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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2395. jpsb
Quoting Skyepony:
By Dvorak #s 13L has weakened some since declared. Was called before suffering the heat of the day. As soon as the ACTF was issued NOAA jumped in too (it was their plane & not AF in there). The persistence rule wasn't applied like the other night when Stewert said a single Thunderstorm doesn't make a Tropical Storm. Being in the middle of the gulf & full of rain like it is..been on the wet side in FL, seen the TRRM passes & it's big like a Faye...no need to wait, it will look well enough in the morning.
Galveston Bay here, barometer down to 1012 wind picking up out of the N.E. and I predicted 93L would be declared a TD today, now please future Lee bring me some RAIN!
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Quoting hunkerdown:
from this run, other than the UK, it seems all others have given up the ghost on the bend back to the west...



umm... GFDL?
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Quoting MississippiWx:
Some of you guys are getting too caught up in the technicalities. I've already said that I don't believe it's quite a TD yet. However, I think we can all agree that it's going to become a TD and very likely even a tropical storm late tomorrow. Then we must think of why we actually have the NHC. Isn't their job to classify things such as this to get the word out to the public? If this system were making landfall today, they wouldn't have classified it because it would be nothing more than a rain-maker. However, they realize that it could possibly have several more days over water. Why not give the public one half day more of extra notice when this thing could be very damaging in some form or fashion. It had a closed low, and there was no doubt about it. It had a lot of convection and the convection is persisting. The winds were high enough. It's close enough to their definition of a tropical depression, so yeah, classify it now. It's a good move on the part of the NHC, regardless of our small technicalities.


A tropical depression by tomorrow? We have one now ;)
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2392. Skyepony (Mod)
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.


94L never got unattached from that front.


Hope we get a good sat pass of 13L tonight.
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Quoting RukusBoondocks:
if the center of 13 forms under the deeper storms would FL be at more risk?


No.
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Quoting palmpt:


Bastardi just said Gulf Coast will be more in play...


well, if that is the case maybe TX will get better rain luck next time.
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Some of you guys are getting too caught up in the technicalities. I've already said that I don't believe it's quite a TD yet. However, I think we can all agree that it's going to become a TD and very likely even a tropical storm late tomorrow. Then we must think of why we actually have the NHC. Isn't their job to classify things such as this to get the word out to the public? If this system were making landfall today, they wouldn't have classified it because it would be nothing more than a rain-maker. However, they realize that it could possibly have several more days over water. Why not give the public one half day more of extra notice when this thing could be very damaging in some form or fashion. It had a closed low, and there was no doubt about it. It had a lot of convection and the convection is persisting. The winds were high enough. It's close enough to their definition of a tropical depression, so yeah, classify it now. It's a good move on the part of the NHC, regardless of our small technicalities.
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Could the nhc put up tropical storm warnings, while 93l was still a wave or do they have state it is a depression before these types of watches and warnings go up. Trying to understand rationale since many in the blog are on either side of the fence debating if this is a true depression
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Quoting TexasHurricane:


huh? It is a LA storm.


beat me to it
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Quoting twincomanche:
I think anyone with that name probably needs a ignore,



AMEN!





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Quoting mcluvincane:



Anyone want to guess where she might go? I thought yesterday and part of the day today that Katia's out to sea path was written in stone, but it seems that may not be the case
from this run, other than the UK, it seems all others have given up the ghost on the bend back to the west...
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2383. Remek
Quoting HurricaneDean07:
Sorry, but that is completely the opposite of what we need.
Any kind of rain, we dont CARE, AT ALL. let it be an allison, let it flood, we need 18 inches of rain out of the 20 anyway. Dont be calling out to TX and telling us what we dont and should need, RAIN is RAIN, and we need ALOT OF IT NOW.
Don't Mess With Texas, boy...


Very much agree!

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I just got back from Dauphin Island Alabama and the wind is steady at 20MPH with gust to 26mph.... Waves are at 5 to 7 feet.... No rain as of yet but I think we will get about 15 to 18 inches..... All I can say is I might need a bigger Boat :o)

Taco :o)
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I posted this earlier from SJU NWS read the full report on my blog

AFTER KATIA CLEARS THE AREA EARLY NEXT WEEK...MODELS SHOW A
SIGNIFICANT CHANGE TO THE UPPER LEVEL PATTERN WITH TUTTS/TROUGH
THAT ARE CURRENTLY PRESENT ACROSS THE ATLC TO BE REPLACED BY A
STRONG RIDGE ALOFT. THIS WILL BLOCK ANY POTENTIAL TROPICAL
CYCLONES ORIGINATING IN THE TROPICAL ATLC FROM TAKING THE NORTHERN
ROUTE. WHILE WE ARE MORE THAN LIKELY TO DODGE THE BULLET WITH
KATIA THIS MAY NOT BE THE CASE FOR FUTURE STORMS IN THE NEXT 7-14
DAYS.
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Quoting Jasonsapology:
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.

This a blog and a discussion. People are entitled to their opinions. You call them idiots, however the "experts" are not right all of the time. If you have a probelm with what people post on this blog, then please find other material to read.
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Quoting galvestonhurricane:
TD 13: Gone to Texas!


huh? It is a LA storm.
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2377. Oct8
Quoting Barbados:
http://www.nhc.noaa.gov/ seems to be down


Not for me!
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Quoting yoboi:
patrap how many Gallons of water can the pumps in nola pump per hour?


I am not Pat but the pumps can handle 1 inch the first hour and half an inch after that.
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2374. Skyepony (Mod)
By Dvorak #s 13L has weakened some since declared. Was called before suffering the heat of the day. As soon as the ACTF was issued NOAA jumped in too (it was their plane & not AF in there). The persistence rule wasn't applied like the other night when Stewert said a single Thunderstorm doesn't make a Tropical Storm. Being in the middle of the gulf & full of rain like it is..been on the wet side in FL, seen the TRRM passes & it's big like a Faye...no need to wait, it will look well enough in the morning.
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TD 13: Gone to Texas!
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2372. palmpt
Quoting wunderweatherman123:
just curious the next 10 days what does the pattern favor in terms of tracks for cape verde storms. out to sea, bermuda east coast or Gulf coast. the wave off africa right now should be maria in around 48 to 96 hours


Bastardi just said Gulf Coast will be more in play...
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if the center of 13 forms under the deeper storms would FL be at more risk?
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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 would be correct.
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Quoting atmoaggie:
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.)


Thank you! Great to have that local knowledge :)
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2368. emcf30
Quoting Barbados:
http://www.nhc.noaa.gov/ seems to be down

Working for me..
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At this rate we might surpass the 2005 Atlantic Hurricane Season, if the NHC keeps wasting names on these pep squeak storms, in fact it will make 2005 seem like a pushover, when in reality it is not! And tarnish the infamous legacy of that year, by putting this year on top as the most active. Hopefully I'm wrong and we don't surpass 2005 as that year should remain in a class of its own.
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2365. Oct8
Quoting Jasonsapology:
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.


I think you need a Fresca!
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Quoting Barbados:
http://www.nhc.noaa.gov/ seems to be down


Not for me.
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In any case, wind shear is loosening its grip on TD #13. So, it should look significantly better by the end of tomorrow.

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Quoting mcluvincane:



Anyone want to guess where she might go? I thought yesterday and part of the day today that Katia's out to sea path was written in stone, but it seems that may not be the case


My guess: She makes it to 65W before 25N.
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2361. CCkid00
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.


see post #2313
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2360. palmpt
Quoting Tazmanian:
guys with wind shear now falling i think TD 13 center is now refroming under the deeper t-storms
I agree. This thing could consolidate faster than some think.
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Quoting outlookchkr:
I was trying to maintain some sense of decorum.


Sorry :( ill go sit in my corner now
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http://www.nhc.noaa.gov/ seems to be down
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Anyone want to guess where she might go? I thought yesterday and part of the day today that Katia's out to sea path was written in stone, but it seems that may not be the case
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just curious the next 10 days what does the pattern favor in terms of tracks for cape verde storms. out to sea, bermuda east coast or Gulf coast. the wave off africa right now should be maria in around 48 to 96 hours
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2354. Drakoen
Quoting P451:


Good for recon. They should scan the globe for other closed areas of warm core circulation and declare them too then.

Sorry, not buying it, this thing is an absolute mess, and should in no way be declared as a tropical cyclone.

There are plenty of storms with a closed surface low and winds to TD force. They're not declared because there's more to it than that.

This thing is a mess. It's not stacked. The surface is broad and not located near any convection at all. The convection is stretched and focused along a trof. The winds are located far from the center. Has ratings of 1.0?

It's a mess.

Yet all the reservations I have about it mean nothing. If the NHC wants to declare it they will declare it and it will be called TD13.

If it were out in the Atlantic farther from land it would still be labeled an invest.



Totally agree.
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guys with wind shear now falling i think TD 13 center is now refroming under the deeper t-storms
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Quoting MississippiWx:
Shear is certainly loosening its grip:

Yeah.

You could be referring to TD13 but Katia should escape the shear right?
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Quoting MississippiWx:
Shear is certainly loosening its grip:




not good
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Quoting Halon056:
WOW!!! Did anyone check out Cantore's tie tonight? Talk about LOUD! He must have dressed in the dark.....

Lol!! with that shirt it makes it even harder to look at who needs 3-d tv that thing is jumping out the tv!!
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2348. yoboi
patrap how many Gallons of water can the pumps in nola pump per hour?
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Quoting Fresca:
.
It's been my only goal in life to meet a living can of Fresca. That goal=completed.
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Quoting outlookchkr:
Whiskey, ice... Bourbon, ice... Gin, ice... Vodka, ice... in a pinch, Tequila, ice...
you guys are ruining good alcohol. I cant see why you would destroy the taste of ice cold Patron Silver with Fresca...nor do I remotely comprehend how Makers 46 and Fresca would be enjoyable...I could see sipping a nice Makers 46 Old Fashion reading the entertainment on this blog.
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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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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.