Hurricane Irene pounds Puerto Rico, heads for Hispaniola

By: Dr. Jeff Masters , 2:40 PM GMT on August 22, 2011

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Hurricane Irene strengthened into the season's first Atlantic hurricane at 5am EDT this morning as the eye moved over San Juan, Puerto Rico, and crossed into the ocean just north of the island. Overnight, Irene held its own as the eye passed over the most mountainous portion of Puerto Rico, the El Yunque region. Winds in the higher mountains likely reached Category 2 strength, 96 - 110 mph, according to measurements from the San Juan Terminal Doppler Radar, and the hurricane pounded the island with damaging winds and flooding rains, resulting in widespread tree damage and power failures that hit 800,000 people. The San Juan Airport recorded top winds of 41 mph, gusting to 55 mph, and 2.87" of rain, as of 9am AST. Tropical storm conditions affected the Virgin Islands, with St. Thomas recording sustained winds of 40 mph, gusting to 67 mph, and 4.03" of rain as of 6am AST today. At 7am EDT, the ship Horizon Trader measured sustained northeast winds of 69 mph and wave heights of 11.5 feet at 19°N, in the northern eyewall of Irene. Latest observations from an Air Force hurricane hunter aircraft indicate that Irene is slowly intensifying, with a central pressure of 989 mb observed at 9:42am EDT. The eyewall is not fully formed yet, with a gap on the south side. This gap will need to close off before the hurricane can undergo rapid intensification.


Figure 1. A direct hit: the center of Hurricane Irene passed directly over the Terminal Doppler Radar at San Juan, Puerto Rico between 4am and 5am AST this morning.

Track forecast for Irene
The computer models show good agreement that Irene will pass along the north coast of Hispaniola today, but just a slight wobble in Irene's track to take it farther offshore--or push it onshore, over the mountains--will have major impacts on the ultimate path and strength of the hurricane. A trough of low pressure is expected to move across the Eastern U.S. on Wednesday and Thursday, turning Irene more to the northwest by Wednesday. The timing and strength of this trough varies considerably from model to model, and will be critical in determining where and when Irene will turn to the north. Irene's strength will also matter--a stronger Irene is more likely to turn northward earlier. The most popular solution among the models is to take Irene to the northwest through the Bahamas on Wednesday and Thursday, then into the Southeast U.S. coast in South Carolina or North Carolina on Saturday. Irene would then travel up the mid-Atlantic coast, arriving near Long Island, New York on Monday morning as a strong tropical storm or Category 1 hurricane. One of the models proposing this solution is our best model, the ECMWF. However, we have two other of our very good models suggesting a landfall near Miami on Thursday night is likely (the GFDL and UKMET models.) NHC forecaster Stacy Stewart gave some good reasons in this morning's discussion to favor a track close to the east coast of Florida, but just offshore. Last years' worst performing major the model, the NOGAPS, predicts that Irene will pass out to sea, missing the Southeast U.S. coast. Keep in mind that the average error of a 4-day forecast from NHC is 200 miles, and just a small deviation in the path of a storm moving roughly parallel to the coast will make a huge difference in where it ultimately makes landfall. The NOAA jet will be flying its first dropsonde mission into Irene today, which should result in a more reliable set of model runs first thing Tuesday morning.

Intensity forecast for Irene
Irene is embedded in a large envelope of moisture now, and wind shear is expected to remain low, 5 - 10 knots, for the next five days. With water temperatures very warm, 29 - 30°C, these conditions should allow for intensification except when land is interfering. Satellite loops show that Irene is steadily growing in size, which will protect the storm against major disruption by its passage along the north shore of Hispaniola today. The storm is lacking much development on its southwest side, where dry air is interfering with development. This dry air may help keep southern portions of the Dominican Republic and Haiti from receiving more than 3 - 6 inches of rain. There is at least a 30% chance that passage of the eye over Hispaniola will reduce Irene to a tropical storm tonight and into Tuesday. Due to Hispaniola blocking inflow of moist air from the south, Irene will likely compensate by building an even larger region of heavy thunderstorms to the north, offshore. Thus, when Irene's center finally moves well away from the coast on Tuesday, it will be a bigger storm, with the potential to spread hurricane conditions over a wider area later in the week when it intensifies. One limiting factor for intensification may be in the upper-level outflow pattern. The hurricane is lifting a huge amount of air from the surface to the upper atmosphere, and all that mass has to be efficiently transported away in order for the hurricane to intensify. Right now, upper level outflow is only well-established to the north and east, and the forecast outflow pattern for the coming five days is only moderately favorable. Overall, I think the official NHC forecast of a Category 3 hurricane by Thursday is the right one, though Irene could easily be a Category 2 or Category 4 storm.

Irene's impact on the Dominican Republic
Heavy rains from Irene have already reached the eastern tip of the Dominican Republic, where Punta Cana has seen wind gusts up to 29 mph this morning. The northeast coast of the country near Samana will receive the worst of Irene's wrath, with sustained winds of 50 - 70 mph and gusts above hurricane force likely to cause widespread tree damage and power outages today. Passage along the coast of the island may weaken Irene to a tropical storm by Tuesday morning, and wind damage in Puerto Plata may be less severe than at Samana. The capital of Santo Domingo will see lesser winds, perhaps 30 - 50 mph, with gusts to 60 mph. The main danger to the Dominican Republic will be Irene's torrential rains, which are likely to reach 20 inches in some mountainous regions, causing dangerous flash floods and mudslides.

Irene's impact on Haiti
No nation in the Caribbean is more vulnerable to hurricanes than Haiti, whose northern reaches are expected to receive torrential rains of 5 - 10 inches from Irene. During the 2008 hurricane season, four storms--Fay, Gustav, Hanna, and Ike--dumped heavy rains on Haiti, leaving over 1,000 people dead or missing. The path and intensity of Hurricane Irene are very similar to that of Hurricane Jeanne of 2004, which dumped 13 inches of rains on the nation's northern mountains. The rugged hillsides, stripped bare of 98% of their forest cover thanks to deforestation, let flood waters rampage into large areas of the country, killing over 3000 people, mostly in the town of Gonaives, the nation's 4th largest city. Jeanne ranks as the 12th deadliest hurricane of all time on the list of the 30 most deadly Atlantic hurricanes, and Irene's rains are capable of causing a similar disaster. During 2004 and again this year, ocean temperatures off the coast of Haiti were 1 - 1.5°C above average, one of the top five values seen in the past 100 years. Since more water vapor evaporates into the air from record warm waters, the potential for devastating floods from hurricanes is much higher in these situations. However, satellite images of Jeanne show the storm had much more moisture on its south side when it hit Hispaniola than Irene currently has, so I am hopeful that Irene's rains will not be as intense as Jeanne's were.


Figure 2. Track of Hurricane Jeanne of 2004, which followed a path very similar to what is expected from Hurricane Irene along the north coast of Hispaniola. Irene is not going to do a big loop like Jeanne did, though.

As bad as the hurricanes of 2004 and 2008 were, the January 2010 earthquake was far worse. Up to 316,000 may have been killed, and the capital city of Port-Au-Prince was devastated, leaving over 1.5 million people living under tarps during the 2010 hurricane season. Fortunately, Hurricane Tomas missed making a direct hit on Haiti, and Haiti escaped major loss of life during the 2010 hurricane season. This year, approximately 595,000 Haitians still live underneath tarps outdoors thanks to the earthquake, and these unfortunate people will be at risk of being swept away by flash flooding from Irene's torrential rains. However, Port-Au-Prince lies to the south of where Irene's main rains will fall, and I doubt the earthquake refugee camps will suffer from a major flooding disaster.


Figure 3. Hospital admissions (black bars) and death rate in percent (red line) for Haiti's cholera epidemic of 2010 - 2011. The cholera epidemic surged out of control after Hurricane Tomas dumped heavy rains on Haiti on November 4, 2010, with hospitalizations increasing by a factor of three for over a month. Over 3% of all people who contracted cholera died after Tomas' rains. However, sanitation and medical care improved in the following months, and the death rate fell by a factor of five to 0.7% by the summer of 2011. Another surge in cholera cases occurred in June 2011, doubling after heavy rainy season rains occurred. Cholera deaths doubled during the surge, but the death rate remained constant at 0.7%. Image credit: Pan American Health Organization.

Another danger is that Irene's rains will worsen the cholera epidemic that surfaced after the earthquake. Cholera is a water-borne disease, and spreads readily after heavy rains. As of August 12, 2011, the 2010 - 2011 cholera epidemic had infected 419,000 Haitians, killing 5,968. After Hurricane Tomas passed on November 5, 2010, cholera cases exploded, with hospital admissions more than tripling for over a month. Similarly, heavy rains in June 2011 during the country's usual rainy season caused doubled cholera cases and deaths for several weeks. We can expect that Irene's rains will cause at least a doubling of cholera cases for a month or more. This will lead to several hundred additional cholera deaths, given the disease's 0.7% mortality rate this summer in Haiti (during June and July 2011, 95,212 cases were reported, with 626 deaths.) An increase in cholera deaths due to Irene's rains is also a concern in the Dominican Republic, where cholera has sickened 14,000 people and killed 92 as of the end of July.

Organizations Active in Haitian Relief Efforts:
Portlight disaster relief
Lambi Fund of Haiti
Haiti Hope Fund
Catholic Relief Services of Haiti

Links
For those of you wanting to know your odds of receiving hurricane force or tropical storm force winds, I recommend the NHC wind probability product.

Wunderground has detailed storm surge maps for the U.S. coast.

See my 2010 post, Haiti's tragic hurricane history.

An exceptionally active of hurricane season
Hurricane season is only one-third over, and we've already had almost a full years' activity already. Tropical Storm Irene is the 9th named storm this year, and an average season has just 10 - 11 named storms. Irene's formation date of August 20 ties 2011 with 1936 as the 2nd earliest date for formation of the season's 9th storm. Only 2005 was more active this early. However, the first eight storms of the year have done far less damage than is typical. All eight storms stayed below hurricane strength, making 2011 the first hurricane season since record keeping began in 1851 to have more than six consecutive tropical storms that did not reach hurricane strength. As I discussed in Friday's post, a major reason for this is the lack of vertical instability over the tropical Atlantic so far this year. We've had a large amount of dry, sinking air over the tropical Atlantic, and the usual amount of dry, dusty air from the Sahara, both helping to keep the atmosphere stable and stop this year's storms from intensifying into hurricanes. Hurricane activity typically ramps up big-time by August 20, with more than 80% of all the hurricanes and 65% of all the tropical storms occurring after that date. At our current pace, 2011 will become the second busiest Atlantic hurricane season on record, with 24 - 27 named storms. There are only 21 names in the list of names for a hurricane season, so we may have to break out the Greek alphabet again in late October this year, as occurred in 2005. Ironically, this was the last time the current set of names was used in the Atlantic, so 16 of this year's 21 names are repeats of 2005. I'm not too happy about seeing another hurricane season challenge the Hurricane Season of 2005 in any way, and let's hope we don't retire another five names this year, like occurred in 2005! With vertical instability much lower this year than in 2005, and that year having already seen one storm (Dennis) retired by this point in the season, I doubt that will happen, though.


Figure 4. The annual cycle of average hurricane frequency in the Atlantic. Historically, about 35% of all the tropical storms and 15% of all the hurricanes will have occurred by August 20.

Which model should you trust?
Wunderground provides a web page with computer model forecasts for many of the best-performing models used to predict hurricane tracks. So which is the best? Well, the best forecasts are made by combining the forecasts from three or more models into a "consensus" forecast. Over the past decade, NHC has greatly improved their forecasts by relying on consensus forecast models made using various combinations of the GFS, GFDL, NOGAPS, UKMET, HWRF, and ECMWF models. If you average together the track forecasts from these models, the NHC official forecast will rarely depart much from it, and the NHC forecast has been hard to beat over the past few years. The single best-performing model over the past two years has been the ECMWF (European Center model). This model out-performed the official NHC forecast in 2010 for 1-day, 2-day, 3-day and 4-day forecasts, and in 2009 for 4-day and 5-day forecasts. You can view ECMWF forecasts on our wundermap with the model layer turned on. The European Center does not permit public display of tropical storm positions from their hurricane tracking module of their model, so we are unable to put ECMWF forecasts on our computer model forecast page that plots positions from the other major models. As seen in Figure 5, over the past two years, the GFS and GFDL model have been the next best models, with the UKMET model not far behind. Last year, the NOGAPS model did very poorly, forcing NHC to come up with some new consensus models this year, the TCOA and TVCA, that do not include the NOGAPS model. For those interested in learning more about the models, NOAA has a great training video (updated for 2011.)


Figure 5. Skill of computer model forecasts of Atlantic named storms 2010. OFCL=Official NHC forecast; GFS=Global Forecast System model; GFDL=Geophysical Fluid Dynamic Laboratory model; HWRF=Hurricane Weather Research Forecasting model; NOGAPS=Navy Operational Global Prediction System model; UKMET=United Kingdom Met Office model; ECMWF=European Center for Medium Range Weather Forecasting model; TVCN=one of the consensus models that lends together all (or most) of the above models. Image credit: National Hurricane Center 2010 verification report.

Next post
There will be 2 - 3 posts per day in my blog this week during Irene, with Angela Fritz and Rob Carver doing some of the afternoon and evening posts.

Jeff Masters

Tropical Storm Irene hits Puerto Rico (lobdellJ)
Tropical Storm Irene hits the north coast of Puerto Rico
Tropical Storm Irene hits Puerto Rico
Tropical Storm Irene from Maunabo, PR (ronmil)
The first bands or Irene approaching Maunabo, Puerto Rico (SE corner)...
Tropical Storm Irene from Maunabo, PR
Irene (reefchild)
Irene @OPkB OceanParkBeach Puerto Rico 7pm
Irene

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Quoting 7544:
cat THREE close to so fla anywobble could spell trouble for se fla keep a close eye on her she could try to get further west before the the nw turn not out of the woods yet
I will watch her for the next couple of days but I don't have that huge knot in my stomach anymore.
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Quoting sunlinepr:
Local meteorologist assures, highest gust was 76mph registered in Vieques...
That seems about right.

Wouldn't expect any gusts higher than that on PR, with the south side of Irene, for the most part.
Member Since: August 16, 2007 Posts: 6 Comments: 12463
Quoting RukusBoondocks:
is FL safe???
Well i once got mugged in Miami..
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Quoting Drakoen:
Irene doesn't look to great on satellite imagery. Multiple outflow boundaries advecting off to the west. The northerly and northwesterly inflow is beginning to back up against the terrain of Hispaniola. The gap between her llc and the outer rainbands is primarily due to dry air.


If the Irene weakens as it comes across Hispaniola, will that affect the track much? Obviously the further west it goes, the worse for Florida.

But I guess the question is if the troughs that will lift Irene north will have the same affect if it weakens coming across the island?

Thanks! good to see you
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all i know is that Irene went from TS to Hurricane while or just after crossing PR...that is bothering me...it should have hindered intensification...now it is to hit just to my south by Sat am...this is not good for us...i would rather take the eye head on esp with a cat 3...
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Quoting sdswwwe:
So with Irene closing her south eyewall, what does this mean for intensity?


Irene willbe able to strengthen more rapidly. Not neccassarily rapidly, but faster then she is right now
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Quoting Drakoen:
Irene doesn't look to great on satellite imagery. Multiple outflow boundaries advecting off to the west. The northerly and northwesterly inflow is beginning to back up against the terrain of Hispaniola. The gap between her llc and the outer rainbands is primarily due to dry air.


That's what Levi was talking about in his tidbit. He also mentioned that as soon as she clears away from Hispaniola, then she'll start her true strengthening phase, which I tend to agree with.
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Well the gfs brings the eye wall right over Staten Island... Why do you hate me gfs?
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is FL safe???
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09L/H/I/C1
MARK
19.30N67.89W






ALWAYS FOLLOW NHC/TPC FORECASTS FOR ALL WARNINGS REGARDING THIS STORM
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Collapsing thunderstorms to her northwest (yellow rings), probably because of dry air.
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Quoting farhaonhebrew:
Irene is not coming back right?
How did you fare?
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473. JRRP
Quoting Orlando11:
was actually a small wobble to the WSW.. just woke up so a wobble is big. LOL

west
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472. 7544
cat THREE close to so fla anywobble could spell trouble for se fla keep a close eye on her she could try to get further west before the the nw turn not out of the woods yet
Member Since: May 6, 2007 Posts: 0 Comments: 6857
Irene is not coming back right?
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Gfs has Moe, Larry and Curly rolling along later in the run - LOL!




180 hrs - just for fun!
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468. wpb
Quoting KEEPEROFTHEGATE:
thanks for this post. has nam moved more west. thought last runs were at 76 w 25n?
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Irene doesn't look to great on satellite imagery. Multiple outflow boundaries advecting off to the west. The northerly and northwesterly inflow is beginning to back up against the terrain of Hispaniola. The gap between her llc and the outer rainbands is primarily due to dry air.
Member Since: October 28, 2006 Posts: 57 Comments: 30563
466. Gorty
Quoting mossyhead:
When the rain completely surrounds the eye, then it is closed off.


Ohhh ok thanks.
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465. BA
Quoting Patrap:
San Juan
TDWR High Definition Radar



looks like it is wobbling SW in that radar loop
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We have triplets... :)

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Quoting Gorty:


How can you tell?
When the rain completely surrounds the eye, then it is closed off.
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Quoting caneswatch:


HA. It'll be a Category 3 hurricane over Grand Bahama Island when it passes to the east. That's not trollin' to me, brother. Grand Bahama is pretty close to South Florida.


Its about a 100 miles east of West Palm Beach. So if the eye were to pass over Grand Bahama and according to the last discussion tropical force storm winds extend out over 160 n miles so south florida could experience tropical storm conditions if that path plays out
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So with Irene closing her south eyewall, what does this mean for intensity?
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Local meteorologist assures, highest gust was 76mph registered in Vieques...
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Viewing the radar, it looks like Irene may be taking a break. She doesn't seem to have moved very far in the latest loop.
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Quoting USAFwxguy:
395 ...

Not so much location of the weakness as it comes through, but rather strength of Irene sufficient enough to really feel its pull.

GFS may be too aggressive on the strength of the trough, however.

I too wonder about the GFS's depiction of the strength of the trough. About mid last week, the GFS was showing a HUGE trough over the East that would certainly have brought a fall-like weather pattern with people breaking out light jackets in the Ohio valley and temps here in Nashville likely being in the 70s day/50s night. Just a couple days afterwards though, that trough retrograded back to the north and now isn't nearly as strong. So I'm thinking the strength of the trough shown on the GFS needs to be taken with a bit of a grain of salt.
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p451 I agreed with you all day yesterday but the storm, not any features, clearly jogged to the WSW. It's just a jog, no big deal. take it easy man.

I agree with the SC landfall/NHC forcast btw.
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Quoting Twinkster:
when will the data from the gulfstream IV be in the models. I'm thinking for 00z but i'm not sure
Yes, too late for 18 UTC, but will be in the 00 UTC, barring aircraft issues.

At least the 18 UTC GFS will get extra upper air data from the special weather balloon launches in the SE US.
Member Since: August 16, 2007 Posts: 6 Comments: 12463
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Look at the history of hurricanes in this position. There needs to be a big high to the northeast for this to go to Florida. We have none.
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Quoting saylo2mylilfren:
I'm in SWFL about how much of a wobble to the west will it take for us to be impacted? I remember charlie they said Tampa then a short wobble turned out to make a 100 mile difference. Since Florida's coastline is almost straight what do you think?
A wobble can make a big difference. Depends how close to the hurricane you are. Thats why they warn there could be a 200 to 300 mile error rate 4 days down the road. Pay attention to the cone, not the center line.
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Irene wanna come back to P.R ...go!
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Quoting Twinkster:
when will the data from the gulfstream IV be in the models. I'm thinking for 00z but i'm not sure



yes should be in 00z runs
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446. Gorty
Quoting SPLbeater:
From the PR radar loop...Irene looks to be completing her eyewall. Uh oh


How can you tell?
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Quoting cat5hurricane:

I think you mean the globe's tenth billion-dollar disaster. The Earthquake and Tsamuni were in Japan.


...and weren't weather related, either...
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Yeesh, I hope the power comes back soon. That generator isn't gonna last forever. But I'm not optimistic, since the entire city of Vega Alta is without water or electricity.
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Quoting divdog:
they r just trollin for takers


HA. It'll be a Category 3 hurricane over Grand Bahama Island when it passes to the east. That's not trollin' to me, brother. Grand Bahama is pretty close to South Florida.
Member Since: October 8, 2008 Posts: 14 Comments: 4553
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when will the data from the gulfstream IV be in the models. I'm thinking for 00z but i'm not sure
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From the PR radar loop...Irene looks to be completing her eyewall. Uh oh
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was actually a small wobble to the WSW.. just woke up so a wobble is big. LOL
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heading west... agree with NHC track though
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Quoting NICycloneChaser:
I suspect Levi's arrival is imminent....
The GFS has Him arriving at 1PM and the UKMET has him arriving at 2PM. I guess it depends on the model :)
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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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