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 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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There is another apparent LLC forming around 29w and , around 8n. Recent satellite imagery suggests that this system is organizing rapidly. Convection is increasing and 850mb vorticity is getting stronger. Also 94L looks very intense, with the LLC quite intense, but the deep convection is sheared off to the east.
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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.



Good afternoon (or morning in Alaska)!

Talk about heartache on this blog! LOL.
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18Z

AL, 93, 2011090118, , BEST, 0, 270N, 905W, 30, 1010, DB, 0, , 0, 0, 0, 0,
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Quoting Oct8:


One would think that the NHC should get more funding to deal with these types of complexities, since the Return on Investment is great for hurricane prediction. Funny how politics play out.


Yes, as Dr Masters suggested, return on investment is massive. It costs millions to evacuate areas needlessly. The amount "saved" by cutting funding to NOAA/NWS is trivial compared to what is saved through their forecasts.
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Quoting IKE:
Makes landfall near NO,LA on day 5.

Im not tellin' Pat, you tell Pat
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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.

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487. jpsb
Quoting HurricaneHunterJoe:
thats where they found 1009.1mb,but no north or west winds to go with the lowest pressure
Speaking of 1009, I am reading 1013 here on W.Galveston bay, if that means anything. Dropped 1 millibar in the last couple of hours. Old Ships' barometer I have to whack it a couple of times but it is pretty accurate. (+-.2mb)
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Quoting tropicfreak:


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


Actually Zeta is the 6th letter of the greek alphabet.
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Quoting Oct8:


One would think that the NHC should get more funding to deal with these types of complexities, since the Return on Investment is great for hurricane prediction. Funny how politics play out.


Yea they could have used that 535 million we wasted on Solyndra.
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Quoting tropicfreak:


Actually the last name on the greek alphabet would be zeta.
I guess you were never in a frat...actually it is Omega!
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Quoting AllStar17:
Need to start seeing a wind shift soon on recon.


As soon as I say that they are now finding south winds. Needs to now shift to SW, W, etc.
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Quoting tropicfreak:


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

No: http://www.nhc.noaa.gov/aboutnames_greek.shtml
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481. IKE
Makes landfall near NO,LA on day 5.
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Quoting P451:


If the surface circulation I see were to be the dominant surface feature you would see convection build over that (when shear begins to relax) and the larger mass tend to wane some - perhaps some remaining as a "tail", some being drawn in to the surface feature, but most would dissipate over time.

One problem is there is a lot of shear out there and what could occur is the nice surface feature south of LA could continue west and dissipate while a new surface feature could form under the mid-level feature hanging further back in the convection.

It's a fairly disorganized entity right now with a number of organizational outcomes.


Thanks
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479. IKE
Day 5...120 hours....


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Need to start seeing a wind shift soon on recon.
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Quoting hurricanehanna:

now just cut that out!! ;)
hahaha..Pleeze!
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Quoting IKE:

intensifying....from day 3 to day 4.


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.
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475. IKE

Quoting ILwthrfan:


IKE is that 984mb??
Looks like 989mb's.
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Quoting IKE:

intensifying....from day 3 to day 4.

***runs from room screaming*** arrrrgghhhh!
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473. IKE

Quoting scott39:
Is he just sitting there and smiling, or is he headed on shore?
To be honest...looks to drop just slightly south from day 3 to day 4.
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Quoting IKE:
WOW!

96 hours...




IKE is that 984mb??
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471. Oct8
Quoting Neapolitan:
Only the uneducated or truly ignorant--or those who blindly hate anything having to do with the government--would find fault with the overall job the NHC does. And since those people are fools whose opinion doesn't really matter much, I doubt anyone at the NHC will lose much sleep over what they think. But, yes, I too feel sympathy, or at least empathy, for the NHC folks; when things get this crazy, they definitely get put through the wringer.


One would think that the NHC should get more funding to deal with these types of complexities, since the Return on Investment is great for hurricane prediction. Funny how politics play out.
Member Since: August 26, 2011 Posts: 0 Comments: 39
I had my first taste of what a strong storm surge would feel like yesterday when a fierce outgoing tide pulled me out thru an inlet. Fought my way back twice, but third time kayak flipped. Was in the water 25 minutes till a passing boat saw me and pulled me out. Wow, I salute anyone who survives a hurricane's fast moving waters!
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Quoting rmbjoe1954:

Well I am hoping never to see Hurricane Omega (the last)!


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

Quoting hurricanehanna:

now just cut that out!! ;)
intensifying....from day 3 to day 4.
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Quoting P451:


If the surface circulation I see were to be the dominant surface feature you would see convection build over that (when shear begins to relax) and the larger mass tend to wane some - perhaps some remaining as a "tail", some being drawn in to the surface feature, but most would dissipate over time.

One problem is there is a lot of shear out there and what could occur is the nice surface feature south of LA could continue west and dissipate while a new surface feature could form under the mid-level feature hanging further back in the convection.

It's a fairly disorganized entity right now with a number of organizational outcomes.


We don't want this to eject it's north llc and relocate further south or southeast. This would just give more time over water and be further away from dry contental air; however, I'd say 93L will kick out its northern most llc and its already evident now that its the process of doing so. The shear is just too high 30-40 knots.

I do not see a TD yet, not even close. Like you said way too many negatives going for it. I'm thinking Saturday, maybe late Friday we get our TD, but to where it forms remains the million dollar question.
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Quoting P451:
An area SSE of LA was investigated as they did a little loop.

Appears nothing of significance was found however.






thats where they found 1009.1mb,but no north or west winds to go with the lowest pressure
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Quoting cat5hurricane:
Data coming in indicates TS Lee is out there...
need west winds first to indicate a closed low unless I am missing something.
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Quoting IKE:
WOW!

96 hours...


Is he just sitting there and smiling, or is he headed on shore?
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i think it would be a good idea to upgrade to td get people ready or we are going to have another straight to storm name
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Quoting IKE:
WOW!

96 hours...




I can't open that- what did you see (may I ask)?
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Quoting IKE:
WOW!

96 hours...



now just cut that out!! ;)
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Quoting P451:


If the surface circulation I see were to be the dominant surface feature you would see convection build over that (when shear begins to relax) and the larger mass tend to wane some - perhaps some remaining as a "tail", some being drawn in to the surface feature, but most would dissipate over time.

One problem is there is a lot of shear out there and what could occur is the nice surface feature south of LA could continue west and dissipate while a new surface feature could form under the mid-level feature hanging further back in the convection.

It's a fairly disorganized entity right now with a number of organizational outcomes.
How many hours until shear is forecasted to let up?
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458. IKE
WOW!

96 hours...


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no north or west winds yet
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Quoting IKE:
Oh my....

72 hour 12Z ECMWF....


That looks like a repeat of 12 UTC NAM.
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Quoting JNCali:
Hurricane Alpha just sounds foreboding...

Well I am hoping never to see Hurricane Omega (the last)!
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Quoting P451:
Flight level 30-35kt readings so far. If they were to upgrade we'd see TD13.




To me the system seems too disorganized to consider an upgrade at this time.

I would think and have expected tomorrow to be the day for significant organization of 93.

Timing depends on when that shear lets up and I do agree with you.
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452. IKE

Quoting scott39:
Quit drawing on the map Ike, your have me concerned a little bit.
lol....
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Quoting IKE:
Oh my....

72 hour 12Z ECMWF....


Quit drawing on the map Ike, your have me concerned a little bit.
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Hurricane Alpha just sounds foreboding...
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Quoting JamesGalloway:


They will likely find a closed circulation, IMO.


I agree.
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448. IKE
Oh my....

72 hour 12Z ECMWF....


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Quoting interstatelover7165:
Do we have a closed low?

Haven't seen any W winds
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93L is going to bring major flooding to the N Gulf Coast. It reminds me of Danny back in 95/96 I think thats when it was, He sat and sat and sat! Flooding everywhere on the N Gulf Coast. We need to be thankful that the wind shear from W to E is still kicking over 93L.
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They will likely find a closed circulation, IMO.
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About JeffMasters

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