Gulf of Mexico disturbance 93L a Lousiana flood threat; Katia a hurricane

By: Dr. Jeff Masters , 3:28 PM GMT on September 01, 2011

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Surface winds over the northern Gulf of Mexico are rising, pressures are falling, and heavy thunderstorms are building today thanks to a tropical disturbance (Invest 93L) that is the product of a tropical wave interacting with an upper-level low pressure system. At 8:35 am CDT, winds at the Mississippi Canyon 711 oil rig were south-southeast at 38 mph. This is just 1 mph below tropical storm force, but the wind instrument was 348 feet (106 m) above the ocean surface, and winds near the surface were probably considerably lower, near 30 mph. Long range radar out of Mobile, Alabama shows heavy rain showers building along the northern Gulf Coast, but these rain showers are not organized into spiral bands and show no signs of rotation. Strong upper-level winds out of the west-northwest are creating 30 knots of wind shear over 93L, keeping the storm's heavy thunderstorms disorganized. Strong onshore winds raising tides to 1 - 2 feet above normal are likely along the northern Gulf Coast through the weekend, and coastal flood statements have been issued for the region.


Figure 1. Predicted rainfall for the 5-day period ending at 8am EDT Sep 6, 2011. A large region of rains in excess of 15 inches is expected over Southeast Louisiana. Image credit: NOAA/HPC.


Figure 2. U.S. drought conditions on August 30. The rains from 93L have the potential to bring major drought relief to drought-stricken portions of the coast. Image Credit: U.S. Drought Monitor.

By late tonight, wind shear is expected to drop to the moderate range, below 20 knots, and 93L should begin to organize into a tropical depression. Wind shear is expected to remain moderate, 10 - 20 knots, into Monday. There is some cold, dry air aloft that will retard this process, and I think the earliest we would see a tropical depression is Friday afternoon. NHC is giving 93L a 70% chance of developing into a tropical depression by Saturday morning. All of the major models develop 93L near the Louisiana coast, and show a slow and erratic movement due to weak steering currents. Coastal Louisiana, Mississippi, Alabama, and the extreme western Panhandle of Florida will likely receive very heavy flooding rains beginning this afternoon and intensifying Friday and Saturday. The latest rainfall forecast from NOAA Hydrological Prediction Center (Figure 1) shows that a large area of 15+ inches of rain is expected over Southeast Louisiana. The region is under moderate drought, so flooding problems will be delayed compared to what we'd normally expect from heavy rains of over a foot. Nevertheless, minor to moderate freshwater flooding is likely from 93L, and flash flood watches are posted for New Orleans and surrounding areas, and rainfall amounts of 1 - 3 inches per hour are possible in some of the heavier rain squalls. Ocean temperatures are near record warmth, 88°F (31.3°C), which will provide plenty of moisture for heavy rains, and plenty of energy to help 93L strengthen into a tropical storm. Most of the models predict 93L will have some motion to the west by Saturday, which would bring rains to the Texas coast near the Louisiana border. Steering currents will be weak in the Gulf this weekend and early next week, making it difficult to predict where the storm might go. If 93L stays over water through Tuesday, like the ECMWF model is predicting, the storm would be a threat to intensify into a hurricane. Most of the other models predict 93L will move ashore over Louisiana by Sunday, limiting the storm's development to just tropical storm strength. I think it at least 50% likely 93L will be a tropical storm with 40 - 60 mph winds along the coast of Louisiana by Sunday.

Hurricane Katia
Hurricane Katia intensified into the 2nd hurricane of the 2011 season last night, and continues its long trek across the Atlantic Ocean today. Katia is expected to arrive at a position several hundred miles north of the Northern Lesser Antilles Islands by Monday. The islands are not in the cone of uncertainty, and it appears unlikely that they will receive tropical storm-force winds from Katia. Satellite images show that Katia is a well-organized storm with plenty of heavy thunderstorms, but the storm has been struggling with dry air and moderate wind shear of 10 -20 knots, and is looking less organized than it did last night. These problems will likely diminish by Friday night, as the upper low bringing the wind shear moves away. It is still unclear how much of a threat Katia may post to the U.S. Dr. Bob Hart's Historical Tropical Cyclone Probability web page suggests shows that tropical storms in Katia's current position have an 16% chance of hitting North Carolina, a 21% chance of hitting Canada, a 12% chance of hitting Florida, and a 54% chance of never hitting land. I suspect that Katia will turn north before reaching the U.S. and potentially threaten Bermuda and Canada, based on what past storms in similar situations have done, and assuming the jet stream maintains its current pattern of bringing frequent troughs of low pressure off the coast of the U.S. It will be another day or two before the models will begin to have a handle on the long-term fate of Katia, though.


Figure 3. Morning satellite image of Katia.

94L
A well-organized low pressure system with a surface circulation and limited heavy thunderstorm activity has developed between Bermuda and the Canadian Maritimes. This disturbance, (94L), is headed out to sea, and is being given a 10% chance of developing into a tropical depression by NHC. 94L is under a very high 30 - 40 knots of wind shear, and will not be able to intensify very much. However, Tropical Storm Jose formed from a similar type of system, and we might get surprised by 94L.

I'll have more on Irene in tomorrow's post.

Jeff Masters

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Quoting LAlurker:

????????


Oh really. Don't remember this part of Florida being annex to Alabama!
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Quoting 69Viking:


Get your facts straight, Dennis made a direct hit on Northwest Florida.
I live in the Pensacola Florida area and Dennis was terrible. Somebody needs to do their research! We were without power for days and had significant damage.
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See if this works so people get the picture of where Dennnis landed and keep in mind the East side of storms are the nastiest.

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Florida's 2005:

Hurricane Dennis:



Hurricane Katrina:



And, Hurricane Wilma:

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Quoting LAlurker:

????????



Just put the idiot on ignore, its just-another-goof.
Member Since: July 6, 2010 Posts: 113 Comments: 32033
Quoting 996tt:


Doubt it. Monetary policies QE XXX and inflation when calcated under real and prior formulas is more of a factor. Droughts suck, but beef, poultry and especially cotton comes from places other than Texas and demand will be met. Flood and tornado devastation was pretty bad this year also. Lots of people hurting. Perhaps the hurricane Gods will be afraid of rising beef cost and cast a Cat 5 in your direction.


I don't appreciate that last statement. I live in Kemah with my infant son and an ailing father. I own property here. You appear to have confused my message with a wish for a large destructive storm. I was hoping for a good soaking from that Invest in the Gulf. Texas needs it regardless of what you think.

PS - my statement came directly from a study conducted at A&M. The numbers are real and certainly didn't warrant you wishing me and my fellow Texans harm.
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Quoting AtHomeInTX:


What? We're 45 inches down since 2010. And 20+ down this year??
Parts of Southeast Texas have had a little bit more rain than Central Texas but they average about twice as much. The Houston area has had about as much rain as I have had and that is unbelievable because I use to go to Houston often and it seemed like it rained every time i went there but not this past year.
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Quoting bohonkweatherman:
Stop complaining, LOL, at least you have a chance, 95 percent of Texas wont even get a shower from the system in La.


I am not really complaining in the sense for just us but for "all" of us. Was really hoping LEE could make landfall and go through the state. (nothing major however) :)
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Quoting Levi32:


And it stays within 50 miles of that location for the next 4 days....very bad for flooding in that area. Their discussion mentions the amplifying trough but says nothing about the Texas ridge, which is the important feature which will determine when 93L's WNW/NW progress gets halted. It could be as close to the coast as the HPC suggests, or farther offshore. It's hard to say when the resistance will reach a critical level.

Ah ok. Thanks for clearing that up for me. My heads sore from all the scratching.
Lol.
Member Since: August 24, 2010 Posts: 0 Comments: 151
1085. GetReal
Quoting Drakoen:
I don't like the way 93L looks like satellite imagery. It looks like it could become a large system and powerful. The upper level low inhibiting the system is gradually moving out and the upper level outflow is already being established over the eastern portion of the system. RGB imagery clearly indicates broad rotation at the lower levels occurring.




You forgot to mention the extremely warm GOM waters it is casually moving across....
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Quoting CaicosRetiredSailor:
Eight days without telephone and Internet is cruel....
it's been down since Irene... only lost power for 48 hrs.
finally got my phone/Internet back so now I have a lot of news etc. to catch up on.


So glad to hear from you - let us know how you are doing, please. We've been waiting impatiently - though not so impatiently as you, I suppose.
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1083. Levi32
Quoting TropicalAnalystwx13:


What are the odds of it becoming a hurricane and major hurricane? IYO (In your opinion)..

Levi, you too :P


Euro last night I think was overdone, but illustrated how the environment will support strengthening. I think if 93L is over the water Monday, it will likely be a hurricane. If it comes ashore before the weekend is over, it may just be a tropical storm.
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1082. WBNC
Wow...Katia sure looks a lot like Fran :/
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Quoting notanothergoof:
florida hasnt had a hurricane since 2004

????????
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Quoting Drakoen:
I don't like the way 93L looks like satellite imagery. It looks like it could become a large system and powerful. The upper level low inhibiting the system is gradually moving out and the upper level outflow is already being established over the eastern portion of the system. RGB imagery clearly indicates broad rotation at the lower levels occurring.



Recon has already found west winds...just a broad circulation.

Levi has mentioned this a few times, but the outflow is indicative of just how much heat this system is putting into the atmosphere and it should be able to better its own environment. I don't see how the upper level low stands a chance against all of this heat, especially since the upper low is fairly weak already.
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1079. WxLogic
@84HR NAM:



@84HR NAM Parallel:



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Quoting CaicosRetiredSailor:
Eight days without telephone and Internet is cruel....
it's been down since Irene... only lost power for 48 hrs.
finally got my phone/Internet back so now I have a lot of news etc. to catch up on.


Glad you called in was beginning to wonder how you fared.
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Agree Drak, and the WV imagery really reinforces that. If this thing has 3.5-4 D+ over water, it could prove very dangerous and spin up with little warning. In this scenario, the cyclonic meandering of a major TC could bust any sound forecast easily. Gunna be a nail biter along the northern gulf coast.
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Closest ob to 94L:

2011-Sep-01 19:30 N 37°13' W 064°16' pressure 1005.4 water temperature 28.2

Link
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1075. Drakoen
Quoting TropicalAnalystwx13:


What are the odds of it becoming a hurricane and major hurricane? IYO (In your opinion)..

Levi, you too :P


Let's wait till it becomes an actual system first.
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Quoting JeffMasters:


Recurvature is a term from physics describing the motion of a spinning storm system on the surface of the Earth. Low pressure systems in the NH will always recurve towards the pole, and high pressure systems will recurve towards the Equator.

From:
http://www.applet-magic.com/recurvature.htm

"The explanation for recurvature lies in the fact that cyclones (and anticyclones) possess angular momenta with respect to their spin axes. This will be referred to as their spin angular momenta. They also possess angular momenta with respect to the axis of rotation of the Earth, which will be called their terrestrial angular momenta. The turning of the spin angular momentum vector with the rotation of the Earth is a forced precession which creates a torque on the cyclone that accelerates it toward the nearest pole. As the cyclone moves toward its pole it gets closer to the axis of rotation of the Earth. The preservation of the terrestrian angular momentum then requires it to increase its velocity toward the east."

Jeff Masters


Thanks for the clarification Dr. Masters!
Member Since: July 6, 2010 Posts: 113 Comments: 32033
1073. Levi32
Quoting JeffMasters:


Recurvature is a term from physics describing the motion of a spinning storm system on the surface of the Earth. Low pressure systems in the NH will always recurve towards the pole, and high pressure systems will recurve towards the Equator.

From:
http://www.applet-magic.com/recurvature.htm

"The explanation for recurvature lies in the fact that cyclones (and anticyclones) possess angular momenta with respect to their spin axes. This will be referred to as their spin angular momenta. They also possess angular momenta with respect to the axis of rotation of the Earth, which will be called their terrestrial angular momenta. The turning of the spin angular momentum vector with the rotation of the Earth is a forced precession which creates a torque on the cyclone that accelerates it toward the nearest pole. As the cyclone moves toward its pole it gets closer to the axis of rotation of the Earth. The preservation of the terrestrian angular momentum then requires it to increase its velocity toward the east."

Jeff Masters


Thanks Dr. Masters. That's exactly right, and I believe is part of the explanation of the "Beta effect," but I think our discussion here is more about the correct use of the word, and also whether the prefix "re" is necessary. If it's a physical term though, that should be good enough for us.
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Quoting TomTaylor:
Or its just an extrapolation error. Or its the result of a downdraft. I've seen this happen many times this year (higher extrapolated surface winds than flight level winds), seems especially common with weak storms (ie weak TSs or yet to be TSs like 93L), although this may just be because most of our storms so far have been weak.
? The surface winds are stronger than at flight level all around 93L.

Really, talking to a tropical met PhD here, now, about it. Baroclinic instability-driven system...
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Quoting PakaSurvivor:

Live in the Panhandle and Dennis caused $1500 in roof damage. Some of the damage may have been caused by Ivan the year before and wasn't discovered.
1500 dollars? that's the LEAST amount of money i've seen a hurricane do?
Member Since: August 18, 2011 Posts: 0 Comments: 994
Quoting notanothergoof:
those 3 storms just gave some of the edge to florida but not a direct hit or to close to a hit the last were jeanne francis and charley in 2004


Get your facts straight, Dennis made a direct hit on Northwest Florida.
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Quoting AtHomeInTX:


What? We're 45 inches down since 2010. And 20+ down this year??


Hi AtHome :)
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1068. pcola57
Quoting JeffMasters:


Recurvature is a term from physics describing the motion of a spinning storm system on the surface of the Earth. Low pressure systems in the NH will always recurve towards the pole, and high pressure systems will recurve towards the Equator.

From:
http://www.applet-magic.com/recurvature.htm

"The explanation for recurvature lies in the fact that cyclones (and anticyclones) possess angular momenta with respect to their spin axes. This will be referred to as their spin angular momenta. They also possess angular momenta with respect to the axis of rotation of the Earth, which will be called their terrestrial angular momenta. The turning of the spin angular momentum vector with the rotation of the Earth is a forced precession which creates a torque on the cyclone that accelerates it toward the nearest pole. As the cyclone moves toward its pole it gets closer to the axis of rotation of the Earth. The preservation of the terrestrian angular momentum then requires it to increase its velocity toward the east."

Jeff Masters


Well put and Thanks Dr. Masters.
V/R
Moe
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Quoting LouisianaWoman:
Hey--Could someone tell all those models that have Lee taking a similiar path as Lily did...(up Vermilion Bay) that they need to recheck themselves. I live here and I didn't invite Lee over. No one likes uninvited houseguests.

lol! I hated Lily. She took my power for a week.
Member Since: September 5, 2007 Posts: 0 Comments: 3487
Quoting Drakoen:
I don't like the way 93L looks like satellite imagery. It looks like it could become a large system and powerful. The upper level low inhibiting the system is gradually moving out and the upper level outflow is already being established over the eastern portion of the system. RGB imagery clearly indicates broad rotation at the lower levels occurring.



What are the odds of it becoming a hurricane and major hurricane? IYO (In your opinion)..

Levi, you too :P
Member Since: July 6, 2010 Posts: 113 Comments: 32033
lol and two hours later everyone is talking about the legitimacy of the term "recurve." Glad somebody pointed out the difference between "re-curve" and "recurve." Anyway why is this even worth arguing about? lol
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Eight days without telephone and Internet is cruel....
it's been down since Irene... only lost power for 48 hrs.
finally got my phone/Internet back so now I have a lot of news etc. to catch up on.
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Quoting LouisianaWoman:
Hey--Could someone tell all those models that have Lee taking a similiar path as Lily did...(up Vermilion Bay) that they need to recheck themselves. I live here and I didn't invite Lee over. No one likes uninvited houseguests.


You may be getting two to three times as much rainfall as you did with Lily...Up to 20".

Member Since: July 6, 2010 Posts: 113 Comments: 32033
1062. Levi32
Quoting AtHomeInTX:


Sigh. I'm with you there. But as was pointed out the NAM keeps us wet for days. And then there's this, which I don't understand after having read their discussion that talked about the trough amplifying. Leaves it here thru day 6.






And it stays within 50 miles of that location for the next 4 days....very bad for flooding in that area. Their discussion mentions the amplifying trough but says nothing about the Texas ridge, which is the important feature which will determine when 93L's WNW/NW progress gets halted. It could be as close to the coast as the HPC suggests, or farther offshore. It's hard to say when the resistance will reach a critical level.
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Quoting BrockBerlin:


That is actually not accurate, both Katrina and Wilma (and Dennis I think as well) impacted the state at hurricane status in 2005.

Live in the Panhandle and Dennis caused $1500 in roof damage. Some of the damage may have been caused by Ivan the year before and wasn't discovered.
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Quoting notanothergoof:
florida hasnt had a hurricane since 2004


Excuse me but Hurricane Dennis went right over my house in July of 2005 so check your facts again!
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Quoting angiest:

Hah, the corner of SE Texas than needs it the least (due to heavy July rainfall.)

What? We're 45 inches down since 2010. And 20+ down this year??
Member Since: August 24, 2010 Posts: 0 Comments: 151
Member Since: July 6, 2010 Posts: 113 Comments: 32033
1057. Drakoen
I don't like the way 93L looks like satellite imagery. It looks like it could become a large system and powerful. The upper level low inhibiting the system is gradually moving out and the upper level outflow is already being established over the eastern portion of the system. RGB imagery clearly indicates broad rotation at the lower levels occurring.

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Hey--Could someone tell all those models that have Lee taking a similiar path as Lily did...(up Vermilion Bay) that they need to recheck themselves. I live here and I didn't invite Lee over. No one likes uninvited houseguests.
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Quoting xtremeweathertracker:

SE Texas should get rain from this depending on how the NW quadrant of the storm fills out if 93L stalls say south of Lake Charles or Lafayette we should see quite a bit of rain and gusty winds from the Northeast!! IMO


Thanks, sometimes we are not considered Texas by most folks. Sure wish my hill country family could get some rain, they really need it.
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1054. goavs4
Well good thing Texas won't get any rain at all out of this, what we really need is a good north wind generated by the western side outflow of a major hurricane to dry us out some more.....................

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1053. JeffMasters (Admin)
Quoting TomTaylor:
And this is exactly why the debate began in the first place.

As Levi said, people are not using the word properly. A recurve simply means the storm will curve a second time.

In this case with Katia, a recurve will still happen, the question is whether or not it will occur over the ocean or over land. In other words, no the recurve is not looking less likely, the recurve before land is looking less likely...there is a difference lol


Recurvature is a term from physics describing the motion of a spinning storm system on the surface of the Earth. Low pressure systems in the NH will always recurve towards the pole, and high pressure systems will recurve towards the Equator.

From:
http://www.applet-magic.com/recurvature.htm

"The explanation for recurvature lies in the fact that cyclones (and anticyclones) possess angular momenta with respect to their spin axes. This will be referred to as their spin angular momenta. They also possess angular momenta with respect to the axis of rotation of the Earth, which will be called their terrestrial angular momenta. The turning of the spin angular momentum vector with the rotation of the Earth is a forced precession which creates a torque on the cyclone that accelerates it toward the nearest pole. As the cyclone moves toward its pole it gets closer to the axis of rotation of the Earth. The preservation of the terrestrian angular momentum then requires it to increase its velocity toward the east."

Jeff Masters
Quoting TexasHurricane:
I won't be surprised if they start decreasing our rain chances over the weekend.
Stop complaining, LOL, at least you have a chance, 95 percent of Texas wont even get a shower from the system in La.
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Quoting MississippiWx:
The shape of the coastline where 93L is likely to stall should also help it wind up more quickly. 93L could end up being more than just a rain threat for South Central Louisiana. The constant rains will make the soil very soft and large trees will be much more susceptible to being uprooted in strong tropical storm/hurricane force winds.



Just like the Bay of Campeche and Texas. I wonder...The Georgia coast is kind of curved also...Would that potentially help a system in the area??

Member Since: July 6, 2010 Posts: 113 Comments: 32033
Quoting notanothergoof:
those 3 storms just gave some of the edge to florida but not a direct hit or to close to a hit the last were jeanne francis and charley in 2004


Wilma did more damage to Doral, FL than any 2004 storm. The eye went right over my house and I was without power for almost 2 weeks. Nothing like that happened in 2004.

Some reported CAT 3 gusts but not sure if that's true.
Member Since: October 5, 2010 Posts: 0 Comments: 269
Quoting Samantha550:
I thought 93 l was supposed to loop around for several days? People are talking as if Tx won't get any rain now. What will the effect of SE Tx/ SW La be? Thanks

SE Texas should get rain from this depending on how the NW quadrant of the storm fills out if 93L stalls say south of Lake Charles or Lafayette we should see quite a bit of rain and gusty winds from the Northeast!! IMO
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Quoting TexasHurricane:
I won't be surprised if they start decreasing our rain chances over the weekend.

Sigh. I'm with you there. But as was pointed out the NAM keeps us wet for days. And then there's this, which I don't understand after having read their discussion that talked about the trough amplifying. Leaves it here thru day 6.




Member Since: August 24, 2010 Posts: 0 Comments: 151
Quoting notanothergoof:
those 3 storms just gave some of the edge to florida but not a direct hit or to close to a hit the last were jeanne francis and charley in 2004


Incorrect again..... Hurricane Wilma was a direct hit coming in from the west coast accross S.E. Florida
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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.