CSU predicts a very active hurricane season: 16 storms, 9 hurricanes

By: Dr. Jeff Masters , 4:30 PM GMT on June 01, 2011

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A very active Atlantic hurricane season is on tap for 2011, according to the seasonal hurricane forecast issued June 1 by Dr. Phil Klotzbach and Dr. Bill Gray of Colorado State University (CSU). The CSU team is calling for 16 named storms, 9 hurricanes, and 5 intense hurricanes, and an Accumulated Cyclone Energy (ACE) 166% of average. Between 1950 - 2000, the average season had 10 named storms, 6 hurricanes, and 2 intense hurricanes. But since 1995, the beginning of an active hurricane period in the Atlantic, we've averaged 14 named storms, 8 hurricanes, and 4 intense hurricanes per year. The new forecast is identical to their April forecast. The forecast calls for a much above-average chance of a major hurricane hitting the U.S., both along the East Coast (48% chance, 31% chance is average) and the Gulf Coast (47% chance, 30% chance is average). The risk of a major hurricane in the Caribbean is also high, at 61% (42% is average.)

The forecasters cited four main reasons for an active season:

1) Neutral to weak La Niña conditions are expected during the most active portion of this year's hurricane season (August-October). This should lead to average to below average levels of vertical wind shear.

2) Above average May sea surface temperatures in the tropical Atlantic.

3) Below average surface pressures during May in the tropical Atlantic.

4) We are in the midst of a multi-decadal era of major hurricane activity, which began in 1995. Major hurricanes cause 80-85 percent of normalized hurricane damage.

Analogue years
The CSU team picked five previous years when atmospheric and oceanic conditions were similar to what we are seeing this year: neutral to weak La Niña conditions in the equatorial Eastern Pacific, and above-average tropical Atlantic and far north Atlantic SSTs during April - May. Those five years were 2008, which featured Hurricane Ike and Hurricane Gustav; 1996, which had two hurricanes that hit North Carolina, Fran and Bertha; 1989, which featured Category 5 Hurricane Hugo; 1981, a very average year with 12 named storms, 7 hurricanes, and 3 intense hurricanes; and 1951, a year that featured 6 major hurricanes. The mean activity for these five years was 12 named storms, 8 hurricanes, and 4 intense hurricanes.

How accurate are the June forecasts?
The June forecasts by the CSU team between 1998 and 2009 had a skill 19% - 30% higher than a "no-skill" climatology forecast for number of named storms, number of hurricanes, and the ACE index (Figure 1). This is a decent amount of skill for a seasonal forecast, and these June forecasts can be useful to businesses such as the insurance industry and oil and gas industry that need to make bets on how active the coming hurricane season will be. Unfortunately, the CSU June 1 forecasts do poorly at forecasting the number of major hurricanes (only 3% skill), and major hurricanes cause 80% - 85% of all hurricane damage (normalized to current population and wealth levels.) This year's June forecast uses a brand new formula never tried before, so there is no way to evaluate its performance. An Excel spreadsheet of their forecast skill (expressed as a mathematical correlation coefficient) show values from 0.41 to 0.62 for their June forecasts made between 1984 and 2010, which is respectable.


Figure 1. Comparison of the percent improvement over climatology for May and August seasonal hurricane forecasts for the Atlantic from NOAA, CSU and TSR from 1999-2009 (May) and 1998-2009 (August), using the Mean Squared Error. Image credit: Verification of 12 years of NOAA seasonal hurricane forecasts, National Hurricane Center.


Figure 2. Comparison of the percent improvement in mean square error over climatology for seasonal hurricane forecasts for the Atlantic from NOAA, CSU and TSR from 2001-2010, using the Mean Square Skill Score (MSSS). The figure shows the results using two different climatologies: a fixed 50-year (1950 - 1999) climatology, and a 2001 - 2010 climatology. Skill is poor for forecasts issued in December and April, moderate for June forecasts, and good for August forecasts. Image credit: Tropical Storm Risk, Inc.

TSR predicts 25% more activity than normal
Expect the Atlantic hurricane season to be about 25% more active than usual, the British private forecasting firm Tropical Storm Risk, Inc. (TSR) said in their pre-season forecast issued on May 24. TSR calls for 14.2 named storms, 7.6 hurricanes, 3.6 intense hurricanes, and an Accumulated Cyclone Energy (ACE) of 124, which is 22% above average. Their May 24 forecast numbers are very close to their previous forecast issued in April. TSR predicts a moderate 55% chance that activity will rank in the top 1/3 of years historically, and a 59% chance that U.S. landfalling activity will be above average. TSR rates their skill level as 16-25% higher than a "no-skill" forecast made using climatology, though an independent assessment by the National Hurricane Center (Figure 1) gives them somewhat lower skill numbers.

TSR projects that 4.4 named storms will hit the U.S., with 1.9 of these being hurricanes. The averages from the 1950-2010 climatology are 3.1 named storms and 1.5 hurricanes. They rate their skill at making these June forecasts for U.S. landfalls at 7 - 11% higher than a "no-skill" forecast made using climatology. In the Lesser Antilles Islands of the Caribbean, TSR projects 1.3 named storms, 0.6 of these being hurricanes. Climatology is 1.1 named storms and 0.5 hurricanes.

TSR cites two main factors for their forecast of an active season:

1) Their model predicts that sea surface temperatures will be 0.11°C warmer than average in August and September over the Main Development Region (MDR) for Atlantic hurricanes. They define this as the area between 10°N and 20°N, between the coast of Africa and Lesser Antilles Islands (20°W and 60°W). It is called the Main Development Region because virtually all African waves originate in this region. These African waves account for 85% of all Atlantic major hurricanes and 60% of all named storms. When SSTs in the MDR are much above average during hurricane season, a very active season typically results (if there is no El Niño event present.)

2) Their model predicts slower than normal trade winds in August and September over the Main Development Region (MDR). Trade winds are forecast to be 0.19 meters per second (about 0.4 mph) slower than average. This would create more spin for developing storms, and allow the oceans to warm up, due to reduced mixing of cold water from the depths and lower evaporational cooling.

FSU predicts a very active hurricane season: 17 named storms
The Florida State University (FSU) Center for Ocean-Atmospheric Prediction Studies (COAPS) issued their third annual Atlantic hurricane season forecast today. This year's forecast calls for a 70% probability of 14-20 named storms and 8-10 hurricanes. The mean forecast is for 17 named storms, 9 hurricanes, and an accumulated cyclone energy (ACE) of 163. They cite warm tropical North Atlantic sea surface temperatures, a weakening of La Niña conditions, and the ongoing positive phase of the Atlantic Multi-decadal Oscillation as the major factors influencing their forecast.

Other seasonal forecasts
The UK Met Office's Glosea4 model is predicting a moderately more active season than normal, with 13 named storms and a ACE index of 151. The Cuba Institute of Meteorology is calling for 13 named storms and 7 hurricanes. NOAA predicts 15 named storms, 8 hurricanes, and 4.5 intense hurricanes. Pennsylvania State University predicts 16 named storms.

A surprise tropical disturbance for Florida
The Atlantic hurricane season is officially underway, and Mother Nature appears to be taking her cue from the calendar, as we have a surprise storm off the coast of Florida that is a threat to develop into a tropical depression later this week, after it crosses Florida into the Gulf of Mexico. An cluster of thunderstorms called a Mesoscale Convective System (MCS) pushed across southern New England early yesterday, emerged over the ocean, and rotated clockwise towards Florida, steered by a large high pressure system centered over Kentucky. The center of the disturbance stayed over the warm waters of the Gulf Stream, a region of low pressure developed, and intense thunderstorms began to build yesterday afternoon. Early this morning, the National Hurricane Center (NHC) designated the disturbance Invest 93L, and gave it a 10% chance of developing into a tropical depression. At 8am EDT, they upped those chances to 30%. Invest 93L is becoming increasingly organized, with Melbourne, Florida radar showing the beginnings of some rotation, with a solid band of heavy rain on the southwest side of the disturbance. The pressure and winds have leveled out at Buoy 41012, 40 nm ENE of St. Augustine, Florida. Winds peaked at 19 mph, gusting to 22 mph, at 10:50am EDT. Satellite imagery shows a small but intensifying region of thunderstorms. Sea surface temperatures (SSTs) are about 26°C (79°F) off the east coast of Florida, which is just warm enough to support formation of a tropical depression, and about 0.5°C above average. Wind shear is a low 5 - 10 knots, and it is likely that 93L will continue intensifying until it makes landfall over Central Florida this afternoon. A 50-mile wide swath of Florida from Daytona Beach to just north of Tampa can expect 1 - 3 inches of rain from 93L as it tracks over the state this afternoon and tonight. A Windsat pass this morning did not show a closed circulation, and I doubt 93L has enough time to develop into a tropical depression before landfall in Florida. The coast between Daytona Beach and Cocoa Beach could see wind gusts of 25 - 35 mph this afternoon, though.


Figure 3. Afternoon radar image of 93L from the Melbourne, Florida radar.

Fate of 93L once in the Gulf of Mexico
Since 93L is expected to continue its rapid west-southwest motion at 15 - 20 mph through Thursday, it will cross the Florida Peninsula in about 12 hours and emerge over the Gulf of Mexico early Thursday morning. It is possible that the passage over Florida will greatly disrupt 93L, since it is such a small system. I give a 40% chance that the storm will see its peak strength this afternoon, and not significantly regenerate over the Gulf of Mexico. However, the latest SHIPS model forecast predicts that wind shear will remain low to moderate, 5 - 15 knots, as 93L moves westwards over the Gulf of Mexico Thursday and Friday. SSTs in the Gulf are about 27°C (81°F), 0.5 - 1.0°C above average, and it is possible that 93L could gain enough strength to become Tropical Depression One as it crosses the Gulf. Since 93L will be moving parallel to the coast a short distance offshore, it is difficult to predict where the storm might make a second landfall, since a slight change in heading will make a large difference in landfall location. I don't expect widespread heavy rains from 93L along the Gulf Coast, since the storm is so small, but some locations close to the coast could receive 2 - 4 inches as 93L brushes by. Heavier rains are possible at the eventual landfall location. Since 93L is so small, the computer models are having trouble seeing the system, and are not very helpful forecasting the behavior of the storm over the Gulf of Mexico. The Hurricane Hunters are on call to fly into 93L Thursday afternoon at 2pm EDT, if necessary.

Central Caribbean disturbance
Moisture and heavy thunderstorm activity continues to slowly increase in the region between Central America and Jamaica, and wind shear is falling. With wind shear now 20 - 30 knots, we can expect this disturbance to show increased organization today, and recent satellite images show the beginnings of a surface circulation trying to get going about 100 miles off the coast of Northeast Nicaragua. All of the computer models predict that an area of low pressure will form in this region by Thursday, and this low will have the potential to develop into a tropical depression late this week or early next week. A surge of moisture accompanying a tropical wave currently south of Hispaniola may aid development when the wave arrives in the Western Caribbean on Thursday. Water temperatures in the Central Caribbean are about 1°C above average, 29°C, which is plenty warm enough to support development of a tropical storm. Residents of Jamaica, Cuba, the Cayman Islands, Haiti, Honduras, and Nicaragua should anticipate the possibility that heavy rains of 2 - 4 inches may affect them Thursday through Saturday this week.


Figure 4. Satellite image of the Central Caribbean disturbance.

Catch my intro to the 2011 hurricane season on Internet radio
I'll be discussing the coming hurricane season on our Internet radio show, the Daily Downpour, tomorrow (Thursday) at 4:30pm EDT. Fellow wunderground meteorologists Shaun Tanner and Tim Roche will be hosting the show. We'll talk about the latest model runs, hurricane research, modeling accuracy, and hurricane climatology, and answer any questions listeners email in or call in. The email address to ask questions is broadcast@wunderground.com. Welcome to the hurricane season of 2011!

Jeff Masters

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Quoting scott39:
Do you think there is too much shear, for it to close any time soon?


Not too much, but it's on the edge. The system is fragile and not hanging on by much for now. These things can surprise you if they get going though, so we'll have to keep an eye on it.

Out 'til later.
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Member Since: July 17, 2009 Posts: 71 Comments: 27210
My hurricane season risk map...Please do not criticize me if you don't agree, and please don't criticize me for it being sloppy :)

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000
NOUS42 KNHC 011515
WEATHER RECONNAISSANCE FLIGHTS
CARCAH, NATIONAL HURRICANE CENTER, MIAMI, FL.
1115 AM EDT WED 01 JUNE 2011
SUBJECT: TROPICAL STORM STORM PLAN OF THE DAY (TSPOD)
VALID 02/1100Z TO 03/1100Z JUNE 2011
WSPOD NUMBER.....11-001

I. ATLANTIC REQUIREMENTS
1. SUSPECT AREA -- GULF OF MEXICO
FLIGHT ONE -- TEAL 70 FLIGHT TWO -- TEAL 71
A. 02/1800Z A. 03/1200Z
B. AFXXX 01AAA INVEST B. AFXXX 0201A CYCLONE
C. 02/1700Z C. 03/1000Z
D. 28.0N 87.0W D. 28.0N 94.0W
E. 02/1730Z TO 02/2200Z E. 03/1100Z TO 03/1600Z
F. SFC TO 10,000 FT. F. SFC TO 10,000 FT.

2. SUCCEEDING DAY OUTLOOK.....NEGATIVE.

II. PACIFIC REQUIREMENTS
1. NEGATIVE RECONNAISSANCE REQUIREMENTS
2. OUTLOOK FOR SUCCEEDING DAY.....NEGATIVE.

NOTE: THIS IS THE FIRST OF A DAILY MESSAGE WHICH WILL
BE TRANSMITTED THROUGHOUT THE HURRICANE SEASON.
JWP
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Quoting eyestalker:
BAMD parks Arlene over San Antonio for three days.
It looks like a loop, spread out over 24 hours or so. Nothing like a TS Allison-esque loop of insanity.
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Quoting Levi32:
Checking in for 5 minutes at lunch. The new burst of convection over the water west of Florida associated with 93L is encouraging, perhaps evidence that it has survived the crossing still intact. It does not appear to have a closed circulation at this time, though.





I told you it would. You never listen to me! :-)
Member Since: July 17, 2009 Posts: 71 Comments: 27210
Quoting sammywammybamy:


You are Correct. Not Likely... but not impossible.



Man that is crazy. Where do we think it will go from there? I don't see any big trofs to dig it out and shove it east of the coast on that map anywhere.
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Quoting jeffs713:
by "hours" you mean "several days", right?

I could deal with 1-2" per day for 3-4 days, easily.

(my mower may curse the rain out for what it will do to my still-healthy grass, but I will be darn near dancing in the street)


Nope, hours. The dark greens/yellows/oranges for hours of soaking rain
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Quoting clwstmchasr:


Very nice steady rain over the Tampa Area. The local mets really blew this one big time. As of this morning we had just a slight chance of rain from the local NWS.
slight chance of rain = still a chance of rain.

If they had 0% and it did rain, then its a blown forecast. but if there is any leeway in the probability... kinda hard to blow it.
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Quoting Levi32:
Checking in for 5 minutes at lunch. The new burst of convection over the water west of Florida associated with 93L is encouraging, perhaps evidence that it has survived the crossing still intact. It does not appear to have a closed circulation at this time, though.



Do you think there is too much shear, for it to close any time soon?
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Quoting P451:


Absorption does occur in the tropics but these two systems are too far apart with one motoring along and the other just sitting around.

The dominant system will strip the weaker system of it's moisture leaving a naked swirl that is either also absorbed, ripped apart, or ejected and left to dissipate.

I've seen Hurricanes absorb Tropical Storms in the past. I seem to recall quite a while ago, 90s at the latest, a system named Karen (or K storm) was ejected northward at 65mph on the eastern edge of a Hurricane (Igor? I just don't recall, sorry) before stalling dead north of the hurricane and being run over/absorbed.



Best recent example of this was probably Wilma absorbing Alpha in 2005.
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Quoting cchsweatherman:




If you look at the wind shear Invest 93L has been experiencing thus far through its life time, then you would see that its approaching increasing wind shear in relation to the wind shear it has been experiencing.

In addition, mid level wind shear is quite high in the area its exiting into.


maybe slightly increased shear. But shear over the gulf is dropping

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Quoting RitaEvac:
Scattered crap like Florida has gotten today hit and miss aint gonna cut it here in TX, need widespread shield of constant rain for hours
by "hours" you mean "several days", right?

I could deal with 1-2" per day for 3-4 days, easily.

(my mower may curse the rain out for what it will do to my still-healthy grass, but I will be darn near dancing in the street)
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Quoting Speeky:
I think 93L came form the same storm system that produced the Joplin Tornado


That would be interesting, but it's actually from a later severe outbreak that went through Michigan and Chicago.
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Scattered crap like Florida has gotten today hit and miss aint gonna cut it here in TX, need widespread shield of constant rain for hours
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TROLL BE GONE

Member Since: July 15, 2006 Posts: 178 Comments: 56141
Quoting sammywammybamy:


Thanks....

It took me a while to make it.

The Validity of that Cone is Enhanced by Model Support:



Texas will be getting Rain.


Where did you find this map?
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Quoting sammywammybamy:


Thanks....

It took me a while to make it.

The Validity of that Cone is Enhanced by Model Support:



Texas will be getting Rain.

I agree with Rita - very nicely done map.

That said.. I'm liking BAMD the best for track, as long as it stays a very shallow storm (weak TS, with a good amount of rain).
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Quoting CajunTexan:


Thanks, glad you enjoy them. Greetings to you as well. A couple of storms to watch aint bad for June 1st, huh?


Not bad at all. :)
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467. IKE
Nice blowup in the extreme NE GOM...


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Checking in for 5 minutes at lunch. The new burst of convection over the water west of Florida associated with 93L is encouraging, perhaps evidence that it has survived the crossing still intact. It does not appear to have a closed circulation at this time, though.



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I think 93L came form the same storm system that produced the Joplin Tornado
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Quoting sarahjola:

models say its going to turn back and hit florida as a cat 4! just kidding:) it will probably go to texas or mexico as no more than what it is now.
Good thing you were just kidding....I almost believed you!:) We all need rain from the Panhandle to Texas. I wish that little baby would ride the Gulf Coast! Its good to see familiar "faces" again.
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461. Skyepony (Mod)
Quoting eyestalker:

That occurs almost exclusively with African systems. We're still a month away from that.


That happens all over the tropical world. & More in the EPAC than off Africa, WPAC more than either. It happens in the Caribbean too.
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Quoting sammywammybamy:


Thanks....

It took me a while to make it.

The Validity of that Cone is Enhanced by Model Support:



Texas will be getting Rain.


Not so sure, it's so small it'll have to really ramp up and expand in size, and ramp up I mean to 50mph storm, that way the NE and E side is where the convection would be to throw over TX
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Quoting Speeky:
What are the chances of Tropical Depression #1 forming within this week?

Does 50 percent sound okay?


I would say it has a good chance of forming by the morning.
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Quoting CJ5:
The "children" of this blog are not really taking over. The constant talking about the "children" of this blog is what is taking over. Lets just stick to the tropics.

Very true. I will admit I've been guilty of giving the trolls snacks, but if everyone ignores the trolls and the children, people could actually come here to do stuff like "learn" and "teach" about the tropics.
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So where does everyone think that 94L/pre Arlene is going? And did I hear that cmc turns it into a major already??
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453. Skyepony (Mod)
Quoting aspectre:
Since there is low-to-no Fujiwhara repulsion, can two Invests join together into a cyclone?
Is there any record of two having done so?


That's when one blob consumes another.. we've seen that plenty.
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look at that blob go ,it hit the GOM and exploded
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Quoting TropicalAnalystwx13:


Shear isn't increasing the GOMEX, its decreasing.


Quoting MrstormX:


Wait a minute, isn't the shear actually decreasing somewhat...


If you look at the wind shear Invest 93L has been experiencing thus far through its life time, then you would see that its approaching increasing wind shear in relation to the wind shear it has been experiencing.

In addition, mid level wind shear is quite high in the area its exiting into.


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Quoting CosmicEvents:
Your prose is always appreciated and always brings a smile to my face. Nice to see you back.


Thanks Cosmic, always nice to see familiar faces.
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449. Skyepony (Mod)
Quoting scott39:
Hello everyone, Are conditions going to be favorable for developement of 93L, once in the GOM? What are the some thoughts on track?


I like Galveston to Corpus Christi in about 2 days.

It's a really small storm, far enough from land, shear is fairly light, water temps warm enough. Looks more impressive now then it has since it left IL the other day..I'd say conditions are most favorable.
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Quoting CosmicEvents:
Thank you.
I don't see much change. Of course, I can't interpret these legal things too well....I'm a lay man.


Found this on the summary of the bill. Seems like it is legislativease for "raise rates"

The bill specifies that the aggregate amount of mitigation discounts granted by an insurer should not exceed the aggregate expected reduction in losses resulting from the mitigation techniques. An insurer that demonstrates that its aggregate mitigation discounts exceed the expected reduction in aggregate loss created by the mitigation may recover the lost revenue through an increase in its base rates. The bill deletes the requirement that the OIR develop a method of calculating mitigation discounts that directly correlates to the uniform home grading scale.
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Since there is low-to-no Fujiwhara repulsion, can two Invests join together to form a cyclone?
Is there any record of two having done so?
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446. CJ5
The "children" of this blog are not really taking over. The constant talking about the "children" of this blog is what is taking over. Lets just stick to the tropics.
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Quoting CosmicEvents:
Thank you.
I don't see much change. Of course, I can't interpret these legal things too well....I'm a lay man.


Thanks Cosmic. That was helpful ...
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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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