Isaac slamming Gulf Coast with damaging floods, tornadoes

By: Dr. Jeff Masters , 4:44 PM GMT on August 30, 2012

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Slow-moving Tropical Storm Isaac continues to hammer coastal Louisiana, Mississippi, Alabama, and Florida's Panhandle with tornadoes, torrential rains, high winds, and a damaging storm surge. Over the past 24 hours, destructive tornadoes have touched down in Biloxi and Pascagoula, Mississippi, and one person was killed by a tree falling on a car in Pearl River County, Mississippi. A major flood event is occurring in Slidell, Louisiana, where Isaac's storm surge filled Bayou Bonfouca and the W-14 Canal, inundating portions of the city with 1 - 5 feet of water. While Isaac is now a weakening minimal-strength tropical storm, it is still a potent rainmaker, and will cause damaging floods all along its path for the next three days. Major river flooding is occurring or is about to occur on a number of rivers in the landfall area. In north central Tangipahoa Parish in southeast Louisiana and southwestern Pike County in southern Mississippi, a mandatory evacuation has been ordered for all low-lying areas and along the Tangipahoa River, due to the potential failure of the Lake Tangipahoa dam. Audubon Park in New Orleans, recorded 11.19" of rain as of 7 pm Wednesday night. An earlier amount of 19" was found to be erroneous, and this is not a 24-hour precipitation record for the city. According to wunderground's weather historian, Christopher C. Burt, New Orleans' greatest 24-hour rainfall on record is 14.01" on July 24 - 25, 1933. The Louisiana official state 24-hour record is 22.00" on Aug. 29, 1962 at Hakberry, although U.S. Army Corps of Engineers `Storm Studies' mentions a 23.80" falling in a 24-hour period at Millers Island during a TS on Aug 7-8, 1940. Storm total was 37.50" over a 60-hour period there during that event.

A few other rainfall totals from Isaac, through 11 am EDT on Thursday:

15.02" Marion, MS
10.09" Hattiesburg, MS
10.15" Gulfport, MS
9.80" Slidell, LA
9.74" Biloxi, MS
8.52" Mobile, AL
5.57" Baton Rouge, LA


Figure 1. Isaac's winds and storm surge overcomes the seawall and floods South Beach Boulevard in Waveland, Miss., Wednesday, Aug. 29, 2012, the seventh anniversary of Hurricane Katrina hitting the Gulf Coast. (AP Photo/Rogelio V. Solis). Waveland experienced a storm surge in excess of 5' for 36 hours.

Isaac's storm surge winds down
Storm surge levels along the coast of Mississippi and surrounding areas are gradually receding, and the surge has finally fallen below 5' at Waveland, which experienced a storm surge in excess of 5' for 36 hours. Isaac's storm surge levels were characteristic of a Category 2 hurricane, and lasted for an exceptionally long period of time. Waveland, Mississippi experienced a peak surge of 8' and peak storm tide of 9' (surge plus the natural high tide), which beat the levels that occurred during Category 2 Hurricane Gustav of 2008 (7' of storm tide.) The peak 11.06' storm surge at Shell Beach, which is in Lake Borgne, 30 miles southeast of New Orleans, exceeded the 9.5' surge recorded there during Gustav. According to an article in nola.com, Isaac pushed a storm surge of 13.6' into Lake Borgne, on the east side of New Orleans. This is not far from the 15.5' storm surge Hurricane Katrina brought to the location. It is quite possible that Isaac's storm surge might have breached levees of the east side of New Orleans, flooding areas inhabited by tens of thousands of people, had the Army Corps of Engineers not completed their $14.5 billion upgrade to the New Orleans flood defenses this year. I estimate that storm surge damage from Isaac will exceed $2 billion. Isaac has likely caused $2.5 billion in insured damage not related to flooding, insurance firm Eqecat estimated yesterday. Here were some of the peak storm surge values that were recorded at NOAA tide gauges during Isaac:

11.1' Shell Beach, LA
8.0' Waveland, MS
3.5' Pensacola, FL
4.6' Pascagoula, MS
3.8' Mobile, AL


Figure 2. A TRMM satellite 3-D view of rainfall on Aug. 28 showed a few very powerful thunderstorms near Isaac's eye were reaching heights of almost 17 km (10.6 miles.) Intense bands of rain around Isaac were occasionally dropping rain at a rate of over 2.75 inches per hour. Image credit: SSAI/NASA, Hal Pierce.

Isaac's storm surge on the Mississippi River
A storm surge estimated at 12' moved up the Mississippi in Plaquemines Parish near Port Sulphur, LA, near 8:30 pm EDT Tuesday, causing overtopping of the levees and flooding of homes in the mandatory evacuation areas behind the levees. These levees were not part of the $14.5 billion levee upgrade New Orleans got after Hurricane Katrina, and were not rated to Category 3 hurricane strength, like the levees protecting New Orleans are. Since salt water is more dense than fresh water, the surge travelled along the bottom of the river, with the fresh water flow of the river lying on top. The surge continued upriver, and before reaching New Orleans, encountered an underwater barrier in Plaquemines Parish. This barrier was constructed by the Army Corps of Engineers beginning on August 15, in order to keep salt water from moving upstream and contaminating drinking water for Plaquemines Parish and New Orleans. Salt water had made it 90 miles upriver to the outskirts of New Orleans, due to the low flow rate of the river (which had dropped 7' below average in height due to the drought of 2012.) According to a spokesperson for the National Weather Service River Forecast Office, this barrier was probably able to completely block the flow of salt water upriver due to Isaac's storm surge, and no salt water made it as far as New Orleans. However, the massive intrusion of ocean water into the river channel caused the mighty Mississippi's fresh water flow to back up for hundreds of miles. Water levels were elevated by 10' in New Orleans (103 miles upstream from the mouth of the Mississippi), 8' in Baton Rouge (228 miles upstream), and 1.4' at Knox Landing, an amazing 314 miles upstream.

Hurricane Kirk in the Central Atlantic
Hurricane Kirk intensified into a 75 mph Category 1 hurricane this morning, becoming the busy 2012 Atlantic hurricane season's fifth hurricane. With the season's mid-point of September 10 still almost 2 weeks away, we've already had 12 named storms and 5 hurricanes, which is close to what an entire season experiences in an average year (11 named storms and 6 hurricanes.) Kirk should stay well out to sea and not trouble any land areas.


Figure 3. Morning satellite image of Hurricane Kirk.

Tropical Storm Leslie forms in the Central Atlantic
Tropical Storm Leslie has formed in the Central Atlantic. Leslie's formation on August 30 puts 2012 in 2nd place for earliest formation date of the season's 12th 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. Leslie is organizing quickly, and appears destined to become a hurricane before the week is out. 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. In the long term, it remains unclear if Leslie will follow Kirk and fully recurve out to sea. The latest 2 runs of the GFS model have predicted that Leslie will recurve out to sea and not threaten any land areas, but the latest 2 runs of the ECMWF model have predicted that the trough of low pressure pulling Kirk to the northeast will not be strong enough to recurve Leslie out to sea. Instead, the ECMWF predicts that a ridge of high pressure will build in early next week, forcing Leslie more to the northwest, making the storm a potential threat to Bermuda, then to the Northeast U.S. and Canada in 8 - 11 days.

Jeff Masters

Hurricane Isaac Louisiana (apphotos)
Two men walk in the storm surge from Isaac, on Lakeshore Drive along Lake Pontchartrain, as the storm approaches landfall, in New Orleans, Tuesday, Aug. 28, 2012. (AP Photo/Gerald Herbert)
Hurricane Isaac Louisiana
west palm beach flood isaac (alishu)
West Palm Beach flood from Isaac
west palm beach flood isaac
Hurricane Isaac Impacts Navarre Beach & Pier10 (jennjeff1)
Hurricane Isaac versus Navarre Beach Pier, the longest concrete pier on the Gulf of Mexico
Hurricane Isaac Impacts Navarre Beach & Pier10

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Quoting NCHurricane2009:


I am more like A and 1....there are too many troughs swinging in to recurve systems out to sea (like we are seeing with Kirk and Leslie computer model runs)...and if El Nino comes around for the winter...the troughs are only going to get stronger as we push into October...November...

What about home-brews?
Member Since: May 12, 2012 Posts: 11 Comments: 2870
Quoting JrWeathermanFL:
Kirk could easily become the season's first major.
And now that we have Leslie, we have 8 named storms in August.
We could very well se Alpha this year.
I doubt it. I don't think we'll see more than another 5 storms at the most, which will take us to, what, the S or T name?

OTOH, I'm basing my prognisication on the expectation of a genuine El Nino onset, which seems less likely now than it did 8 weeks ago...
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Quoting wunderkidcayman:


yep it sure does stormwatcherCI and TAZ

oh Taz stick around I got a surprise for you I think you may like



oh boy is it you in a dress?
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Quoting opal92nwf:
Alright, I have a questionnaire! Of what percentage do you think we will see another Gulf storm this year?

A) 10%
B) 30%
C) 50%
D) 70%
E) 90%

And then what time of year do you think it will be?

1) anytime in September
2) early September
3) late September
4) anytime in October
5) November

My guess is D, 1


I am more like A and 1....there are too many troughs swinging in to recurve systems out to sea (like we are seeing with Kirk and Leslie computer model runs)...and if El Nino comes around for the winter...the troughs are only going to get stronger as we push into October...November...
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Just wanted to come on today and thank the folks on this site who were constantly giving good info while the chaos of the storm was going on. I think I speak for a lot of folks that were and still are and will be affected by the hurricane that we appreciate everything you guys try to accomplish on here. And to the "trolls" that come on here giving false info to folks that need honest info, shame on you. There is absolutely no time nor the need for that on here in a situation like that. I think most people know to always listen to your local authorities but there is some really trusted bloggers on here that give you some really good info. Anyways just wanted to say thank you to all that helped contribute and keep up the good work in the future
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18z GFS is running. 54 hours:

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Quoting clwstmchasr:


That is an indiation that the high is not as strong and it may begin in turn wnw as indicated by the NHC.



sorry but not evere thing gos has plan all so not evere track follows what the nhc says this storm is not moveing at 21mph has the nhc say it is to me it has really slowed down too 10 too 15mph all so right now it will keep moveing W
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Kirk will become a Major by the morning.
Leslie will become a Hurricane by Saturday Afternoon.
Isaac will be Retired.

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Alright, I have a questionnaire! Of what percentage do you think we will see another Gulf storm this year?

A) 10%
B) 30%
C) 50%
D) 70%
E) 90%

And then what time of year do you think it will be?

1) anytime in September
2) early September
3) late September
4) anytime in October
5) November

My guess is D, 1
Member Since: May 12, 2012 Posts: 11 Comments: 2870
Quoting stormwatcherCI:



It is building back in. Latest steering.
Quoting Tazmanian:



looks like the L storm will go W


yep it sure does stormwatcherCI and TAZ

oh Taz stick around I got a surprise for you I think you may like
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Quoting opal92nwf:
Wow, if Kirk is strengthening this much in the "cooler" water he is in, then a major is still possible anywhere in the Gulf.
Yes.But storms this year have had a opportunity to take advantage of those waters but thanks to the unfavorable conditions none have so far.Thank goodness.
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Quoting TropicalAnalystwx13:

Well...it looks like it will be half right.

If the XTRP is right, which it usually is, it may get pretty close to Maine... So maybe it will be completely right.



Edit: But that still wouldn't be Florida.
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Quoting opal92nwf:
Wow, if Kirk is strengthening this much in the "cooler" water he is in, then a major is still possible anywhere in the Gulf.
That is just the deep heat content not the surface temps.
Member Since: August 2, 2010 Posts: 0 Comments: 2000
Quoting NCHurricane2009:

Good point...but I don't think the shear is gonna go up until Saturday....so in a low shear scenario the low-level inflow and upper outflow are allowing Kirk to create his own moist environment...which will keep the dry air at bay....

And it looks like he is doing the most impressive RI (rapid intensification) episode we've seen so far this season...so he could easily be a major before Saturday comes around IMO...


Yep, could be, but small, intense hurricanes get upset the same way a fast spinning top falls over. We'll see if Captain...err...major hurricane Kirk wins this one. :)
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Quoting opal92nwf:
Wow, if Kirk is strengthening this much in the "cooler" water he is in, then a major is still possible anywhere in the Gulf.

Not sure how this TCHP (tropical cyclone heat potential) really works...I am not that convinced...for example Gordon bombed-out to cat 2 in the NE Atlantic earlier this month...

I use sea-surface temp maps. The one on my blog shows Kirk over 29 deg C this morning...plenty warm for development. The Gulf temps are 29 to 30 deg C...so using sea-surface temps...the Gulf is not that different from where Kirk is....
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Quoting Tazmanian:




DOOM DOOM DOOM


Lol.
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Leslie sure dos not look like its moveing at 21mph too me it has really slow down
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Wow, if Kirk is strengthening this much in the "cooler" water he is in, then a major is still possible anywhere in the Gulf.
Member Since: May 12, 2012 Posts: 11 Comments: 2870
Quoting njandtmp:
Looks Like I may get alot of rain this weekend.

Link


Or not. Check on the accuracy record of HPC predictions. They make even the worst hurricane model look good.
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Quoting yqt1001:
I've been gone for a few days so excuse my tardiness...


Well...it looks like it will be half right.
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Quoting hurricanewatcher61:
Is it just my untrained eyes or does Leslie look to be missing her next forecast points?

Looks to be following dead-nuts to me so far...

And it looks like Leslie will be this season's first "she-cane" (unless you believe Beryl should have been a hurricane)...
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I've been gone for a few days so excuse my tardiness...

Quoting WxGeekVA on December 1st 2011:

Breaking News: Cleverbot says that Florida will get hit by a major hurricane next year!!!!

Me: Will the United States get hit by a major hurricane next year?
Cleverbot: No, the flamingos will.
Me: So Florida is going to
get hit?
Cleverbot: No, Florida is a state.
Me: I mean, is Florida going to get hit by a major hurricane next
year?
Cleverbot: Probably.
Me: How many?
Cleverbot: Me.
Me: You are a major hurricane?
Cleverbot: No
.
Me: I'm going to ask you again: Are you a major hurricane?
Cleverbot: Yes.
Me: What is your hurricane
name?
Cleverbot: Kirkland is my middle name.
Me: You will be Major Huricane Kirk, and hit Florida, right?

Cleverbot: Indeed.
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Quoting JrWeathermanFL:
Kirk could easily become the season's first major.
And now that we have Leslie, we have 8 named storms in August.
We could very well se Alpha this year.


Could be, since we only have for names left.

In other news, the dam that was going to collapse in 90 minutes at 10:00 am CDT hasn't. A total of 18 families did evacuate, and some farmers moved their cows to higher ground. Parish President Gordie has been quoted as saying "Well, it could have happened, and I did manage to make it on the national news." :)
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Quoting stormpetrol:
Not saying Leslie won't recurve, but I've seen that recurve tune played before and the storms didn't dance to it.

I agree with that one expamle early days of Isaac show the same thing curves out to atlantic and we all saw where that ended up

I am not saying it will or it won't but what I will say if TS leslie does not slow down and ridge builds back in that could mean big trouble if it slow down and ridge opens up more and stays that way well it could be big problems for the fishy
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Quoting stormwatcherCI:



It is building back in. Latest steering.



looks like the L storm will go W
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Kirk looks to well define to not be a major.He's in a favorable environment as well.
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Quoting DavidHOUTX:
Where is Leslie going? N or W? That high needs to build in quickly or I think she will escape to the North.




It is building back in. Latest steering.
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Quoting Tazmanian:
too bad we cant get a recon in there for Captain Kirk
yeah, have you seen fuel prices?? way to expensive to get an plane out that far for a 'fish'
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Quoting Chucktown:


Stop the gloom and doom please.




DOOM DOOM DOOM
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Looks Like I may get alot of rain this weekend.

Link
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Quoting sar2401:


OTOH, because he's such a small storm, any dry air entrainment or wind shear could also kill him off. I'm just glad we're watching a fish storm instead of another Isaac.

Good point...but I don't think the shear is gonna go up until Saturday....so in a low shear scenario the low-level inflow and upper outflow are allowing Kirk to create his own moist environment...which will keep the dry air at bay....

And it looks like he is doing the most impressive RI (rapid intensification) episode we've seen so far this season...so he could easily be a major before Saturday comes around IMO...
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I think the NHC is right regarding Leslie's track. Just look at the TS Winds probability graphic... confidence is high. Well, I need to take a nap now, it feels like april here in the Leewards : boring!
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Quoting TropicalAnalystwx13:

Not if Kirk has anything to say about it.


At Kirk's rate of intensification a major hurricane wouldn't shock me.
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Quoting will40:


the final NHC track is hinting at that also

Yea if it manages to have energy left then will have to watch.Just need to watch it as it travels though the midwest.
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Quoting earthlydragonfly:


Kirk will never be a major..... He's a Captain dog gone it!


I knew we'd have problems when I saw the name "Kirk" in the 2012 list. Too many weather geeks are also Trekkies. :)
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Kirk could easily become the season's first major.
And now that we have Leslie, we have 8 named storms in August.
We could very well se Alpha this year.
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Quoting STXHurricanes2012:

Yes...the euro and a few gfs esmemble members show this. It would be interesting though,

Oye...I am tired of Isaac...I hope he gets absorbed on Labor Day weekend by the frontal system sweeping him into the Great Lakes area...
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Quoting STXHurricanes2012:

Yes...the euro and a few gfs esmemble members show this. It would be interesting though,


the final NHC track is hinting at that also
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Quoting NCHurricane2009:

I think he could become a major...unlike Isaac...this is a small storm so any pressure drop amounts to a more signficant increase in wind due to tight pressure gradient...

Morevoer...he's got a very tight core....which helps focus the latent heat release over the center such that most of the pressure drops are at the center rather than spread over a large area near the center....this keeps the pressure gradient even more tight...


OTOH, because he's such a small storm, any dry air entrainment or wind shear could also kill him off. I'm just glad we're watching a fish storm instead of another Isaac.
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Quoting will40:


i think he is talking about if it gets back in the Atlantic

Yes...the euro and a few gfs esmemble members show this. It would be interesting though,
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Where is Leslie going? N or W? That high needs to build in quickly or I think she will escape to the North.

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Quoting LisafromMs:


He's not quite dead here yet. In fact, we are in a dry spell and getting the strongest winds that we have seen from him. And here in central Ms, its going to be another long night with these bands coming out of south Ms. Winds are at around 50mph here right now.


There's hope ahead. For the first time in days, Moble only has scattered clouds and the barometer is rising. The rainbands in west and central AL are falling apart and a little drier air is working its way onto the area. It will still take a bit for the winds to calm down in MS since the pressure gradient is much steeper there but you should see a dramatic improvement within 6 hours. Isaac is finally starting to give up the ghost.
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Quoting Progster:


I know but I'm saying they'll be nothing recognizable left after it sits over the drought belt for a few days.


i agree with that.
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Quoting Chucktown:


Stop the gloom and doom please.


??? What do you mean? Everyone has opinions and the status of Leslie warrants serious thought.
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Quoting TropicalAnalystwx13:
Kirk is probably close to Category 2 status right now. Deep convection going off in the eyewall.


I think he could become a major...unlike Isaac...this is a small storm so any pressure drop amounts to a more signficant increase in wind due to tight pressure gradient...

Morevoer...he's got a very tight core....which helps focus the latent heat release over the center such that most of the pressure drops are at the center rather than spread over a large area near the center....this keeps the pressure gradient even more tight...
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Quoting will40:


i think he is talking about if it gets back in the Atlantic


I know but I'm saying they'll be nothing recognizable left after it sits over the drought belt for a few days.
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Quoting bajelayman2:
For all in the islands, prepare for Leslie, i.e. dont panic, but prepare.

I have a feeling this will be one for the books.


Stop the gloom and doom please.
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Me and WNPR were discussing about how non threatening the the name Leslie sounded.she better stay out to sea.
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I did an update on the Atlantic tropics very early this morning...the usual details are in there...including my custom charts that show the birdseye view of the basin. I do these every 24 to 36 hrs...so feel free to drop in once a day....guarentee 99% of the time it will be updated....

Looks like my aggressive intensity forecast for Kirk was not intense enough....and since I wrote that blog update 98L is now Leslie....
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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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