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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2895. KEEPEROFTHEGATE (Mod)
Tropical.Cyclone.Formation.WARNING
013/TD/L/CX
MARK
25.95N/89.91W


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Quoting Methurricanes:
im sorry, I guess having a life and not staring at a satilite all day is frowned upon on this Blog


I beg your pardon. I haven't been staring at a satellite all day either. I have work/school as a college student. I didn't say anything snooty to you, so why the smarta## remark?
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Quoting LillyMyrrh:


You're welcome to join me in the rain dance. The more the merrier. We've tried almost everything else, may as well try this.


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.
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2892. KEEPEROFTHEGATE (Mod)
T.C.F.W.
012/H/K/C1
MARK
17.65N/51.05W


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Quoting SLU:


That looks like a hurricane to me.
Member Since: September 2, 2006 Posts: 110 Comments: 6878
Quoting tropicfreak:
extreme236 just like Franklin.


Pretty much. I'd say Franklin was a little more organized but yeah.
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2889. JLPR2


Africa keeps producing.
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Quoting atmoaggie:
It doesn't really, not sure why I put that there. (But I've been on the phone for the last 12 hours).

My comment should have been about the potential vorticity inversion my friend keeps talking about. (He's a phunny guy, but a former PhD student of Bill Gray's)

Still haven't fully grasped all that he was talking about. I'm looking for papers on it, but the notion seems to be an obscure one...

Here is a small one: http://ams.confex.com/ams/pdfpapers/21588.pdf
yea, I wasn't sure what you meant by that. Thanks for clearing that up.

And wow that's a long time to be on the phone
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Quoting KoritheMan:


Yeah, I would keep your guard up for sure. I would imagine at the very least, tropical storm force winds will impact most of that parish before the center moves inland.


If it slides any further east maybe not if it slides further west then maybe more so...kinda in the middle right now...its interesting that the storm just sits right on the coast just south of me for almost a day though...that would keep us with almost 24 hour nasty weather
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2885. JGreco
Blog unusually slow tonight...
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2884. jpsb
Quoting LillyMyrrh:


But seriously, I'll be so glad when the "Texas Rain Shield" finally goes away.
The Texas Rain Shield is forecast to be with us thru next summer. With luck we might get some rain this winter with northers, maybe.
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Quoting MississippiWx:


Might want to check the NHC site. :-)
im sorry, I guess having a life and not staring at a satilite all day is frowned upon on this Blog
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extreme236 just like Franklin.
Member Since: September 2, 2006 Posts: 110 Comments: 6878
Quoting WaterWitch11:


grand marnier in shot form


More like a sazerac- double the absinthe.
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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..
How about with Katia?
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Member Since: September 16, 2010 Posts: 0 Comments: 1496
Quoting GTcooliebai:
I'm thinking that also.

Can't make heads or tails of the mess in the Gulf, some folks here are pretty good at finding centers in developing systems. Where do you think the center is located?
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Quoting yoboi:
I think Patrap skipped the fresca went straight to the southern comfort he is silent


grand marnier in shot form
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Quoting txag91met:


I did this in college at A&M...fun stuff.
You finished a Masters, right? Or am I confusing you with someone else?

Also, was Steve Lyons still a prof when you went to A&M?
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2875. SLU
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2874. JGreco
Quoting GTcooliebai:
I'm thinking that also.

I also think the center will probably be located further South. Though I wonder what that will do with track and intensity?
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2873. Skyepony (Mod)
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..
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2872. SLU
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Quoting ConnecticutWXGuy:
I think people will find that many forecasts of tropical cyclones in the same area as Katia is were similar to that of Andrews. The similarities in that aspect are nearly irrelevant. If Katia becomes another Andrew it will be pure luck... not something that you can accurately forecast basing it on similarities between Andrew's origins and Katia's origins.


But but but... it's so fun to speculate!
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beell, where is your dmin/dmax chart?

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850mb vorticity didn't change much with TD13 in the last 3 hours. It got a bit stronger, but stayed basically in the same location. Satellite loops don't suggest a center reformation is occurring yet either.

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Quoting gbreezegirl:
I feel your pain! Been there done that. Thank goodness I am off the weekend and Monday but where I work at they may evacuate the patients to P'cola if we are under any warnings. UGH!


Best of luck if you do. At least I won't have to evac any body - just shoo the cars out of the drive-up when it's time to close - lol
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On the other hand, 94L's is firing some little updrafts on the northern side of its circulation. This popcorn convection as we head into the diurnal maximum is usually indicative of a system that's ready to organize. We'll see what happens. Personally I believe 94L has been a cyclone since this morning, but hell, what do I know?

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Quoting atmoaggie:
It doesn't really, not sure why I put that there. (But I've been on the phone for the last 12 hours).

My comment should have been about the potential vorticity inversion my friend keeps talking about. (He's a phunny guy, but a former PhD student of Bill Gray's)

Still haven't fully grasped all that he was talking about. I'm looking for papers on it, but the notion seems to be an obscure one...

Here is a small one: http://ams.confex.com/ams/pdfpapers/21588.pdf


I did this in college at A&M...fun stuff.
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Quoting louisianaboy444:


Either way in Central to Eastern Acadia Parish I look to be in the cross-hairs with this one...but if i get the wind threat from the Center you will receive more of the heavy rain threat further SE


Yeah, I would keep your guard up for sure. I would imagine at the very least, tropical storm force winds will impact most of that parish before the center moves inland.
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Quoting Tazmanian:
i think the recon will find a new center
I'm thinking that also.
Member Since: August 31, 2009 Posts: 0 Comments: 5628
I think people will find that many forecasts of tropical cyclones in the same area as Katia is were similar to that of Andrews. The similarities in that aspect are nearly irrelevant. If Katia becomes another Andrew it will be pure luck... not something that you can accurately forecast basing it on similarities between Andrew's origins and forecast track and Katia's origins and forecast track. There have been dozens of potential Andrews since 1992.
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If 94L can generate even just a small increase in convection near the center it should be classified Maria.
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Quoting AllyBama:
Isn't this just ducky! Of all weekendsthat I got to open the dang bank on Saturday - not only is it labor day weekend but it will be pouring..everybody will be in a panic to get to the bank to draw out money..I'm gonna cry...lol
I feel your pain! Been there done that. Thank goodness I am off the weekend and Monday but where I work at they may evacuate the patients to P'cola if we are under any warnings. UGH!
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Quoting MississippiWx:


Might want to check the NHC site. :-)



NHC downgraded Katia to a Tropical Storm.......that is UNREAL looking at Satellite.......HUM
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Quoting KoritheMan:


Well in my experience, ridging for September storms is usually overdone. Gustav and Ike are perfect examples.

I think the hurricane center's track is a good one for now. We will know more over the coming days.


Either way in Central to Eastern Acadia Parish I look to be in the cross-hairs with this one...but if i get the wind threat from the Center you will receive more of the heavy rain threat further SE
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View from a different perspective:

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I noticed on the past several GFS runs it has dropped any TC activity behind Katia for the most part in the next several days, but I've noticed it tends to pick things back up once they start to show some signs of development.
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i think the recon will find a new center
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Katia redeveloping an eyewall, intensification to resume soon, Hurricane at the 5 AM, and should see a category 2 tomorrow night.

TD13 will slowly get it's act together, and become a TS midday tomorrow, and should intensify gradually, as it crawls to the WNW/NW.

94L, Well, Maria possible if it can take advantage of DMAX it will have a brief chance, but has to blow up warm core convection on it Maria will form... just another brief system to add though so don't count on the NHC jumping to Name it, and bend backwards trying to motivate it to form either so... with that good night everyone
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Quoting hahaguy:
The main question for Katia should be how far north will she make it before the ridge builds in.



This is reminding me much of that storm that starts with the letter "A"......just don't like the High Pressure that has the possiblity of building overhead. Those ULL need to keep tugging hard!
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Quoting louisianaboy444:


Yeah me2 I'm thinking more from Jeff Davis Parish to Lafayette parish i agree it will turn North or maybe North North East but i dont think that trough will be that strong to pull it NE that sharply IMO


Well in my experience, ridging for September storms is usually overdone. Gustav and Ike are perfect examples.

I think the hurricane center's track is a good one for now. We will know more over the coming days.
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Quoting MississippiWx:
Updated shear tendency...Shear continues to fall over TD13:




thats not good for both of are storm
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Quoting Methurricanes:
Katia is Already a Hurricane though.


Might want to check the NHC site. :-)
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Quoting TomTaylor:
Repost for atmoaggie

It doesn't really, not sure why I put that there. (But I've been on the phone for the last 12 hours).

My comment should have been about the potential vorticity inversion my friend keeps talking about. (He's a phunny guy, but a former PhD student of Bill Gray's)

Still haven't fully grasped all that he was talking about. I'm looking for papers on it, but the notion seems to be an obscure one...

Here is a small one: http://ams.confex.com/ams/pdfpapers/21588.pdf
Member Since: Posts: Comments:
2849. KEEPEROFTHEGATE (Mod)


map is filling up

got less than 90 days left now of the 2011 atlantic hurricane season

we could still see another eight to ten storms
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Updated shear tendency...Shear continues to fall over TD13:

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Isn't this just ducky! Of all weekendsthat I got to open the dang bank on Saturday - not only is it labor day weekend but it will be pouring..everybody will be in a panic to get to the bank to draw out money..I'm gonna cry...lol
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2846. MZT
Yeah, weird scenario building up... It's good for Lee to strengthen and his outflow help to separate the storms. But not strengthen so much as to become a menace. And nobody seems to have a good idea how long he'll dawdle in the Gulf.
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Quoting weatherganny:



I know sorry Taz...I couldn't get it to load.



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

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