ATL GUSTAV: Tropical Depression - Discussion

[RainWind]

Hardly anyone I know left Baton Rouge! It is gonna be a rough 24 hours. RW

[Enzo Aquarius]

Just wondering if someone can explain why the hurricane warning has been extended west...

thanks!

http://forecast.weather.gov/wwamap/wwat ... %20warning

HURRICANE GUSTAV LOCAL STATEMENT
NATIONAL WEATHER SERVICE LAKE CHARLES LA
633 PM CDT SUN AUG 31 2008

...HURRICANE WARNING EXTENDED WEST TO JUST EAST OF HIGH ISLAND...

.AT 400 PM CDT...THE CENTER OF HURRICANE GUSTAV WAS LOCATED NEAR
LATITUDE 26.4 NORTH...LONGITUDE 87.3 WEST...OR ABOUT 215 MILES
SOUTH- SOUTHEAST OF THE MOUTH OF THE MISSISSIPPI RIVER.

From the looks of Gustav on IR, upon landfall, the outer bands will probably affect Texas.

[KWT]

Won't be long before the N.O levees get their real test, surge should be building up from the south soon and as the center moves closer to LA the winds will be easterly and we shall the surge pour into the lake, then its just a matter of hoping

[Bunkertor]

Anyone an idea what those blinking lights mean ?

http://www.nola.com/bridgecam/index.ssf

[Steve Cosby]

Just wondering if someone can explain why the hurricane warning has been extended west...

thanks!

http://forecast.weather.gov/wwamap/wwat ... %20warning

HURRICANE GUSTAV LOCAL STATEMENT
NATIONAL WEATHER SERVICE LAKE CHARLES LA
633 PM CDT SUN AUG 31 2008

...HURRICANE WARNING EXTENDED WEST TO JUST EAST OF HIGH ISLAND...

.AT 400 PM CDT...THE CENTER OF HURRICANE GUSTAV WAS LOCATED NEAR
LATITUDE 26.4 NORTH...LONGITUDE 87.3 WEST...OR ABOUT 215 MILES
SOUTH- SOUTHEAST OF THE MOUTH OF THE MISSISSIPPI RIVER.

Hurricane conditions are expected in that area - probably partly a function of the angle of "attack" as well as the possibility of a left hook of Gustav right before landfall hinted at by the models.

[Ed Mahmoud]

Hidden danger after the fact- 18Z GFDL shows 40 cm of rain in a good part of East Texas, to almost DFW, after the fact. 25.4 cm is ten inches, so that is roughly over 16 inches in 5 days, mostly day 2 to day 4.

GFS shows 5 day rain over 30 cm in parts of Arkansas.


The path after landfall is still uncertain, and very important.

[Steve Cosby]

You have to remember that the center is quite a large area 20-25 miles across now. You can't judge movement from two VDMs.

No offense....but what are you talking about? Please explain.

The center referenced in any VDM could vary by 20-25 miles from point to point just because the center is large.

[tallywx]

RECON turning back to base now because of onboard troubles. Does this mean that that we're not going to have recon. coverage in the most critical hours before landfall, especially considering the strengthening trend?

[Hurricanewatcher2007]

Unfortunately, even New Orleans is probably not 100% evacuated. There are people who have stayed for whatever reason (or lack thereof). I have not heard any official estimates, but I would be surprised if the official evac percentage is higher than 90-95%.

Granted, that 5-10% probably is not waiting for the SPC to issue a watch.

Last I heard it was 90% but these are unofficial numbers. They were saying that with the growth in the Homeless rate in N.O. that its really not possible to know the exact percent but from what they could see it was about 90%

[Enzo Aquarius]

Anyone an idea what those blinking lights mean ?

http://www.nola.com/bridgecam/index.ssf

The ones near the top of the video screen? Look like warning lights for planes to prevent collision.

[KWT]

Also I do know what Wxman57 is saying about recon, the center is quite large therefore the VDM may 'center' any point in the broader center and that may make it look like its on a different motion than it is, thats why i like to use several fixes to see a better motion.

However equally eyeballing it with at best a very infrequant changing eye would probably lead to the same sort of error distances.

In about 6hrs time radar will become increasingly useful.

[Wthrman13]

Let me just expand upon what Dan said...hopefully I don't confuse anyone.

Most shear computations that I've seen on line compute the difference between the 850MB wind and 250MB wind to compute the amount of upper tropospheric shear. Some use layers centered about each level. It's not just one windspeed minus another windspeed....it's a vector difference. For those who have not taken vector math, this may help...

http://www.wunderground.com/education/shear.asp

One can assume that if the storm motion is reasonably close to the magnitude and direction of the 850MB wind vector, then the shear computed is probably accurate.

Thanks Tony, I should have pointed out that shear is a vector difference, not a simple magnitude difference.

[wxman57]

No offense....but what are you talking about? Please explain.

I believe that the eye was last measured at about 25 miles across. It's a large area of relatively light winds. The plane flies around in there and tries to find a center of lowest pressure. That center may not be in the center of the 25 mile diameter ring. And the next time they fly through they may estimate a center in a different part of the eye. So you can't connect two VDMs and get a heading. They'll jump left and right of the actual track, depending upon where the plane fixes the lower pressure center each pass. The VDM does not identify the center of the eye (at least, not necessarily).

[Bunkertor]

I have to agree with what has been said, with these tornado warnings and the strength of this band in the N.O. area, shouldn't a Tornado Watch be issued?

They will launch it soon, but think the got loads of work to do, now.

[wxman57]

Is there ANY WAY to turn off this "New Post Review" feature? I can't even reply to a message here any more tonight as each time I hit "Submit" it tells me that a new post has been made while I was typing and asks if I want to read it before replying. Took me 20 hits of "Submit" last time to get my post in. You people are posting too fast to let a new message in.

[Weatherfreak000]

No offense....but what are you talking about? Please explain.

I believe that the eye was last measured at about 25 miles across. It's a large area of relatively light winds. The plane flies around in there and tries to find a center of lowest pressure. That center may not be in the center of the 25 mile diameter ring. And the next time they fly through they may estimate a center in a different part of the eye. So you can't connect two VDMs and get a heading. They'll jump left and right of the actual track, depending upon where the plane fixes the lower pressure center each pass. The VDM does not identify the center of the eye (at least, not necessarily).

Understood...thanks for your always valuable information, Wxman!


Im watching this thing intensifying coming straight for my house and im somewhat freaking out.

[Windy]

Any word on why Recon canceled? Equipment problems? When's the next recon scheduled?

[KWT]

Hidden danger after the fact- 18Z GFDL shows 40 cm of rain in a good part of East Texas, to almost DFW, after the fact. 25.4 cm is ten inches, so that is roughly over 16 inches in 5 days, mostly day 2 to day 4.

GFS shows 5 day rain over 30 cm in parts of Arkansas.


The path after landfall is still uncertain, and very important.

Yeah I've mentioned that, given the slow down we could see quite a lot of flooding rains, evem when this is a depression inland could see some bad flooding.

I think its probably steady state now, probably not going to change much at all in terms of winds now I guess...still should be a major hurricane.

[Ed Mahmoud]

USAFR recon just turned back (see recon thread). Mechanical issue, I guess. Don't know how long NOAA plane can stay out there, but they'll be a satellite eclipse early morning. I hope there is a plane in there then...

[Enzo Aquarius]

Getting closer and closer to New Orleans, main bands are getting quite close.

http://radar.weather.gov/radar.php?rid= ... 11&loop=no