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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Member Since: August 2, 2010 Posts: 21 Comments: 9648
Quoting tatoprweather:
Sorry for the question but...it's the CV season over?


No, probably won't be for another month.
Member Since: July 15, 2006 Posts: 17 Comments: 10156
I just don't see how they could classify this even with a closed circulation. It has no organization at all according to satellite estimates. It should be at least T1.5.

01/1745 UTC 26.6N 90.8W TOO WEAK 93L -- Atlantic
Member Since: August 2, 2007 Posts: 19 Comments: 19234
Quoting txag91met:


It won't be too bad...but expect power outages.

Oh gosh! Our AC broke the other day I was crying after two hours! I couldn't even sleep @ my house!
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Seem's like a very weak circulation

Might not even get a VDM
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Look at the Growth rate in the Channel 4 IR..

Floater - Infrared Channel 4 Loop
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Sorry for the question but...it's the CV season over?
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They could make it real short and sweet at NWS NOLA.... Here it is...

"HELLS BELLS!!!!! We have no fragging clue right now. Get back to us in a few days."

LOL!!!
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Quoting GTcooliebai:
Very weak west winds, but would that be enough to classify it though?
They found Irene with weak west winds.
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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
Very good article. And great job -credible - keep it up.
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They have found west winds and a broad circulation. they have East, south, west and NW winds so far. See it using the Google earth HH app
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Quoting hahaguy:


That proves women can't drive LOL.


now come on, Lee is in the GOM with a busted GPS and wont ask for directions...
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Quoting Levi32:


Oh yeah it could still try to slip in near the TX/MX border, especially if it remains very weak. I think it will strengthen enough to propel itself northward though.
1) Whenever the NHC determines the true center and how far W 93L tracks, will that determine where on the Gulf Coast 93L makes landfall? 2) What are the conditions going to be in the GOM starting on Friday until Wednesday? Fair, moderate, or rocket fuel for a TC?
Member Since: June 13, 2009 Posts: 0 Comments: 6706
Quoting GTcooliebai:
Very weak west winds, but would that be enough to classify it though?


We saw weaker west winds when Irene developed, so yeah I'd say that's enough to classify it.
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Wow, they actually found West winds...

Time: 18:28:00Z
Coordinates: 25.7833N 90.8W
Acft. Static Air Press: 958.5 mb (~ 28.30 inHg)
Acft. Geopotential Hgt: 466 meters (~ 1,529 feet)
Extrap. Sfc. Press: 1010.2 mb (~ 29.83 inHg)
D-value: -
Flt. Lvl. Wind (30s): From 267° at 4 knots (From the W at ~ 4.6 mph)
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Quoting GTcooliebai:
Very weak west winds, but would that be enough to classify it though?


More than likely, yes. The west winds will probably be a tad stronger further away from the center.
Member Since: July 15, 2006 Posts: 17 Comments: 10156
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Hi, Levi, if you are on...

I find it very strange that the ITCZ is almost non-existent right now....
Apart from a wave in the East Atl, nothing for a couple of days.

Any idea on this?
Why it should be so?
Dont recall seeing this in Aug/Sept before.

Thanks!
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575. ackee
I hink 94L will be LEE at 5pm
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Quoting ncstorm:


I hope not..


Until there IS reason. LOL!!!

Just kidding P451. Not giving you crap or anything. But yeah. Still too many upper air variables that just aren't cut and dry here.
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Quoting xtremeweathertracker:
West winds!!!!
Very weak west winds, but would that be enough to classify it though?
Member Since: August 31, 2009 Posts: 0 Comments: 5628
Quoting NolaJoniW:
Levi,
I just recently moved out if my parents house. I live in south Louisiana...lower than new Orleans. Should I start preparing with food and candles and things...is it even going to get that bad?


It won't be too bad...but expect power outages.
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West winds
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do we have a closed low yet? thanks
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Levi,
I just recently moved out if my parents house. I live in south Louisiana...lower than new Orleans. Should I start preparing with food and candles and things...is it even going to get that bad?
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Poor NWS NOLA:

"LONG TERM...
FOR THE LAST FEW DAYS OR MORE...MODELS HAVE INDICATED THE
DEVELOPMENT OF AN UPPER AND SURFACE LOW IN THE WESTERN GULF JUST OFF
THE LOUISIANA COAST. AT THIS TIME IT APPEARS THE SYSTEM WILL BE A
SUBTROPICAL OR HYBRID STORM OF SORTS. THE MAIN CONCERN ISNT SO MUCH
WHETHER ITS COMPLETELY TROPICAL OR NOT AND ITS INTENSITY BUT RATHER
THE RAINFALL POTENTIAL WITH THIS EVENT. THOUGH THERE HAS BEEN A
GENERAL LACK OF RUN TO RUN AND MODEL TO MODEL CONTINUITY...THE BASIC
AGREEMENT IS THERE WILL BE PLENTY OF RAIN...ESPECIALLY ALONG THE
COAST. SO...BIGGEST CHANGE FROM PREVIOUS FCST IS THE RATHER LARGE
INCREASE IN AREAL RAIN CHANCES THROUGH THIS WEEKEND. DIVULGING INTO
A FEW OF THE MODELS:

CANADIAN...DEVELOPS LOW SOUTH OF SABINE PASS FRIDAY AND BRINGS IT
INTO SOUTHERN TEXAS COAST SUNDAY NIGHT.

NAM12...DEVELOPS LOW SOUTH OF LCH TONIGHT AND BRINGS IT INTO
VERMILLION BAY SATURDAY NIGHT. DGEX CONTINUES THE LOW ON A WOBBLY
NEWD TRACK THROUGH EARLY NEXT WEEK.

SREF...IS SAME AS NAM12 BUT SLIGHTLY SLOWER ON INLAND MOVEMENT WITH
THE LOW STILL IN VERMILLION BAY MID DAY SUNDAY.

ECMWF...DEVELOPS THE LOW TONIGHT SOUTH OF SABINE PASS...BRINGS IT
NORTHEAST TOWARDS THE SOUTH CENTRAL LA COAST THROUGH MIDDAY
SUNDAY...TRACKS SWWD AWAY FROM THE COAST TILL THE MIDDLE TO LATE
NEXT WEEK AND THEN BACK NORTHEAST ACROSS THE AREA TOWARDS THE
APPALACHIAN MTNS.

GFS...DEVELOPS THE LOW FARTHER SOUTH OF LCH THAN THE OTHERS
TONIGHT...BRINGS IT INLAND OVER SOUTH CENTRAL LA SATURDAY NIGHT...
THEN BACK OFF SHORE AND CONTINUED SOUTHWEST TO BROWNSVILLE TX
MIDWEEK.

SLEW OF MULTIPLE TROPICAL MODELS...IT WOULD TAKE A BOOK TO DESCRIBE
THEM AS THE SOLUTIONS ARE VERY WIDELY SPREAD IN TRACKS AND TIMING.
THEY SEEM TO ZIG ZAG OFF THE LA COAST AND THE LOW COULD BE ANYWHERES
FROM NORTHERN MEXICO TO EASTERN GULF IN 5 DAYS ACCORDING TO THESE
MODELS.

SO...LOOKING AT ALL THIS MODEL DATA...DIFFERENT ONES HAVE
SIMILARITIES IN PARTS OF ITS SOLUTIONS WITH OTHERS. WITH THE
FORECAST...HAVE TRIED TO INCORPORATE AN ENSEMBLE OF ALL OF THESE
RESULTS INTO A SOMEWHAT CONSISTENT SOLUTION. THE RESULT IS THAT
THERE SHOULD BE A SUBSTANTIAL AMOUNT OF RAINFALL ACROSS SOUTHEAST
LA/MS MAINLY FROM FRIDAY THROUGH AT LEAST THE WEEKEND. THINKING IS
THAT THROUGH THE NEXT 5 DAYS...AMOUNTS WILL RANGE FROM AROUND 3
INCHES OVER FARTHER INLAND AREAS SUCH AS BATON ROUGE AND THEN
UPWARDS TO POSSIBLY NEAR 1 FOOT ALONG COASTAL LOUISIANA PARISHES.
ALL IS PLAUSIBLE WITH SUCH A TROPICAL AIRMASS TO BE IN PLACE. MODEL
SOUNDINGS INDICATE 2.65+ INCHES OF PRECIP WATER AT MSY FRIDAY AND
SATURDAY. SO...WILL BE A VERY EFFICIENT RAIN PRODUCING ENVIRONMENT
WITH HEAVY RAIN EXPECTED. GOING WITH THIS THEME...WILL BE ISSUING
FLASH FLOOD WATCH WITH FCST PACKAGE THIS MORNING. DECIDED ON
ASSUMPTION PARISH TO LAKE PONTCHARTRAIN AND SOUTHWARD AS WELL AS
COASTAL MS COUNTIES. FOR TIMING...THE BULK OF THE HEAVY RAIN LOOKS
LIKE IT WILL BE FROM FRIDAY THROUGH SUNDAY SO FRI-12Z TO MON-00Z.
AREAL COVERAGE OF THE WATCH COULD EXPANDED NORTH AND TIME MAY BE
LENGTHENED WITH LATER FCSTS BUT FOR NOW IS THE BEST FIRST GUESS.
JUST LOOKS TO BE LIKE TOO WET OF A SCENARIO ABOUT TO PLAY OUT TO
NOT HAVE THE WATCH OUT."

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unenhanched IR

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Quoting ncstorm:
that was a hard left turn for Katia..for real..LOL!!


That proves women can't drive LOL.
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West winds!!!!
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Hello everybody, nice to see you again.

I would like to APOLOGIZE up front for anyone on the Gulf Coast (Oddly I am in SW Georgia so yeah) but anyways I see that "Lee" will causing a lot of flooding problems on the Gulf Coast. He will also wander around a bit and likely could easily become a hurricane. ALL these "billion" dollar disasters this year are astonishing 2011 is now the worst year for natural disasters in US history thanks to Hurricane Irene.

Katia looks like she is wanting to come further west and I wonder how the "current westward" motion will affect her eventual path.
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Member Since: August 2, 2010 Posts: 21 Comments: 9648
Quoting P451:


I see no reason to put any worry or trust into this model run.



I hope not..
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oh crap..it went back to the North..
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Once again, the GFS is WAAAAAAY too slow with Katia. Run after run, that model has Katia creeping along. While in real time, Katia is booking it west.
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556. IKE
Day 8....


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Quoting hurricanehanna:

I'd gas up now as gas prices are sure to rise, and you should always have scotch on hand
Ours in Pensacola area already went up.
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553. jpsb
Quoting hurricanehanna:

I'd gas up now as gas prices are sure to rise, and you should always have scotch on hand
lol, i think you are correct and I am going to take action immediately.
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that was a hard left turn for Katia..for real..LOL!!
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528. Patrap 6:38 PM GMT on September 01, 2011

Looks like explosion of fireworks over the water..uurrgghhh
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Quoting baytwntx11:


Doesn't it appear the majority of the models are trending back to the west on this, Pat? Or a I missing something....


Dunno,,we can watch her in real time so the models are kinda post moot really in this one.
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Quoting scott39:
Levi, Is there still a grain of hope that 93L can go into Texas or just S of it?


Oh yeah it could still try to slip in near the TX/MX border, especially if it remains very weak. I think it will strengthen enough to propel itself northward though.
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168hrs out Katia approaching the Bahamas, South of the 0z run. Link
Member Since: August 31, 2009 Posts: 0 Comments: 5628
Quoting Patrap:
NHC Model Runs for Investigation Area


Doesn't it appear the majority of the models are trending back to the west on this, Pat? Or a I missing something....
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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.