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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722. viman
Reading all the posts and is thinking that this thing is getting uncomfortably close for sonething that is supposed to pass 400 miles away to the NE... Just saying...
What is it with storms this year, Decision Makers worse nightmare...geesh man...
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Quoting kmanislander:


It will be if Leslie does not make another " stair step " move

True, that!
Member Since: October 24, 2005 Posts: 0 Comments: 25474
Member Since: July 17, 2009 Posts: 71 Comments: 27600
Quoting allancalderini:
I hate that class so much when I was in 9th grade it was the only time I had went to recuperation. Geometry in 10th is easy. but pre- calculus in 11th is Hell I had fail my two quizzes until know.


I am going to say if I get a D on my report card I will get banished from the computer for a whole marking period which is what, two months?
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Quoting sunlinepr:




that looks like a really strong trough that means business
Member Since: April 26, 2006 Posts: 5 Comments: 3237
Quoting GTcooliebai:
You know Leslie could just keep going west and bust through the trough, especially if that trough flatens out and the high behind it builds and bridges with the Azores high.

I dont care in the least bit where the heck it goes! Hope its a fish. Nice swell and no damage :) but hope it doesnt hit haiti. there too poor :(
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Quoting WeatherNerdPR:
The MDR can't have a single, well organized storm this year. The better organized storms (Chris, Gordon and Kirk) have formed way north of the MDR. Ernesto and Isaac didn't become better organized until they were near landfall, while the other two storms (Florence and Joyce) failed to organize significantly and died in the middle of the MDR. Alberto and Beryl didn't even form in the actual season, and don't even get me started on Debby and Helene.
Bizarre season so far. More interesting than last year for sure.
Levi was talking about this, storms this year will have an easier time north of the MDR and struggle in the caribbean and central atlantic. Effects of El nino must still be around i guess.
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Quoting washingtonian115:
The weaker Leslie stays the more west she goes and not will only affect the islands but the U.S will have to start looking at this closely as well.
















Do you think a path somewhat similar to Isaac is possible?
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Speechless

Member Since: October 6, 2007 Posts: 0 Comments: 6556
Quoting WeatherNerdPR:
The MDR can't have a single, well organized storm this year. The better organized storms (Chris, Gordon and Kirk) have formed way north of the MDR. Ernesto and Isaac didn't become better organized until they were near landfall, while the other two storms (Florence and Joyce) failed to organize significantly and died in the middle of the MDR. Alberto and Beryl didn't even form in the actual season, and don't even get me started on Debby and Helene.
Bizarre season so far. More interesting than last year for sure.

To say the least, it is the most annoying year in a while.
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So vixen Leslie another example of don't under estimate the sub tropical ridge because it's strengthening in the east of the system as we speak and the trough is dipping but however the shear and trade winds could play it part in weakening leslie so it wobbles a bit south west could be intresting to watch tonight for the Antilles

IMO...

btw fellow trinis happy 50 independence..
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Quoting sunlinepr:




Holy dry air!
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Quoting pottery:

Fun season, for storm tracking.
Bum season for some though.


It will be if Leslie does not make another " stair step " move
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hello everyone ended up with 8.75 inches of rain


wrote a blog With pictures of the devestation.

feel free to take a look and comment.Link
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Quoting WeatherNerdPR:
The MDR can't have a single, well organized storm this year. The better organized storms (Chris, Gordon and Kirk) have formed way north of the MDR. Ernesto and Isaac didn't become better organized until they were near landfall, while the other two storms (Florence and Joyce) failed to organize significantly and died in the middle of the MDR. Alberto and Beryl didn't even form in the actual season, and don't even get me started on Debby and Helene.
Bizarre season so far. More interesting than last year for sure.
Fast trade wind flow and dry air...both are symptoms of an El Nino.
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Quoting DDR:

Very long indeed,i won't surprised if we get a couple more stronger ones as the storm gets closer to the chain.

Absolutely.
Member Since: October 24, 2005 Posts: 0 Comments: 25474
Quoting kmanislander:
Good evening

Leslie looks like a prime candidate for a center relocation. Seems to be the trend of late.

Fun season, for storm tracking.
Bum season for some though.
Member Since: October 24, 2005 Posts: 0 Comments: 25474
Quoting Tazmanian:



We won't stop posting the gifts this be come it makes your computer a little laggy. You need. A faster and newer computer where not going too stop posting some I this be come your computer is a little laggy



You guys are more then welcome too post has many of them gifts has you want there no rules about it that we can post them on here


Perhaps you might consider the many, both in the US and around the world, who don't have access to high-speed connections and/or don't have the money for the latest and fastest computers. They may use this information, too, and some may really need it. No one is suggesting that anyone stop posting, but simply that they just consider that the animated gifs do slow the download speeds for many of us.
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702. DDR
Quoting pottery:

I was surprised when I saw the loops and realised that it was a feeder band. That was a long one, man!

Very long indeed,i won't surprised if we get a couple more stronger ones as the storm gets closer to the chain.
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The MDR can't have a single, well organized storm this year. The better organized storms (Chris, Gordon and Kirk) have formed way north of the MDR. Ernesto and Isaac didn't become better organized until they were near landfall, while the other two storms (Florence and Joyce) failed to organize significantly and died in the middle of the MDR. Alberto and Beryl didn't even form in the actual season, and don't even get me started on Debby and Helene.
Bizarre season so far. More interesting than last year for sure.
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Quoting Articuno:

Mine drained my whole energy out of me I swear.

I have had problems with mine, I had the same teacher in 6th but I think she moved to 8th just to torture me again..
Her class was my first D I ever got.
I hate that class so much when I was in 9th grade it was the only time I had went to recuperation. Geometry in 10th is easy. but pre- calculus in 11th is Hell I had fail my two quizzes until know.
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Quoting DDR:
A very weak feeder at most pottery.

It was, but it was there all right.
Member Since: October 24, 2005 Posts: 0 Comments: 25474
Quoting DDR:

Hey yes i did was watching it on radar

I was surprised when I saw the loops and realised that it was a feeder band. That was a long one, man!
Member Since: October 24, 2005 Posts: 0 Comments: 25474
This was 3 hours earlier.

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Quoting CybrTeddy:


Yea but people where thinking that might end up as a hurricane into Florida when it died overnight, I can assure you that the disappointment on here was quite abundant. Some things never change. Leslie though is OTS either way, the W-WSW motion you're seeing is actually convection being shunted off to the south some as the LLC is on the northern edge of the convection. I'm not going to call it decoupled though as per the latest microwave pass it appears to have a very well defined circulation + it's not clocking at 22mph like Ernesto and Isaac where. MLC and LLC's don't just decouple for no reason at all, it's usually a combination of trade winds and forward speed.
Or some shear as we are seeing here. The LLC and MLC are definitely not stacked at the moment, so idk how you could call the system stacked/not decoupled. Almost looks like the LLC will become exposed on the shortwave loop, but we shall see.
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695. DDR
A very weak feeder at most pottery.
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Quoting washingtonian115:
It would be foolish for people in the northern islands to write this storm off.
we never write off storms to the east of us :)
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That high preasure behind that trough is moving and building in quickly as well as the BH, closeing the gap! Quote me if i am wrong, just going by what i see on the maps.
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Quoting JLPR2:
A mid level hurricane! XD

Looks like a giant tomato.
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Good evening

Leslie looks like a prime candidate for a center relocation. Seems to be the trend of late.
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Low level steering currents

Member Since: July 17, 2009 Posts: 71 Comments: 27600
689. DDR
Quoting pottery:

Hey DDR.
Did you notice very heavy rains in Diego at noon, caused a lot of concern that the river would overflow again.

That was the tail end of a feeder from Leslie.
Check the Rainbow loops...

Hey yes i did was watching it on radar
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Interesting Leslie tonight. Tough with such a dense CDO and no eye to track. However, HP seems to have temporarily built in overhead.

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Quoting JLPR2:
A mid level hurricane! XD



Eye?
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Quoting NativeSun:
Pottery, stay safe and I know you are ready just in case.

Thanks.
All's well here.
Could use a little rain actually, its been kind of dry for the last couple of days, and temps are 93-95 every day.
Member Since: October 24, 2005 Posts: 0 Comments: 25474
Quoting JLPR2:
A mid level hurricane! XD

Looks like an eye wants to pop out, would also be south of where the NHC has her.
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Quoting JLPR2:
A mid level hurricane! XD

haha very funny

Dave
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Quoting 1900hurricane:


Looks like a good fix to me. Note the vigorousness of the low level center of circulation to the NE of the most intense thunderstorms a bit.

*EDIT to correct NW to NE.
Quoting 1900hurricane:

I'm not so sure about a relocation; a low level center that well defined doesn't just go away, which we found out firsthand with Isaac during his trek through the Caribbean. Once again, I must lament that this is occurring at night when visible imagery is unavailable. Vis would definitely be helpful at a moment like this.
Agreed and thanks for posting that microwave imagery, Leslie is definitely decoupled.
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sure hope this sw movement doesnt continue.....


Link
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Member Since: July 17, 2009 Posts: 71 Comments: 27600
Quoting CaicosRetiredSailor:
(CBS News) BRAITHWAITE, La. - The storm clouds cleared over the Gulf Coast Friday and the full impact of Hurricane Isaac is becoming clear. The first hurricane to hit the U.S. this season left at least five people dead. More than 20 inches of rain combined with the storm surge to leave whole neighborhoods under water.

The power is still out for more than half a million homes and businesses. And the storm damage could top $2 billion. We spoke with some people who may have lost nearly everything.

For the first time Friday, we were able to look from the air at the abandoned neighborhoods in Plaquemines Parish, swamped by five feet of Isaac's storm surge. Crews have begun cutting as many as 10 holes in its levees east and west banks to help drain the water.


Yeah, but it was totally over-hyped by the media. Let's not even mention Madisonville, Laplace, Mandeville Lakefront, New Orleans Lakefront, Ascension Parish, etc.

It is unreal some of the comments people make about this storm being "nothing."
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Quoting WeatherNerdPR:

My Algebra teacher. xD

Mine drained my whole energy out of me I swear.

I have had problems with mine, I had the same teacher in 6th but I think she moved to 8th just to torture me again..
Her class was my first D I ever got.
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Quoting JLPR2:
If I didn't know any better I would say the center is around 16.1n.



Really confusing storm, if this keeps up the circulation should be exposed by tomorrow, there isn't much intense convection above 17n.
It very well could be, new center could be redeveloping, I might get heat for this, but i think we are safe in Puerto Rico, But I'm a little worried for Barbuda and even Antigua. They will get effects from this I'm sure.

Dave
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677. JLPR2
A mid level hurricane! XD

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It would be foolish for people in the northern islands to write this storm off.
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Quoting JLPR2:
If I didn't know any better I would say the center is around 16.1n.



Really confusing storm, if this keeps up the circulation should be exposed by tomorrow, there isn't much intense convection above 17n.


You're right IMO, There is some who just refuse to go against the models thats all!
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Pottery, stay safe and I know you are ready just in case.
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Ex-Isaac

Member Since: July 17, 2009 Posts: 71 Comments: 27600
Quoting stormpetrol:
Leslie is different from Ernesto and Isaac IMO , there ain't displacement per se of COC.



Almost perfectly vertical.
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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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