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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It appears we are going to miss out on this rain event here on the central Texas coast, again. I think what happened to Don has scared his brother Lee.......
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uh, Katia is outrunning the CDO, and is on a bee-line West. there is NOTHING that will draw it wnw. She is south of the forecasted points, and will continue her trek Westward. by the time the models catch up to what she is gonna do, Florida will be under the gun, as will be the entire CONUS.

As for our little mischief in the GOM.

it will blow up into a major hurricane, because it is meandering out there in bathtub hot water.

where it goes? who knows.
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I thought he was the "Atmospheric Avenger" ?
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342. IKE

Joe Bastardi
The storm in the gulf is
3-5 days of problems. US models have no clue.. last night taking it
into Mexico, now taking into the lower ms vly
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Whatever center the is appears to be broad...but, nonetheless, this is where I would place the "center".
(Image is clickable for magnification)
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340. LBAR
Quoting P451:


No, I don't. I'm not even sure if Katia can survive her environment.

There is a chance, and it is an outlier for certain, that she could weaken significantly (which isn't a stretch), and potentially slip under the Atlantic features that would otherwise serve to force her north and north east.

She could be left behind in a weakened state and reorganize and slip towards the Mid-Atlantic coastline.

Given what I see now I'd give it an incredibly low chance of occurring.

Pay special attention to the tightly developed entity off of the NC coastline. See how it is sliding SE? Yesterday it was modeled to head NE and out to sea. This is a huge change and could cause all recent models to prove useless.

That entity could continue SE along with the trof which is quite strong (which was modeled to weaken and lift NE as well but has not). and pick up and punt Katia out to sea.

Or, that entity could stall, turn NE and pull out to sea along with the trof in time to leave a weakened Katia behind to slip under it.

So, we're in a wait and see game watching what transpires here.



In the meantime the ULL right to her NW is injected the dry air into her core and is shearing her. She may even decouple causing her demise.

Again, conditions can change quickly, just as they did quite the opposite just last night's models expected....and that's why we now have a weakened Katia clinging to hurricane strength (might not be one anymore) instead of steadily intensifying into the major she was modeled to be.

I would ignore model runs the next day or two on Katia - as they, like us, wait out these upper level Atlantic features.



Does't the GFS struggle with incorporating upper-level lows into its forecast?
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P451, that is some strong vorticity with 94L, I think we may be looking at Lee now.

850 mb

Member Since: September 2, 2006 Posts: 110 Comments: 6814
Well, well, well....Wadda we have here?!
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ZCZC MIATWOAT ALL
TTAA00 KNHC DDHHMM

TROPICAL WEATHER OUTLOOK
NWS NATIONAL HURRICANE CENTER MIAMI FL
200 PM EDT THU SEP 1 2011

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

THE NATIONAL HURRICANE CENTER IS ISSUING ADVISORIES ON HURRICANE
KATIA...LOCATED ABOUT 1050 MILES EAST OF THE NORTHERN LEEWARD
ISLANDS.

1. A BROAD AREA OF LOW PRESSURE LOCATED A COUPLE HUNDRED MILES SOUTH OF
THE LOUISIANA COAST IS PRODUCING A LARGE AREA OF CLOUDINESS...
THUNDERSTORMS...AND GUSTY WINDS OVER THE EASTERN AND CENTRAL GULF
OF MEXICO. UPPER-LEVEL WINDS ARE FORECAST TO BECOME MORE CONDUCIVE
FOR DEVELOPMENT...AND THIS SYSTEM COULD BECOME A TROPICAL
DEPRESSION DURING THE NEXT DAY OR SO. A NOAA HURRICANE HUNTER
AIRCRAFT IS SCHEDULED TO INVESTIGATE THE AREA LATER THIS AFTERNOON.
THIS SYSTEM HAS A HIGH CHANCE...80 PERCENT...OF BECOMING A TROPICAL
CYCLONE DURING THE NEXT 48 HOURS AS IT MOVES SLOWLY NORTHWESTWARD.
INTERESTS ALONG THE ENTIRE NORTHERN GULF OF MEXICO COAST SHOULD
MONITOR THE PROGRESS OF THIS DISTURBANCE.

2. A LOW PRESSURE SYSTEM LOCATED ABOUT 360 MILES NORTH OF BERMUDA HAS
CHANGED LITTLE OVER THE PAST FEW HOURS. THIS SYSTEM IS PRODUCING
WINDS OF TROPICAL STORM FORCE...AND ONLY A SLIGHT INCREASE IN
ORGANIZATION COULD RESULT IN THE FORMATION OF A TROPICAL STORM.
THE LOW IS MOVING LITTLE AT THIS TIME...BUT SHOULD BEGIN TO MOVE
NORTHEASTWARD AT 10 TO 15 MPH TONIGHT. THIS SYSTEM HAS A MEDIUM
CHANCE...50 PERCENT...OF BECOMING A TROPICAL CYCLONE DURING THE
NEXT 48 HOURS.

ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.

$$
FORECASTER PASCH
NNNN
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dangerously too close

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Quoting WetBankGuy:


Gotta say I'm more worried about the Noah scenario right how than the Moses one. "Noah?" "Yes, Lord." "How long can you tread water?"



I wish Nash Roberts was alive, his felt pen always gave me comfort.

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Quoting WeatherInterest:
Joe Bastardi stated on his latest video blog east coast of the us not out of the woods with Katia.
Do you agree?


Joe B. said a storm could threaten the East Coast?!

Pardon me while I lie down from the shock.

(Yes, of course Katia's path isn't set in stone for anywhere yet, but c'mon, it's Joe B. That's the only prediction he can make.)
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Quoting Patrap:
Just Videoed and took pics of the Biggest Green Grasshopper or my Furst Locust on my Porch.

That cant be good at all.


Gotta say I'm more worried about the Noah scenario right how than the Moses one. "Noah?" "Yes, Lord." "How long can you tread water?"
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Time: 17:19:30Z
Coordinates: 27.6667N 87.4W
Acft. Static Air Press: 649.2 mb (~ 19.17 inHg)
Acft. Geopotential Hgt: 3,818 meters (~ 12,526 feet)
Extrap. Sfc. Press: 1011.3 mb (~ 29.86 inHg)
D-value: -
Flt. Lvl. Wind (30s): From 117° at 30 knots (From the ESE at ~ 34.5 mph)
Air Temp: 7.1°C (~ 44.8°F)
Dew Pt: 7.5°C (~ 45.5°F)
Peak (10s) Flt. Lvl. Wind: 32 knots (~ 36.8 mph)
SFMR Peak (10s) Sfc. Wind: 39 knots (~ 44.8 mph)
SFMR Rain Rate: 0 mm/hr (~ 0 in/hr)
(*) Denotes suspect data

All we need now is west winds and we have Lee
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Quoting PcolaDan:


Dan I just hope the tourists know to stay out of that mess this weekend or we're going to have a few drownings. High Surf and strong rip current advisories have already been issued.
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Quoting Patrap:
I guess were gonna see how well the new COE Outfall Canal Pumps are gonna work pumping excessive rainwater into Lake P.
yep...good test coming.
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Quoting groundswell:
So, maybe a swell from 93L on Florida's west coast?....nah, off to east coast for some long period Katia for days & days......


amen! I'll have to settle for whatever 93 throws towards Venice Jetty's! No wheels :( Pray for surf, not destruction. Unfortunately they usually go hand in hand in the GOM!
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Quoting TampaTom:
I didn't realize that one of the local papers was doing a profile on me...

Hurricane Preparedness - the Man Behind the Mission


That is such a nice tribute, TTom....and thank you for all you do :)
Member Since: September 16, 2010 Posts: 0 Comments: 1492
The chatter in the News started.

Link
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Quoting IKE:
Agree...they are trending to move a system inland and then ENE...or east...could be a big flooding event....
Will be interesting to see what happens to Katia on this run. How many hours out does the CMC go?
Member Since: August 31, 2009 Posts: 0 Comments: 5628
Quoting WeatherInterest:
Joe Bastardi stated on his latest video blog east coast of the us not out of the woods with Katia.
Do you agree?


the GFS has gone farther west with Katia in the latest run..its one model run but it could be a beginning to a westward trend..
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Looks to be forming due South of Grand Isle by 200 Miles or so,,

Drifting Nnw

ZOOM and other available

93L Floater - RGB Color Infrared Loop
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Quoting IKE:

Agree...they are trending to move a system inland and then ENE...or east...


Indeed... we'll see now if the trend continues with 12Z ECMWF and other track/intensity models (e.g. GFDL, HWRF, ect...).
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000
URNT15 KWBC 011710
NOAA2 01HHA INVEST HDOB 06 20110901
170030 2744N 08548W 6484 03839 0154 +056 +035 143012 013 029 000 00
170100 2744N 08551W 6485 03837 0149 +060 +034 145014 014 028 000 00
170130 2744N 08553W 6485 03837 0149 +059 +034 152014 014 028 000 00
170200 2744N 08556W 6486 03835 0146 +061 +032 149015 015 029 000 00
170230 2744N 08559W 6484 03835 0146 +059 +031 152013 013 028 000 00
170300 2743N 08601W 6484 03835 0145 +059 +032 158012 012 029 000 00
170330 2743N 08604W 6486 03832 0144 +061 +032 157011 011 030 000 00
170400 2743N 08606W 6485 03834 0143 +061 +033 155011 011 030 000 00
170430 2743N 08609W 6484 03834 0141 +062 +031 150011 011 031 000 00
170500 2743N 08611W 6487 03830 0137 +065 +030 143011 011 031 000 00
170530 2743N 08614W 6486 03832 0135 +066 +028 139012 012 032 000 00
170600 2743N 08616W 6486 03831 9137 +072 +026 139034 075 032 000 00
170630 2743N 08619W 6487 03830 0130 +069 +025 139013 014 033 000 00
170700 2743N 08621W 6488 03828 0125 +072 +024 142013 013 032 000 00
170730 2743N 08624W 6485 03829 0121 +074 +022 146013 014 032 000 00
170800 2743N 08626W 6486 03829 0122 +073 +020 149015 015 034 000 00
170830 2743N 08629W 6487 03828 0122 +072 +020 151014 015 036 000 00
170900 2743N 08631W 6487 03825 0120 +073 +020 152014 014 038 002 00
170930 2743N 08634W 6487 03825 0123 +071 +021 146015 015 039 000 00
171000 2743N 08637W 6488 03826 0125 +071 +021 149014 015 044 004 00
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316. IKE
Quoting WxLogic:
12Z CMC looks to be more in line with 12Z GFS.

As we currently stand 00Z ECMWF, 12Z CMC/GFS look about the same.
Agree...they are trending to move a system inland and then ENE...or east...could be a big flooding event....
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I think the one of the dropsondes hiccuped - had pressure of 913.7
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314. IKE
@ 120 hours...


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12Z CMC looks to be more in line with 12Z GFS.

As we currently stand 00Z ECMWF, 12Z CMC/GFS look about the same.
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312. cdo13
First post ever here....hopefully that large area of convection in the Gulf will move west.
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Quoting cloudburst2011:
MAYOR LANDRIEU IS HOLDING A NEWS CONFERENCE THIS AFTERNOON CONCERNING THE POTENTIAL LEE FORMING IN THE GOM SOUTH OF THE LA COAST...

ssshhhh...stop yelling.... :)
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310. txjac
Quoting TampaTom:
I didn't realize that one of the local papers was doing a profile on me...

Hurricane Preparedness - the Man Behind the Mission


Congratulations! What an article!
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There's a NOAA aircraft flying into 93L at the moment. It's having some entertaining problems with its readings - every now and then, it throws up a bizarre extrapolated surface pressure or SFMR windspeed. But it's recently entered a broad swathe of 30kt+ surface winds, and is in a band of showers where winds would seem to be sustained at 40kts+. If this thing gets organized when shear dies down tonight, it could spin up in a hurry.
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308. IKE
Hmm....12Z CMC @ 96 hours...


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Member Since: September 16, 2010 Posts: 0 Comments: 1492
306. 7544
does anyone have a webcam link for the biloxi beach thanks will be appreciated
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As always, thank you all for your replies to my comments they are appreciated.
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Quoting JNCali:

Check the verbiage the 'scientist' uses in this article... community collage REPRESENT!


:P
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New Frame shows the expansion and organization continuing.



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Member Since: September 16, 2010 Posts: 0 Comments: 1492
Quoting debaat:
FEMA problems portend a major problem if anything hits ANY US coast from here forward. A Congress in gridlock is just going to make it worse. Living on the FL coast (I do) makes me wonder, though I just got back from CT yesterday and it is still bad there... Thanks everybody for the insightful information on this blog...



Yes, Connecticut got it pretty bad as they took the RFQ straight off the Atlantic and Long Island sound.
Crazy video shows hurricane force winds and surge in CT


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Good afternoon everyone.

Looks like 93L will be a messy rainmaker and could present life threatening flooding to many on the gulf coast.

Katia could be a bit of a surprise for the ECONUS depending on how amplified these troughs are that are forecast to erode the subtropical ridge. Stay tuned.
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I guess were gonna see how well the new COE Outfall Canal Pumps are gonna work pumping excessive rainwater into Lake P.
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Joe Bastardi stated on his latest video blog east coast of the us not out of the woods with Katia.
Do you agree?
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Quoting Levi32:
We're going to have a long time to watch 93L sit there, and it will take it a while to wind up into a storm due to the wind shear and its broadness. If it becomes a TD late tonight or tomorrow morning it would likely remain one for some time before beginning to strengthen.

Back after breakfast.

Hello Levi ,what about Katia we are watching her from here PR cause you knows she is moving west! do you think she has a probability to Scare us!
Regards
Luigi
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Do you think New Orleans will get massive flooding? Less than Katrina but pretty close?
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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.