An Active Atlantic Hurricane Season Still Predicted by NOAA, CSU, and TSR

By: Dr. Jeff Masters , 4:07 PM GMT on August 09, 2013

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As we stand on the cusp of the peak part of hurricane season, all of the major groups that perform long-range seasonal hurricane forecasts are still calling for an active 2013 Atlantic hurricane season. NOAA forecasts an above-normal and possibly very active Atlantic hurricane season in 2013, in their August 8 outlook. They give a 70% chance of an above-normal season, a 25% chance of an near-normal season, and 5% chance of a below-normal season. They predict a 70% chance that there will be 13 - 19 named storms, 6 - 9 hurricanes, and 3 - 5 major hurricanes, with an Accumulated Cyclone Energy (ACE) 120% - 190% of the median. If we take the midpoint of these numbers, NOAA is calling for 16 named storms, 7.5 hurricanes, 4 major hurricanes, and an ACE index 155% of normal. This is well above the 1981 - 2010 average of 12 named storms, 6 hurricanes, and 3 major hurricanes. Hurricane seasons during the active hurricane period 1995 - 2012 have averaged 15 named storms, 8 hurricanes, and 4 major hurricanes, with an ACE index 151% of the median.


Figure 1. Tropical Storm Dorian on July 25, 2013, when the storm reached peak intensity--sustained winds of 60 mph. Formation of early-season tropical storms like Chantal and Dorian in June and July in the deep tropics is usually a harbinger of an active Atlantic hurricane season. Image credit: NASA.

NOAA cites five main reasons to expect an active remainder of hurricane season:

1) Sea Surface Temperatures (SSTs) are above average in the Main Development Region (MDR) for hurricanes, from the coast of Africa to the Caribbean. As of August 9, SST were 0.4°C (0.8°F) above average.
2) Trade winds are weaker than average across the MDR, which has caused the African Monsoon to grow wetter and stronger, the amount of spin over the MDR to increase, and the amount of vertical wind shear to decrease.
3) No El Niño event is present or expected this fall.
4) There have been two early-season tropical storms in the deep tropics (Tropical Storms Chantal and Dorian), which is generally a harbinger of an above-normal season.
5) We are in an active hurricane period that began in 1995.

Colorado State predicts a much above-average hurricane season
A much above-average Atlantic hurricane season is on tap for 2013, according to the seasonal hurricane forecast issued August 2 by Dr. Phil Klotzbach and Dr. Bill Gray of Colorado State University (CSU). The CSU team is calling for 18 named storms, 8 hurricanes, and 3 intense hurricanes, and an Accumulated Cyclone Energy (ACE) of 142. The forecast calls for an above-average chance of a major hurricane hitting the U.S., both along the East Coast (40% chance, 31% chance is average) and the Gulf Coast (40% chance, 30% chance is average). The risk of a major hurricane in the Caribbean is also above average, at 53% (42% is average.)

Analogue years
The CSU team picked five previous years when atmospheric and oceanic conditions were similar to what we are seeing this year: cool neutral ENSO conditions and slightly above-average tropical Atlantic sea surface temperatures. Those five years were 2008, a very active year with 16 named storms and 4 major hurricanes--Gustav, Ike, Paloma, and Omar; 2007, an active year with 15 named storms and two Category 5 storms--Dean and Felix; 1996, an above average year with 13 named storms and 6 major hurricanes--Edouard, Hortense, Fran, Bertha, Isidore, and Lili; 1966, an average year with 11 named storms and 3 major hurricanes--Inez, Alma, and Faith; and 1952, a below average year with 7 named storms and 3 major hurricanes. The average activity during these five analogue years was 12.4 named storms, 7.2 hurricanes, and 3.8 major hurricanes.

TSR predicts an above-average hurricane season: 14.8 named storms
The August 6 forecast for the 2013 Atlantic hurricane season made by British private forecasting firm Tropical Storm Risk, Inc. (TSR) calls for an active season with 14.8 named storms, 6.9 hurricanes, 3 intense hurricanes, and an Accumulated Cyclone Energy (ACE) of 121. The long-term averages for the past 63 years are 11 named storms, 6 hurricanes, 3 intense hurricanes, and an ACE of 103. TSR rates their skill level as good for these August forecasts--47% - 59% higher than a "no-skill" forecast made using climatology. TSR predicts a 58% chance that U.S. land falling activity will be above average, a 26% chance it will be near average, and a 16% chance it will be below average. They project that 4 named storms will hit the U.S., with 1.8 of these being hurricanes. The averages from the 1950-2012 climatology are 3.1 named storms and 1.4 hurricanes. They rate their skill at making these August forecasts for U.S. landfalls just 9% - 18% higher than a "no-skill" forecast made using climatology. In the Lesser Antilles Islands of the Caribbean, TSR projects 1.4 named storms, 0.6 of these being hurricanes. Climatology is 1.1 named storms and 0.5 hurricanes.

TSR's two predictors for their statistical model are the forecast July - September trade wind speed over the Caribbean and tropical North Atlantic, and the forecast August - September 2013 sea surface temperatures in the tropical North Atlantic. Their model is calling for warmer than average SSTs and near average trade winds during these periods, and both of these factors should act to increase hurricane and tropical storm activity.


Figure 2. 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 3. Comparison of the percent improvement in mean square error over climatology for seasonal hurricane forecasts for the Atlantic from NOAA, CSU and TSR from 2003-2012, 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 2003 - 2012 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.

FSU predicts an above-average hurricane season: 15 named storms
The Florida State University (FSU) Center for Ocean-Atmospheric Prediction Studies (COAPS) issued their fifth annual Atlantic hurricane season forecast on May 30, calling for a 70% probability of 12 - 17 named storms and 5 - 10 hurricanes. The mid-point forecast is for 15 named storms, 8 hurricanes, and an accumulated cyclone energy (ACE) of 135. The scientists use a numerical atmospheric model developed at COAPS to understand seasonal predictability of hurricane activity. The model is one of only a handful of numerical models in the world being used to study seasonal hurricane activity and is different from the statistical methods used by other seasonal hurricane forecasters such as Colorado State, TSR, and PSU (NOAA uses a hybrid statistical-dynamical model technique.) The FSU forecast has been one of the best ones over the past four years:

2009 prediction: 8 named storms, 4 hurricanes. Actual: 9 named storms, 3 hurricanes
2010 prediction: 17 named storms, 10 hurricanes. Actual: 19 named storms, 12 hurricanes
2011 prediction: 17 named storms, 9 hurricanes. Actual: 19 named storms, 7 hurricanes
2012 prediction: 13 named storms, 7 hurricanes. Actual: 19 named storms, 10 hurricanes

Penn State predicts an above-average hurricane season: 16 named storms
A statistical model by Penn State's Michael Mann and alumnus Michael Kozar is calling for an active Atlantic hurricane season with 16 named storms, plus or minus 4 storms. Their prediction was made using statistics of how past hurricane seasons have behaved in response to sea surface temperatures (SSTs), the El Niño/La Niña oscillation, the North Atlantic Oscillation (NAO), and other factors. The statistic model assumes that in 2013 the May 0.87°C above average temperatures in the MDR will persist throughout hurricane season, the El Niño phase will be neutral to slightly warm, and the North Atlantic Oscillation (NAO) will be near average.

The PSU team has been making Atlantic hurricane season forecasts since 2007, and these predictions have done pretty well, except for in 2012, when an expected El Niño did not materialize:

2007 prediction: 15 named storms, Actual: 15
2009 prediction: 12.5, named storms, Actual: 9
2010 prediction: 23 named storms, Actual: 19
2011 prediction: 16 named storms, Actual: 19
2012 prediction: 10.5 named storms, Actual: 19

UK Met Office predicts a slightly above-average hurricane season: 14 named storms
The UKMET office forecast for the 2013 Atlantic hurricane season, issued May 13, calls for slightly above normal activity, with 14 named storms, 9 hurricanes, and an ACE index of 130. In contrast to the statistical models relied upon by CSU, TSR, and NOAA, the UKMET model is done strictly using two dynamical global seasonal prediction systems: the Met Office GloSea5 system and ECMWF system 4. In 2012, the Met Office forecast was for 10 tropical storms and an ACE index of 90. The actual numbers were 19 named storms and an ACE index of 123.


Figure 4. Total 2013 Atlantic hurricane season activity as predicted by twelve different groups.

NOAA predicts a below-average Eastern Pacific hurricane season
NOAA's pre-season prediction for the Eastern Pacific hurricane season, issued on May 23, calls for a below-average season, with 11 - 16 named storms, 5 - 8 hurricanes, 1 - 4 major hurricanes, and an ACE index 60% - 105% of the median. The mid-point of these ranges gives us a forecast for 13.5 named storms, 6.5 hurricanes, and 2.5 major hurricanes, with an ACE index 82% of average. The 1981 - 2010 averages for the Eastern Pacific hurricane season are 15 named storms, 8 hurricanes, and 4 major hurricanes.

NOAA predicts a below-average Central Pacific hurricane season
NOAA's pre-season prediction for the Central Pacific hurricane season, issued on May 22, calls for a below-average season, with 1 - 3 tropical cyclones. An average season has 4 - 5 tropical cyclones, which include tropical depressions, tropical storms, and hurricanes. Hawaii is the primary land area affected by Central Pacific tropical cyclones.

West Pacific typhoon season forecast not available this year
Dr. Johnny Chan of the City University of Hong Kong usually issues a seasonal forecast of typhoon season in the Western Pacific, but did not do so in 2012 or 2013. An average typhoon season has 27 named storms and 17 typhoons. Typhoon seasons immediately following a La Niña year typically see higher levels of activity in the South China Sea, especially between months of May and July. Also, the jet stream tends to dip farther south than usual to the south of Japan, helping steer more tropical cyclones towards Japan and Korea.

Quiet in the Atlantic this weekend
There are no Atlantic threat areas to discuss today, and none of the reliable models for tropical cyclone formation is predicting development during the coming seven days. However, there are some indications that the atmosphere over the tropical Atlantic will become more conducive for tropical storm formation beginning around August 15. The Madden Julian Oscillation (MJO), a pattern of increased thunderstorm activity near the Equator that moves around the globe in 30 - 60 days, may move into the Atlantic then, increasing tropical storm formation odds. At the same time, the computer models are indicating an increase in moisture over the tropical Atlantic, due to a series of tropical waves expected to push off of the coast of Africa. There will also be several eastward-moving Convectively-Coupled Kelvin Waves (CCKWs) traversing the Atlantic during that period. These atmospheric disturbances have a great deal of upward-moving air, which helps strengthen the updrafts of tropical disturbances. Formation of the Eastern Pacific's Hurricane Gil and Henriette were aided by CCKWs. These same CCKWs will cross into the Atlantic and increase the odds of tropical storm formation during the period August 15 - 20.

Have a great weekend, everyone!

Jeff Masters

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Quoting 182. Levi32:
So far only 4 out of 20 of the GFS EnKF T574 ensemble members show a significant storm in the western Caribbean or Gulf of Mexico in 7 days, but the models are gradually picking up on this threat area, as they probably should given the pattern.

latest run of GFS doesn't show much of CV development, wonder why
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Quoting 177. PensacolaDoug:




Not likely as a 5.
Coming up the west coast of Florida, shelf waters are shallow and incoming air would have been off of land.
That's true about the shallow depth of the continental shelf and the air wasn't quite as moist up here since the front was draped across the area. What I find interesting was that Charley was never forecasted to become anything higher than a 115 mph. Category 3. He maxed out at 145 mph. as he began to make the turn, the front may have provided some energy for that strengthening to occur.
Member Since: June 30, 2013 Posts: 9 Comments: 6660
Quoting 179. GTstormChaserCaleb:
Hmm???



I think that low near the SW Car could slide off overland, but we'll see.
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This was a nice 5 Day SAL forecast from GOES





And this is a possible cooldown next week (image by Brad Panovich)


Member Since: February 11, 2012 Posts: 0 Comments: 9451
So far only 4 out of 20 of the GFS EnKF T574 ensemble members show a significant storm in the western Caribbean or Gulf of Mexico in 7 days, but the models are gradually picking up on this threat area, as they probably should given the pattern.

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The factor I was waiting for: wind shear on that Fl low? Strong wind shear is in it's path, but that is expected to dissipate & slide off to the SW soon.

In that case, I see little to stop the Low from possibly developing. Conditions seem ripe for it to do so, but I do not have the experience that some have. Anything I'm missing? Anyone?
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Quoting 170. GeorgiaStormz:
zzzzzzzzzzzzzzzzzzzz................


Henriette rapidly declines....E-Pac Activity falls apart.

Atlantic activity non-existent.
Conus Wx not particularly interesting (some heat and flooding)


zzzzzzzzzzzzzzzzzzzz...............


The eastern pacific has been active since May 15
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Hmm???

Member Since: June 30, 2013 Posts: 9 Comments: 6660
Quoting 162. GTstormChaserCaleb:
Me and my family stayed behind here in the Tampa area during Charley and on that same morning August Friday the 13th, 2004 I went for a walk over to my Grandmother's house actually to help her pack some things as she was planning to come over and stay by us for the night, the place was dead quiet! All of a sudden I heard what sounded like Tornado Sirens going off. I got scared out of my pants when I heard that. I tell you Washi, we lucked out here in the Tampa Bay area a few more hours for Charley over water and he would have likely struck Tampa Bay as a Category 5 hurricane.




Not likely as a 5.
Coming up the west coast of Florida, shelf waters are shallow and incoming air would have been off of land.
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Wow, I actually see big, puffy clouds in the sky today. What a changee!
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Quoting wunderkidcayman:
Hello guys


Hey wunderkidcayman. What's up, bro?
Member Since: July 27, 2013 Posts: 0 Comments: 501
Hello guys
Member Since: June 13, 2009 Posts: 2 Comments: 9548
The NAVGEM also looks to be showing development in 4 days another model that has been particularly consistent in showing this area of the Caribbean.

Member Since: June 30, 2013 Posts: 9 Comments: 6660
Quoting 171. 69Viking:
Well as my boys would say, I'm off to go to the Alabama Boondocks for a weekend in the woods without cell phones or computers! Talk to you all on Monday, in the meantime play nice and enjoy the tranquility because we all know it's not going to last much longer!
Have a good time :)
Member Since: June 30, 2013 Posts: 9 Comments: 6660
Well as my boys would say, I'm off to go to the Alabama Boondocks for a weekend in the woods without cell phones or computers! Talk to you all on Monday, in the meantime play nice and enjoy the tranquility because we all know it's not going to last much longer!
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zzzzzzzzzzzzzzzzzzzz................


Henriette rapidly declines....E-Pac Activity falls apart.

Atlantic activity non-existent.
Conus Wx not particularly interesting (some heat and flooding)


zzzzzzzzzzzzzzzzzzzz...............
Member Since: February 11, 2012 Posts: 0 Comments: 9451
TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE NEXT FIVE DAYS.

I like this new outlook.
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Quoting 166. Tropicsweatherpr:
TROPICAL WEATHER OUTLOOK
NWS NATIONAL HURRICANE CENTER MIAMI FL
200 PM EDT FRI AUG 9 2013

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE NEXT FIVE
DAYS.

&&

FIVE-DAY FORMATION PROBABILITIES ARE EXPERIMENTAL IN 2013. COMMENTS
ON THE EXPERIMENTAL FORECASTS CAN BE PROVIDED AT...

WWW.NWS.NOAA.GOV/SURVEY/NWS-SURVEY.PHP?CODE=ETWO

$$
FORECASTER BEVEN

I am happy
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TROPICAL WEATHER OUTLOOK
NWS NATIONAL HURRICANE CENTER MIAMI FL
200 PM EDT FRI AUG 9 2013

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE NEXT FIVE
DAYS.

&&

FIVE-DAY FORMATION PROBABILITIES ARE EXPERIMENTAL IN 2013. COMMENTS
ON THE EXPERIMENTAL FORECASTS CAN BE PROVIDED AT...

WWW.NWS.NOAA.GOV/SURVEY/NWS-SURVEY.PHP?CODE=ETWO

$$
FORECASTER BEVEN

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no development for 5 days
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That FL low is near an area of high Tropical Cyclone Heat Potential, passing through & entering an area of high SST's, and close to a Sea-height anomaly zone. Seems to be lots of potential unless winds aloft are too unfavorable. If it cotinues towards LA, there is an area of very warm water in the NC GOM off the TX/LA coast.
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Quoting 157. washingtonian115:
Thanks goodness Charley didn't have more time over water.Could have been west coast Florida's Andrew.
Me and my family stayed behind here in the Tampa area during Charley and on that same morning August Friday the 13th, 2004 I went for a walk over to my Grandmother's house actually to help her pack some things as she was planning to come over and stay by us for the night, the place was dead quiet! All of a sudden I heard what sounded like Tornado Sirens going off. I got scared out of my pants when I heard that. I tell you Washi, we lucked out here in the Tampa Bay area a few more hours for Charley over water and he would have likely struck Tampa Bay as a Category 5 hurricane.
Member Since: June 30, 2013 Posts: 9 Comments: 6660
Thanks, Doc, for keeping us informed. Have a great week-end and enjoy the good weather while it last.
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Quoting 145. SouthernIllinois:
Good afternoon from the lush oak hickory forests deep in the heartland!! As you can see from ze radar, showers and embedded downpours knocking on my doorstep here in Cypress.

Was out at the barn earlier this morning. The rain gauge was dumped and the 4 wheelers all re-fueled. Anticipating a good soaking soon. The BEST part is it won't be disappointed even if we only get a .10" since we got an inch the last seven days. In other words, you can't disappoint me at this point Mother Nature. I am already happy. But if you decide to sweep by and drop a 2" at the last minute, I got room for more joy. :)

Natalie





The leading edge of the rain was moving northeast at 25 mph and will cross the Mississippi River into Southern Illinoise and Western Kentucky early this afternoon. Rainfall amounts with the strongest storms were near one inch per hour. The fast movement of these storms will mitigate flash flooding this afternoon.


You got mail, I'll be in the woods this weekend myself! Keep your promise and start keeping the rain, somehow it keeps sneaking away and showing up in NW Florida!
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Quoting 154. hydrus:
Trough shows up well on here too..

Thanks goodness Charley didn't have more time over water.Could have been west coast Florida's Andrew.
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Even the highest of high tech computer models from the highest agencies have bugs and glitches. Link

Also this computer glitch suspended the NASA Mars Rover operation. Link
Member Since: June 30, 2013 Posts: 9 Comments: 6660
Quoting 143. washingtonian115:
The trough saved Tampa and knocked my temps down into the 70's that Saturday and brought cloudy conditions with it.2004 the deep troughs kept coming.I wasn't complaining however :).
Trough shows up well on here too..

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Quoting 149. hydrus:
We took a direct hit from Charley. It was the shortest and most violent hurricane I have been through. I saw a lot of people suffer terribly.
The videos also don't lie Hydrus.I saw Mike Thesis video and Charley was something scary for sure.Flipping cars ripping buildings to shreds.
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Quoting 150. 62901IL:

Hi andre!
hello 62901L.
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Quoting 132. weatherlover94:


I mean do you think they will mention the African wave ?....it already has an area of low pressure with it

I know, I was being a smartass. ;)

I doubt they do. This particular wave doesn't have any model support.

One of these will develop though. I place my bet on the wave two behind the one off the coast.
Member Since: July 6, 2010 Posts: 108 Comments: 30241
Quoting 148. HurricaneAndre:

Hi andre!
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Quoting 143. washingtonian115:
The trough saved Tampa and knocked my temps down into the 70's that Saturday and brought cloudy conditions with it.2004 the deep troughs kept coming.I wasn't complaining however :).
We took a direct hit from Charley. It was the shortest and most violent hurricane I have been through. I saw a lot of people suffer terribly.
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usually when they dont highlight anything the TWO would be out by now
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Quoting 143. washingtonian115:
The trough saved Tampa and knocked my temps down into the 70's that Saturday and brought cloudy conditions with it.2004 the deep troughs kept coming.I wasn't complaining however :).
WE ARE GOING TO SEE LOTS OF STORM GOING OUT TO SEA THIS YEAR.
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Me tinks some may have missed Grothar's "sarcasm" with his last.
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Quoting 135. hydrus:
The Mets here in Mid TN even mentioned some fall like weather next week. Hurricane Charley was picked up by an unseasonably deep trough for August...The trough shows up well on this satellite image..




The trough saved Tampa and knocked my temps down into the 70's that Saturday and brought cloudy conditions with it.2004 the deep troughs kept coming.I wasn't complaining however :).
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Quoting 131. 69Viking:


I remember Opal all too well. Spun up in the BOC and then made a beeline towards our area when the front picked her up. I'm afraid something like that could happend this year for some reason. It won't be good for us to even get a small storm with how waterlogged we are already.


Yep, the low looks poised to head for LA, but I do consider that it could hook NE, too. That area has had so much H2O!
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NOTTING MUCH!!
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MAG is still performing updates...if you have a smart phone or other cell phone with internet you will now be able to run html loops.

In Septemeber the GFS, NAM, and RAP will add 925 mb. temperature parameters and enlarge the South Pacific area to include Australia.

Link
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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.