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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545. P451



They have investigated the region that you can see on RGB imagery.



posted at 1753Z
Member Since: December 16, 2007 Posts: 7 Comments: 10202
Quoting IKE:
Day 7...wth?




Ridge builds back in from the northwest, and possibly puts it back over the water.
Member Since: July 15, 2006 Posts: 17 Comments: 10284
ECMWF has Katia moving due west here and too close for comfort:

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542. IKE
Day 7...wth?


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A Gumbo Boils over..

Member Since: July 3, 2005 Posts: 427 Comments: 129411
Quoting jpsb:
Just let me know when I need to gas up the truck and get a bottle of Scotch. Oh and Dog food too.

Nice!!
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Quoting Levi32:


One giant circle lol.

In curious to know
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Quoting tropicfreak:
Alpha
Beta
Gamma
Delta
Epsilon
Zeta
Eta
Theta
Iota
Kappa
Lambda
Mu
Nu
Xi
Omicron
Pi
Rho
Sigma
Tau
Upsilon
Phi
Chi
Psi
Omega


Jesus said he is the Alpha and the Omega...not the Alpha and the Zeta. :-)

Just picking with you, tropics. Saw where you said Zeta is the last letter.
Member Since: July 15, 2006 Posts: 17 Comments: 10284
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NHC Model Runs for Investigation Area
Member Since: July 3, 2005 Posts: 427 Comments: 129411
Quoting jpsb:
Just let me know when I need to gas up the truck and get a bottle of Scotch. Oh and Dog food too.

I'd gas up now as gas prices are sure to rise, and you should always have scotch on hand
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Good Lord..Katia took a turn to the west on the Euro for FLORIDA
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533. IKE
Quoting scott39:
is that Miss/La line or Miss/Al. line?
Miss/LA.
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Well looks like ECMWF/GFS on now...throwing the towel, as we will never get rain here in Houston again...trees are dying all over, and I expect massive fires this autumn across SE TX!
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Levi, Is there still a grain of hope that 93L can go into Texas or just S of it?
Member Since: June 13, 2009 Posts: 0 Comments: 6912
Recon is finding a broad pressure minimum near where I think the center is, and winds are light.

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Quoting GTcooliebai:
Oh boy...Katia better find that trough, or it's trouble for someone.

Trough looks like it will start to catch Katia by about day seven or so this run.

link
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Member Since: July 3, 2005 Posts: 427 Comments: 129411
Quoting tropicfreak:


Oh ok.


No problem.;^)
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526. jpsb
Quoting Levi32:


One giant circle lol.
Just let me know when I need to gas up the truck and get a bottle of Scotch. Oh and Dog food too.
Member Since: June 30, 2009 Posts: 0 Comments: 1250
Alpha
Beta
Gamma
Delta
Epsilon
Zeta
Eta
Theta
Iota
Kappa
Lambda
Mu
Nu
Xi
Omicron
Pi
Rho
Sigma
Tau
Upsilon
Phi
Chi
Psi
Omega
Member Since: Posts: Comments:
Quoting P451:
An area SSE of LA was investigated as they did a little loop.

Appears nothing of significance was found however.






This is showing a lot of surface winds higher than flight level.

Consistent with the potential vorticity inversion method of cyclogenesis.

If they find a closed circulation, I'd think all of the 34 knot surface winds would be a TD.
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A great Katia photo from the ISS taken yesterday. Click for larger image:
Katia
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Quoting PrivateIdaho:


no, Omega is the last letter in the greek alphabet.


Oh ok.
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Quoting IKE:
Day 6..inland over Mississippi....




Lol...The L is directly over the top of me.
Member Since: July 15, 2006 Posts: 17 Comments: 10284
Quoting IKE:
Day 6..inland over Mississippi....


is that Miss/La line or Miss/Al. line?
Member Since: June 13, 2009 Posts: 0 Comments: 6912
Quoting Levi32:


Maybe a tiny bit. It'll take until tomorrow for conditions to really start improving significantly.

6 hours ago:



Current:



You can see the upper level ridge over the SW Gulf building northeast.
Member Since: July 15, 2006 Posts: 17 Comments: 10284
HH at 25.5n 90.0w getting near,just se of the exposed circulation ,pressures dropping again 1009.xmb
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Quoting IKE:
Day 6..inland over Mississippi....


Oh boy...Katia better find that trough, or it's trouble for someone.
Member Since: August 31, 2009 Posts: 0 Comments: 5628
Quoting scott39:
Do you think the NHC will have a very big cone when 93L developes/


One giant circle lol.
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Main are of concern continues to be a disturbance near 8n and 29w.
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Quoting scott39:
Do you think the NHC will have a very big cone when 93L developes/

They'll have to use a bowl instead of a cone
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Quoting scott39:
Is the wind shear relaxing?


Maybe a tiny bit. It'll take until tomorrow for conditions to really start improving significantly.

6 hours ago:



Current:

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"I am the Alpha and the Omega--the beginning and the end," Revelations 1:8.
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Quoting Levi32:
The 12z ECMWF actually supports my track of 93L initially moving WSW closer to Texas and then looping back around northeast towards Louisiana, with a landfall on Tuesday next week. This setup would likely have 93L as a Cat 1 hurricane, which is much more realistic than what the 0z run showed last night - a 930mb hurricane after 8 days over water.

Do you think the NHC will have a very big cone when 93L developes/
Member Since: June 13, 2009 Posts: 0 Comments: 6912
510. IKE
Day 6..inland over Mississippi....


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94L pressure down two millibars. Just waiting for full tropicality, says the NHC:

AL, 94, 2011090118, , BEST, 0, 372N, 639W, 35, 1006, LO, 34, NEQ, 60, 0, 0, 60, 1012, 120, 30, 0, 0, L, 0, , 0, 0, INVEST, S,
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Quoting Levi32:
The 12z ECMWF actually supports my track of 93L initially moving WSW closer to Texas and then looping back around northeast towards Louisiana, with a landfall on Tuesday next week. This setup would likely have 93L as a Cat 1 hurricane, which is much more realistic than what the 0z run showed last night - a 930mb hurricane after 8 days over water.


well that makes alot of sense although wouldnt Lee get stronger than a cat 1 if he was sitting in the water for 4 to 6 days? i mean low wind shear HOT water although dry air from texas could be a problem and the ridge will prevent significant outflow from the NW side. i dont particulary agree with the 0z Euro which showed a 930mb storm. more of 950mb sounds realistic to me although it could be higher due to dry air.
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Quoting nash28:


Last thing anyone needs is a 1-2 punch with Katia giving the finger to the troughs and slamming the SE CONUS while Lee drills the Gulf coast.
LMAO!!!!
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506. DFWjc
Quoting PrivateIdaho:


no, Omega is the last letter in the greek alphabet.


here

Member Since: July 19, 2011 Posts: 1 Comments: 1006
REPOST
11:00am Advisory
*Click graphics to magnify (Graphics can also be magnified more by clicking on them in the Link window)

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Quoting Levi32:


I'd put it closer to 91W IMO GR, but yeah it's in that general area and starting to look a little more like a true low pressure center.
Is the wind shear relaxing?
Member Since: June 13, 2009 Posts: 0 Comments: 6912
Quoting Levi32:


I'd put it closer to 91W, GR, but yeah it's in that general area and starting to look a little more like a true low pressure center.


Let's settle for 90.5 then.
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502. IKE

Quoting Txrainstorm:
458. IKE 6:19 PM GMT on September 01, 2011 +0

That is a scary picture..
Wind and possible flooding rains.
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nice analysis kman
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Quoting GetReal:


IMHO, I do believe that the culprit LLC has formed near 27N and 90W.

Link


I'd put it closer to 91W IMO GR, but yeah it's in that general area and starting to look a little more like a true low pressure center.
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Quoting tropicfreak:


Actually the last name on the greek alphabet would be zeta.


no, Omega is the last letter in the greek alphabet.
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458. IKE 6:19 PM GMT on September 01, 2011 +0

That is a scary picture..
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IMHO, I do believe that the culprit LLC has formed near 27N and 90W.

Link
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Quoting IKE:

To be honest...looks to drop just slightly south from day 3 to day 4.
These model runs with 93L are entertaining, but at the same time makes you go Hmmm.
Member Since: June 13, 2009 Posts: 0 Comments: 6912
Quoting IKE:
Oh my....

72 hour 12Z ECMWF....




Ike....am I seeing the reincarnation of Hurricane Ike on that map?....please say no.
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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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