Irene roars into life; may become the season's first hurricane

By: Dr. Jeff Masters , 12:03 AM GMT on August 21, 2011

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Tropical Storm Irene roared into life this evening, transitioning from a tropical wave to a 50 mph tropical storm in just a few short hours. An Air Force hurricane hunter aircraft in the storm was finishing up its mission when it suddenly came across a region with intense thunderstorms and surface winds of 50 mph. The aircraft found that a center of circulation had barely closed off on the southwest edge of this region, though the plane found almost no winds from the west around the circulation center. The 6:10pm EDT center fix found a central pressure of 1007mb, which is quite high for the observed 50 mph winds. Dry air to the north and west is slowing development, as well as moderate wind shear of 10 - 20 knots, as analyzed by the University of Wisconsin CIMSS group. Infrared satellite loops and radar out of Martinique show the storm is poorly organized, with no evidence of spiral bands. The center of Irene is expected to cross over the Caribbean island of Dominica early Sunday morning, but the heaviest thunderstorms lie to the north of the center, and will affect Guadeloupe, Antigua, and St. Kitts and Nevis.


Figure 1. Evening satellite image of Irene.

The computer models have shifted southwards since yesterday, and now take Irene south of Puerto Rico on Monday, and along the south shore of the Dominican Republic on Tuesday. On Wednesday, Irene should pass near or over southern Haiti, Eastern Cuba, and Jamaica. On Wednesday and Thursday, the models agree that a trough of low pressure will dip down over the Eastern U.S., which is likely to turn Irene to the north. The exact 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. We can expect that Irene will impact Central Cuba, the Bahamas, and the Florida Keys on Thursday, but it is uncertain whether Irene's turn to the north will take the storm into the Gulf of Mexico or not. Irene most reminds me of Tropical Storm Fay of 2008. Fay formed just off the coast of Puerto Rico, and was never quite able to get organized enough to become a hurricane, due to passage over Hispaniola and Cuba. Fay topped out as a strong tropical storm with 70 mph winds, and did over $500 million in damage in the U.S., mostly due to flooding rains in Florida that accumulated to over 25 inches in a few areas. Fay also dumped heavy rains on Hispaniola, triggering flooding that claimed eight lives.


Figure 2. Track of Tropical Storm Fay of 2008.

Irene will be battling dry air and moderate wind shear of 10 - 20 knots through Sunday, and it will take the storm 1 - 3 days to build up an eyewall and intensify into a hurricane. Irene is more of a threat than Tropical Storm Emily of early August was, since Irene has closed off a center farther east than Emily did and has more time to organize before encountering Hispaniola. I don't think passage over Hispaniola will destroy Irene, since it is a fairly large storm, and is likely to be a hurricane by then. However, if Irene follows the NHC forecast, it will have an extended encounter with Hispaniola and Cuba on Tuesday through Wednesday that will probably weaken the storm below hurricane force. Keep in mind that the average error for an official 5-day forecast from NHC for a developed storm is 200 - 250 miles. Irene could easily miss Florida and move up the East Coast and hit North or South Carolina, or pass through the Florida Keys and into Gulf of Mexico, ending up who knows where. Given the uncertainties, this weekend would be a good time to go over your hurricane preparedness if you live anywhere in the Caribbean, Bahamas, or U.S. coast, since Irene could well be paying you a visit as a tropical storm or hurricane sometime in the next week.

Harvey hits Belize
Tropical Storm Harvey made landfall at 2pm EDT on Saturday near Dangriga Town, Belize, as a tropical storm with 60 mph winds. Harvey continues to dump very heavy rains on northern Guatemala, Belize, and portions of Mexico's Yucatan Peninsula as the storm tracks westwards at 12 mph. Dissipation is expected Sunday as the storm pushes inland. Harvey was a small storm, and the strongest winds were confined to a short stretch of coast near where the center came ashore. Winds at Belize City, Belize on Saturday topped out at 15 mph.


Figure 3. Radar image of Harvey taken at 11:30am EDT on Saturday, August 20, 2011, a few hours before landfall in Belize. A small closed eye is visible just south of the offshore islands of Belize. Image credit: Belize National Meteorological Service.

An exceptionally active early part of hurricane season
It's been a strangely hyperactive season for weak storms in the Atlantic so far this year. Tropical Storm Irene is the 9th named storm this year, and its formation date of August 20 ties 2011 with 1936 as the 2nd earliest date for formation of the season's 9th storm. Only 2005 had an earlier date. The first eight storms this year have 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 2. 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.

Invest 98L near the Cape Verde Islands
A tropical wave near Cape Verde Islands off the coast of Africa, Invest 98L, is spreading heavy rains and strong gusty winds to those islands today. So far this morning, top sustained winds measured in the Cape Verde Islands were 23 mph at Mindelo. 98L has a long stretch of ocean to cross before it could affect any land areas. Approximately 70 - 80% of all tropical cyclones that pass this close to the Cape Verde Islands end up curving out to sea and not affecting any other land areas, according to Dr. Bob Hart's excellent historical probability of landfall charts. The latest set of long-range model runs go along with this idea, and I'd be surprised if 98L threatens any land areas.

Jeff Masters

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Quoting KennyNebraska:


You can see in that model run that the high pressure ridge is blocking the trough.

No one should be counting chickens today, tomorrow, or Tuesday. 72 hours is a long time from now.


72 hrs is a long time and 140+ even longer...Right now; I am primarily interested in where she is when it gets to DR/PR. Just S of or over; and those mountains should do a number on her. Just N of and all bets are off.
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Quoting kmanislander:
Good morning folks

I see that overnight we had a center reformation with Irene.

This jump to 16N has resulted in the model runs shifting further N and E in the various runs. That was to be expected.

Looking at the steering ridge this morning and taking into account the fact that Irene has not deepened so far, I would expect to see Irene resume a more W than WNW heading for today. If this happens then the models will come to the left again.

Looking ahead I still believe Irene has a good chance to pass between Jamaica and Cuba before swinging to the NW but this is all dependent on how strong the system becomes. If it deepens significantly it will push its way towards the weakness around Wednesday. If it gets no stronger than CAT 1 then there would be a better chance IMO for it to push a little farther West than the present track forecast. Here is the current steering flow.



I agree with what you are saying. NHC says a stout ridge influencing westward movement for 72 hours and a weakness EXPECTED after that to influence more WNW/NW movement. This is what got me.
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2968. WxLogic
Quoting kmanislander:
Good morning folks

I see that overnight we had a center reformation with Irene.

This jump to 16N has resulted in the model runs shifting further N and E in the various runs. That was to be expected.

Looking at the steering ridge this morning and taking into account the fact that Irene has not deepened so far, I would expect to see Irene resume a more W than WNW heading for today. If this happens then the models will come to the left again.

Looking ahead I still believe Irene has a good chance to pass between Jamaica and Cuba before swinging to the NW but this is all dependent on how strong the system becomes. If it deepens significantly it will push its way towards the weakness around Wednesday. If it gets no stronger than CAT 1 then there would be a better chance IMO for it to push a little farther West than the present track forecast. Here is the current steering flow.





I agree, as long as it doesn't deepens too quickly which I have a feeling it won't, given the lingering dry air in the area (not much but is there still) and the land interaction.
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Quoting TampaBayWX:


Tampa is covered in a protective shield..... :-)



Right. We just get slapped around a bit by storms cris-crossing the state, or on their way to the north Gulf Coast.
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Looks like the GFDL is still South........
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Quoting WxLogic:


Let's see where it decides to go this time.
Already moving WNW through Hispañola. Changed its mind from the prior Caribbean trek.
Member Since: September 2, 2009 Posts: 130 Comments: 21032
BULLETIN
TROPICAL STORM IRENE INTERMEDIATE ADVISORY NUMBER 3A
NWS NATIONAL HURRICANE CENTER MIAMI FL AL092011
800 AM AST SUN AUG 21 2011

...IRENE MOVING INTO THE NORTHEASTERN CARIBBEAN SEA...


SUMMARY OF 800 AM AST...1200 UTC...INFORMATION
----------------------------------------------
LOCATION...16.5N 62.0W
ABOUT 35 MI...55 KM WNW OF GUADELOUPE
ABOUT 45 MI...70 KM SSW OF ANTIGUA
MAXIMUM SUSTAINED WINDS...50 MPH...85 KM/H
PRESENT MOVEMENT...W OR 280 DEGREES AT 21 MPH...33 KM/H
MINIMUM CENTRAL PRESSURE...1005 MB...29.68 INCHES
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Quoting TampaBayWX:


Tampa is covered in a protective shield..... :-)



Hell yes it is...........:)
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2961. Dakster
Quoting nrtiwlnvragn:
00Z COAMPS joins the UKMET and GFDL




That could be a Texas drought buster... But where is the TX high located at?

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Quoting USAFwxguy:
GFDL rolling



You can see in that model run that the high pressure ridge is blocking the trough.

No one should be counting chickens today, tomorrow, or Tuesday. 72 hours is a long time from now.
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My Irene prediction, as I am no expert.

I look at the models. I see the storm passing more north than predicted, and up the East Coast at some point, hitting Florida or not. Either way, the models in their current mode have a bad karma in it for New Jersey. If it's strong, and it hits on the west side, we have trouble. If it's strong on hits on the east side, we have trouble. Hurricane of 1878, 79's David hit on the west side. The '38 and the '44 and 60's Donna were to our east, and we were in a hot mess. Remember there are no fronts to speak of that will make it a quick extratropical transition. At upper latitudes, the storms move more quickly. I think this could be a major player for the least-prone hurricane state on the East Coast. If I'm wrong, I will eat my hat, and I possibly will have to. Nothing is set in stone, and no one can predict nature. I've just studied the past, and realize that so will go the future.
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Quoting weatherwart:



Or Tampa Bay. :)


Tampa is covered in a protective shield..... :-)
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Quoting WxLogic:


ECMWF is similar to HWRF. In ECMWF which goes further out in time (therefore to be taken cautiously later in the time period as we know) it attempts to make landfall around the NE FL coast SE GA coast area.

Basically following along the FL E coast.


Thanks. I was at our beautiful beach yesterday (E. Central FL) just hoping we wouldn't have another storm come through and destroy it. One riding up the coast could be worse than a direct hit as far as that goes. SO the wait begins...we're all set here except for the need of one piece of plywood to replace some warped window coverings. We've had them since Floyd (Frances and Jeanne), so they've seen better days.
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2956. emcf30
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Good morning folks

I see that overnight we had a center reformation with Irene.

This jump to 16N has resulted in the model runs shifting further N and E in the various runs. That was to be expected.

Looking at the steering ridge this morning and taking into account the fact that Irene has not deepened so far, I would expect to see Irene resume a more W than WNW heading for today. If this happens then the models will come to the left again.

Looking ahead I still believe Irene has a good chance to pass between Jamaica and Cuba before swinging to the NW but this is all dependent on how strong the system becomes. If it deepens significantly it will push its way towards the weakness around Wednesday. If it gets no stronger than CAT 1 then there would be a better chance IMO for it to push a little farther West than the present track forecast. Here is the current steering flow.



Member Since: August 19, 2006 Posts: 0 Comments: 15671
ECMWF 0z
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Quoting StormJunkie:


That should almost be reassuring...We all know storms don't hit Savannah ;~)



Or Tampa Bay. :)
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Quoting USAFwxguy:
GFDL rolling


I already hate it! LOL
Member Since: July 7, 2010 Posts: 0 Comments: 5519
Quoting barotropic:


I think GOM chances of strike are becoming much slimmer.


They are indeed slim, but Irene is already feeling the effects of the high pressure ridge right above her. She's headed west and a bit south now. The longer she goes that-a-way, the more the GoM is in play.
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2947. WxLogic
Quoting USAFwxguy:
GFDL rolling



Let's see where it decides to go this time.
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2946. Gearsts
Time: 11:44:00Z
Coordinates: 17.3667N 63.1167W
Acft. Static Air Press: 843.3 mb (~ 24.90 inHg)
Acft. Geopotential Hgt: 1,564 meters (~ 5,131 feet)
Extrap. Sfc. Press: -
D-value: -
Flt. Lvl. Wind (30s): From 36° at 40 knots (From the NE at ~ 46.0 mph)
Air Temp: 14.7°C* (~ 58.5°F*)
Dew Pt: -*
Peak (10s) Flt. Lvl. Wind: 41 knots (~ 47.1 mph)
SFMR Peak (10s) Sfc. Wind: 32 knots (~ 36.8 mph)
SFMR Rain Rate: 4 mm/hr (~ 0.16 in/hr)
(*) Denotes suspect data
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Quoting WxLogic:


From what I can tell is the placement and speed of Irene. The weakness for now (based on 00Z/06Z) is now being modeled to be a bit further E not much in the big scope of things and the Bermuda High not pushing Irene further W as before based on some of the model suite as some of them still don't buy it... yet.

One thing to note is that HWRF brings Irene further E when crossing DR which would imply the track that is taking which is a bit further away from the E FL coast, but if Irene doesn't do this which is not expected to at this time then I would expect HWRF to shift back to the W some... closer to GFS.


Well said...

I think it may come back west a tick or two... but then again could tick more east.

I'm one of those people that thinks a thousand things are going to happen between now and Thurs-Fri and we're on number 14.

I just don't have a high confidence in the precision of the track at all until a day or two out.
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I go to bed thinking Wilmington, NC is safe........
wake up seeing the new models and am VERY nervous, as these are the first few runs of the models WITH the HH flight data put into them.

I am only on for a very short time and wondering can anyone tell me how strong the models have Irene towards landfall? I am guessing the longer it stay east of florida, in the hot gulf stream waters, the worse it will be for me in wilmington. Also, I realize the current center path of the models is still well south of here, but trending east and being on the NE side of the storm still makes me nervous.

Also, Irene looks better than last night at first quick glance, am I right?
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Quoting BoroDad17:
Ouch GFS has savannah in the crosshairs this morning.


That should almost be reassuring...We all know storms don't hit Savannah ;~)
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2941. WxLogic
Quoting nrtiwlnvragn:
00Z COAMPS joins the UKMET and GFDL




Only 00Z and 12Z runs?
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2940. WxLogic
Quoting MiamiHurricanes09:
Quick check in before Recon heads into the cyclone. Already descended and finding some tropical depression-force winds, but the extrap pres. doesn't appear to be operating.

114400 1722N 06307W 8433 01564 //// +147 //// 036040 041 032 004 01
$$


Yeah... they still having some issues from what I can see.
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Quoting Vincent4989:

May get to a high DOOM™ once it leaves the 2 largest islands of the Carribean.


The DOOMcon chart was established for all territories, not just the CONUS.
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2938. WxLogic
Quoting surfsidesindy:


Do you know the EMCWF take on things yet this morning?


ECMWF is similar to HWRF. In ECMWF which goes further out in time (therefore to be taken cautiously later in the time period as we know) it attempts to make landfall around the NE FL coast SE GA coast area.

Basically following along the FL E coast.
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I want a donut.
Member Since: July 7, 2010 Posts: 0 Comments: 5519
Quick check in before Recon heads into the cyclone. Already descended and finding some tropical depression-force winds, but the extrap pres. doesn't appear to be operating.

114400 1722N 06307W 8433 01564 //// +147 //// 036040 041 032 004 01
$$
Member Since: September 2, 2009 Posts: 130 Comments: 21032
Quoting WeatherNerdPR:

F-F-Fine! H-H-How are y-you???

Wow, sure,but i 75% guarantee it will go north or south of PR and cause s-s-s-s-o-o-o-me w-w-RECKAGE!!!!
Member Since: November 13, 2009 Posts: 2 Comments: 728
Quoting negriltracy:


I was actually in St Thomas USVI at a fishing tournament to scatter my father's ashes where he caught his world record marlin and it was pretty intense there but nothing like what happened here a few days later :(
We lost infrastructure for months, it was a total nightmare!!!
I have a really bad feeling about this one so am heading to Pricesmart as soon as they open to stock up on EVERYTHING we use regularly...
One Love
I understand that "feeling". I think Irene is going to stay south of the big islands until she reaches at least as far west as Central Cuba. I have no scientific data to back this up but this is my opinion.
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Quoting WeatherNerdPR:

J-Just extremely n-nervous.


She's a biggin', but not too powerful. Have a shot of tequila. :)
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Quoting scooster67:
When is the next HH flight going in?


I see the answer to that is now :)
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Quoting scooster67:
When is the next HH flight going in?


They are on the way now.
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2930. 34chip
Honestly I really do not know. But one set of models will be west 4 hours later it could be east, 4 hours later it could be in the middle. We honestly dont know. But to say anyone is in the clear is just plain crazy to say. Just watch and wait, and stop with this place or that place is in the clear!!!!
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Ouch GFS has savannah in the crosshairs this morning.
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2928. WxLogic
Product: Air Force Tropical RECCO Message (URNT11 KNHC)
Transmitted: 21st day of the month at 11:39Z
Aircraft: Air Force Aircraft (Last 3 digits of the tail number are 300)
Storm Number: 09
Storm Name: Irene (flight in the North Atlantic basin)
Mission Number: 2
Observation Number: 01

Mandatory Data...

Observation Time: Sunday, 11:33Z
Radar Capability: Yes
Aircraft Altitude: Below 10,000 meters
Coordinates: 17.8N 63.5W
Location: 174 miles (279 km) to the ESE (104°) from San Juan, Puerto Rico (USA).
Turbulence: None
Conditions Along Flight Route: In the clear
Pressure Altitude: 1,520 meters
Flight Level Wind: From 60° at 33 knots (From the ENE at ~ 37.9 mph)
- The above is a spot wind.
- Winds were obtained using doppler radar or inertial systems.
Flight Level Temperature: 17°C
Flight Level Dew Point: Not available, probably because the dew point hygrometer was not working.
Weather (within 30 nautical miles): Clear
850 mb Surface Altitude: 1,507 geopotential meters

Optional Data...

Estimated Surface Wind: From 70° at 20 knots (From the ENE at ~ 23.0 mph)

Remarks Section - Remarks That Were Decoded...

Surface Wind Speed (likely by SFMR): 21 knots (~ 24.2mph)

Remarks Section - Additional Remarks...

NW ENTRY PT
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Quoting clwstmchasr:


I don't disagree at all. But the US has been sparred now for 3 years (5 years with a major) that sometimes it is hard to buck the trend. I do think it will make landfall - where? Somewhere between Mobile and the OBX.


I think GOM chances of strike are becoming much slimmer. Northward relocations and model runs seem to suggest an eastward trend with track. I believe now we should watch for a continued trend to the east with the models as shown just a bit by the new 006z hwrf run, keeping Irene off florida.
Member Since: August 22, 2010 Posts: 0 Comments: 652
Quoting WxLogic:


From what I can tell is the placement and speed of Irene. The weakness for now (based on 00Z/06Z) is now being modeled to be a bit further E not much in the big scope of things and the Bermuda High not pushing Irene further W as before based on some of the model suite as some of them still don't buy it... yet.

One thing to note is that HWRF brings Irene further E when crossing DR which would imply the track that is taking which is a bit further away from the E FL coast, but if Irene doesn't do this which is not expected to at this time then I would expect HWRF to shift back to the W some... closer to GFS.


Do you know the EMCWF take on things yet this morning?
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Quoting scooster67:
When is the next HH flight going in?


On its way now. In the outer spiral bands.
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00Z COAMPS joins the UKMET and GFDL


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Quoting weatherwart:



F-F-fine. lol You're not cold, are you?

J-Just extremely n-nervous.
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2922. Relix
Nice news to wake up to. Reminds me of Jeanne. You know what'd be hilarious? If it actually ended up going north of PR
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Quoting WeatherNerdPR:

F-F-Fine! H-H-How are y-you???



F-F-fine. lol You're not cold, are you?
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About JeffMasters

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.