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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18z HWRF doesn't seem too realistic on Katia. Notice how it turns the cyclone almost towards the NNW in a matter of 6 hours. That intensity at the end of the run is bizarre.

Member Since: Posts: Comments:
1994. breald
Quoting blsealevel:


That said 2 ft of rain through out a 5 day span
Tropical storm warnings just flashed on the TV right after kickoff "figures" :)


Wow 2ft!! I guess the Texas Governor prayed for rain for the wrong state.
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Quoting atmosweather:


Hurricane Humberto in 2008...from TD to Category 1 in 18 hours.
Thx atmo wow that was pretty fast.
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1992. doubtit
Quoting notanothergoof:
thats not funny they all say we shouldnt turn our backs on this storm and i believe them so dont make jokes this can be a very serious situation if the models are right

The only joke is you, please go back to eating crayons. You are a fool. You are not funny, you are a wedgie, a pain in the ***.
Member Since: Posts: Comments:
Quoting doorman79:


Sure that aint cypress trees or lolly leaf pines Pat? kinda blurry, I have never seen a Pine uproot. They always break about 5 foot up. Looks like a bounch of splinters!


They will uproot depending on the soil. You are correct that they tend to snap though.
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The big question is...where is Jim Cantore gonna be in all this. knew when IKE hit we were screwed because he was in Galveston!
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Quoting HurricaneNewb:
Anyone know what the fastest a storm went from TD to hurricane is in hours?


Hurricane Humberto in 2008...from TD to Category 1 in 18 hours.
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1987. aquak9
Quoting AtHomeInTX:

Lol. Aqua may need to aim a little to my north.  :)  I agree though. Still hoping for more rain not less.

I'm aiming for the goofball. Not the storm.
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Quoting doorman79:


Sure that aint cypress trees or lolly leaf pines Pat? kinda blurry, I have never seen a Pine uproot. They always break about 5 foot up. Looks like a bounch of splinters!
Yeah, ours are snap-crash.

The uprooting ones are *usually* seen leaning on a house, rather than laying completely through it.

An Irene example (and not even a very good one):


Another:


Saw a great many around here post-K where the tree trunk literally cut the house in two and the trunk was laying on the foundation.
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Quoting xtremeweathertracker:
18Z GFDL HMMMM I dunno i dont think SE Texas would get a drop of rain from this!!! Sarcasm Flag: ON

Lol. Aqua may need to aim a little to my north.  :)  I agree though. Still hoping for more rain not less.
Member Since: August 24, 2010 Posts: 0 Comments: 253
Quoting bappit:
Now you can't tell me this isn't the signature of a well developed rapidly intensifying cyclone!

Shame on the NHC for dragging this out all day. Lives could have been lost as a result!

Stay safe, NOLA, this is "THE ONE".


Is this trolling?

Sarcasm.
Member Since: Posts: Comments:
1981. bappit
Now you can't tell me this isn't the signature of a well developed rapidly intensifying cyclone!

Shame on the NHC for dragging this out all day. Lives could have been lost as a result!

Stay safe, NOLA, this is "THE ONE".


Is this trolling?
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{{{Aua}}}
Looks like we gonna get a little nasty here....
Quoting aquak9:
(grabs Jug'o'Haldol and rocket launcher)

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Quoting summerland:

That DOES say two feet of rain on NOLA in 5 days, doesn't it. Good lord.


That said 2 ft of rain through out a 5 day span
Tropical storm warnings just flashed on the TV right after kickoff "figures" :)
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1978. emcf30
Quoting Patrap:

Hey Pat, how are the river levels in your area?
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Quoting atmosweather:


Impossible to tell because all storms are unique and come with different set of circumstances in different atmospheric patterns. Those who are trying to make it seem like Katia is the second coming of Hurricane Andrew are clutching at straws. There are SOME similarities with the first 2 DAYS of the overall synoptic history...that's all. There is not, however, going to be an unusually strong and deep area of high pressure stretching from MS to the western Atlantic to steer Katia towards Florida after reaching the western Atlantic, like there was with Andrew. There was an amazing amount of large scale changes that affected Andrew that were extremely lucky for the storm and were also unusual for the time of year.


There will be, however, a high coming into the Atlantic from the midwest. That alone bears watching Katia.
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Taz, are we DOOM?
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Anyone know what the fastest a storm went from TD to hurricane is in hours?
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Quoting washingtonian115:
No offense....but T.D 13 has got to be one of the ugliest T.D's I have seen.


SHHHH, you're making it angry!
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Just got a text from State of LA - tropical storm warning in effect for upper Jefferson parish.
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Quoting KoritheMan:
Well I must say, the track from the NHC for TD13 wasn't exactly what I was expecting.


Well what did you expect?
Member Since: July 6, 2010 Posts: 113 Comments: 32711
1971. scott39
I will feel better when TD 13 moves inland as soon as possible. Yes, flooding will be the worst part of a weak lingering TC, but when you add hurricane force winds, and a higher storm surge too, then you have a much bigger problem.
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Lee will sit offshore waiting for reinforcements. But like at Gettysburg they don't come. So he will charge for higher ground. His campaign to become a hurricane is lost!
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1969. KEEPEROFTHEGATE (Mod)
Quoting aquak9:
(grabs Jug'o'Haldol and rocket launcher)


HERE LET ME HELP YOU OUT
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Quoting notanothergoof:
that right and we are getting prepared and gonna get the window boards ready and hit walmart and home depot tommorow before the panic sets in


Why wait? Just leave for Walmart now ... then stay off the computer and hide in the bathtub for the rest of the season.
Member Since: Posts: Comments:
1966. Levi32
Quoting JGreco:


What is the likelihood of the depression reforming in the area of less shear and greater convection near the Yucatan to the Southeast of the original center?


I would say no because the circulation doesn't extend down that far to the southeast, but the center could relocate a little bit within the broad circulation.

Back later. Gotta be on the BarometerBob show for a few minutes.
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1965. SLU
Pre-LEE may be no KATRINA but this system could produce a Tropical Storm Allison(2001)-like flooding disaster.

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1963. DFWjc
Quoting notanothergoof:
wheres a good place to get generator oil ? gonna try to get some tommorow


I've got some headlight fluid and elbow grease for ya...
Member Since: July 19, 2011 Posts: 1 Comments: 1006

Quoting aquak9:
(grabs Jug'o'Haldol and rocket launcher)
Ha!  Lol. I'll be good now. :D
Member Since: August 24, 2010 Posts: 0 Comments: 253
Why do we have to fear the crows? I don't get it. :|
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1959. NCSCguy
Quoting HurricaneNewb:
At some point this morning on here someone posted about some breaking news that a physic had forcasted Katia to coninue west over florida. Think i might see if i can find that story cause if that happened im sure that person might know this weeks Powerball numbers.
I seem to remember some physic twins that predicted a hurricane moving up the eastern seaboard sometime this season....
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Well I must say, the track from the NHC for TD13 wasn't exactly what I was expecting.
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18Z GFDL HMMMM I dunno i dont think SE Texas would get a drop of rain from this!!! Sarcasm Flag: ON

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1956. DFWjc
Quoting AtHomeInTX:

Is it a "Special" grenade? :)


ROTFLMFAO!!!
Member Since: July 19, 2011 Posts: 1 Comments: 1006
If 94L develops tomorrow and TD13 becomes a TS we will tie 2005 with the earliest formation of the M storm
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1954. Patrap
Quoting doorman79:


Sure that aint cypress trees or lolly leaf pines Pat? kinda blurry, I have never seen a Pine uproot. They always break about 5 foot up. Looks like a bounch of splinters!


The Levee and Lake is on the right,just outta view,thats right on the Shorthshore.


Member Since: July 3, 2005 Posts: 427 Comments: 129439
1953. DFWjc
Quoting Tazmanian:
poor TX no rain for you


AtHome would beg to differ, Taz....
Member Since: July 19, 2011 Posts: 1 Comments: 1006
Quoting JLPR2:
Katia, 13, 94L and these two...


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1951. JGreco
Quoting Levi32:


Hmm? Monday is 96 hours from now.


What is the likelihood of the depression reforming in the area of less shear and greater convection near the Yucatan to the Southeast of the original center?
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Quoting DFWjc:


I've got an unused grenade on my desk AtHome..
Is it a "Special" grenade? :)
Member Since: August 24, 2010 Posts: 0 Comments: 253
Quoting Levi32:


I did? I'm confused. I said it would be a hurricane if it was still over water Monday, but not before. It appeared that you misunderstood and thought that I thought this would pull a Humberto.
Umm, no, I just think it could.

Not analyzing what you might have said about it.
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1947. DFWjc
Quoting vince1:

Only to have it evaporate within the hour?


Nopers, we all had it going for an hour, since WE pay the water bill, the manager didn't say anything, and we can't do it until after 6pm, and we did it from 8-9pm.

We are under water restriction from 10am to 6pm here in NRH.
Member Since: July 19, 2011 Posts: 1 Comments: 1006
poor TX no rain for you
Member Since: May 21, 2006 Posts: 5091 Comments: 115437
1945. Patrap
Member Since: July 3, 2005 Posts: 427 Comments: 129439

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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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