Unanswered questions concerning Hurricane Isaac

By: Dr. Jeff Masters , 4:35 PM GMT on August 31, 2012

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The top winds of Tropical Depression Isaac have fallen to 25 mph, but the storm continues to be a potent rain-maker as it heads north-northwest at 11 mph into Missouri. Isaac has spawned up to 20 suspected tornadoes, brought storm surges as high as 13.6' to the coast (in Lake Borgne, LA), and dumped 20" of rain at one station in New Orleans. The 13.27" of rain that fell at Hattiesburg, MS broke the record for wettest August in the city's history (previous record: 13.03" in 1987.) Major flooding is occurring on seven rivers in Louisiana and Mississippi. Isaac is being blamed for at least four deaths in the U.S., 24 in Haiti, and five in the Dominican Republic.

A few notable rainfall totals from Isaac, through 11 am EDT on Friday:

20.08" New Orleans, LA
15.02" Marion, MS
13.99" Pascagoula, MS
13.27" Hattiesburg, MS
10.85" Gulfport, MS
10.39" Slidell, LA
10.17" Biloxi, MS
9.85" Mobile, AL
7.38" Pine Bluff, AR
5.95" Baton Rouge, LA

A major reason for Isaac's heavy rainfall totals has been its very slow motion. This slow speed was due to the fact Isaac has been bumping into a ridge of high pressure that is unusually strong, due to the intense drought over the center of the U.S.; strong drought-amplified high pressure areas are very resistant to allowing any low pressure areas to intrude into their domain. The high pressure area was strong enough this week to allow several all-time records for heat this late in the year to be set:

112° on August 29 at Winner, SD
108° on August 29 at Valentine, NE
107° on August 29 at Corpus Christi, TX
97° on August 29 at Denver, CO (2nd highest so late in the year)


Figure 1. Nighttime view of Hurricane Isaac taken at 1:57 am CDT August 29, 2012, by the Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi-NPP satellite. The VIIRS day-night band detects light in a range of wavelengths from green to near-infrared, and uses light intensification to enable the detection of dim signals. In this case, the clouds of Isaac were lit by moonlight. Image credit: NASA.

Isaac's beneficial rains falling in drought-stricken regions
Hurricanes get a lot of attention because of the billions in damage they cost, and the lives they disrupt. AIR Worldwide estimated today that insured damage from Isaac would cost up to $2 billion. This does not include damage to infrastructure or uninsured damage, so the final price tag of Isaac's rampage will be more like $3 - $5 billion. However, Isaac is now dumping beneficial rains over Arkansas, Missouri, Illinois, Indiana, Ohio, and Kentucky--regions stricken by the worst drought since the 1950s or 1930s, depending upon the exact location. These regions need 9 - 18 inches of rain to pull them out of drought. Isaac's 3 - 6 inches of rain will not end the drought, but will put a pretty good dent in it. I expect that 3 - 6 inches of rain for a wide swath of prime agricultural land in extreme drought is probably worth at least $5 billion, when you consider that a recent estimate by a Purdue economist put the cost of the great drought of 2012 at more than $77 billion. Only Hurricane Katrina ($146 billion) and the drought of 1988 ($78 billion) have been more expensive disasters, according to NOAA's National Climatic Data Center. Unfortunately, Isaac's arrival is poorly timed, as the storm is arriving during harvest season. The strong winds associated with the storm will flatten many crops, making it more difficult to harvest them, and Isaac's winds may cost farmers several hundred million dollars due to unharvestable crops. Still, the rains from Isaac will be highly beneficial for the success of the upcoming winter wheat season, and for next year's growing season.


Figure 2. Predicted precipitation for the five-day period ending on Tuesday evening shows that Isaac is expected to bring a large region of 3 - 6 inches of rain (red, orange, and brown colors) to Arkansas, Missouri, Illinois, Indiana, Ohio, and Kentucky. Image credit: NOAA/HPC.


Figure 3. The great drought of 2012 has brought so little rain to the Midwest that some areas require over 15" of rain (dark purple colors) to end the drought. Image credit: NOAA/CPC.

Unanswered questions about Hurricane Isaac

1. Did the passage of Hurricane Isaac stir up oil from the Deepwater Horizon oil spill? Isaac was the first hurricane to pass over the site of the 2010 Deepwater Horizon oil spill. We know that large hurricanes are capable of creating currents in deep water at the bottom of the Gulf of Mexico; Hurricane Ivan caused upwelling currents of 0.5 cm/s at a depth of about 500 meters. In an August 28 article in the Huffington Post, Nick Shay, professor of meteorology and physical oceanography at the University of Miami, said: "Winds will push water away from the center of a storm, which causes an upwelling as the ocean tries to adjust. It brings whatever is near the bottom up higher in the water column and currents can then push it towards the coast." Up to 1 million barrels of oil from the spill are estimated to still be present in the deep water sediment, on beaches, and in the marshes of Louisiana, and it is possible some of this oil will wash up on the Gulf Coast in coming months. The storm surge of Isaac also likely flushed out oil lodged in the coastal marshes of Louisiana, but it is unknown how much of a concern this might be.

2. What's the deal with these super-sized Category 1 and 2 hurricanes that have been hitting the U.S.? The past three landfalling hurricanes in the U.S.--Isaac (2012), Irene (2011), and Ike (2008)--have all been exceptionally large, among the top ten on record for horizontal extent of tropical storm-force winds. Each of these storms had an unusually low pressure characteristic of a storm one full Saffir-Simpson category stronger. Is this the new normal for U.S. hurricanes?

3. Did the new $14.5 billion upgrade to the New Orleans levee system cause worse flooding elsewhere? Whenever a new levee or flood control structure is created, you make someone else's flood problem worse, since the water has to go somewhere. Where did the water was stopped by the new $1.1 billion, 1.8 mile-long Lake Borgne flood barrier on the east side of New Orleans go? Did it flow south and contribute to the overtopping of the levees near Braithwaite? Or did it go north and contribute to the 36 hours of storm surge in excess of 5' observed along the Mississippi coast at Waveland? I posed this question to NHC's storm surge expert Jaime Rhome, and he said it was impossible to know without doing detailed storm surge modeling studies.

4. Can only hurricanes beginning with the letter "I" hit the U.S. now? Isaac (2012), Irene (2011), and Ike (2008) are the last three hurricanes to hit the U.S. It turns out that hurricanes that begin with the letter "I" and "C" have more names on the list of retired hurricanes than any other letter (nine each.) I'm thinking Isaac will get its name retired, letting storms beginning with "I" take over sole possession of first place on the retired storms list.

Hurricane Kirk in the Central Atlantic
Hurricane Kirk intensified into a 105 mph Category 2 hurricane this morning, becoming the 2nd strongest hurricane of the 2012 Atlantic hurricane season. Hurricane Gordon was the only stronger storm; Gordon hit sustained winds of 110 mph just before reaching the Azores Islands on August 18. Kirk has probably peaked in intensity, and is about to move over colder waters and gradually decay. Kirk is not a threat to any land areas.


Figure 4. Morning satellite image of Tropical Storm Leslie.

Tropical Storm Leslie a long-range threat to Bermuda, Canada, and the U.S. East Coast
Tropical Storm Leslie formed on Thursday in the Central Atlantic. Leslie's formation date of August 30 puts 2012 in 2nd place for earliest formation date of the season's 12th tropical storm. Only 1995 had an earlier formation date of the season's 12th storm. With records dating back to 1851, this year is only the second time 8 total storms have formed in August. The other year was 2004, when the first storm of the season formed on August 1 (Alex), and the 8th storm (Hermine) formed on August 29th. Satellite loops show that Leslie has a modest amount of heavy thunderstorm activity, and respectable low-level spiral bands and upper-level outflow. Conditions appear ripe to allow Leslie to intensify into a Category 2 hurricane by Sunday. Fortunately, Hurricane Kirk is weakening the ridge of high pressure to the north of Leslie, and Leslie is expected to turn to the northwest and miss the Lesser Antilles Islands. However, steering currents for Leslie are expected to collapse early next week, as Leslie gets stuck between two upper level lows. The storm will then slowly meander over the open ocean for many days, potentially threatening Bermuda. Leslie will stay stuck until a strong trough of low pressure approaches the U.S. East Coast around September 8. This trough should be strong enough to pull Leslie to the north and then northeast by September 9. At that time, Leslie may be close enough to the coast that the storm will make landfall in New England, Canada, or the Mid-Atlantic states. Leslie could also miss land entirely; this all depends upon the timing and strength of the September 8 trough of low pressure. Regardless, Leslie is expected to bring an extended period of high waves to the U.S. coast. According to NOAA's Wavewatch III model, large swells from Leslie will reach Bermuda by Monday, and arrive along the U.S. East Coast on Tuesday. These waves will be capable of creating dangerous rip currents and beach erosion.

Portlight disaster relief charity responds to Isaac
The Portlight.org disaster relief charity, founded and staffed by members of the wunderground community, are in Mississippi, helping out with Isaac relief efforts. You can check out their progress or donate to Portlight's disaster relief fund at the portlight.org website.

I'm planning on taking Saturday off, but will have a new post for you on Sunday. Have a great holiday weekend, everyone!

Jeff Masters

Hurricane Isaac Louisiana (apphotos)
People play in the storm surge from Hurricane Isaac, on Lakeshore Drive along Lake Pontchartrain, as the storm nears land, in New Orleans, Tuesday, Aug. 28, 2012. (AP Photo/Gerald Herbert)
Hurricane Isaac Louisiana
Portlight volunteers at Biloxi shelter (Portlight)
Portlight volunteers at Biloxi shelter
Hurricane Isaac Louisiana (apphotos)
Research students from the the University of Alabama measure wind speeds as Hurricane Isaac makes landfall, Wednesday, Aug. 29, 2012, in New Orleans, La. Isaac was packing 80 mph winds, making it a Category 1 hurricane. It came ashore early Tuesday near the mouth of the Mississippi River, driving a wall of water nearly 11 feet high inland and soaking a neck of land that stretches into the Gulf. The storm stalled for several hours before resuming a slow trek inland, and forecasters said that was
Hurricane Isaac Louisiana
TS Isaac (Raine911)
Between the rain bands
TS Isaac

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Good evening all from beautiful Antigua. Very quiet in my neighbourhood but by the look of things it might not be come Sunday if Leslie has anything to say about it. Not worried though.
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Tracks haven't changed much. I wonder what the new EURO will have?

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Leslie meaning and name origin:

Leslie \l(e)-slie, les-lie\ as a girl's name (also used as boy's name Leslie), is pronounced LESS-lee, LEZ-lee. It is of Scottish and Gaelic origin, and the meaning of Leslie is "holly garden". Also possibly "the gray castle".

Interesting ... considering the video published earlier in the season, used to pay tribute to another tropical system that made landfall on Memorial Day.

I'll have to research the etymology of "Leslie" a little more to figure out why the references to a gray tower or fort.

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819. JLPR2
Quoting stormpetrol:


Keep is right IMO , it has taken a slight dive WSW.


The dive to the SW is probably the MLC taking over, which is bad for the storm as it would mean the LLC is now pulling WNW without its convection, but these are all opinions.

I wish recon were in there. :\
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Leslie may very well pass NE of the Leewards, but if I was in the northern Leeward Islands right now, I'd be watching it very closely.
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Quoting Grothar:


It is still moving WNW.


Are you sure about that 'old man'?

My best guess is W

But that is just a shot in the dark, so to say....

Very interesting, and hardly annoying!
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Quoting kmanislander:
If you believe it



Don't buy it or believe it, though I could be wrong!
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Quoting washingtonian115:
This comment can go both ways.Positive or negative.
Member Since: October 24, 2005 Posts: 0 Comments: 24060
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Quoting Articuno:

It almost looks as if it shrunk.


Keep is right IMO , it has taken a slight dive WSW.
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Quoting justsouthofnola:
most of nola is still without power..........


Link


Wow! That's a huge area.
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Quoting pottery:

I thought that your "FAIL" post was really great !
But then, I understood it.
This comment can go both ways.Positive or negative.
Member Since: August 14, 2010 Posts: 10 Comments: 16435
Quoting zoomiami:


Pottery -- I think your trying to stir up trouble! Are you bored tonight?

Moi ??
Si !
Member Since: October 24, 2005 Posts: 0 Comments: 24060
Quoting GTcooliebai:
What are you seeing for the rest of the season, numbers wise?


Realistically, I'm seeing a slow down in the insane activity we've been seeing, but by no means a crash. Probably 4 in September, giving us up to 16 named + 1 in October or November, giving us a total of 17 named, 8 hurricanes, and 2 major hurricanes (Leslie and another)
Member Since: July 8, 2005 Posts: 259 Comments: 23611
Since my last mapping
31Aug.12pm's 15.9n48.4w has been re-evaluated&altered
1Sept.12am's 15.8n48.6w-16.4n50.3w-17.1n52.0w are now the most recent positions
(The previous vectors and straightline projections have been corrected for this mapping)

All times in GMT. Derived from NHC_ATCF data for TropicalStormLeslie at 1Sept.6pm

The easternmost dot on the kinked line is where Invest98L became TropicalDepressionTwelve.
The easternmost dot on the longest line is TS.Leslie's most recently reported position

The longest line is a straightline projection through TS.Leslie's 2 most recent positions to it's closest approach to (NGC)Anegada, the northernmost island of the LesserAntilles
31Aug.06am: TS.Leslie had been headed toward passage 176miles(283kilometres)NNEast of Anegada (blob hanging from straightline projection)
31Aug.12pm: TS.Leslie had been headed toward passage 221miles(355kilometres)NNEast of Anegada (dot above the straightline projection)
31Aug.06pm: TS.Leslie had been headed toward passage 127miles(205kilometres)NNEast of Anegada (free-floating dot below the straightline projection)
1Sept.12am: TS.Leslie was heading toward passage 184miles(396kilometres)NNEast of Anegada

Copy&paste ngd-18.749n64.333w, 21.178n63.479w, 21.754n63.138w, 20.53n63.814w, bgi, 13.8n42.6w- 14.2n44.5w- 14.5n45.7w- 15.1n47.1w- 15.8n48.6w, 15.8n48.6w-16.4n50.3w, 16.4n50.3w-17.1n52.0w, 16.4n50.3w-21.281n63.412w, 18.749n64.333w-21.281n63.412w into the GreatCircleMapper for a larger map and other information
The previous mapping for comparison
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Put the center where it looks like it is and you have yourself a budding hurricane. Outflow looks pretty stellar.

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If you believe it

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Quoting pottery:

C'mon, Gro !
Make a comment to go with the pretty pictures.
Otherwise, we will start to think you are working for NHC.

(sorry. couldn't resist..):))


Me, work for a weather service? LOL
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Quoting washingtonian115:
Who's saying this season is a bust?.I said it's a fail because what everyone has thought about this season never came true.From the seasonal predictions to the intensity/track forecast.

I thought that your "FAIL" post was really great !
But then, I understood it.
Member Since: October 24, 2005 Posts: 0 Comments: 24060
803. viman
Quoting JLPR2:


Actually I'm starting to get Isaac vibes and if the center does reform then my vibes will be confirmed.


Isaac wasnt bad for us, Earl on the other hand, i got 100+mph winds, and he was supposed to pass just as far north as this one. He kept inching west and inching west, and ended up blowing up into a cat4 just north of here. would rather not go thru that again...
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Quoting pottery:

C'mon, Gro !
Make a comment to go with the pretty pictures.
Otherwise, we will start to think you are working for NHC.

(sorry. couldn't resist..):))


Pottery -- I think your trying to stir up trouble! Are you bored tonight?
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Getting stronger everyday.... Ernesto, Isaac, Leslie.... this could become a major hurricane...


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Who's saying this season is a bust?.I said it's a fail because what everyone has thought about this season never came true.From the seasonal predictions to the intensity/track forecast.
Member Since: August 14, 2010 Posts: 10 Comments: 16435
798. JLPR2
Quoting CybrTeddy:


Yea, I'm not seeing any of the tightly rotating cirrus clouds on the north side that one would see in the event that a circulation is becoming exposed, which tells me the LLC is weakening. If convection starts to fade rapidly, that will be your hint that exactly that is happening. If convection continues to be strong and circular and you don't see an obvious exposed LLC, then the MLC is taking over. Not sold until I see ASCAT data.


Yep, I'm on the same bus for the moment. With no evidence pointing to a reformation we cant say anything, just watch and wait. :\ Really hate this situations.
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Quoting stormwatcherCI:
Every time KOG puts his co-ordinates they seem a lot more realistic than the NHC.


Leslie is doing one of two things. Either relocating the center or about to stair step Northward another notch. Have to wait and see.
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most of nola is still without power..........


Link
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Grothar, I see the GFS model is spot on to the movement of Leslie. Maybe if you invert that track it will be right on track.
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Quoting Grothar:

C'mon, Gro !
Make a comment to go with the pretty pictures.
Otherwise, we will start to think you are working for NHC.

(sorry. couldn't resist..):))
Member Since: October 24, 2005 Posts: 0 Comments: 24060
Quoting Bielle:


I was wondering about him myself. Last I heard was when he posted photos of the new puppies.
He has been checking in with Presslord and all is as well as can be expected.
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Quoting KEEPEROFTHEGATE:
T.C.F.W.
12L/TC/L/CX
MARK
15.85N/53.55W


Yea, I'm not seeing any of the tightly rotating cirrus clouds on the north side that one would see in the event that a circulation is becoming exposed, which tells me the LLC is weakening. If convection starts to fade rapidly, that will be your hint that exactly that is happening. If convection continues to be strong and circular and you don't see an obvious exposed LLC, then the MLC is taking over. Not sold until I see ASCAT data.
Member Since: July 8, 2005 Posts: 259 Comments: 23611
Quoting pottery:

Eh ??
Every time KOG puts his co-ordinates they seem a lot more realistic than the NHC.
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Quoting GTcooliebai:
Anybody heard from Patrap yet?


I was wondering about him myself. Last I heard was when he posted photos of the new puppies.
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787. JLPR2
Quoting viman:

thanks, so same motion would ensue, but it would probably pass closer to us...this has an EARL type of feeling to it...


Actually I'm starting to get Isaac vibes and if the center does reform then my vibes will be confirmed.
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Quoting NativeSun:
No, I'm the one confused ,this storm was suppose to be a lot farther North and West and so to my untrained eyes it's moving some where between the two directions I jhst mentioned. Hope this helps.

Sure it does.
I think..... :):))
Member Since: October 24, 2005 Posts: 0 Comments: 24060
Leslie looks Potent
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Quoting Maineweatherguy20023:

So you think the 1 word to describe this season is "FAIL"?? Be glad its not 09!
Yes.I'm to lazy to really explain.But in my post you quoted I stated why this season is one big fail.
Member Since: August 14, 2010 Posts: 10 Comments: 16435
Quoting CybrTeddy:
No one should be considering 2012 a bust season, a season that was predicted at most to have 11 named is already at 12 and it's not even September yet (will be in a few hours). We got 8 named storms in August including a hurricane that caused bad damage to areas in the Gulf Coast, Isaac. If anything, this season is an unpleasant slap in the face to everyone that even El Nino years can be active.
What are you seeing for the rest of the season, numbers wise?
Member Since: August 31, 2009 Posts: 0 Comments: 5628
Quoting pottery:

A minor jog.
Nothing to worry about, right?

:):))


Maybe. An unpredictable year this one.
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No, I'm the one confused ,this storm was suppose to be a lot farther North and West and so to my untrained eyes it's moving some where between the two directions I just mentioned. Hope this helps.
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Quoting kmanislander:


Short term WSW LOL

A minor jog.
Nothing to worry about, right?

:):))
Member Since: October 24, 2005 Posts: 0 Comments: 24060
778. viman
Quoting JLPR2:


Would move to the WNW or NW as predicted.

thanks, so same motion would ensue, but it would probably pass closer to us...this has an EARL type of feeling to it...
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Quoting NativeSun:
Grothar, it looks to be moving a little South of due W/NW or is that North of W/SW?



what?!?
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Quoting CybrTeddy:


I have some doubts, mostly due that I can be conservative on things such as LLC relocation until I see buoy data and or ASCAT data showing such a situation developing..

OK, thanks.
Member Since: October 24, 2005 Posts: 0 Comments: 24060
Quoting pottery:

Eh ??


Short term WSW LOL
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Quoting WeatherNerdPR:

And yet parts of the equatorial pacific are cooling. It's possible we won't have more than a weak el Nio before heading towards neutral/weak la Nia conditions in 2013.
The traditional nino regions we base the southern oscillation off of may have cooled slightly, but you still have all this anomalous heat in the eastern Pacific. This will favor lower pressures in that area, enhancing the pressure gradient between the low pressures in the east Pacific and the Bermuda high. Stronger gradient produces stronger trade wind flow making it harder for storms to consolidate. Stronger winds over the basin also promote downward motion, which will tend to dry out the atmosphere.

But yeah, the climate models don't seem to excited about the possibility of a full blown El Nino. Not surprising given the cold PDO.

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Quoting KEEPEROFTHEGATE:
T.C.F.W.
12L/TC/L/CX
MARK
15.85N/53.55W

Eh ??
Member Since: October 24, 2005 Posts: 0 Comments: 24060

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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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