Leslie near hurricane strength; Son of Isaac (90L) emerges in the Gulf

By: Dr. Jeff Masters , 3:05 PM GMT on September 05, 2012

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Tropical Storm Leslie is growing more organized and is approaching hurricane strength on its slow voyage northwards at 2 mph towards the island of Bermuda. Moderately high wind shear of 15 - 20 knots due to strong upper-level winds out of the northwest continues to keep most of Leslie's heavy thunderstorms pushed to the east side of the storm, but satellite loops show that Leslie now has an impressive blow-up of heavy thunderstorms with cold cloud tops near its center. Leslie's slow forward speed means that the storm is staying over the cold water stirred up by the storm's winds, inhibiting intensification, but the waters underneath Leslie are warm to great depth, making this less of a factor than usual. According to the latest SHIPS model forecast, the shear is expected to fall steadily today, reaching the low category, 5 - 10 knots, by Thursday afternoon. Leslie is over warm ocean waters of 29 - 30°C, and the reduction in shear and warm waters should aid intensification, and potentially allow Leslie to be at Category 2 strength at its closest pass by Bermuda Saturday night and early Sunday morning, as indicated by the official NHC forecast. The latest 11 am EDT NHC wind probability forecast calls for a 48% chance that Leslie will be a Category 2 or stronger hurricane Sunday morning at 8 am EDT. Leslie is a huge storm, and tropical storm-force winds are expected to extend outward from its center 250 miles by Friday. Bermuda is likely to see a 42-hour period of tropical storm-force winds beginning Saturday morning near 2 am AST, and lasting until 8 pm AST Sunday night. The official NHC forecast shows Leslie nearly making a direct hit on Bermuda, and Leslie will be capable of bringing an extended period of hurricane-force winds lasting six or more hours to Bermuda Saturday night through Sunday morning, should a direct hit materialize. NHC is predicting that hurricane-force winds will extend outwards from the center of Leslie by 35 miles on Thursday night, and I expect this will increase to at least 60 miles by early Sunday morning, when Leslie will be making its closest pass by Bermuda.


Figure 1. Morning satellite image of Tropical Storm Leslie. Heavy thunderstorms have built near the center of the storm, and Leslie is near hurricane strength.

Leslie's impact on Canada
Leslie will stay stuck in a weak steering current environment until a strong trough of low pressure approaches the U.S. East Coast on Saturday. The timing of this trough is such that Leslie will be pulled northwards and then north-northeastwards over the weekend. There are still significant differences among the models in the timing and speed of Leslie's track over the weekend, but we can now dismiss the threat of Leslie making a direct hit on New England. The storm is likely to make landfall in Nova Scotia or Newfoundland, though there are significant differences in the models' predictions of the timing of Leslie's arrival in Canada. The GFS model predicts an early Tuesday landfall in Newfoundland, but the ECMWF model is much faster and farther west, predicting a Monday afternoon landfall in Nova Scotia. Large swells from Leslie are pounding the entire Eastern Seaboard, and these waves will increase in size as Leslie grows in strength this week. The Hurricane Hunters are scheduled to make their first flight into Leslie on Thursday afternoon.


Figure 2. Morning radar image of Invest 90L off the coast of the Florida Panhandle.

Son of Isaac: Invest 90L emerges in the Gulf of Mexico
During Tropical Depression Isaac's trek across the center of the U.S. during the Labor Day weekend, the storm was ripped in half. One portion of the storm moved over the Northeast U.S., bringing heavy rains there, and another portion sank southwards over Alabama. You can see this split by studying an animation of the vorticity at 850 mb (the amount of spin at low levels of the atmosphere, near 5,000 feet above sea level) from the University of Wisconsin. This remnant of Isaac, which still maintained some of Isaac's spin, brought heavy rains of 5 - 10 inches that caused flooding problems over portions of Alabama on Tuesday. The storm has now emerged over the Gulf of Mexico near the Florida Panhandle, and was designated Invest 90L this morning by NHC. In their 8 am Tropical Weather Outlook, NHC gave 90L a 20% chance of developing into a tropical depression by Friday morning. According to NHC naming rules, "if the remnant of a tropical cyclone redevelops into a tropical cyclone, it is assigned its original number or name". Since "the remnant" refers to the primary remnant, and 90L does not fit the definition of a "primary remnant", the storm will be given a new name should it develop into a tropical storm, according to information posted on the NHC Facebook page. Esau or Jacob--the names of the sons of the biblical Isaac--would be fitting names for 90L, but the next storm on the list of Atlantic storms is Nadine.

Long-range radar out of Mobile, Alabama shows a large area of heavy rainfall along the coast due to 90L. The echoes do show some spiral banding behavior, but there is only a slight evidence of rotation to the storm. Infrared satellite loops show that the thunderstorms associated with 90L are not that vigorous and do not have particularly cold cloud tops, and the area covered by the thunderstorms is relatively small. Wind shear is a high 20 - 30 knots over the northern Gulf of Mexico, but is predicted to fall to the moderate range, 10 - 20 knots, by Thursday afternoon. Ocean temperatures in the Gulf have been cooled down considerably by the passage of Hurricane Isaac last week, and are 28 - 28.5°C. This is still plenty warm enough to support formation of a tropical storm, and I expect 90L will increase in organization on Thursday and Friday as it moves slowly south or south-southwest. 90L could become a tropical depression as early as Thursday, though Friday is more likely. A hurricane hunter aircraft is scheduled to investigate 90L on Thursday afternoon. A trough of low pressure and an associated surface cold front will move southeastwards over the northern Gulf of Mexico on Sunday, and this trough should be capable of pulling 90L to the northeast to a landfall along the Florida Panhandle or west coast of Florida on Sunday.


Figure 3. Morning satellite image of Tropical Storm Michael.

Tropical Storm Michael in the Central Atlantic
Tropical Storm Michael has strengthened to 50 mph winds, and appears to have a favorable enough environment to become a hurricane later this week. Satellite loops show that this is a small tropical cyclone, far out over the open Atlantic, and none of the models show that Michael will threaten any land areas.

Elsewhere in the Atlantic
The GFS and ECMWF models are predicting that a new tropical wave due to move off the coast of Africa on Friday will develop into a tropical depression by the middle of next week. It's too early to tell if this system might threaten the Lesser Antilles Islands.

Jeff Masters

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Special advisories issued for both storms....I just found out..
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Very good view of the LLC of 90L south of Pensacola!

Link
Member Since: July 4, 2005 Posts: 204 Comments: 8898
Bermuda residents, lucky men, have fun for us...
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Quoting dxdy:
What is the chance of a Fujiwara interaction between Leslie and Michael? Will they do the tango?


No, I don't think so. They are far enough apart, and the projected paths are different enough, that it should be more like square dancing. :)
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Quoting LargoFl:


Is this the route Nadine is goin' to take?
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Correction to earlier post, there was not a tremor 50 SE of StL, it was just a coal mine blast! Thought that was a weird spot for one, 150 mi S or SE would be more likely. Peabody has a big new power plant / mine in Sparta where they had it centered, so makes a lot more sense.

It's trying to get to you ILwthr, but looking a lot less healthy, that bad shield of yours may be knocking down another one. Did get a little over an inch from this morning's line when checked my unofficial guage, lots of little branches in yard as well when went home for lunch.
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268. 7544
may yellow circle soon at 15n/32w ? then there will be 4 lol makes a pretty map
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Quoting coondini:
So I see we're up to Code Orange now. I wonder how long it'll be before we get Code Red...I say by tonight or perhaps tomorrow morning.


Code red for 90L...by tonight or tomorrow morning? You wouldn't like to place some money on that bet, would you? :)
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266. dxdy
What is the chance of a Fujiwara interaction between Leslie and Michael? Will they do the tango?
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Eye clearing out in Hurricane Leslie.
Member Since: July 8, 2005 Posts: 259 Comments: 24580
Quoting CaribBoy:
I guess we have to wait until all these wave STOP developing to FINALLY SEE A BIT OF RAIN!!!!!!!!!!


I can relate to your feelings, I often think the same thing during months long stretches of sunny weather and highs in the 80s. I like more exciting (but not destructive) weather, and what can I say-I like the rain.

It would probably be helpful for you to share this particular thought in only one comment periodically (per day, every few days, etc.) and share your thoughts on existing weather events going on elsewhere too. What do you think of Leslie's projected path toward Bermuda?
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Some real charmers on the board today.

_I_ will think of post-Isaac as Esau, entirely because I joked in my head that the other blob he threw at FL that flooded West Palm Beach was clearly Jacob.

That wasn't a "storm" either, I suppose, but it sure pounded the heck out of FL for a day. Wind speeds don't tell the whole tale, as Isaac should have made clear by now.
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Quoting icmoore:


Beauty is in the eye of the beholder :)


No beauty is in the eye of the BEER holder. hehehehe. Now back to weather.......
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AL, 90, 2012090518, , BEST, 0, 300N, 870W, 25, 1010, LO, 34, NEQ, 0, 0, 0, 0, 1013, 100, 60, 0, 0, L, 0, , 0, 0, INVEST, M,

Moving SSW and pretty much PRES/WND remain constant. For now...
Member Since: August 14, 2008 Posts: 4 Comments: 5038
Quoting tropicfreak:


Not if it can develop an anticyclone and ventilate it from the shear, which is what it's doing right now.





You see an anitcyclone over 90L right now? Boy, you've got better eyes than I do. The eastern side looks like it's already getting sheared off.
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Quoting GeorgiaStormz:


+Grothar's Age

btw i don't drink pizza rolls, just fresca


Gro has to have all his food mashed up.
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Quoting aspectre:
201 CallInBatonRouge: I was here for Katrina, and remember the bloggers jumping on the danger bandwagon well before doc...

That ain't sayin' much. There's folks here who get all ChickenLittle cuz the SCROFULA model shows a 999millibar low at 780hours.
"Oh nooooes. The chocolate fell into the peanut butter. DOOOOM!!!!!!!!!!! "


Now that is funny!

All the unwarranted drama provides entertainment for the lonely clinging to this blog, and those dishing it get to be the center of attention until Mom kicks them off the computer.
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Quoting CloudGatherer:
Ladies and gents, Hurricane Leslie:

05/1745 UTC 25.8N 62.5W T4.0/4.0 LESLIE

We already know. A special advisory was issued at 1:45.
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Quoting CloudGatherer:
Ladies and gents, Hurricane Leslie:

05/1745 UTC 25.8N 62.5W T4.0/4.0 LESLIE


Man, it's about time. :) She still has quite a bit of shear to shake off but, once she's through that shower curtain, it looks like clear sailing towards Bermuda and the Maritimes. :(
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Quoting sar2401:


Actually, the shear is pretty high over the area 90L will be moving. The further east, the more wind shear she should run into.


Not if it can develop an anticyclone and ventilate it from the shear, which is what it's doing right now.



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Quoting Grothar:


I wrote it in my blog 3 days ago that it was coming. They must have just got around to reading it.


Gro, I told you that you should have been using "blob ©" all along. Now you've lost your big chance in weather history. :)
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Quoting LargoFl:
well we have 4 days in the gulf to see huh..4 whole days in mid 80's water and low shear...I for one..hope your right, but i dont think so, way too long in the gulf
Your forgetting that ugly word shear
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So I see we're up to Code Orange now. I wonder how long it'll be before we get Code Red...I say by tonight or perhaps tomorrow morning.
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Ladies and gents, Hurricane Leslie:

05/1745 UTC 25.8N 62.5W T4.0/4.0 LESLIE

Update: Ack. I missed the NHC upgrade. They play dirty poker - they used the satellite estimates when they came out, but didn't put them up on the site for 45 minutes.

At any event, here are the other two from the 1745Z SAB run:

05/1745 UTC 30.2N 86.5W TOO WEAK 90L
05/1745 UTC 28.7N 42.8W T3.5/3.5 MICHAEL


No one tell Largo about the 90L numbers; he'll be too disappointed.
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201 CallInBatonRouge: I was here for Katrina, and remember the bloggers jumping on the danger bandwagon well before doc...

That ain't sayin' much. There's folks here who get all ChickenLittle cuz the SCR(ofula)model shows a 999millibar low at 996hours.
"Oh nooooes... The chocolate fell into the peanut butter. DOOOOM!!!!!!!!!!! "
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Quoting snowboy:


Easy for you to say. If you were in a boat in the North Atlantic you might have a different perspective..


Or even a ship. Hardly anyone survives in a boat in the North Atlantic. :) Sorry, just some nautical humor there.
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Quoting Charmeck:

Sorry, I'm not that knowledgeable but you can usually see clusters of quakes around the "Ring of Fire" which I understand to be the coasts of the Pacific (both Asia and Americas). If you look at the map of the 30 day Data Feed you can see what I'm talking about.


Small earthquakes all along those pacific ring faults are really common, yeah, most too small for anybody to really notice. I don't know whether the data would show more big ones over the last bit than average, but it sure does seem that way to me. I'd have to hunt to find out whether that's a fair impression, though.

Good thoughts to folks down there. Anything above 7 is pretty sucky to go through, hopefully any damage is minor. Depends on other factors some, like direction of motion, soil types, length...
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Quoting earthlydragonfly:


its not.... its an afternoon thunder storm


Don't pop Largo's bubble now. He/she's already got cookies and milk out hoping for Cantore's arrival.
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Quoting LargoFl:
well we have 4 days in the gulf to see huh..4 whole days in mid 80's water and low shear...I for one..hope your right, but i dont think so, way too long in the gulf


Actually, the shear is pretty high over the area 90L will be moving. The further east, the more wind shear she should run into.
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245. VR46L
Quoting earthlydragonfly:


its not.... its an afternoon thunder storm


I know !! LOL
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Quoting VR46L:


When did a low of 1010 mb become a storm ? Just wondering





Lol... to a desperate LargoFL that's when.
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Quoting Gearsts:
Leslie is not what i would call a beautiful hurricane yet still has a lot of work to do and upwelling is a big issue.


Beauty is in the eye of the beholder :)
Member Since: July 18, 2005 Posts: 9 Comments: 4147
Isaac would remind me more of Ivan(not as in strength) but it somewhat surviving a major amount of time on land and a possible redevelopment. So much energy, once that atmosphere gets into motion
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Quoting MysteryMeat:
Wonder why they bothered doing a special advisory package for Michael when it's still only up 15 mph? It's a tiny storm in the middle of nowhere. Maybe if it shot up to a Cat 2 out of thin air I could see it, but they couldn't wait another three and a half hours for the 5 p.m. package?


Easy for you to say. If you were in a boat in the North Atlantic you might have a different perspective..
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blog update


Link
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Quoting VR46L:


When did a low of 1010 mb become a storm ? Just wondering





its not.... its an afternoon thunder storm
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Quoting pottery:

They will never learn ! Twits !!


I wrote it in my blog 3 days ago that it was coming. They must have just got around to reading it.
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Isaac kinda reminds me of our ever so cooperative Emily from last year. She later split off around the northern periphery of the high pressure and the other area of low pressure that split became Gert.
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236. VR46L
Quoting LargoFl:
new GFS at 123 hours..its a tampa bay storm again


When did a low of 1010 mb become a storm ? Just wondering



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Quoting MysteryMeat:
Wonder why they bothered doing a special advisory package for Michael when it's still only up 15 mph? It's a tiny storm in the middle of nowhere. Maybe if it shot up to a Cat 2 out of thin air I could see it, but they couldn't wait another three and a half hours for the 5 p.m. package?


Might as well "kill two birds with one stone," seeing as Leslie was also upgraded.
Member Since: August 26, 2012 Posts: 0 Comments: 142
Wonder why they bothered doing a special advisory package for Michael when it's still only up 15 mph? It's a tiny storm in the middle of nowhere. Maybe if it shot up to a Cat 2 out of thin air I could see it, but they couldn't wait another three and a half hours for the 5 p.m. package?
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Quoting Ameister12:
Afternoon, everybody!

Wow! I was not expecting Leslie to become such a beautiful hurricane once I got home. She looks great.


And little Michael is very close to becoming a hurricane.
Leslie is not what i would call a beautiful hurricane yet still has a lot of work to do and upwelling is a big issue.
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231. JLPR2
Well now, that was a lot of updates from the NHC. xD
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Afternoon, everybody!

Wow! I was not expecting Leslie to become such a beautiful hurricane once I got home. She looks great.


And little Michael is very close to becoming a hurricane.
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SHORT TERM FORECAST
NATIONAL WEATHER SERVICE TAMPA BAY AREA - RUSKIN FL
147 PM EDT WED SEP 5 2012

FLZ039-042-043-048>052-055>057-060>062-065-GMZ830 -850-853-856-870-
873-876-051845-
BONITA BEACH TO ENGLEWOOD 20 TO 60 NM-
BONITA BEACH TO ENGLEWOOD OUT TO 20 NM-CHARLOTTE-CITRUS-DESOTO-
ENGLEWOOD TO TARPON SPRINGS 20 TO 60 NM-
ENGLEWOOD TO TARPON SPRINGS OUT TO 20 NM-HARDEE-HERNANDO-HIGHLANDS-
HILLSBOROUGH-LEE-LEVY-MANATEE-PASCO-PINELLAS-POLK -SARASOTA-SUMTER-
TAMPA BAY WATERS-TARPON SPRINGS TO SUWANNEE RIVER 20 TO 60 NM-
TARPON SPRINGS TO SUWANNEE RIVER OUT TO 20 NM-
147 PM EDT WED SEP 5 2012

.NOW...
THROUGH 245 PM. SCATTERED SHOWERS AND A FEW THUNDERSTORMS ARE MOVING
TO THE NORTHEAST AT 10 TO 15 MPH ACROSS INTERIOR PORTIONS OF
CITRUS...HERNANDO...HILLSBOROUGH...MANATEE...POLK ...CHARLOTTE...AND
LEE COUNTIES. AT 145 PM...STRONGEST AREAS OF ACTIVITY WERE LOCATED
OVER SOUTHERN CHARLOTTE COUNTY AND SOUTHERN MANATEE COUNTY NEAR
MYAKKA CITY. BRIEF PERIODS OF HEAVY RAIN...WIND GUSTS OF UP TO 25
MPH...AND OCCASIONAL LIGHTNING STRIKES ARE POSSIBLE IN AND NEAR THESE
SHOWERS AND STORMS.
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Quoting Grothar:



I know, this is what gets me about the NHC. They move it up to 40% when I've only posted 4 Blob alerts. I told them to wait until the 5th alert.
LMAO gro
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Quoting dabirds:
Guess I waited to long, but I'll let Chuck sing it when she forms, be it 90L or the next African wave, lol.


Bit late reaction, but I couldn't get on the blog.
I love this version, even more then Chuck's. But he is the original for sure.
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Quoting Grothar:



I know, this is what gets me about the NHC. They move it up to 40% when I've only posted 4 Blob alerts. I told them to wait until the 5th alert.

They will never learn ! Twits !!
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Hurricane LESLIE Update Statement

Home Public Adv Fcst Adv Discussion Wind Probs Graphics Archive UPDATE

000
WTNT62 KNHC 051753
TCUAT2

HURRICANE LESLIE TROPICAL CYCLONE UPDATE
NWS NATIONAL HURRICANE CENTER MIAMI FL AL122012
145 PM AST WED SEP 5 2012

CORRECTED LATITUDE IN SUMMARY INFORMATION

...LESLIE STRENGTHENS INTO THE SIXTH HURRICANE OF THE SEASON...

SATELLITE INTENSITY ESTIMATES INDICATE LESLIE HAS STRENGTHENED INTO
A HURRICANE. MAXIMUM SUSTAINED WINDS ARE NOW 75 MPH...120 KM/H...
WITH HIGHER GUSTS.

SUMMARY OF 145 PM AST...1745 UTC...INFORMATION
------------------------------------------------- -
LOCATION...25.8N 62.5W
ABOUT 465 MI...750 KM SSE OF BERMUDA
MAXIMUM SUSTAINED WINDS...75 MPH...120 KM/H
PRESENT MOVEMENT...N OR 360 DEGREES AT 2 MPH...4 KM/H
MINIMUM CENTRAL PRESSURE...987 MB...29.15 INCHES

$$
FORECASTER STEWART

13-6-0
Member Since: July 8, 2005 Posts: 259 Comments: 24580
Quoting StormHype:


Well you have it from your own quote above that there's a 60% chance it's not. Even a TD isn't a 'storm' for that matter. I will guess it will amount to about 25% of what Debby was. Mainly because it will fly through and not stall out like Debby once the trough picks it up.
well we have 4 days in the gulf to see huh..4 whole days in mid 80's water and low shear...I for one..hope your right, but i dont think so, way too long in the gulf
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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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