2004-09-03 FCST: Ivan (Atlantic)

[Carrie Halliday]

Originally posted by Chris Sokol
Interesting tidbit in this mornings advisory:

OCCUPANTS OF HIGH-RISE BUILDINGS WITHIN THE
HURRICANE WARNING AREA CAN EXPECT HIGHER WINDS THAN THOSE
EXPERIENCED AT THE SURFACE...ABOUT ONE SAFFIR-SIMPSON CATEGORY HIGHER AT THE TOP OF A 30-STORY BUILDING.

I never really thought about this before.

I saw that too Chris and thought the same thing. One whole Cat higher?

 

[Kurt Silvey]

Levee heights

Levee heights along the Mississippi River-Gulf Outlet and Intracoastal Waterway in the area range from 17.5 to 19 feet. Butler's estimates put the 100-year flood level at 16.3 feet above sea level, meaning waves on top of that would wash over the top and flood areas inside.

http://www.nola.com/washingaway/risk_5.html

A surge of 10 - 16 ' + high tide + wave action = Big test for levee system

Ivan appears to be right on track with the latest forcast point, confirming the northward turn

 

[B Ozanne]

If its just waves crashing over the levees NO is probably ok. The pumps can handle that kind of water. Now, if the levees are broken by the wave action, or they are totally overtopped the pumps will not be able to keep up. The pumps wouldn't even matter, it would be like pumping the Atlantic into the Pacific.

 

[Glen Romine]

Originally posted by Jeff Snyder
This huge chunk of dry air has progressively been getting wrapped into the circulation, with the leading edge now being in the southeast quadrant of the storm.

Might extend further into the system than this. Microwave imagery shows a lack of precip wrapping all the way around:

http://cimss.ssec.wisc.edu/tropic/real-tim...sBy12hr_27.html

TLH sounding still showing plenty of deep moisture moving east ahead of the storm (though the upper portions are in Ivan's exhaust), but there is a lot of dry air in the upper atmosphere at SIL moving SEward - so tough to say how close the dry air is really getting to the core region of Ivan. Definitely over the warm core eddy now - so that is good news for the Gulf coast with Ivan currently weakening.

Glen

 

[Glen Romine]

Originally posted by Carrie Halliday

I saw that too Chris and thought the same thing. One whole Cat higher?

Yeah, all the trees, houses, etc... slow the wind down near the ground - so the higher up you go friction has less of an effect to slowing the wind down. Hurricanes have the strongest winds about 500 m above the ground - so the closer you get to this height the stronger the winds will be.

Glen

 

[Chris Sokol]

The eye is now visible on radar.

http://www.srh.noaa.gov/radar/loop/DS.p20-...r/si.kmob.shtml

 

[Carrie Halliday]

http://www.ssd.noaa.gov/PS/TROP/DATA/RT/fl...t-vis-loop.html

This is what I have been watching. I am seeing a wobble (?) to the NW again..........or think I am.

 

[Jeff Snyder]

Latest recon / vortex message continues to show the effects of dry air entrainment, as central pressure is up to 940mb, with max flight-level winds of 123kts. This indicates that Ivan is likely down to 110kts at the surface, making it a cat 3. There does appear to be some stronger convection developing and wrapping around the south side of the storm, which may have to stabilize the weakening.

The 1145UTC water vapor loop shows very well this entrainment...
[Broken External Image]:http://www.tornadocentral.com/now/dryentrainmentivan.jpg

 

[David Draun]

Originally posted by Chris Sokol
Interesting tidbit in this mornings advisory:

OCCUPANTS OF HIGH-RISE BUILDINGS WITHIN THE
HURRICANE WARNING AREA CAN EXPECT HIGHER WINDS THAN THOSE
EXPERIENCED AT THE SURFACE...ABOUT ONE SAFFIR-SIMPSON CATEGORY HIGHER AT THE TOP OF A 30-STORY BUILDING.

I never really thought about this before.

What if the winds are high category 5 at the surface? We're gonna have a problem here. Innundated New Orleans with violently swaying, and possibly falling buildings. Remember also that the destructive power of water increases exponnentially with depth and speed. Floodwaters can do more damage than an F5 tornado. This combination of wind and water could really be devastating even with a glancing blow. Nobody should be near New Orleans right now. The place should be a ghost town.

 

[B Ozanne]

What if the winds are high category 5 at the surface? We're gonna have a problem here. Innundated New Orleans with violently swaying, and possibly falling buildings. Remember also that the destructive power of water increases exponnentially with depth and speed. Floodwaters can do more damage than an F5 tornado. This combination of wind and water could really be devastating even with a glancing blow. Nobody should be near New Orleans right now. The place should be a ghost town.

It's not that bad. High rise buildings are designed to handle CAT 5 winds. The glass, walls, and furniture might be blown out but the buildings wont be collapsing. Also, the flooding in New Orleans (if it happens) would not be like a flash flood. It would just turn into a big, filthy lake.

 

[David Wolfson]

Looking at the hi-rez loop ending 17:33Z, Ivan is definitely wobbling? west of north and loaded for bear. What an awesome presentation! The eye is 40 miles wide at the top at least, but seems to be trying to contract. Also, as noted, the CDO outflow seems most active in the northwest quadrant. It better make it's turn soon or east LA is going to have a rather bad night.

 

[Kurt Silvey]

17:45 utc… It would appear that Ivan will have a hard time hitting the next forecast point. If he continues on this path landfall could be western MS.

 

[Scott Taylor]

I agree... I thought we would've seen that turn to the N or NNE by now, but Ivan is stubbornly plowing NNW towards the LA/MS state border.

 

[Bob Schafer]

Originally posted by Jeff Snyder
Ivan's intensity decrease is interesting... SST and upper-layer heat content is plenty warm, as the storm should be moving over the warm eddy in the northcentral Gulf...

Take a look at buoy data, though:

http://www.ndbc.noaa.gov/radial_search.php...dist=300&time=3

While water temps are pretty warm, basically 80-85F, there was a lot of discussion about 86+ temps feeding Ivan at the time he was pounding Grand Cayman as cat5.

 

[B Ozanne]

Pressure has begun to fall again. Now down to 937mb. Recon reports just came out.

 

[David Wolfson]

The 1 p.m. CDT last-hour obs from BURL1 (at the tip of the thin peninsula poking southwest) just came in. The wind backed six degrees but is still 035 (at 55kt). Meanwhile 42040 (south of Dauphin Is. AL) direction is holding at about 045 (at about 50kt). Still a westward bias....

 

[Carrie Halliday]

It is reported that Ivan is moving North, but I sit and watch the loop over and over and over......I see W of North. You think Pass Christian is in the line of fire AGAIN?????
Do I smell another Camille? :idea:

 

[Carrie Halliday]

http://www.harrison.lib.ms.us/library_serv...mille_track.htm

Camille's path. A bit eeery.

 

[Chris Sokol]

Carrie, I was just doing some plotting, and had come up with the same landfall at Pass Christian, although a jog 50 miles west would be very bad for New Orleans.

 

[David Wolfson]

Camille was a very small storm. You could probably fit the whole CDO circulation inside Ivan's eye!

Another good comparison is Frederick: http://www.geocities.com/hurricanene/hurri...anefrederic.htm
Still not quite the animal we're looking at now IMO.

 

[Tim Vasquez]

Agree, I was seeing a Mississippi landfall too but figured I wasn't looking at enough data. Landfall anywhere in Mississippi puts it within 95 miles of New Orleans. I'm not sure if that's close enough to do any damage, especially being on the western side.

This is why I would hate to be a tropical storm forecaster... I can't even begin to imagine the pressure on these people regarding recurvature.

Tim

 

[Austin Ivey]

Buoy 42040 has now broken the record wave height ever measured in the Gulf of Mexico by a buoy. 42ft as of the last observation!!

http://www.ndbc.noaa.gov/station_page.php?...p?station=42040

And this buoy is still quite a distance from the eye of Ivan.

The previous record wave height of 40ft occurred during Hurricane Lili.


Does anyone else think Ivan seems to be strengthening?? The eye seems much more symmetrical and rigid in the last few infrared shots.

 

[Glenn Rivers]

Bouy winds

Rules of thumb for converting 5 m bouy winds to 10 m winds:

-Multiply 5 m wind by 1.1 for 40 knot bouy wind.
-Multiply 5 m wind by 1.15 for 60 knot bouy wind.

*the factor may be even greater if sheltering behind giant waves is a factor.

P.S. Bouy # 42040 is the best location for a direct hit, if it survives.

 

[Glenn Rivers]

Mobile Bay storm surge

Surge height in Mobile bay will be hyper-sensitive to storm track.....

If W side of eyewall passes E of Mobile Bay, NE winds will back to N and then NW as storm makes landfall. This would actually blow water out of Mobile Bay and create "negative storm surge".

If E side of eyewall passes W of Mobile Bay, storm surge will be maximized. As storm makes landfall, NE winds will veer to E then SE then S, pushing water up Mobile Bay, creating worst storm surge scenario.

A direct hit with the eye moving up the bay would create a scenario much worse than a miss to the E but not as bad as a near miss to the W.

 

[Marc Grant]

Originally posted by B Ozanne
Also, the flooding in New Orleans (if it happens) would not be like a flash flood. It would just turn into a big, filthy lake.

I may be wrong but I see it differently. If the ocean floods into NO and the lake floods into the downtown area, there will be one huge torrent of water from the flooding Mississippi and lake. The river will continue to make it's way to the ocean via the flooded areas.