Global warming and the frequency of intense Atlantic hurricanes: model results

By: Dr. Jeff Masters , 1:37 PM GMT on April 05, 2010

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Could global warming increase wind shear over the Atlantic, potentially leading to a decrease in the frequency of Atlantic hurricanes? There is a growing consensus among hurricane scientists that this is indeed quite possible. Two recent studies, by Zhao et al. (2009), "Simulations of Global Hurricane Climatology, Interannual Variability, and Response to Global Warming Using a 50-km Resolution GCM", and by Knutson et al. (2008), "Simulated reduction in Atlantic hurricane frequency under twenty-first-century warming conditions", found that global warming might increase wind shear over the Atlantic by the end of the century, resulting in a decrease in the number of Atlantic hurricanes. For example, the second study took 18 relatively coarse (>60 km grid size) models used to formulate the 2007 IPCC climate report, and "downscaled" them using a higher-resolution (18 km grid size) model called ZETAC that was able to successfully simulate the frequencies of hurricanes over the past 50 years. When the 18 km ZETAC model was driven using the climate conditions we expect in 2100, as output by the 18 IPCC models, the authors found that a reduction of Atlantic tropical storms by 27% and hurricanes by 18% by the end of the century resulted. An important reason that their model predicted a decrease in the frequency of Atlantic hurricanes was due to a predicted increase in wind shear. As I explain in my wind shear tutorial, a large change of wind speed with height over a hurricane creates a shearing force that tends to tear the storm apart. The amount of wind shear is critical in determining whether a hurricane can form or survive.


Figure 1. Top: predicted change by 2100 in wind shear (in meters per second per degree C of warming--multiply by two to get mph) as predicted by summing the predictions of 18 climate models. Bottom: The number of models that predict the effect shown in the top image. The dots show the locations where tropical storms formed between 1981-2005. The box indicates a region of frequent hurricane formation where wind shear is not predicted to change much. Image credit: Geophysical Research Letters, "Increased Tropical Atlantic Wind Shear in Model Projections of Global Warming", by Vecchi and Soden, 2007.

Since the Knutson et al. study using the 18 km resolution ZETAC model was not detailed enough to look at what might happen to major Category 3 and stronger hurricanes, a new study using a higher resolution model was needed. This was done by a team of modelers led by Dr. Morris Bender of NOAA's GFDL laboratory, who published their results in Science in February. The authors used the GFDL hurricane model--the model that has been our best-performing operation hurricane track forecasting model over the past five years--to perform their study. The GFDL hurricane model runs at a resolution of 9 km, which is detailed enough to make accurate simulations of major hurricanes. The researchers did a double downscaling study, where they first took the forecast atmospheric and oceanic conditions at generated by the coarse (>60 km grid) IPCC models, used these data to initialize the finer resolution 18 km ZETAC model, then used the output from the ZETAC model to initialize the high-resolution GFDL hurricane model. The final results of this "double downscaling" study suggest that although the total number of hurricanes is expected to decrease by the end of the century, we should expect an increase of 81% in the number of Category 4 and 5 storms in the Atlantic. This trend should not be clearly detectable until about 60 years from now, given a scenario in which CO2 doubles by 2100. The authors say that their model predicts that there should already have been a 20% increase in the number of Category 4 and 5 storms since the 1940s, given the approximate 0.5°C warming of the tropical Atlantic during that period. This trend is too small to be detectable, given the high natural variability and the difficulty we've had accurately measuring the exact strength of intense hurricanes before the 1980s.The region of the Atlantic expected to see the greatest increase in Category 4 and 5 storms by the year 2100 is over the Bahama Islands (Figure 2), since wind shear is not expected to increase in this region, and sea surface temperatures and atmospheric instability are expected to increase there.

The net effect of a decrease in total number of hurricanes but an increase in the strongest hurricanes should cause an increase in U.S. hurricane damages of about 30% by the end of the century, the authors compute, assuming that hurricane damages behave as they did during the past century. Over the past century, Category 4 and 5 hurricanes made up only 6% of all U.S. landfalls, but accounted for 48% of all U.S. damage (if normalized to account for increases in U.S. population and wealth, Pielke et al., 2008.)


Figure 2. Expected change in Atlantic Category 4 and 5 hurricanes per decade expected by the year 2100, according to the Science paper by Bender et al. (2010).

Commentary
These results seem reasonable, since the models in question have been successfully been able to simulate the behavior of hurricanes over the past 50 years. However, the uncertainties are high and lot more research needs to be done before we can be confident of the results. Not all of the IPCC models predict an increase in wind shear over the tropical Atlantic by 2100, so the increase in Category 4 and 5 hurricanes could be much greater. Also, the GFDL model was observed to under-predict the strength of intense hurricanes in the current climate, so it may not be creating enough Category 4 and 5 hurricanes in the future climate of 2100. On the other hand, IPCC models such as the UKMO-HadCM3 predict a very large increase in wind shear, leading to a drastic reduction in all hurricanes in the Atlantic by 2100, including Category 4 and 5 storms. So Category 4 and 5 hurricane frequency could easily be much greater or much less than the 81% increase by 2100 found by Bender et al.

The estimates of a 30% increase in hurricane damages by 2100 may be considerably too low, since this estimate assumes that sea level rise will continue at the same pace as was observed in the 20th century. Sea level rise has accelerated since the 1990s, and it is likely that this century we will see much more than than the 7 inches of global sea level rise that was observed last century. Higher sea level rise rates will sharply increase the damages due to storm surge, which account for a large amount of the damage from intense Category 4 and 5 hurricanes.

Keep in mind that while a 30% in hurricane damage by the end of the century is significant, this will not be the main reason hurricane damages will increase this century. Hurricane damages are currently doubling every ten years, according to Pielke et al., 2008. This is primarily due to the increasing population along the coast and increased wealth of the population. The authors theorize that the Great Miami Hurricane of 1926, a Category 4 monster that made a direct hit on Miami Beach, would have caused about $150 billion in damage had it hit in 2005. By 2015, the authors expect the same hurricane would do $300 billion in damage. This number would increase to $600 billion by 2025 (though I think it is likely that the recent recession may delay this damage total a few years into the future.) It is essential that we limit coastal development in vulnerable coastal areas, particularly along barrier islands, to reduce some of the astronomical price tags hurricanes are going to be causing. Adoption and enforcement of strict building standards is also a must.

The authors of the GFDL hurricane model study have put together a nice web page with links to the paper and some detailed non-technical explanations of the paper.

References
Bender et al., 2010, "Modeled Impact of Anthropogenic Warming on the Frequency of Intense Atlantic Hurricanes", Science, 22 January 2010: Vol. 327. no. 5964, pp. 454 - 458 DOI: 10.1126/science.1180568.

Vecchi, G.A., B.J. Soden, A.T. Wittenberg, I.M. Held, A. Leetmaa, and M.J. Harrison, 2006, "Weakening of tropical Pacific atmospheric circulation due to anthropogenic forcing", Nature, 441(7089), 73-76.

Vecchi, G.A., and B.J. Soden, 2007, "Increased Tropical Atlantic Wind Shear in Model Projections of Global Warming", Geophysical Research Letters, 34, L08702, doi:10.1029/2006GL028905, 2007.

Jeff Masters

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Quoting msgambler:
Yes, I now live on Mobile Bay which most already know but parents still live in Gulfport. They have lived there since 62'
Mobile bay has had there share of bad hurricanes also. I have only met 4 people over the years that witnessed Camille.
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Quoting hydrus:
You went thru Camille?
Yes, I now live on Mobile Bay which most already know but parents still live in Gulfport. They have lived there since 62'
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Cant afford to have a dry spring, we'll either burn up like last year, or get hit by a storm
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Morning gang,
So when is it we can expect the droughts to end in the Caribbean? I had been hearing a lot of people saying it was going to be much wetter than usual here. When is this supposed to happen?
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Quoting Chicklit:
I think I see the future low on that sat pic Chicklit. Right on the coast, N.E. Brazil.
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Quoting weathermanwannabe:


Hey Adrian.......Guess your're thinking that "earlier" development into a hurricane out in the middle of the MDR, if that is indeed the case, will give them an opportunity to curve out to sea?..........It's the other waves, that don't get their act together until they start approaching the Caribbean, that I'm worried about.....:)


It's still to early to discern the exact position of the Bermuda High this year and what impact it will have on the upcoming hurricane season but if you dont mind i can briefly explain how it works for those that dont know the mechanics behind it.Imagine the Bermuda High as an enormous blocking wall. Tropical cyclones will move along the southern side of this high pressure system until it finds the western side. This turn to the northeast usually occurs somewhere in the Caribbean. For example the position of the Bermuda High in the 2007 season was farther south and west which, along with the building ridges that extended down into the GOM that year, carried the storms over Central America before the turn to the north took place.

Here's a picture i like to use from nasa to go along with what I'm trying to explain..



How far north the Bermuda High moves will be one of the more significant factors in determining what type of hurricane season Florida will experience. As you can see from the graphic of the BH i posted above, just a slight movement of the BH to the south and your turn to the north will be delayed so to speak, and landfall would be displaced to the west of Florida. The same goes if the BH in that image was more to the north. Your turn to the north and eventually to the northeast would be sooner, and Florida would have more of a heightened chance of being impacted. Of course, other steering patterns play a role in a tropical systems track.Tropical systems follow the least path of resistance, so even if the BH were to signify a panhandle landfall, you could have a building ridge that blocks northern movement and the system ends up moving westward towards Texas or Mexico. Using the same scenario of a building ridge, you could have a cut off low build up over Florida behind the ridge, creating a weakness that would draw the system northward towards Florida.
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Quoting RitaEvac:
Speaking of rain, texas coast is already running below normal. Galveston nearing 3 inches below normal. If we don't get rain starting this month and next were in trouble.
Texas has had some strange weather past 3 months.
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Quoting pottery:
If that model is good, then we can expect the low to pass north of here. But that could be just what we need, to pull some ITZC stuff from the south and give the islands in the south Caribbean some rain.
Your right. I have seen that happen quite a few times in that region. I know you are in a drought. I believe your drought will be over soon.
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Speaking of rain, texas coast is already running below normal. Galveston nearing 3 inches below normal. If we don't get rain starting this month and next were in trouble.
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Quoting hydrus:
The sad part is the low is headed right at Haiti. If this pans out, they might have big trouble.


I would rather face another couple of weeks with no rain than to have heavy rain fall in Haiti.
As you say, it's a model. We will see how it works out.
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Quoting pottery:
If that model is good, then we can expect the low to pass north of here. But that could be just what we need, to pull some ITZC stuff from the south and give the islands in the south Caribbean some rain.
The sad part is the low is headed right at Haiti. If this pans out, they might have big trouble.
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If that model is good, then we can expect the low to pass north of here. But that could be just what we need, to pull some ITZC stuff from the south and give the islands in the south Caribbean some rain.
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Quoting Chicklit:
Yikes dire straits, Pottery. Let's hope merciful rain drops gently from the skies.
That low looks like it will go north of pottery, But it will be close. This is 6 days out too, so there is always the possibility that forecast is off the mark. It certainly looks impressive on the model run.
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Quoting pottery:
Hydrus, that is looking a little ominous, LOL.
Actually, heavy rain anywhere here will be big problems, due to the amount of fires we have had. Run-off would be fast and furious and cause all kinds of issues. Especially in the steep valleys.
We need 2 weeks of gentle showers to stabilize things. Should be an interesting season.
It has been said recently, that we have water (nationally) to last to the end of April. So if we dont get some rain,..........
I thought so too. It almost resembles a Tropical cyclone with all that heavy precip. hmmmmm...
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Yikes dire straits, Pottery. Let's hope merciful rain drops gently from the skies.
Later Gaters.

CaribbeanLoop
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Quoting Patrap:
Well..Hwy 90 is still there..as it is in Fla,Miss,Ala,and Fla and LA..

..hard to move a shoreline.

Unless your a Major Cane,then well..its easy.

I-10 is well inland and is the Main artery E and W...and 90 remains a scenic route chicklit.



Highway 90 definitely is a scenic route. It is right on the beach. (as in you can park your car, walk 15 feet, and be walking on the beach)

They did put some areas behind a concrete seawall, though.
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Hydrus, that is looking a little ominous, LOL.
Actually, heavy rain anywhere here will be big problems, due to the amount of fires we have had. Run-off would be fast and furious and cause all kinds of issues. Especially in the steep valleys.
We need 2 weeks of gentle showers to stabilize things. Should be an interesting season.
It has been said recently, that we have water (nationally) to last to the end of April. So if we dont get some rain,..........
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Quoting Patrap:
Only Katrina in 2005 hushed the Whispers of the Word "Camille",..and those of us who experienced both,..wont soon forget those 2.

No sir..not ever,..

I was 9 for Camille in 69,and 45 for the other.

Some things are best left to memory..cuz words fail to translate the experience.





Frank, who lived behind us was like a big brother to me, and as his father had died, my Dad sorta filled the void. Frank was in the Air Force and was part of the body recovery efforts after Camille. Shortly afterward, he came home on leave and immediately sought out my Dad. I remember the two of them talking in the carport when Frank broke down and began crying. Dad held Frank in an embrace as Frank sobbed about the horrors he had witnessed as they recovered bloated bodies. My father looked up and saw me and I understood the plea in his eyes.. I left. Dad, the tough ol' homicide cop was crying with him. I was 15, Frank 18. Excepting Mom's death, it's the only time I saw Dad break down
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Quoting Patrap:
Only Katrina in 2005 hushed the Whispers of the Word "Camille",..and those of us who experienced both,..wont soon forget those 2.

No sir..not ever,..

I was 9 for Camille in 69,and 45 for the other.

Some things are best left to memory..cuz words fail to translate the experience.



I can not fathom going through Camille. We were hit by Charley, Highest gusts were about 180 give or take a few. Camille,s sustained winds were faster then our gusts!
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ELOKA web site


I get my Arctic news and info from the source Folks,the Inuit.

Inuit Knowledge Centre launched
Inuit Qaujisarvingat: the Inuit Knowledge Centre, was launched to address the gap between western science and Inuit knowledge, as well as to provide a way for Inuit to respond to a growing interest in the Arctic and Arctic issues. The aim of Inuit Qaujisarvingat will be to help Canada build on its inherent advantage as the steward of remarkable human and natural resources that are of vital global importance, help Canada fulfill its international obligations, and help Canada become a leader in the exchange and use of Inuit and scientific knowledge.

Member Since: July 3, 2005 Posts: 428 Comments: 129902
I was sitting on my balcony just this morning thinking it's great to be alive. It is a beautiful day. Enjoy it everyone. You only get this day once. Good news for China rescuing 115 mine workers; bad news for West Virginians and tears for them.
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Quoting pottery:


Thunderstorms have been predicted on and off for the past week or 10 days. Optimistic I think.
Some showers in parts of Trinidad over the w/e, but no real rain as yet. None at my house!
Looks interesting to the south and west though.
Waiting, waiting............
Good Morning Pottery, I just checked the Canadian GEM model, Check out that big low that moves into the Caribbean From the Atlantic.
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Well..Hwy 90 is still there..as it is in Fla,Miss,Ala, and LA..

..hard to move a shoreline.

Unless your a Major Cane,then well..its easy.

I-10 is well inland and is the Main artery E and W...and 90 remains a scenic route chicklit.


Member Since: July 3, 2005 Posts: 428 Comments: 129902
Did they rebuild Highway 90 in the same place or further from the coastline?
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Quoting PensacolaDoug:



Cool!

Northern icecap just hit a 10 year high for the date!


But it is going to have to stick around for more than a season for it to anything but an aberration. I'm thinking that I read that the most important ice is the older stuff and that the amount of second third and fourth year ice has declined along with the outer edges. It would suit me just fine to see a reversal, colder is better for Florida, sea level rise is not Florida's friend. :)
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Quoting Jeff9641:
Looks like the rainy season is starting early this year in Trinidad. Thunderstorms expected the next 10 days I bet Pottery is loving this weather considering it's been so dry the last several months.


Thunderstorms have been predicted on and off for the past week or 10 days. Optimistic I think.
Some showers in parts of Trinidad over the w/e, but no real rain as yet. None at my house!
Looks interesting to the south and west though.
Waiting, waiting............
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Quoting weathermanwannabe:


Hey Adrian.......Guess your're thinking that "earlier" development into a hurricane out in the middle of the MDR, if that is indeed the case, will give them an opportunity to curve out to sea?..........It's the other waves, that don't get their act together until they start approaching the Caribbean, that I'm worried about.....:)

Steering all depends on where the A/B high sets up. It is possible that CV storms could recurve to open sea, and storms that form on the western side of the MDR plow through the Caribbean and into Central America and CONUS.
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Only Katrina in 2005 hushed the Whispers of the Word "Camille",..and those of us who experienced both,..wont soon forget those 2.

No sir..not ever,..

I was 9 for Camille in 69,and 45 for the other.

Some things are best left to memory..cuz words fail to translate the experience.



Member Since: July 3, 2005 Posts: 428 Comments: 129902
Quoting hurricane23:
With a weaker high and the extreme heat in the central/eastern atlantic its possible a good chunk of the storms could recurve well east of the u.s. this season.


Hey Adrian.......Guess your're thinking that "earlier" development into a hurricane out in the middle of the MDR, if that is indeed the case, will give them an opportunity to curve out to sea?..........It's the other waves, that don't get their act together until they start approaching the Caribbean, that I'm worried about.....:)
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Quoting msgambler:
Born and raised in Gpt, MS been through every storm since Camille. I know what you mean but I will probable never leave
You went thru Camille?
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Quoting msgambler:
re 466: I understand but didn't they do that all along? With the maps they would say from this area expect 2-4' all the way to to the other side and be another 2-4' and in the middle be 6-8, 10-12, etc where the storm was expected to come ashore? Now the inundation maps were not there before which may be a good thing to add but as far as surge potental I never saw a problem with what they had before

The problem in simple surge values is that they only calculate the depth at the shoreline. Some areas slope fairly sharply (for a coastline), and a surge will not travel far inland. Other areas (like around the upper TX coast near Port Arthur), the slope is very shallow, so a large surge can go for miles inland. An inundation index like StormW spoke of would go a very long way to helping. That will help out people who live half a mile (or 2-3 miles) inland, but are not very far above sea level. It will also help account for land features such as canals, railroad tracks, and levees that can cause or prevent water rising in a certain area. (railroad tracks can act as small levees, and both protect and harm an area in a surge or flood event)

For example, I know I live 155' above sea level. I also live 14.5' above the mean water level for the creek nearest my house, Willow Creek. (I'm 5.5' above the 100-year flood level) I also live 100 yards from the creek, so the land slopes fairly sharply for the Houston area.
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Quoting Tropicsweatherpr:


Adrian,in terms of the Caribbean,how do you see things unfold trackwise?


Unfortunately the caribbean should be very favorable come the heart season.
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Quoting hurricane23:
With a weaker high and the extreme heat in the central/eastern atlantic its possible a good chunk of the storms could recurve well east of the u.s. this season.


Adrian,in terms of the Caribbean,how do you see things unfold trackwise?
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With a weaker high and the extreme heat in the central/eastern atlantic its possible a good chunk of the storms could recurve well east of the u.s. this season.
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re 466: I understand but didn't they do that all along? With the maps they would say from this area expect 2-4' all the way to to the other side and be another 2-4' and in the middle be 6-8, 10-12, etc where the storm was expected to come ashore? Now the inundation maps were not there before which may be a good thing to add but as far as surge potental I never saw a problem with what they had before
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Of course, with a storm approaching, when people are told "write your social security number on your arm, so we can identify your body after the storm", you would think they could take the hint to leave.

Unfortunately, as was proven with Ike, some people won't heed warnings, regardless how dire they are.
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Born and raised in Gpt, MS been through every storm since Camille. I know what you mean but I will probable never leave
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Some weather in space recently !

http://www.swpc.noaa.gov/

http://www.swpc.noaa.gov/alerts/archive/current_month.html
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Quoting aquak9:


What you're missing, is that most people aren't as intelligent as you. :)


Yeah, like me. However, after staying through Katrina on the MS Gulf Coast, I have learned the hard way I ain't doing that again!
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A twelve-hour rain and 270mm (10.6 in) on Rio de Janeiro, and still raining.
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Quoting twhcracker:


yeah we could talk about GW instead :)



Cool!

Northern icecap just hit a 10 year high for the date!
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Member Since: July 15, 2006 Posts: 178 Comments: 56141
Quoting gordydunnot:
Please people I know the season is getting closer, but this play by play of all ocean and gulf temperatures is a little crazy. Its not that informative, so lets wait for the season to get a little closer. Imo shear rules the day and we are not close enough to the season to judge its value yet.


yeah we could talk about GW instead :)
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Morning all, Hey jeff9641 looks to be a warm dry spell in w c fl for the next 10 days or so. whats your thinking? TIA
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Not used to getting compliments aqua. Thank You.....lol
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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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