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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2995. jpsb
Quoting GetReal:
Is that an ULL spining on the Tx/La border?
Member Since: June 30, 2009 Posts: 0 Comments: 1190
Quoting NCHurricane2009:


That indeed would be a large leap...it is very likely though at least the center (and a very BROAD one at that) would consolidate toward a convective burst like that...maybe 10-20 miles to the southeast? Really hard to tell without visible sat. pictures...infrared useless tonight with TD 13 in determining center. We can also rely on surface obs in the Gulf of Mexico buoys to see what the center is up to....

That convective burst has all the upper-level support with this system right now...upper anticyclone (outflow) dead nuts over the center of the burst (click HDW-H with this animation)....


The official low-level center is indeed very broad. Low cloud motions prior to sunset confirmed that, as do buoy observations.

Do not forget that there are indications that the upper flow is slowly relaxing over the system, though. That might disallow for a center reformation at 25N 87W. I can see it forming about 10-50 miles to the southeast, but not as far east as 87W.
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Member Since: June 29, 2009 Posts: 13 Comments: 5301
2992. JGreco
Quoting NCHurricane2009:


That indeed would be a large leap...it is very likely though at least the center (and a very BROAD one at that) would consolidate toward a convective burst like that...maybe 10-20 miles to the southeast? Really hard to tell without visible sat. pictures...infrared useless tonight with TD 13 in determining center. We can also rely on surface obs in the Gulf of Mexico buoys to see what the center is up to....

That convective burst has all the upper-level support with this system right now...upper anticyclone (outflow) dead nuts over the center of the burst (click HDW-H with this animation)....


But didn't Irene re-develop its center pretty far North also under her convected burst?
Member Since: September 22, 2005 Posts: 0 Comments: 322
Quoting jpsb:
I am rooting for NOGAPS, come NOGAPS, bring that baby to Texas.


The ensembles are calling for a tourcane or prairiecane, like Erin, if you remember:



Except 13 goes ashore in LA. Erin went all the way across the USA as a remnant, causing extreme flooding.
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Quoting atmoaggie:
Umm, yeah?
(Really?)

I usually don't throw it around in the blogs, so I can see how some may not be aware.

Yeah..really.

I didn't know you were a met until today when you sorta threw it into my face when we were discussing recon's findings.


Quoting atmoaggie:
? 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...



When it comes to that sort of thing, I respect that you're a met and have put in the time, but please don't try and use your schooling as a reason for why you're right, or why I shouldn't question your reasoning. I'm sure your classes have given you a much better understanding behind everything weather related, but it doesn't mean casual enthusiasts can't also know what they're talking about, and it certainly doesn't mean you are always right.

Maybe you didn't intend your wording to come off that way, but thats how I interpreted it when I read your post: "I'm a met, don't question me".
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Quoting TampaSpin:


This would be wild to see 2 storms colliding near North Carolina........thata be really bad, but this model is sure looking like it......HOPE NOT
I guess is it safe to say Fujiwhara flag {on}
Member Since: August 31, 2009 Posts: 0 Comments: 5628
Quoting atmosweather:


It's the best non-alcoholic beverage you can find other than this.
LOL, I'm gonna PM you the best one...hold on.
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Quoting want2lrn:


Since i really only read (lurk) as it is called. I had you pegged by what i perceived as a lot of knowledge. If i may a stab at your screen name. atmo=atmosphere=met, aggie=gig'em? aka HOWDY! Just my 2 cents.
Howdy, backatcha.

G'Nite, all.
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Quoting atmosweather:


It's the best non-alcoholic beverage you can find other than this.


Gross...
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2985. vince1
Quoting DFWjc:


No, I just tired of the f'n division or distractions from what needs to be solve on this planet. If we can't see past color, creed, or any other human trait, then we will never solve the NECESSARY problems of the planet we live on...

I'm not promoting racism, but if we fail to note our differences (and ask why they exist such that they are), then we are making just as grave of a mistake. Same goes for aberrant behavior, and I don't care if this makes me politically incorrect. We are up to our ears in political correctness in this country.
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2984. KEEPEROFTHEGATE (Mod)


we may have something bigger than bargain for
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Quoting Huracaneer:

Koritheman said that it's unlikely the center will relocate so far. I think he is right, but if you seriously think the center could relocated to the center of the convection, then I would start to worry (for the West Coast of FL that is).


Even if that were to happen, the steering pattern still favors the LA/MS area, not Florida, primarily because the first trough is forecast to bypass TD13, which should allow it to keep moving northwest until the second trough picks it up.
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Quoting GTcooliebai:
I've seen Patrap mention that, I'll have to buy a case of that sometime.


It's the best non-alcoholic beverage you can find other than this.
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Landfall over western Louisiana in about 60 hours.

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Quoting KoritheMan:


There is no vorticity there according to surface observations. With all due respect, I do not think the center will reform there. Not to mention, that would be a very sizable jump -- over 200 miles. I've never seen such a drastic center reformation.


That indeed would be a large leap...it is very likely though at least the center (and a very BROAD one at that) would consolidate toward a convective burst like that...maybe 10-20 miles to the southeast? Really hard to tell without visible sat. pictures...infrared useless tonight with TD 13 in determining center. We can also rely on surface obs in the Gulf of Mexico buoys to see what the center is up to....

That convective burst has all the upper-level support with this system right now...upper anticyclone (outflow) dead nuts over the center of the burst (click HDW-H with this animation)....
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Quoting tropicfreak:




Korthe Jim Cantore even pointed out that a new llc may be reforming there.


25N 87W? That would be pretty far south. Not sure about that, but I guess we will see.
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Quoting hahaguy:
I don't always drink soda but when I do I prefer fresca.


He is the most interesting man in America.
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2977. JLPR2
One really odd looking system in the WPac.

Neat to see those swirls spinning around in the center.
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Quoting atmoaggie:
Well, we do some contract work for NOAA, NASA, Navy, and, sometimes, NWS NOLA (actually in Slidell, 2 miles from the office), outside of private, commercial clients.

I could get a job at NWS, but have no real desire to. What I do is more diverse than daily forecasting, which I enjoy.


Since i really only read (lurk) as it is called. I had you pegged by what i perceived as a lot of knowledge. If i may a stab at your screen name. atmo=atmosphere=met, aggie=gig'em? aka HOWDY! Just my 2 cents.
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This would be wild to see 2 storms colliding near North Carolina........thata be really bad, but this model is sure looking like it......HOPE NOT
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Quoting TampaSpin:


Yep that is what i am seeing......that far South could really be a problem coming i hate to say!

Koritheman said that it's unlikely the center will relocate so far. I think he is right, but if you seriously think the center could relocated to the center of the convection, then I would start to worry (for the West Coast of FL that is).
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Quoting Drakoen:
lol some of you guys need to step away from the blog. Wash down a prozac or valium with some Fresca.


Exactly lol.
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2972. KEEPEROFTHEGATE (Mod)
well 89 days remain
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Quoting hahaguy:
I don't always drink soda but when I do I prefer fresca.
I've seen Patrap mention that, I'll have to buy a case of that sometime.
Member Since: August 31, 2009 Posts: 0 Comments: 5628
Quoting Drakoen:


Already there working on some ODE's.


Unfortunately, I'll be having plenty of time away from the blog this weekend into early next week. I'll be studying/reading my life away.
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Quoting KoritheMan:


There is no vorticity there according to surface observations. With all due respect, I do not think the center will reform there. Not to mention, that would be a very sizable jump -- over 200 miles. I've never seen such a drastic center reformation.


Quoting TampaSpin:
LOOKS like 25N 89W is the new LLC


Korthe Jim Cantore even pointed out that a new llc may be reforming there.
Member Since: September 2, 2006 Posts: 110 Comments: 6874


Interesting..
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Quoting jpsb:
I am rooting for NOGAPS, come NOGAPS, bring that baby to Texas.


Horrid model. Way of with katia.
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Quoting TomTaylor:
wait are you having a met party?
Not sure what one would do at a met party...have a forecasting contest?

It is (was?) a birthday party (well, 6 of them in one) and family get together.

Within 3 days, my 2 kids, grandma, uncle, pa pa, and brother all have a b-day. So we naturally have one rather large party. And everyone comes, from as far away as JAX, Nashville, Memphis, Tulsa, Houston. Quite a yearly mess, I have, but worth it.
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Got that nice convective burst over 94L's circulation occurring right now. Let's see if it can persist.

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2963. Zeec94
Quoting hahaguy:
I don't always drink soda but when I do I prefer fresca.


Fresca, the drink 9 out of 10 meteorologists prefer.
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Quoting KEEPEROFTHEGATE:
Nice view, that feature north of the Africa wave, looks like an human eye.
Member Since: August 31, 2009 Posts: 0 Comments: 5628
2961. hahaguy
I don't always drink soda but when I do I prefer fresca.
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how do you add hurricaine hunter to google earth
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2959. jpsb
Quoting Skyepony:
Model preformance..Over all GFDL is pulling away from the rest on TD13. 26nm error today, HWRF hasn't given up with 36, CMC 42 the rest follow, Nogaps still trails..
I am rooting for NOGAPS, come NOGAPS, bring that baby to Texas.
Member Since: June 30, 2009 Posts: 0 Comments: 1190
Quoting atmoaggie:
Well, we do some contract work for NOAA, NASA, Navy, and, sometimes, NWS NOLA (actually in Slidell, 2 miles from the office), outside of private, commercial clients.

I could get a job at NWS, but have no real desire to. What I do is more diverse than daily forecasting, which I enjoy.


That's great, man. I wish you the best in your career.
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Quoting GetReal:


Would that be near 25N and 90W???


Yep that is what i am seeing......that far South could really be a problem coming i hate to say!
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Quoting JNCali:

Just want to make sure.. you guys have all washed your cars and started painting your houses right?? That almost always brings the moisture


I think many of us have done that quite a few times. I cannot help but to notice how almost every care I see is cleaner than mine and I have only gone 2 weeks since last washing mine
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Quoting GTcooliebai:
I'm thinking somewhere in that convective mess around 25 N 87W.

Ok, that's freaky, see my post 2927, just said that if the center were located about there it could be trouble for the West Coast of Fl. So you also think it may be in that heavy convection. That would be bad because it would allow quick and unexpected intensification, so I hope we are both wrong.
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Quoting Klolly23:


U need to make a rain turtle in the sand/dirt...aka your lawn(unfortunately). Trust the rain turtle. Joking aside you all need rain bad. Hope it's not much longer.


Thanks. I just might do that. We're getting desperate.
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2953. Zeec94
Quoting Drakoen:
lol some of you guys need to step away from the blog. Wash down a prozac or valium with some Fresca.


Here we go with the Fresca again. LOL
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Please Prepare, people in Louisiana... FEMA is running out of money! You know what is coming, take necessary pro active measures!
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2951. Drakoen
Quoting MississippiWx:


You can join us, Drak.


Already there working on some ODE's.
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2950. twooks

Quoting AllyBama:
well, if TD13 develops further south, then that gives is more space to grow and more time over water to strengthen..lovely..



Would the track be about the same if it did redevelop south?
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Quoting MiamiHurricanes09:
I definitely see what you're alluding too, and it matches rather closely to where the circulation appears to be on shortwave. Gonna keep watching for persistence though.



Damn, I should probably be sleeping by now, but the tropics are better than sleep...anything is better than sleep haha.
Judging by satilite it looks more exratropical/Subtropical Vs. prue tropical.
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Nobody's posting 00Z GFS runs? I would have thought at least one person would be abusing their F5 button right now...
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Quoting cyberian:
Today was our 5th day without power from Irene, it finally came back on at 6:00pm although now my well pump is not working. Here nor there, I came home this evening to find that the Red Cross had been here. Sitting on one of the coolers were 4 stuffed Mickey Mouse dolls for each of my children, a case of water and a some self-heating MRE's.

I don't know how they knew that there are 4 kids living here, but, to all of you on this blog that are members of the Red Cross, Emergency Response Teams, and other humanitarian groups I want to thank you all. Those Mickey Mouse dolls brought the first smile to my 2 year old twin girls faces that I have seen in nearly a week, that was priceless.



Wow. Best wishes to you and your family from Galveston Bay.
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Quoting Drakoen:
lol some of you guys need to step away from the blog. Wash down a prozac or valium with some Fresca.


You can join us, Drak.
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LOOKS like 25N 89W is the new LLC
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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.