A weakened Gustav still presents a grave danger to New Orleans

By: Dr. Jeff Masters , 12:18 PM GMT on August 31, 2008

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Gustav roared over Cuba as a Category 4 hurricane with 150 mph winds last night, but Cuba exacted a heavy toll on the storm. Gustav weakened to a Category 3 storm after passage over the island, and is still weakening, according to the latest Hurricane Hunter reports. At 9:48 am EDT, the Hurricane Hunters reported a pressure of 962 mb, up 2 mb from their previous pass through the eye at 7 am. Surface and flight level winds measured by the Hurricane Hunters suggest that Gustav may only be at Category 2 strength. Top winds seen by the plane's SFMR instrument so far this morning have been about 105 mph. The top flight level winds of 103 knots at the flight altitude of 10,000 feet also support a surface wind of 105 mph. NHC has elected to keep Gustav at Category 3 120 mph strength with their 11 am advisory, probably because the satellite appearance still supports a Cat 3. The boundary between Category 2 and Category 3 is at 115 mph.

Visible satellite loops show a ragged and lopsided looking hurricane. Upper level winds from the south are creating 10-15 knots of shear over Gustav, and restricting the upper-level outflow on the south side. The 28-mile wide eye is not very distinct, and the Hurricane Hunters reported that the eyewall was missing a chunk on the south side. Long range radar from Key West also shows the missing southern portion of the eyewall.

The latest track forecast
The latest 00Z (8 pm EDT) model runs have united around a strike in central or southeast Louisiana late Monday morning or early afternoon. The GFDL model, which has all along insisted that Gustav would arrive at the coast a day earlier than the other models, has proven to be correct. We should not be surprised if the center comes ashore as far east as New Orleans, or as far west as western Louisiana, given the current spread in the model tracks. Once Gustav makes landfall, it will slow down, and pose a significant rainfall/flooding threat to Louisiana and Texas. Portions of this region are under moderate to severe drought, so the flooding could've been worse. None of the models are currently forecasting that Gustav will drift southwestward back over the Gulf of Mexico after landfall.

The intensity forecast for Gustav
Wind shear has remained in the moderate range (10-15 knots) the past day, and is forecast to increase to marginal late tonight (15-20 knots). Moderate to marginal shear will still allow Gustav to intensify. Gustav is moving further away from the upper-level anticyclone that helped it intensify as it approached Cuba. Overall, the upper level wind environment is favorable for intensification, but not as favorable as during yesterday's rapid intensification. Gustav is currently over the Loop Current, containing the highest heat content waters of the Atlantic (Figure 1). Both the GFDL and HWRF models forecast that these high heat content waters should result in a 15-20 mph increase in Gustav's winds today. By this evening, Gustav will be passing over a cold eddy. The heat content of the Gulf will decrease as Gustav approaches the coast. As seen in a simulation done yesterday using the GFDL model (Figure 2), the relatively shallow depth of warm water near the coast will allow Gustav to upwell large amounts of cold water from the depths. This will chill the surface waters down by up to 5°C (9°F), which should weaken Gustav's winds by about 15 mph. This cooling effect does not occur for Gustav's path over the southern Gulf of Mexico, due to the great depth of warm waters there. Both the GFDL and HWRF models respond to the lower heat content waters near Louisiana by weakening Gustav to a Category 3 hurricane with 115-120 mph winds at landfall. These models are the only ones that incorporate detailed depictions of the thermal structure of the Gulf of Mexico into their runs.


Figure 1. Tropical Cyclone Heat Potential (TCHP, in kJ/cm^2) for August 28, 2008. Values of TCHP greater than 80 are commonly associated with rapid intensification of hurricanes. The forecast points from the NHC 5 am Saturday forecast are overlaid. Gustav is currently crossing over a portion of the Loop Current with extremely high value of TCHP of 120. However, Gustav will then cross over a cold eddy, and will miss crossing the warm Loop Current eddy that broke off in July. Note that this forecast is old, and the newer forecasts bring Gustav much closer to New Orleans. Image credit: NOAA/AOML.


Figure 2. Forecast track and sea surface temperature response to the passage of Gustav, as simulated by the GFDL model at 8 am EDT Saturday 8/30/08. Passage of Gustav over the relatively shallow depth of warm water near the coast will allow Gustav to upwell large amounts of cold water from the depths. This will chill the surface waters down by up to 5°C (9°F). Note that this forecast is old, and the newer forecasts bring Gustav much closer to New Orleans. Image credit: Isaac Ginis, University of Rhode Island.

Gustav's storm surge may breach the New Orleans levees
NHC's current storm surge forecast calls for a storm surge of 12-16 feet to the right of where the center of Gustav comes ashore. The latest computer generated storm surge map shows that highest surge will be along the levee system along the east side of New Orleans. Storm surge levels of this magnitude are characteristic of a Category 3 to 4 hurricane. The levee system of New Orleans is designed to withstand a storm surge characteristic of a Category 3 storm. If the NHC storm surge forecast verifies, there is a significant threat of multiple levee failures in the New Orleans levee system resulting in flooding of portions of the city. The latest 06Z (2 am EDT) model runs have shifted their landfall points a bit further west, slightly reducing the odds of a Category 4 storm surge in New Orleans. My best guess is that New Orleans will suffer a Category 3-level storm surge. Let's hope that the Army Corps of Engineers' assertion that the levee system can withstand a Category 3-level storm surge is correct.

Comparing Gustav to "Billion-Dollar Betsy"
Gustav's track and expected intensity at landfall are similar to those of Hurricane Betsy of 1965. Betsy was a strong Category 4 hurricane as it crossed the Gulf of Mexico, which then weakened to a Category 3 at landfall, right where Gustav is predicted to make landfall (Figure 3). Betsy brought a storm surge of up to 15 feet to Louisiana (Figure 4). According to wikipedia, levees for the Mississippi River Gulf Outlet along Florida Avenue in the Lower Ninth Ward and on both sides of the Industrial Canal failed. The flood waters reached the eaves of houses in some places and over some one story roofs in the Lower Ninth Ward. These levee breaches flooded parts of Gentilly, the Upper Ninth Ward, and the Lower Ninth Ward of New Orleans as well as Arabi and Chalmette in neighboring St. Bernard Parish. Seventy-six people died in Louisiana, and "Billion-Dollar Betsy" became the first billion-dollar hurricane ($10 billion in 2008 dollars). As a result of the hurricane, the Army Corps of Engineers was tasked with the job of upgrading the New Orleans levee system to withstand a future hurricane of Besty's strength--but no stronger.


Figure 3. Track of Hurricane Betsy of 1965.


Figure 4. Simulated maximum storm surge from Hurricane Betsy of 1965, as modeled using the ADCIRC model. Image credit: ADCIRC Development Group.

Links to follow:
Key West radar
New Orleans weather

I'll have a new blog entry later today that will provide an update on Gustav. I'll also cover Hanna, which may hit the U.S. East Coast late this week.

Some prayers this morning for New Orleans would be in order!

Jeff Masters

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1813. dfwWxDude
3:36 AM GMT on September 01, 2008
Look at the date line the article, from Saturday!
Member Since: September 21, 2007 Posts: 0 Comments: 80
1812. saroff
10:58 PM GMT on August 31, 2008
Oh no.... Cat FIVE
.... thoughts about this??

Just posted by the AP:


"WASHINGTON %u2014 The government's disaster relief chief says Hurricane Gustav is growing into a monster Category 5 storm.... "

http://www.tahoedailytribune.com/article/20080830/NEWS/808309994/-1/rss02
1811. ringeaux
10:10 PM GMT on August 31, 2008
Just landed from doing a fly over of New Orleans. traffic is VERY light and appears most have left. Chartoff and the Gov. met at Lakefront and had a lot of assets in place already. Much better than for Katrina...
Member Since: September 21, 2004 Posts: 0 Comments: 60
1810. marinetech47
8:56 PM GMT on August 31, 2008
hi all hope everyone is in a safe place. Looks like Gus is trying to come visit me.
1809. fishwishin
8:45 PM GMT on August 31, 2008
Quoting gordydunnot:
Lastly serious why dont we ck with the doc. maybe we all send in a buck and up grade his servers. Works fine 95% of time but very slow just when you need it most. That way we could get though the post like this one faster.


Or simply put up a paypal link on the main webpage.
Member Since: September 25, 2007 Posts: 0 Comments: 41
1808. matt03blueoptima
8:38 PM GMT on August 31, 2008
isaw the last models and its scary they are starting to shift.. anyone seen this?//
1807. Watchingthegulf
8:37 PM GMT on August 31, 2008
To Stormkatagory -
Sorry but I think you have those of us in TX stirred up. I've had an inkling that Gustav might still turn more to the west but was getting over that feeling and just having empathy for those in LA. How reliable is your source that says TX may still be a player?
Hopefully the storm will continue to weaken.
1806. duajones78413
8:31 PM GMT on August 31, 2008
Whats the story about Texas becoming more of a player? or a more westerly turn from the models? Corpus Christi here
Member Since: August 30, 2008 Posts: 0 Comments: 287
1805. gordydunnot
8:30 PM GMT on August 31, 2008
Lastly serious why dont we ck with the doc. maybe we all send in a buck and up grade his servers. Works fine 95% of time but very slow just when you need it most. That way we could get though the post like this one faster.
Member Since: August 18, 2008 Posts: 0 Comments: 3113
1804. plywoodstatenative
8:28 PM GMT on August 31, 2008
Off the Navy Site: Modis Water Vapor

Member Since: November 15, 2005 Posts: 16 Comments: 4189
1803. jhans624
8:27 PM GMT on August 31, 2008
new blog
Member Since: August 28, 2005 Posts: 0 Comments: 19
1802. SavannahStorm
8:24 PM GMT on August 31, 2008
Its hard to tell just which direction Hanna is moving and how fast- she has no discernible COC! The last HH run they found a large and elongated "central area" of light winds and low pressure, but no true center fix. Hanna is quickly becoming an open wave.
Member Since: September 22, 2005 Posts: 18 Comments: 2343
1801. TexasGurl
8:21 PM GMT on August 31, 2008
It looks like Gustav, 97, and 98 are all looking better, and Hanna looks like she is running for the hills!!! It also looks like eyewall in Gustav is trying to reform just southwest of his previous one. I think Doc had it right... i think the TX/LA border better pack up and get out now!!
1800. DFW2008
8:21 PM GMT on August 31, 2008
Quoting stormkatagory:
WHY is my posts not showing!


BLog hole...where did you see a texas issue for this storm?
1799. KoritheMan
8:21 PM GMT on August 31, 2008
Wait, nevermind. I see what you were saying StormW. Got a bit confused. I'm tired.
Member Since: March 7, 2007 Posts: 598 Comments: 21160
1798. Stormsabrewin
8:21 PM GMT on August 31, 2008
1786 = Possible Strengthening

1787 = Possible Weakening

Make up your mind Gustav!
1797. BioWeather
8:20 PM GMT on August 31, 2008
1777 Voortex - Is it really Hanna moving faster or is it because the HH found the COC in a more westerly position than earlier projected?
Member Since: September 3, 2007 Posts: 0 Comments: 368
1796. kdav
8:20 PM GMT on August 31, 2008
eye was just filled in again fro liek the hundreth time. it cant seem to get its act together. thats a good thing.
1795. dcoaster
8:20 PM GMT on August 31, 2008
Quoting billy305:
soso your saying this fast movement is bad for south floridians


I would think so. Less time for it to turn north. But with the shear, this should be a minor storm. It's laughable that the GFDL has this thing as a Cat 3 at some point...
1794. DeerfieldBeachGuy
8:20 PM GMT on August 31, 2008
I know Gustav is the main act in town but.....


Is Hanna even a tropical entity anymore?

Im having trouble picking out the LLC on visible satellites.

Thanks in Advance

DFB
Member Since: August 2, 2007 Posts: 0 Comments: 333
1793. Drakoen
8:20 PM GMT on August 31, 2008
Quoting StormW:
MAX FL WIND 105 KT NE QUAD 17:30:30 Z

Equals 110 mph surface wind.


Wind speeds lowered from the 1:00pm CDT advisory
Member Since: October 28, 2006 Posts: 57 Comments: 30619
1792. LPStormspotter
8:19 PM GMT on August 31, 2008
Quoting stormkatagory:
Oh crap they are talking of more of a Texas issue. They are expecting a more westerly element in the models soon.


Where are you getting this info?
La Porte TX
Member Since: July 17, 2008 Posts: 0 Comments: 385
1791. billy305
8:19 PM GMT on August 31, 2008
Quoting kdav:
possibly stregthening right now.
who
1790. gulfscout
8:19 PM GMT on August 31, 2008
Link

Are these new model runs?
Member Since: August 19, 2007 Posts: 0 Comments: 342
1789. Orcasystems
8:19 PM GMT on August 31, 2008
Updated Post
With latest Members location file.
Many Thanks to Zoomiami for making and maintaining this file.

Whole picture Tracks and Cones
Hurricane Hunters Vortex Plots, Gustav
Gustav Tracks and Cones, shifting slightly WEST
Hanna Tracks and Cone, no idea where its going.
Ike ?? Tracks, shifting SOUTH

All links can be enlarged after opening them, by clicking on the picture.
Email Zoomiami, the Mistress of the Google Map to be added.

Mistress of the Google Map Overlays and additions.
Member Since: October 1, 2007 Posts: 81 Comments: 26511
1786. kdav
8:19 PM GMT on August 31, 2008
possibly stregthening right now.
1785. sopla2o
8:18 PM GMT on August 31, 2008
Quoting scla08:
Here in Lafayette, LA, my family, my neighbors, and I are planning on riding this thing out.
I wil
Quoting scla08:
Here in Lafayette, LA, my family, my neighbors, and I are planning on riding this thing out.


I wish you the best.... Good luck... After living through Andrew... Never Again will I make that mistake again...
Member Since: August 18, 2008 Posts: 0 Comments: 10
1784. Crisis57
8:18 PM GMT on August 31, 2008
Quoting Vortex95:
If Hanna continues at this clip a more Southernly track will be needed because the push to the North West won't occur untill the 4/5 day.


I agree with you there and seems shes already moving south of due west
1783. KoritheMan
8:18 PM GMT on August 31, 2008
Quoting StormW:
MAX FL WIND 105 KT NE QUAD 17:30:30 Z

Equals 110 mph surface wind.


Isn't that 105 kt wind at flight level?
Member Since: March 7, 2007 Posts: 598 Comments: 21160
1782. Walnut
8:18 PM GMT on August 31, 2008
Eye starting to present rather nicely on satellite.
Member Since: August 21, 2007 Posts: 0 Comments: 185
1780. billy305
8:18 PM GMT on August 31, 2008
so
Quoting Vortex95:
If Hanna continues at this clip a more Southernly track will be needed because the push to the North West won't occur untill the 4/5 day.
so your saying this fast movement is bad for south floridians
1779. DFW2008
8:17 PM GMT on August 31, 2008
Quoting stormkatagory:
Oh crap they are talking of more of a Texas issue. They are expecting a more westerly element in the models soon.


Where did you hear that?
1778. nrtiwlnvragn
8:17 PM GMT on August 31, 2008
1760. IKE

Dvorak, consistency, pressure dropping. From objective measurements, no. Based on objective measurements 105 mph.
Member Since: September 23, 2005 Posts: 14 Comments: 11276
1774. kdav
8:13 PM GMT on August 31, 2008
blog is slow.
1773. rwdobson
8:13 PM GMT on August 31, 2008
Biloxi, you won't get a direct hit probably but will get TS-force winds.
Member Since: June 12, 2002 Posts: 0 Comments: 1589
1771. LloydBentsen
8:12 PM GMT on August 31, 2008
Quoting stormkatagory:
Oh crap they are talking of more of a Texas issue. They are expecting a more westerly element in the models soon.


Whom might 'they' be? I am in SE Houston.
Member Since: August 30, 2008 Posts: 0 Comments: 29
1770. Tazmanian
8:12 PM GMT on August 31, 2008
test
Member Since: May 21, 2006 Posts: 5091 Comments: 115379
1767. IvansEx
8:09 PM GMT on August 31, 2008
Direct from Pensacola, FL:

"Helllooo, Gustav!"

He just introduced himself with a wet, windy squall.
1765. scla08
8:08 PM GMT on August 31, 2008
Here in Lafayette, LA, my family, my neighbors, and I are planning on riding this thing out.
Member Since: July 24, 2006 Posts: 0 Comments: 272

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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

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