ATL GUSTAV: Tropical Depression - Discussion

[Hyperstorm]

So far, wind data only supports a Category 3. Yes, the pressure is nowhere in the 960s as I considered a possibility, but it's probably still rising. You go by the winds and not pressure when classifying a system. If the flight-level winds are no stronger than a Category 3, it will be downgraded to a 3.

I'm not downplaying this system at all. Do not misunderstand my position. I am going by what I'm seeing on satellite and my experience of watching these systems for many years.

[soonertwister]

Dvorak IR intensity is approaching the top of the chart. This is not a weakening storm, regardless of irresponsible posts to the contrary.

http://www.ssd.noaa.gov/goes/flt/t1/bd-l.jpg

I've always wondered how to read the Dvorak T-number off that satellite imaging. If it's not a book to explain, could you please enlighten me? I bet others would be interested also!

I can't chase down a non-technical explanation, but all you really need to know is to look at the intensity legend bar below the image. All that white you see surrounding the eye is extremely intense, note the white in the legend near the right. And the grey and darker gray imbedded in that is of even greater intensity, extremely severe.

Compare the Dvorak IR with the latest color IR floater image:
http://www.ssd.noaa.gov/goes/flt/t1/avn-l.jpg

The blacker color imbedded in the red around the center is extremely cold cloudtops, corresponding to toweringly high storms. The density of moisture in those areas probably well exceeds a total of 50 inches of rain potential per square meter from the cloudtops to sea level.

[tallywx]

Also looking at flight data vs. the last satellite pre-eclipse, it wobbled leftward...moved WNW to almost due west...

stair stepping possibly...

No WNW wobble. According to radar overlaid on top of 11 p.m. track, she's right down the middle of the center line as perfect as can be: http://my.sfwmd.gov/sfwmd/common/images ... 2_anim.gif

[Hyperstorm]

Dvorak IR intensity is approaching the top of the chart. This is not a weakening storm, regardless of irresponsible posts to the contrary.

http://www.ssd.noaa.gov/goes/flt/t1/bd-l.jpg

I've always wondered how to read the Dvorak T-number off that satellite imaging. If it's not a book to explain, could you please enlighten me? I bet others would be interested also!

I can't chase down a non-technical explanation, but all you really need to know is to look at the intensity legend bar below the image. All that white you see surrounding the eye is extremely intense, note the white in the legend near the right. And the grey and darker gray imbedded in that is of even greater intensity, extremely severe.

Compare the Dvorak IR with the latest color IR floater image:
http://www.ssd.noaa.gov/goes/flt/t1/avn-l.jpg

The blacker color imbedded in the red around the center is extremely cold cloudtops, corresponding to toweringly high storms. The density of moisture in those areas probably well exceeds a total of 50 inches of rain potential per square meter from the cloudtops to sea level.

The black colors in the IR which are cloud tops colder than -80*C on the SW side mean the system is definitely trying to push the dry air out of it. If you look at long range radar, you'll see there's very little precipitation in the southern quadrant, which indicates the dry air. This is a very typical situation (explosive bursts with no/little precipitation) when you have dry air entraining into a system. As long as the system continues to produce those extreme bursts on the southern quadrant, it may be able to mix the dry air out of it, but the southerly shear from the upper trough to its west may not allow it to fully do so.

[soonertwister]

952 mb not 960's

952 is lower tha when Gustav left Cuba.

[cheezyWXguy]

952 mb not 960's

952 is lower tha when Gustav left Cuba.

No it was at 948

[RL3AO]

VDM = 960mb. We have a starting point. Lets see if its stronger next time through the center.

[BlackNGoldRules]

Up to 958MB now, 135mph

[HurricaneRobert]

no way... and lili, went over the same area that isadore went over just a week or so earlier.. the water was churned up and cooler along the path... lets put all the peices together before we get carried away... no way the pressure is up that high... the reason the filled was due to land interaction... looking at the convection, it is already coming back..



Jesse V. Bass III
http://www.vastormphoto.com
Hurricane Intercept Research Team

I don't know if Isidore had much to do with Lili's weakening. It would if those were over deep water like the Atlantic, but really shallow water should readjust more quickly.

[RL3AO]

We can but an end to this dry air debate now. Recon shows no dry air in the SW side. There were no drops in dewpoints.

[soonertwister]

952 mb not 960's

952 is lower tha when Gustav left Cuba.

No it was at 948

It topped out at 958.

2 am advisory has winds at 135 mph, still cat-4.

[Thunder44]

Up to 958MB now

That's the pressure they have in the advisory. So I wonder if the drosponde did miss center of the eye after all.

[ConvergenceZone]

Well, it only dropped 5 mph on the last advisory, and I think that's because it was lower, but it has sense begun to slowly strengthen...

now at 135 mph.....

Latest graphic still shows it making landfall as a Cat4

http://www.wunderground.com/tropical/tr ... ml#a_topad

[soonertwister]

Well, it only dropped 5 mph on the last advisory, and I think that's because it was lower, but it has sense begun to slowly strengthen...

now at 135 mph.....

Latest graphic still shows it making landfall as a Cat4

http://www.wunderground.com/tropical/tr ... ml#a_topad

The forecast intensities are only changed during the full updates every six hours. The next one is 5 am EDT.

[ConvergenceZone]

It's moving at a pretty good clip at 14 mph.....Can't wait to read the discussion.

[Hyperstorm]

Regarding the dry air, the system is definitely trying to mix it with its latest burst. There's no question in my mind, however, that dry air (caused by the land interaction and especially the southerly shear) did a part in the sharp jump in the pressure, even if it's not reflected now as the center is moving northward.

We'll have to keep closely monitoring Gustav during the next few hours. The next Air Force Recon vortex message will be crucial to determine if Gustav is still weakening or a strengthening process is beginning.

[ConvergenceZone]

Well, it only dropped 5 mph on the last advisory, and I think that's because it was lower, but it has sense begun to slowly strengthen...

now at 135 mph.....

Latest graphic still shows it making landfall as a Cat4

http://www.wunderground.com/tropical/tr ... ml#a_topad

The forecast intensities are only changed during the full updates every six hours. The next one is 5 am EDT.

that's right, but since it's still a Cat 4 and looking better and better by the hour, I'm sure the intensity forecast will remain the same.

[Pebbles]

It's moving at a pretty good clip at 14 mph.....Can't wait to read the discussion.

that's a few hours from now.. 4 am

[soonertwister]

It's moving at a pretty good clip at 14 mph.....Can't wait to read the discussion.

Next discussion is at 5 am EDT.

[soonertwister]

Regarding the dry air, the system is definitely trying to mix it with its latest burst. There's no question in my mind, however, that dry air (caused by the land interaction and especially the southerly shear) did a part in the sharp jump in the pressure, even if it's not reflected now as the center is moving northward.

We'll have to keep closely monitoring Gustav during the next few hours. The next Air Force Recon vortex message will be crucial to determine if Gustav is still weakening or a strengthening process is beginning.

There was no sharp jump in the pressure, if there was the winds wouldn't be only 5 knots lower.