Which model do you trust? And, Arctic sea ice reaches a record minimum

By: Dr. Jeff Masters , 7:33 PM GMT on August 17, 2007

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Hurricane Dean, now a major Category 3 hurricane with 125 mph winds, continues to intensify and grow larger in size. Dean pounded Martinique and St. Lucia this morning, and claimed its first victim when a 62-year old man died on St. Lucia while trying to save his cow from raging flood waters.

Dean's eye is now visible on long range radar out of Puerto Rico. Buoy 42059 is in Dean's path, and should be interesting to watch.

We're fairly confident of the 1-2 day forecast, which has Dean headed west to west-northwest over the Central Caribbean, very close to Jamaica and the Cayman Islands, then into the Western Caribbean. After that, things become murkier. The latest 12Z runs of the NOGAPS, UKMET, GFS, and HWRF computer models all show Dean hitting the Yucatan Peninsula, and continuing on into the Gulf of Mexico towards a second landfall near or south of the Texas border. The HWRF run is slower, and does not take Dean to the coast at the end of its forecast period. The big outlier is the GFDL model, which now takes Dean northwest into central Louisiana. Which model is correct? The problem is that each model has a different solution for the behavior of an upper-level low pressure system expected to be over the Gulf of Mexico early next week. Which model should we trust?

In 2006, the official NHC forecast performed better than any of the individual computer forecast models. However, several "consensus" forecasts made using an average of the "big four" computer models (GFDL, GFS, UKMET, and NOGAPS), slightly outperformed the official forecast at some time periods (Figure 1). The Florida State Super-Ensemble (FSSE), for example, combines the "big four" models on the basis of past performance in an attempt to correct for biases in those models. (The FSSE is owned by a private company, which makes it available to NHC but not the general public). The Florida State Super Ensemble slightly out-performed the official NHC forecast at most forecast times.

The "big four" models are plotted on wunderground.com's computer model page for Dean, (along with the inferior BAMM model, which is plotted since it is always available quickly, and has done well at longer range forecasts in the past). We do not get tracking points for the ECMWF or HWRF models at this point, so you'll have to go the raw plots to see those forecasts. Note that three of the "big four" models performed well in 2006, with the GFDL and GFS performing the best. The UKMET had a very poor showing in the Atlantic in 2006. However, the UKMET was the best-performing model in the Eastern Pacific in 2006, along with the GFDL and BAMM models.

The European Center's model (ECMWF) outperformed the "big four" consensus models for 72, 96, and 120 hours forecasts in the Atlantic. However, the ECMWF model was generally not available in time to be used by forecasters. Efforts are being made to make the ECMWF available in a more timely fashion for the 2007 season, which would be a big help. We also have the new HWRF (Hurricane Weather Research Forecast) model this year. In tests done on a number of hurricanes for past years, the HWRF performed about as well as the GFDL (Figure 2).



Figure 1. Track forecast skill in 2006 of the official forecast and the various models, compared to a "zero skill" forecast using NHC's CLIPER5 model. The CLIPER model (short for CLImatology and PERsistence) is a model that makes a forecast based on historical paths hurricane have taken, along with the fact that hurricanes tend to keep moving in the direction they are going (i.e., their current motion persists). Note that many models had a negative skill for their 120 hour (5 day) forecast. The official NHC forecast had about 10% skill at 5 days. Image credit: NHC.

Figure 2. Track errors for 48-hour forecasts from the 2006 version of the GFDL model (black) and the new HWRF model (red). The HWRF model performed better on some hurricane than the GFDL, and worse on others. Overall, the two models had about the same performance on the cases tested. Image credit: Naomi Surgi, NOAA Environmental Modeling Center.

In conclusion, the official NHC forecast outperforms all the individual models, particularly at long ranges. Looking at the individual model plots can be helpful to determine the uncertainty in the forecast, but it's tough to beat the NHC. In the case of Dean, where one model is an outlier from the rest, it is usually better to believe the consensus of the other models.

If you want to look at plots of the individual models, I've written a description of the various models and where to find these plots on our tropical weather page.

Arctic sea ice shrinks to record low
The National Snow and Ice Data Center announced today that Arctic sea ice has just surpassed the previous single-day (absolute minimum) record for the lowest extent ever measured by satellite. Satellite measurements began in 1979. Sea ice extent has fallen below the 2005 record low absolute minimum and is still melting. Sea ice extent is currently tracking at 5.26 million square kilometers (2.02 million square miles), just below the 2005 record absolute minimum of 5.32 million square kilometers (2.05 million square miles). This new record was set a full five weeks before the usual late September minima in ice extent, so truly unprecedented melting is occurring in the Arctic. The most recent images from the North Pole webcam show plenty of melt water and rainy conditions near the Pole.


Figure 2. Current extent of the polar sea ice, compared to the normal for this time in August (pink line). Image credit: National Snow and Ice Data Center.

I'll have an update Saturday morning.
Jeff Masters

Hurricane Dean near the island Puerto Rico (Hector777)
the ciclonic surge hard mind in Salinas,Puerto Rico mines the Community Las Ochenta in the south of Puerto Rico
Hurricane Dean near the island Puerto Rico

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635. OUFan919
10:42 PM GMT on August 17, 2007
Is it me or is Dean looking more and more like Wilma when she went under rapid intensification but a little larger?
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634. StormJunkie
10:41 PM GMT on August 17, 2007
456, take the all caps off, it looks too much like the NHC. Even though most of us know it is not, we also know that you don't always post in caps.
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633. StormJunkie
10:37 PM GMT on August 17, 2007
Evening all! Almost done with the Java issue!

Welsh, Good preparedness info, imagery, and model info here.

Also, this buoy will be the next one we need to keep an eye on.
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632. Metallica1990
10:39 PM GMT on August 17, 2007
Posted By: welshcayman at 10:36 PM GMT on August 17, 2007.

I know you guys are worried about where you live (especially those of you in LA) but please remember those of us in the islands who are facing a catastrophic system hitting us within the next 48 hours.

We are coming here for updated info and any helpful advice we can get regarding track and intensity and frankly it is getting tough to find the decent posts in between the all of the 'my city was hit harder than your city' posts.

Just a thought.


are you staying for this thing?
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631. dean2007
10:40 PM GMT on August 17, 2007
Two words, Rapid Strengthening.
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630. littlefish
10:38 PM GMT on August 17, 2007
bekro- the UKMET hjasn't developed Dean enough all along so it should be discounted IMO. Just my opinion.
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629. MrNiceville
10:39 PM GMT on August 17, 2007
Thanks, Ike - y'all be nice to each other - I'll c ya on the other end (in about 4 hours)...
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628. bayoubrotha
10:39 PM GMT on August 17, 2007
I didn't say Mobile didn't flood "buddy".

I said it was not destroyed.
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627. jj292
10:38 PM GMT on August 17, 2007
The UKMET also seems to be moving more into agreement with the GFDL.
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626. Weather456
10:36 PM GMT on August 17, 2007
CENTRAL AMERICA AND THE CARIBBEAN REGION....

TYPICAL AFTERNOON THUNDERSTORMS ARE OVER CENTRAL AMERICA AND CUBA BUT ACTIVITY OVER THE LATTER MAYBE ENHANCED BY AN UPPER LOW TO THE NORTH. A TROPICAL WAVE IS ALONG 80W SOUTH OF 17N MOVING WEST AT 16 KNOTS. THE WAVE SHOWS UP WELL ON SATELLITE IMAGERY AS A SURGE OF MOISTURE INCLUDING THE PERCEPTIBLE WATER BY THE SSMI SENSOR. SHOWERS ARE WITHIN 50 NM EAST OF THE WAVE.

WINDS OVER THE CARIBBEAN ARE MODERATE TO STRONG WITH STRONGEST OVER THE EASTERN CARIBBEAN AND NEAR THE COLOMBIAN COAST.

A MORE COMPREHENSIVE REPORT ON HURRICANE DEAN LATER TONIGHT OR SATURDAY AS MORE INFORMATION FROM THE ISLANDS BECOMES AVAILABLE.
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625. dean2007
10:38 PM GMT on August 17, 2007
Two words, Rapid Strengthening.
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624. jrhms08
10:35 PM GMT on August 17, 2007
I can't believe so many of you are getting worked up over peoples opinions. How can a complete stranger in a blog scare you. Time will tell where the storm lands and I hope it doesn't do any damage. Everyone who lives on the coast has made a decision to live there and should understand what could possibly happen. No different than living in an earthquake prone area or in tornado alley. Many of you just need to relax and wait for the experts to weigh in on it in a few days.
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623. Metallica1990
10:37 PM GMT on August 17, 2007
Posted By: UnderstandingFL at 10:37 PM GMT on August 17, 2007.

Good idea Metallica, we did that, too. There are too many people this area. Traffic becomes a nightmare, and lines are many times hours long for anything (not to mention people are not in the best of moods).


lol way too true
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622. nawlinsdude
10:37 PM GMT on August 17, 2007
The winds during Katrina were North which pushed the water in the lake to the south shore. Thats why on some parts of the lake levee, the water lapped over. I went out after the storm and I could see where the water lapped over. A storm hitting 150 miles west of NOLA is in no way the worst case scenario.
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621. AnthonyJKenn
10:31 PM GMT on August 17, 2007
Ahhhh, Bayoubrotha..I happen to live 20 miles north of Lafayette, in Opelousas.

If that GFDL path pans out, we're flatland.

That would put the eye right over me...with possible 100-120mph winds.

I'm not hoping for another Katrina...but if there is any hint of that path, Lafayette will become a ghost town by Tuesday...and so should any city in that area.

I'm still hopeful, though, that that is an outlier and a Yuc-SoTex-NoMex landfall is still the main forecast. I'd rather that then even a Galveston hit.


Anthony

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620. DocBen
10:36 PM GMT on August 17, 2007
welshcayman - I think the 'assumption' is that ya'll are well prepared. From what little I know most of the islands ride them out fairly well with the notable exception of Hispaniola. Also, my understanding is that the storm surge goes around islands instead of surging in and up.
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619. IKE
5:38 PM CDT on August 17, 2007
Posted By: MrNiceville at 5:35 PM CDT on August 17, 2007.
Well folks - just thought I'd check in before hitting the road - Niceville, here I come.

Just saw the latest GFDL solution - so the outlier says Tue/Wed timeframe? Why did it deviate so drastically from the others? ULL interaction?


Yes...ULL interaction.
Member Since: June 9, 2005 Posts: 23 Comments: 37860
618. C2News
6:37 PM EDT on August 17, 2007


Hurricane Dean is intensifying...and now has a pinhole eye! This is a dangerous situation for anyone in its way...
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617. Baybuddy
10:37 PM GMT on August 17, 2007
You are in my prayers Welsh. Some people seem to think this is a contest.
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616. wetlandsLA
10:37 PM GMT on August 17, 2007
we are all thinking of you welsh....just nothing to give every five min.
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615. Wundermobay
10:36 PM GMT on August 17, 2007
Welshcayman how are preparations for Dean going?
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614. firecane
10:37 PM GMT on August 17, 2007
A few words of caution from a long time reader andfirst time poster:

Some people take our ideas very seriously. There is a lot of good information on this blog. We need to post sensible and responsible information. Life and death decisions could depend on what we say in here. Should they, of course not. On the other hand, people are more computer savy and tend to read blogs more than they listen to the NHC.

With that in mind, I think the gulf coast residents should all be on alert and pay close attention to the updated NHC tracks. We all know that things change and the cone of uncertainity is what to watch. As of now, this includes Mexico, Brownsville, Corpus, and Galveston.
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612. bekroweather
10:36 PM GMT on August 17, 2007
Latest solution from the UKMET model (18Z) seems to be considerably weakening the storm - probably influenced by Haiti and Cuba.
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611. UnderstandingFL
10:37 PM GMT on August 17, 2007
Good idea Metallica, we did that, too. There are too many people in this area. Traffic becomes a nightmare, and lines are many times hours long for anything (not to mention people are not in the best of moods).
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610. littlefish
10:29 PM GMT on August 17, 2007
15N 32W looks to be where the next wave is. No convection, has been that way all day so it may fizzle. Not sure but I think there's a fair amount of SAL that got kicked up from it roaring off Africa and may be inhibiting it.
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609. ruckus83
10:31 PM GMT on August 17, 2007
** my first post ** i am from destin so i have been through a few strong storms but im now in the state capital of tallahassee and i was wondering if anyone knew of any strong stroms or hurricanes at all to ever hit the big bend of florida, i have been trying to find something but cant. Does anyone know why no storms ever hit here? thank you. I LOVE READING EVERYONES COMMENTS
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608. wetlandsLA
10:35 PM GMT on August 17, 2007
Good point Doc...I just tought you may have been saying that K went west of NO and that is wyh it flooded.....
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607. welshcayman
10:33 PM GMT on August 17, 2007
I know you guys are worried about where you live (especially those of you in LA) but please remember those of us in the islands who are facing a catastrophic system hitting us within the next 48 hours.

We are coming here for updated info and any helpful advice we can get regarding track and intensity and frankly it is getting tough to find the decent posts in between the all of the 'my city was hit harder than your city' posts.

Just a thought.
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606. i12BNEi
10:27 PM GMT on August 17, 2007
When was the last time that 2 major hurricanes made landfall with days of eachother?
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605. Baybuddy
10:32 PM GMT on August 17, 2007
Parts of mobile were under 15ft. of water "brotha".
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604. MrNiceville
10:33 PM GMT on August 17, 2007
Well folks - just thought I'd check in before hitting the road - Niceville, here I come.

Just saw the latest GFDL solution - so the outlier says Tue/Wed timeframe? Why did it deviate so drastically from the others? ULL interaction?
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603. bayoubrotha
10:32 PM GMT on August 17, 2007
Betsy was 1965.

Camille was 1969.

Betsy made landfall in New Orleans as a Category 3 hurricane and flooded the city by causing the Mississippi River to overflow the levees all the way to Lake Ponchartrain.

Four years later, Camille made landfall near Biloxi, close to where Katrina made landfall, as a Category 5 hurricane.

Four year apart, two hurricanes worse than Katrina.



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602. miken62
10:34 PM GMT on August 17, 2007
Bayou

Check the records; the coast was beat up all the way to the Fl Panhandle
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601. weathersp
6:32 PM EDT on August 17, 2007
Wetlands,

His point is that when Katrina hit it was east of NOLA. The winds were out of the west over lake Pontchartrain pushing some of the water out of the lake and into the GOM. If it landed west it would be opposite. The wind would bring the water into lake Pontchartrain.
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600. Jedkins
10:31 PM GMT on August 17, 2007
Folks Dean is rapidly strenthening, look at the last few frames on sattelite, it is organizing very rapidly.


This thing is starting to scare me.
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599. DocBen
10:33 PM GMT on August 17, 2007
wetlands - just noting that thinking that being 100 miles away will make you in the clear isn't necessarily a good bet. 100 miles is awful close to a cat 5.

"The wind would bring the water into lake Pontchartrain."

And from there into NOLA.
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598. MisipiGrl
10:31 PM GMT on August 17, 2007
"I do not recall Mobile being devastated by Katrina."

"Devastated" is a harsh word. Mobile DID flood and there was a considerable amount of damage in Mobile, Bayou LaBatre and Gulf Shores. While my home and community were "devastated" by Katrina, I also realize that we are not the only ones who suffered her wrath. A cousin in Destin said they even got surge from her.
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597. miken62
10:29 PM GMT on August 17, 2007
Cleo..
what I was getting at is the fact that it is not as highly popualted ....I have been all down the coast to Tulum and I know of the villages ....Belive me Idon't wish any harm on them ..
thnx
mike
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596. wetlandsLA
10:31 PM GMT on August 17, 2007
what is your point DOC?
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595. CFL
10:30 PM GMT on August 17, 2007
JPLR, i'd at least wait until we get an invest before we start calling this future TD6, but those high probabilities are suspicious
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594. Weather456
10:29 PM GMT on August 17, 2007
....SYNOPSIS....

GULF OF MEXICO/ATLANTIC OCEAN WEST OF 60W....

THE WEST EXTENSION OF THE SUBTROPICAL RIDGE COVERS MOST THE SOUTHWEST NORTH ATLANTIC AND THE GULF OF MEXICO AND COMBINE WITH LOW PRESSURE OVER CENTRAL MEXICO...IS PRODUCING MODERATE SOUTHWESTERLY RETURN FLOW OVER THE WESTERN GULF OF MEXICO . QUIKSCAT SUPPORT A SWATH OF 20-30 KNOT WINDS WEST OF 95W. IN THE UPPER LEVELS...A LARGE RIDGE COVERS THE SOUTH-CENTRAL US AND MOST THE GULF OF MEXICO WITH AN UPPER LEVEL LOW OVER THE NORTHERN BAHAMAS APPROACHING SOUTH FLORIDA.

SHOWERS ARE OVER TEXAS AND LOUISIANA AND THE IMMEDIATE GULF WATERS WHERE UPPER ENERGY FROM THE HIGH/RIDGE AND LOW LEVEL INFLOW FROM THE GULF ALONG WITH MOISTURE LEFT OVER FROM ERIN IS ENHANCING INSTABILITY. ELSEWHERE...SHOWERS ARE OVER THE SOUTHEASTERN US WHERE A COLD FRONT IS DROPPING SOUTH AND SHOWERS ARE OVER THE BAHAMAS ASSOCIATED WITH UPPER LOW. OTHERWISE FAIR WEATHER IS NOTED.

BY WEATHER456
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593. bayoubrotha
10:27 PM GMT on August 17, 2007
Mobile, Alabama, is about 100 miles east of where Katrina made landfall.

I do not recall Mobile being devastated by Katrina.
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592. extreme236
10:30 PM GMT on August 17, 2007
the eye is now void of all convection on infrared. it appears dean has sustained an eye
Member Since: August 2, 2007 Posts: 19 Comments: 19234
591. DocBen
10:28 PM GMT on August 17, 2007
Posted By: bayoubrotha at 10:20 PM GMT on August 17, 2007.

The eye of Katrina came within 40 miles east of New Orleans, not 150 miles

Remember, if the eye is to your east the winds are OFFSHORE. If it is to the west the winds are ONSHORE and are stronger.
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590. JLPR
10:25 PM GMT on Agosto 17, 2007
now i see its that little bad wave off Africa that has 8-10% of probability to develop it looks very good and at the last frame looks to have builded some convection we may be lookng at future TD6
and also we have a mini saharacane inland lol
Africa Sat

Formation Probability
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589. extreme236
10:27 PM GMT on August 17, 2007
Posted By: bayoubrotha at 10:24 PM GMT on August 17, 2007.

THAT'S WHY A CAT 5 LANDING WEST OF NOLA IS BAD!!

GFDL 12z has a Category 4 hurricane coming ashore at Vermillion Bay and hiting Lafayette.

That is 150 miles away. It would not destroy New Orleans, which has survived closer hurricane landfalls: the 1915 Hurricane, Betsy, Camille and Katrina.

Can we please stop the hype and scare tactics?
At this point, we do not have a clear idea of where Dean will end up.


I agree that the hype is a little much but since NOLA has already been majorly damaged by a hurricane, another hurricane could seriously destroy the city. it may have survived other storms but those storms werent 2 years apart
Member Since: August 2, 2007 Posts: 19 Comments: 19234
588. Metallica1990
10:25 PM GMT on August 17, 2007
Posted By: UnderstandingFL at 10:24 PM GMT on August 17, 2007.

MTJax, thanks for the info, even though I couldn't see the images.

I hope it doesn't develop. I don't want to even think about any storm hitting South Florida. The economy and Real Estate down here wouldn't be able to handle it right now.


i used dean as a great example of now is the time to start getting stuff for the season
so weve already gotten suplies if a storm does decide to head our way
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586. cleo85
4:56 PM CDT on August 17, 2007
For miken62.
Just a little correction on your comment. The southern Yucatan can handle a hurricane any better than Cancun or Cozumel. There are hundreds poor little Maya villages with unstable construction and the danger of getting flooded in the Jungle. Believe me. We did a lot of work with "Angelnotion" in the area. We know about the hurricane damages first hand. We suffered Emily, Wilma and Stan in 2005 and did see the damage first hand. We have our property 50ml south of Cancun, 10ml south of Playa del Carmen and 10ml of Cozumel across the sea.
There is nowhere a "good" place to make landfall.
Heidi
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585. sociologyguy
10:20 PM GMT on August 17, 2007
thanks for the article on sea ice...
who knows what brews up there?
More frequent and stronger storms coming out of the artic?
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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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