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Re: Re:

#364 Postby brunota2003 » Wed Oct 07, 2009 7:33 pm

ozonepete wrote:
brunota2003 wrote:You know, looking back on Grace and everyone asking about the eye...I think Grace was more like a polar low, they tend to form eyes and are small...just like Grace was. Could there be a connection between the high altitudes and systems having a clear eye?


Wow, that's a really great observation and question. I was taught "arctic hurricane" is better than polar low because a lot of people confuse the latter term with the larger common polar low pressure areas. Anyway, they are still not that well understood and neither are systems such as Grace. Anyway, there have to be some similar aerodynamics going on in both, since both are the result of very cold upper air over relatively warm water. All I can say is that I'll keep looking for research on both of these pretty rare events and I'll post them here when I find them. I was also thinking of doing an article on arctic hurricanes for my Penn State website, so if I do I promise to let you know.

BTW, that's why this thread was so much fun - there was a lot of arguing about exactly what Grace was and whether a system that small could be "legitimate" TS or hurricane.

This is the one that comes to mind when thinking of Grace (note, this is a picture of a POLAR LOW, not Grace!)

Image


http://nsidc.org/arcticmet/patterns/polar_low.html

Seeing how aircraft data has shown that polar lows may possibly have warm cores, could Grace have been one? It would of been situated right where the coldest air from the front that was sweeping down was, right over that "warm" ocean water, and look at how quickly it vanished after it made landfall
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Re: Re:

#365 Postby Derek Ortt » Wed Oct 07, 2009 7:51 pm

ozonepete wrote:

So you'll have to show me a satellite image of Vince with a RELATIVELY CLEAR eye at least a few hours before 2005-10-09 18Z and one of Michael from at least a few hours before 18Z on 17 October 2005. You can't. They didn't have one. TS's DEVELOPING into HURRICANES don't get an eye visible from satellite until they have become hurricanes. Never seen one.

Interestingly enough, especially because they were similar in time of year and origin to Grace, this strengthens my speculation that Grace very well may have been a hurricane for a time.


Time for some humility, Ozone

http://www.nrlmry.navy.mil/tcdat/tc05/A ... N-200W.jpg

Vince... below hurricane intensity. Just as it was becoming a TS from STS

4 hours later... still not a hurricane

http://www.nrlmry.navy.mil/tcdat/tc05/A ... N-200W.jpg

as I said, these types of tropical storms have eyes. It is VERY common

Also, there is NO evidence that Grace reached hurricane intensity. NONE. Dvorak estimates were only 3.5 (yes, the satellite analysts saw the eye). You need 4.0 for a hurricane

Crazy, your BTs are usually good, but you have a 5-10KT systematic high bias usually
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Re: Re:

#366 Postby ozonepete » Wed Oct 07, 2009 7:55 pm

brunota2003 wrote:This is the one that comes to mind when thinking of Grace (note, this is a picture of a POLAR LOW, not Grace!)

Image


http://nsidc.org/arcticmet/patterns/polar_low.html

Seeing how aircraft data has shown that polar lows may possibly have warm cores, could Grace have been one? It would of been situated right where the coldest air from the front that was sweeping down was, right over that "warm" ocean water, and look at how quickly it vanished after it made landfall


No, Grace couldn't have been. Its origins were from near the Azores, whereas polar lows/arctic hurricanes develop well up in the upper latitudes and never start as warm core or hybrid storms.
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Re: Re:

#367 Postby ozonepete » Wed Oct 07, 2009 9:30 pm

Derek Ortt wrote:
ozonepete wrote:

So you'll have to show me a satellite image of Vince with a RELATIVELY CLEAR eye at least a few hours before 2005-10-09 18Z and one of Michael from at least a few hours before 18Z on 17 October 2005. You can't. They didn't have one. TS's DEVELOPING into HURRICANES don't get an eye visible from satellite until they have become hurricanes. Never seen one.

Interestingly enough, especially because they were similar in time of year and origin to Grace, this strengthens my speculation that Grace very well may have been a hurricane for a time.


Time for some humility, Ozone

http://www.nrlmry.navy.mil/tcdat/tc05/A ... N-200W.jpg

Vince... below hurricane intensity. Just as it was becoming a TS from STS

4 hours later... still not a hurricane

http://www.nrlmry.navy.mil/tcdat/tc05/A ... N-200W.jpg

as I said, these types of tropical storms have eyes. It is VERY common

Also, there is NO evidence that Grace reached hurricane intensity. NONE. Dvorak estimates were only 3.5 (yes, the satellite analysts saw the eye). You need 4.0 for a hurricane

Crazy, your BTs are usually good, but you have a 5-10KT systematic high bias usually


“Time for some humility”? LOL. I’m always humbled in your presence. You are the tropical weather maven, and as you know, since I’ve arrived here, I’ve complimented your analyses a number of times. When I banter with you on this, my main objective is that we all learn something, especially me (just kidding.) So here goes. Bear in mind I’m just trying to be scientifically rigorous, that’s all. And because you make me go back to the literature and do the wearying research, I’m very appreciative. This is where you truly learn.

With that image of Vince, you definitely proved me wrong on my assertion that the relatively clear eye can’t exist while it’s a TS developing into a hurricane. I promise I won’t say that again. :) But what you also did say was “as I said, these types of tropical storms have eyes.” I totally agree because “these types” are a very special case of a hybrid morphing into a warm-core system, not the much more common general case we all are used to seeing.

I don’t think you can say “It is VERY common for these types of storms to have eyes”. This type of storm is so rare and thus not very well observed yet that we can’t make such a conclusion from the handful of cases we’ve had. Since satellites, how many of these have we observed as a percentage of all classified TCs?

“Also, there is NO evidence that Grace reached hurricane intensity. NONE. Dvorak estimates were only 3.5 (yes, the satellite analysts saw the eye). You need 4.0 for a hurricane”.
Your two examples were hurricanes, and their structure and Grace’s are very similar. That’s evidence right there. Dvorak estimates are by the nature of their name, estimates. After all, what are Dvorak estimates but a number gotten from a mathematical algorithm that primarily uses TC appearances to calculate intensity? And we all know that the NHC uses them carefully in combination with a lot of other factors, and we won’t know all of the other factors on GRACE until all of the data are in. They certainly won’t base it purely on the fact that it missed the 4.0 threshold by 0.5. And BTW, I doubt it will get the hurricane classification, and I have no idea if it really was, since nobody was there measuring GRACE during the few hours when it might have been. We will never be 100% sure, will we?

So I agree that we can see a non-obscured eye in a TS developing into a hurricane in the very special case of an unusually small mesoscale hybrid TC morphing into a warm-core system. But for the much more common majority of averaged sized TC’s, I still gotta say, you’d never see it.

I truly enjoy the discussions.
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#368 Postby Derek Ortt » Wed Oct 07, 2009 10:59 pm

it is very rare to see an eye in conventional satellite imagery for a classic tropical cyclone. It is the TT cases where the ~75KT before an eye is visible on satellite rule does not apply
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Re:

#369 Postby ozonepete » Thu Oct 08, 2009 8:09 am

Derek Ortt wrote:it is very rare to see an eye in conventional satellite imagery for a classic tropical cyclone. It is the TT cases where the ~75KT before an eye is visible on satellite rule does not apply


I'm going to try and read up on Tropical Transition. I never studied it enough so I guess this would be a good time. Thanks for the discussion.
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#370 Postby CrazyC83 » Thu Oct 08, 2009 8:55 am

BTW, if my BT estimate is correct (it won't be I am sure), the ACE of Grace leaps up to 6.19.
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Re: ATL : TROPICAL STORM GRACE

#371 Postby Cryomaniac » Thu Oct 08, 2009 1:34 pm

CrazyC83 wrote:Personal Forecast Disclaimer:
The posts in this forum are NOT official forecast and should not be used as such. They are just the opinion of the poster and may or may not be backed by sound meteorological data. They are NOT endorsed by any professional institution or storm2k.org. For official information, please refer to the NHC and NWS products.


If I wrote the best track, here is what I think it should be:

30/1200 - 38.8N / 34.6W - 40 kt - 996mb - Extratropical
30/1800 - 37.4N / 33.1W - 40 kt - 997mb
1/0000 - 36.7N / 31.6W - 40 kt - 996mb - Tropical Storm
1/0600 - 36.9N / 29.8W - 45 kt - 993mb
1/1200 - 37.7N / 29.0W - 60 kt - 986mb
1/1800 - 38.7N / 28.5W - 65 kt - 984mb - Hurricane
2/0000 - 39.5N / 28.8W - 60 kt - 986mb - Tropical Storm
2/0600 - 40.0N / 29.5W - 50 kt - 989mb
2/1200 - 40.2N / 30.0W - 40 kt - 992mb
2/1800 - 41.0N / 30.4W - 40 kt - 993mb
3/0000 - 41.4N / 31.0W - 40 kt - 994mb
3/0600 - 41.4N / 31.8W - 40 kt - 994mb
3/1200 - 40.8N / 32.5W - 40 kt - 993mb
3/1800 - 39.9N / 32.3W - 45 kt - 991mb
4/0000 - 39.1N / 31.3W - 45 kt - 990mb
4/0600 - 38.5N / 29.5W - 50 kt - 988mb
4/1200 - 38.3N / 26.8W - 55 kt - 986mb
4/1800 - 38.8N / 23.9W - 60 kt - 984mb
5/0000 - 40.2N / 21.3W - 60 kt - 984mb
5/0600 - 42.0N / 19.0W - 65 kt - 982mb - Hurricane
5/1200 - 44.3N / 17.2W - 65 kt - 981mb - Peak Intensity
5/1800 - 46.7N / 15.6W - 55 kt - 984mb - Tropical Storm
6/0000 - 48.7N / 14.4W - 50 kt - 986mb
6/0600 - 50.1N / 12.6W - 45 kt - 988mb
6/1200 - 50.7N / 10.8W - 45 kt - 990mb
6/1800 - 51.5N / 7.0W - 40 kt - 994mb
6/2030 - 51.7N / 5.2W - 35 kt - 995mb - Landfall near Marloes, Wales
7/0000 - 52.2N / 2.4W - 30 kt - 998mb - Extratropical
7/0600 - Absorbed into frontal zone


I have doubts the NHC will say it was tropical at landfall. They may well say it became extratropical later than was done operationally though.
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Re: Re:

#372 Postby ozonepete » Thu Oct 08, 2009 7:08 pm

ozonepete wrote:
Derek Ortt wrote:it is very rare to see an eye in conventional satellite imagery for a classic tropical cyclone. It is the TT cases where the ~75KT before an eye is visible on satellite rule does not apply


I'm going to try and read up on Tropical Transition. I never studied it enough so I guess this would be a good time. Thanks for the discussion.


Derek, I've been doing some research into TT and what happened with Grace. I just wanted to know what you thought as far as it's transition origin. I would think Grace's development was the SE case of TT, right? After all, it developed from low pressure associated with an occluded front and a frontal area. The southwesterly flow that developed over it and helped vent it for good convective development would also indicate this. Am I ok here? I'd like to research some of these cases just to learn a little more about how to recognize them when they're developing. Thanks.
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#373 Postby Derek Ortt » Thu Oct 08, 2009 7:49 pm

Grace's development SE of TT?

How would the development be SE of the tropical transition point? Not sure what you're asking
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Re:

#374 Postby ozonepete » Thu Oct 08, 2009 8:22 pm

Derek Ortt wrote:Grace's development SE of TT?

How would the development be SE of the tropical transition point? Not sure what you're asking


Oh, sorry. I wasn't very clear. I was referring to research by Davis and Bosart, et al, where they classify Tropical Transition events as either SE (strong extratropical) or WE (weak extratropical). The SE events occur when a non-tropical low involved with a mid-latitude front slowly becomes tropical due to diabatic redistribution of potential vorticity into the area of the low; this helps to shut down the shear in a small area over the system, allowing a small center of convection to get going. The WE events involve weak baroclinic waves that are not former mid-latitude lows. They don't have enough kinetic energy to cause local vorticity, but they still somehow have enough of an energy source to produce thunderstorm clusters that eventually produce cyclonic vorticity centers that sometimes coalesce into a single radius of maximum winds, i.e. the center/eye.

So I was just asking if Grace wasn't the former case, i.e. it developed from an SE event.
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Re: ATL : TROPICAL STORM GRACE

#375 Postby ozonepete » Fri Oct 09, 2009 11:49 am

Here's a link to one of the papers on TT that references SE and WE tropical transitions.

http://ams.allenpress.com/archive/1520-0477/85/11/pdf/i1520-0477-85-11-1657.pdf

I noticed that in this newer edition the authors refer to TT events as SEC and WEC (Strong/Weak Extratropical Cyclone) rather than SE and WE.

The NHC's initial discussion on Grace sure sounds a lot like the SE or SEC case.
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