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 Skyepony:


Tropical Depressions are not attached to fronts..it has to cut off first...
I don't think it is attached to a frontal boundary. I'm pretty sure the NHC wouldn't be saying "ONLY A SLIGHT INCREASE IN ORGANIZATION COULD RESULT IN THE FORMATION OF A TROPICAL STORM" if that were the case.

We should have 14L if 13L was classified. I see that's the whole argument this evening, lol.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
2444. DFWjc
Quoting wxguesser:


You must not be from round here..we all say anything more than an inch an hour will overwhelm the pumps and the streets will flood... (lol) :-)


just going by what the army corp of engineers have said about the "new" temporary pumps..
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Quoting taco2me61:
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)


yep blowing pretty good over in Orange Beach also..
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94L, at least to MY primitive eyes, *looks* essentially the same as Jose did. If there are other categorizers that are different between the two, I'm not really aware. Just MHO.
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Quoting DFWjc:


A 5,000-horsepower diesel engine spins the pump’s four-blade propeller 150 times a minute. Together the 13 pumps move 150,000 gallons of water per second, the equivalent of about 15 Olympic-size pools every minute.


You must not be from round here..we all say anything more than an inch an hour will overwhelm the pumps and the streets will flood... (lol) :-)
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Quoting Jasonsapology:

So when the opinion is good for the masses then no problem. This is a blog so we should be able to give our thoughts to improve it. I'll let you all go back to arguing for the next 12 hours if the mess in the Gulf is a depression or a trough. God save the Queen.


I am going to take twins advice and ignore the troll... Labeling people "idiot's" for their opinion is like me labeling you an idiot for having an opinion in the first place.... Enough said...
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2438. DFWjc
Quoting yoboi:
where are the weakest levees at in nola ????


here's a story about the levee and the temp pumps

Link
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ok guys cantorie is playing the doom song again and thats my cue to go to bed and visit shpongle land good nite
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The NHC classifying Invest 93L as TD 13 is an absolute joke.
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2435. bayeloi
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.)


I'm not even sure that Gause flooded in the May '95 flood.
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Quoting Joshfsu123:
NHC makes the decision - they know what they are doing. Deal with it.


(nods)
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Quoting Patrap:
Me tinks some Fla and Tex folks are a tad tropically depressed.



Try a cold Fresca.
Honestly it is difficult not being depressed going through this hot and dry weather for so long, seeing things die around you including animals is tough to deal with and you cannot do anything about it, having relatives and friends lose their homes due to fires but I make the most of every day and do my best. Hope you don't get too much rain in New Orleans.
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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.


I'll buy that. It can't hurt.

From a purely scientific standpoint... maybe it's up for debate whether 13 follows the letter of the law...

But if the object of the game is to keep the public informed (it IS the first thing in NHC's mission statement)... it's the right call.

For those who haven't seen NHC's mission statement:

The NHC mission statement is to save lives (my emphasis in bold), mitigate property loss, and improve economic efficiency by issuing the best watches, warnings, forecasts and analyses of hazardous tropical weather, and by increasing understanding of these hazards.
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The wind is definitely up here tonite (Port Arthur, TX). We had gusts to 22kts at work this afternoon. But now it's almost up to 30. Certainly NOT the pattern we've had most of the summer (as they usually go 00000 or near so at nite).

Does anyone know what the spin is just onshore across mid-coastal LA? Is it just a vorticy coming out/off the low? An ULL? We were just curious. TIA!
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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.


You couldn't be more right.
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Quoting P451:


But...if it's not a TD, then, it's not a TD. Issue a flood warning.

So now a system with a 1.0 rating has weakened?

Come'on....... there was no reason to toss the checklist just because the system is near land.

We've seen recon find a closed low in systems plenty of times and we watch the NHC keep them as an invest because of ---- exactly what we see right now: A very disorganized system.

I have little doubt that 93L would eventually become TD13 but I see no reason to upgrade it when it's clearly not.

But, again, my reservations are meaningless given they decided to name it.

However, making the rules as you go is not something an official agency should be doing.


if classifying it is the conservative action, why is it that big of deal?
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Quoting MississippiWx:
By the definition though, this should be a tropical cyclone as well:

yuck that thing is really ugly lol anyways do you know the upcoming pattern for the next 10 days in terms of steering from the euro and gfs? the wave off africa looks to become maria and if it becomes a cape verder im wondering where it would go most likely like the gulf east coast bermuda or out to sea
Member Since: August 23, 2011 Posts: 0 Comments: 1728
evening everyone...did a little surfing today thanks to TD 13...looking at the gom satalite..is the center trying to form around..24 88?? just curious...hey Patrap don't be drinking too many of those Fresca's now...lol keep up the great work everyone...going to be a nasty holiday along the gulf coast...but hey it's college FOOTBALL TIME!!!
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2424. yoboi
where are the weakest levees at in nola ????
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2423. Skyepony (Mod)
Quoting MississippiWx:
By the definition though, this should be a tropical cyclone as well:



Tropical Depressions are not attached to fronts..it has to cut off first...
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Quoting dsenecal2009:


Thank you! Great to have that local knowledge :)
I work near Robert Rd. and Gause, one of the lower spots along that corridor. There is water on the road after every decent rain.

Katrina was bad, but did not flood anyone out there, that I know of (hey, is possible someone had a flood issue, just not prevalent, there).
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2421. JGreco
Quoting KoritheMan:


No.


not exactly true, the Western Florida Panhandle region still has some ensembles in play. Furthermore, If the storm came in as far East as Miss/Alabama line depending if there was a reformation of the center, that would put the Western Panhandle region on the Eastern side. Everybody remembers Ivan. Landfall in Alabama/Mississippi but devastated the region from Pensacola to Destin on the right hand side.
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Quoting JGreco:


Maybe the Western Florida Panhandle, but any further I would say no.
I don't know with the steering currents being weak and a trough coming down from the Central Plains region it would make sense for it to shoot off to the Northeast.
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2419. ncstorm


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Once the shear relaxes i believe this thing will really take off i mean it has alot of convection and heat to work with that westerly shear is killing it but its starting to diminish now...it will be important to see how much it organizes tonight
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2416. gugi182
I wish that there where no hurricanes, no tropical storms or depressions, no snowstorms just plain and simple rain no flooding a place where residents don't have to worry about natural disasters. I wish a world free of hunger, a world where everybody got a long great, that weather would threat us nicely year round. i love weather no doubt about it but it is sad that weather is so beautiful and treats us so bad in certain periods of our life. I love seeing hurricanes developing only in the oceans not affecting people, seeing how mother nature work, seeing how it blossoms, we need to be more greener, we need to understand that we are destroying our planet a grain of salt a day. I wish for a better planet, a better day. Now that i got that out of my system. ANYBODY KNOWS WHERE KATIA IS GOING?
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Complete Update

TS BUSTED FORECAST ALIBI





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2413. yoboi
wow thanks so 3 inches an hr for a storm in nola means severe flooding
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Quoting Jasonsapology:

AND THATS MY OPINION, SO WHATS THE PROBLEM???????


There is a difference between an opinion and labeling....
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Quoting taco2me61:
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)


North of no above average winds prolly 5 to 10 mph pressure is at 1012 an falling ts warnings up but it might take what three days to make landfall
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By the definition though, this should be a tropical cyclone as well:

Member Since: July 15, 2006 Posts: 17 Comments: 10284
Quoting MississippiWx:


You didn't understand my point.


I know...
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Quoting mcluvincane:



umm... GFDL?
The GFDL and NOGAPS were very much in line with the current UK in the previous 3 runs. It has shifted significantly North compared to where it was.
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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
That cluster seems to be moving more westward as a week system moves more westward.
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NHC makes the decision - they know what they are doing. Deal with it.
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The DisturBance of 6pmGMT has been re-evaluated&upgraded to a TropicalDepression for TD.13's_12amGMT_ATCF
25.6n88.7w, 26.1n90.0w, 26.6n91.4w have also been re-evaluated&altered
25.4n88.7w, 26.0n90.0w, 26.3n90.8w, 26.6n91.4w are now the most recent positions
Starting 1Sept_12amGMT and ending 2Sept_12amGMT

The eastern line-segment represents TropicalDepression13's path
and the westernmost line-segment is the straightline projection.

Using straightline projection of the travel-speed&heading derived from the ATCF coordinates spanning the 6hours between 6pmGMT then 12amGMT :
TD.13's travel-speed was 7.2mph(11.5k/h) on a heading of 299.2degrees(WNW)
TD.13 was headed toward passage over the SouthTexasNuclearGeneratingStation between Palacios and BayCity,Texas in a bit more than ~1day17hours from now

Copy&paste 24.5n87.5w, 25.4n88.7w, 26.0n90.0w, 26.3n90.8w-26.6n91.4w, psx, 26.3n90.8w-28.675n95.8w, bbc, 28.796n96.049w into the GreatCircleMapper for more info
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Quoting hunkerdown:
this has been repeated many time over the past couple seasons...at this point, I will believe it when I see it.
well i dont want to believe it already had to through away everything in my fridge and freezer because of Irene i cant afford to do it again
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Quoting Barbados:
http://www.nhc.noaa.gov/ seems to be down

don't think so - think they are working on the graphics - may be wrong - but that is the only area i see that is not working....
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Quoting TropicalAnalystwx13:


A tropical depression by tomorrow? We have one now ;)


You didn't understand my point.
Member Since: July 15, 2006 Posts: 17 Comments: 10284
2398. JGreco
Quoting RukusBoondocks:
if the center of 13 forms under the deeper storms would FL be at more risk?


Maybe the Western Florida Panhandle, but any further I would say no.
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2397. DFWjc
Quoting nolacane2009:


I am not Pat but the pumps can handle 1 inch the first hour and half an inch after that.


A 5,000-horsepower diesel engine spins the pump’s four-blade propeller 150 times a minute. Together the 13 pumps move 150,000 gallons of water per second, the equivalent of about 15 Olympic-size pools every minute.
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Quoting mrpuertorico:
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
.
this has been repeated many time over the past couple seasons...at this point, I will believe it when I see it.
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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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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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