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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I just got power on in Mass. an hour ago. I feel for those in VT. who are still struggling. Please no more storms!
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Quoting mrpuertorico:
Well i can mention a couple of aditions to that list but i am a good boy now :P
I was trying to maintain some sense of decorum.
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Quoting Drakoen:
If Recon flew out to 94L they would find a closed low level center too so should it be 14L? Earlier today 94L had plenty of organized convection, more so than 93L, and high enough winds to be classified as a tropical storm. 93L has a weak closed low with disorganized broken convection.


Drak, I live in the path of this thing. Don't make it angry. ;) ;)
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Quoting Fresca:
Fresca barbs?
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guys whats done has been done now whats move on
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Shear is certainly loosening its grip:

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All we need here in Northern NJ to finish us off for good.....would be Katia. Landfall in Wilmington as a very weak Cat 3, 11.5 more inches of rain here in Wayne. Can't wait!!
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Quoting muddertracker:

What mixes with Fresca?


Gin is really good with Fresca!
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Quoting aislinnpaps:
Mike Seidel on his way to New Orleans. At least you didn't get Cantore. The mayor of NO just made some declaration, but I didn't get to hear what it was.


Weather Channel guys headed to NOLA?? Ok Texas, look out, here comes your storm!
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I fearlessly predict that there will not be twenty inches of rain in Louisiana from this storm.
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Quoting Drakoen:
If Recon flew out to 94L they would find a closed low level center too so should it be 14L? Earlier today 94L had plenty of organized convection, more so than 93L, and high enough winds to be classified as a tropical storm. 93L has a weak closed low with disorganized broken convection.


Yes, 94L should have been classified too, and it still has a chance.
Member Since: July 6, 2010 Posts: 113 Comments: 32505
Quoting Delsol:


Pretty similar no?


Too similar, I'm not getting too extremely concerned yet but I am not saying I'm safe at all.
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Quoting Tazmanian:
guys it is what it is and you cant do any thing about it


Try telling that to my grandmother, who is practically glued to TWC. ;)
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Quoting Delsol:


Pretty similar no?
similar to what, a five day track ?? Otherwise, there is nothing similar...
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WOW!!! Did anyone check out Cantore's tie tonight? Talk about LOUD! He must have dressed in the dark.....
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Quoting mrpuertorico:
There will be several vorticies spinning around that mess i can asure you


as long as there are competing vorticies it may make things tough to get going... remember all the trouble Emily had once she cleared Hispaniola getting reorganized.

Messed her up by about a day.
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2329. BDAwx
Quoting MississippiWx:
This part of the NHC discussion is good enough for me:

SATELLITE...SURFACE...AND NOAA RECONNAISSANCE AIRCRAFT DATA INDICATE
THAT THE LOW PRESSURE AREA OVER THE CENTRAL GULF OF MEXICO HAS
ACQUIRED A CLOSED CIRCULATION THAT IS DEFINED ENOUGH TO BE
CONSIDERED A TROPICAL DEPRESSION.


Note that they said "defined enough to be considered a tropical depression" rather than, "well defined". I can agree with that. Maybe.
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2328. Drakoen
If Recon flew out to 94L they would find a closed low level center too so should it be 14L? Earlier today 94L had plenty of organized convection, more so than 93L, and high enough winds to be classified as a tropical storm. 93L has a weak closed low with disorganized broken convection.
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guys it is what it is and you cant do any thing about it
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Quoting P451:


Yep, and the rest of my post is not aimed at you, just chose to put out the POV in the space below LOL

+++++++++++++++++++++++++++++++

Hey, Two Feet of rain is a very serious situation. No doubt about it. This storm can turn out to be catastrophic for many individuals.

That said...

I don't see the reason to upgrade a mess into a tropical cyclone to get the point across though.

Put out a flood warning.

When the system actually organizes into a tropical cyclone then upgrade it and issue additional warnings.



Recon data supports a tropical depression, you cannot deny that.
Member Since: July 6, 2010 Posts: 113 Comments: 32505
Quoting Patrap:


Southern Comfort, ice..
I like Fresca but that sounds downright nasty.
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Quoting whepton3:
Guys...

It looks like it's spinning at the weirdest place..

Take a look at 29.5N 92.5W

Half way across the LA coastline... watch the spin.. very strange.

Rainbow loop:

Link
There will be several vorticies spinning around that mess i can asure you
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Quoting Thrawst:


Correct me if i'm wrong anybody with a more knowledgeable answer, but I think that's an upper level low, not TD-13 itself. :P


You are correct.

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Quoting Patrap:


Southern Comfort, ice..
Whiskey, ice... Bourbon, ice... Gin, ice... Vodka, ice... in a pinch, Tequila, ice...
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2321. P451
Quoting TropicalAnalystwx13:
For those who don't know, even though it is relatively old news...

* Louisiana has declared a state of emergency.


Yep, and the rest of my post is not aimed at you, just chose to put out the POV in the space below LOL

+++++++++++++++++++++++++++++++

Hey, Two Feet of rain is a very serious situation. No doubt about it. This storm can turn out to be catastrophic for many individuals.

That said...

I don't see the reason to upgrade a mess into a tropical cyclone to get the point across though.

Put out a flood warning.

When the system actually organizes into a tropical cyclone then upgrade it and issue additional warnings.

Member Since: December 16, 2007 Posts: 7 Comments: 10202
Quoting Skyepony:
It was obviously a TD from recon data. We knew it by the data & it was called moments later.
That's my viewpoint.
Member Since: August 16, 2007 Posts: 6 Comments: 12463
2319. Delsol


Pretty similar no?
Member Since: August 25, 2006 Posts: 0 Comments: 65
Quoting Patrap:


Southern Comfort, ice..

Grand marnier. I made shrimp creole tonight it was yummy.
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Every storm 80% of the people on this blog disagree with the NHC, the EXPERTS. Then we find out the EXPERTS are correct and so the excuses start.

Then theres the wishcasters, or as I refer to them idiots. There is nothing fun about flooding, destroyed homes and lives, or living without power for weeks. REALLY????

If your going to post that you think the storm is going this way or that and that it will be a CAT 10, try to give a reason other than i just have a bad feeling.

Finally, why do people have to post the same images and discussions 50 times from the NHC, do you not think that the people on this blog go to the NHC site?

You can call me a troll, but I'm not. I love to learn from the folks like LEVI32 or see the images and charts that are not as easy to find as the NHC postings.

I mean is it really worth getting so upset when someone says fish storm. Let's put this site into the reality of what it is.
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2316. Fresca
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Quoting TropicalAnalystwx13:


Flooding from TD #13.

Is it supposed to stall? Just checked the map...scary.
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2314. Thrawst
Quoting whepton3:
Guys...

It looks like it's spinning at the weirdest place..

Take a look at 29.5N 92.5W

Half way across the LA coastline... watch the spin.. very strange.

Rainbow loop:

Link


Correct me if i'm wrong anybody with a more knowledgeable answer, but I think that's an upper level low, not TD-13 itself. :P
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2313. Skyepony (Mod)
It was obviously a TD from recon data. We knew it by the data & it was called moments later.
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Quoting dsenecal2009:


Thanks to you both. There will most certainly be at least minor flooding here, and I think my little cottage might take some water. Live about 75' off of Gause Blvd. We had a couple inches of sporadic downpours and drizzle today up to Pearl River, and the streets were hazardous even then. Cannot imagine what peak 3-5 inches an hour will do on top of a weekend-long storm.


Your welcome..wasn't implying per hour, just total rain for one day...be safe my friend.

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Quoting dsenecal2009:


Thanks to you both. There will most certainly be at least minor flooding here, and I think my little cottage might take some water. Live about 75' off of Gause Blvd. We had a couple inches of sporadic downpours and drizzle today up to Pearl River, and the streets were hazardous even then. Cannot imagine what peak 3-5 inches an hour will do on top of a weekend-long storm.
Well, don't base your decision on whether or not Gause has standing water on it. That happens ~20 times a year...

I can tell you that Katrina's ~12 inches of rain in Slidell didn't flood any houses that I know of along Gause. (Nor did the storm surge.)
Member Since: August 16, 2007 Posts: 6 Comments: 12463
2310. Fresca
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Quoting muddertracker:


Huh? The fires? Leaking BP oil rig? The large cluster of thunderstorms in the gulf? Nagin's back?



Flooding from TD #13.
Member Since: July 6, 2010 Posts: 113 Comments: 32505
Quoting outlookchkr:
What could be better?
Well i can mention a couple of aditions to that list but i am a good boy now :P
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Guys...

It looks like it's spinning at the weirdest place..

Take a look at 29.5N 92.5W

Half way across the LA coastline... watch the spin.. very strange.

Rainbow loop:

Link
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2306. Patrap
Well the squirrels are out nut hunting I see.

Superdome Beer is up to 40F now.

Enjoy yer phun and pun.
Member Since: July 3, 2005 Posts: 426 Comments: 129089
This part of the NHC discussion is good enough for me:

SATELLITE...SURFACE...AND NOAA RECONNAISSANCE AIRCRAFT DATA INDICATE
THAT THE LOW PRESSURE AREA OVER THE CENTRAL GULF OF MEXICO HAS
ACQUIRED A CLOSED CIRCULATION THAT IS DEFINED ENOUGH TO BE
CONSIDERED A TROPICAL DEPRESSION.
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Quoting Fresca:
.


Ok, Fresca's here. Now it's a party.
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Quoting Jamiekins:
had to share this from Facebook


lmao XD
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I think the early call on TD13 has a lot to do with the rigs. I know a lot of you think that they should stick to their own rules no matter what, but let's face it, lives are at stake. Thousands of men and women work on oil rigs. Most of those rigs won't pull people off until they know for sure something is coming.
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2301. Fresca
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2300. Fresca
.
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Quoting MiamiHurricanes09:
Probably gonna see more than that in October...especially since this has been a home brew year. Who knows though, like you said, this type of forecasting is nearly pointless lol.
What's creepy that this is the same naming list as the good old 2005 season.
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Quoting Patrap:
Me tinks some Fla and Tex folks are a tad tropically depressed.



Try a cold Fresca.


... That's a really terrible pun ...

I haven't tried Fresca before, I might give it a shot sometime.
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Quoting Drakoen:


Sorry but this cloud signature at the lower levels and convective presentation is not unique. I have seen this for storms in the beginning stages when they want to form a well defined circulation. Dvorak T numbers clearly reflect the lack of organization. I think they could have waited till tomorrow. The only reason this is a depression is because it is in the GOM near land.


I think the NHC would rather "have told them so" and it didn't happen tban "wish they had said something" and it did happen. They don't put out advisories for invests so this was probably the best way to get the word out to the public about a potentially damaging rain event starting very soon in a vulnerable area.
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Just checking in. I see we are in the cone. Not sure for how long though. Any new model runs?
Member Since: July 2, 2009 Posts: 0 Comments: 2811
Quoting TropicalAnalystwx13:
For those who don't know, even though it is relatively old news...

* Louisiana has declared a state of emergency.


Huh? The fires? Leaking BP oil rig? The large cluster of thunderstorms in the gulf? Nagin's back?

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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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