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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This morning I said: What is that ball of convection near Burmuda?
Now NHC says: 50% of TS formation. Only a slight increase in convection will result in TS formation.
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Quoting atmoaggie:
Ah, I used to live in Nerdland. Off of Spurlock near NHS. (The former tiny road that got 4-laned, but no new speed limit signs at the request of DPS...)


LOL, I'm not far from Spurlock. I'm over by hwy 69, helena ave. area.
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Quoting wunderweatherman123:

does that mean until the death ridge breaks down completly texas wont get a system to go across most of the state like and ike where it moved through all of eastern texas.. man that death high wont just break apart..


Yeah unfortunately. It could happen, but the timing would have to be perfect and everything. We're in the pattern of the 1950s. You've heard me and others mention it regarding more than one kind of weather pattern. Here it's the dryness in Texas. The mid-1950s was a perpetual drought period for that area.
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742. IKE
Zeroing in on 93L?


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Quoting P451:


She is also just about to enter a wall of higher shear than she's been experiencing.

And it's not just the ULL in her proximity it's that other strong feature along the trof moving SE from North Carolina.

That feature and the trof were modeled to pull NE as weaker entities today. Instead they strengthened and headed SE.

It makes me curious if the computer models are handling that change properly or not. I would guess no seeing the ECMWF bringing Katia further west AND remaining an intense system. Both can't happen given the present setup.

First off she can't strengthen in this environment. If she remains weak she has to stay fairly far south to dive under all this mess and get left behind by the trof. Doing that she might just be torn apart.

A lot of uncertainty remains with katia - we can only go on what we see right this moment - and that is an increasingly hostile environment.

I view models of Katia as low confidence today.
Are you talking about the feature around 35N 70W?

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Quoting Levi32:
Wall of shear:

Is it showing any signs of weakening? Because when that wall collapses, 93L owns the GOM!
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Quoting cycleranger:


If we're lucky the border of TX/LA gets 1-2 inches from 93L.

Nothing different than some of the brief disturbances we've gotten over the Summer.


This is just crazy. We have a storm so close and it will be of no help at all.

I guess we can only hope for another one to help down the road but I'm not holding my breath.
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Quoting bluebonnetgirl:
It's cool to see some from SE TX on here. I'm in Nederland and
I sure hope 93L gives us some rain in SE TX this weekend.

I'm further south in Rockport.
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Quoting P451:


I'm surprised I haven't heard it's going to NOLA!

oh, wait lol.

lol
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HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE LAKE CHARLES LA
1106 AM CDT THU SEP 1 2011

GMZ432-LAZ027>033-041>045-051>055-TXZ180-201-215- 216-259>262-
021615-
CALCASIEU LAKE-VERNON-RAPIDES-AVOYELLES-BEAUREGARD-ALLEN-
EVANGELINE-ST. LANDRY-CALCASIEU-JEFFERSON DAVIS-ACADIA-LAFAYETTE-
UPPER ST. MARTIN-CAMERON-VERMILION-IBERIA-ST. MARY-
LOWER ST. MARTIN-TYLER-HARDIN-JEFFERSON-ORANGE-NORTHERN JASPER-
NORTHERN NEWTON-SOUTHERN JASPER-SOUTHERN NEWTON-
1106 AM CDT THU SEP 1 2011

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF THE NORTHWEST
GULF OF MEXICO...LA...CENTRAL LOUISIANA...SOUTH CENTRAL
LOUISIANA...SOUTHWEST LOUISIANA...WEST CENTRAL LOUISIANA...
SOUTHEAST TEXAS AND TX.

.DAY ONE...TODAY AND TONIGHT
A LARGE TROPICAL WAVE HAS STALLED ACROSS THE WESTERN GULF OF MEXICO.
SHOWERS AND THUNDERSTORMS WILL INCREASE ACROSS ACADIANA FOR THE
REMAINDER OF TODAY.

IN ADDITION...INCREASING EASTERLY WINDS OVER THE NEARSHORE WATERS
MAY CAUSE A PILE-UP OF WATER AT THE COAST. A COASTAL FLOOD WATCH
IS NOW IN EFFECT.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY
UNCERTAINTY REMAINS HIGH ABOUT FURTHER DEEPENING AND MOVEMENT OF
THE TROPICAL WAVE. AT PRESENT...VERY HEAVY RAINFALL IS LIKELY...
WITH FLASH FLOODING A POSSIBILITY.


.SPOTTER INFORMATION STATEMENT...
ACTIVATION OF STORM SPOTTERS MAY BE NEEDED THIS WEEKEND...PRIMARILY
FOR COASTAL FLOODING AND FLASH FLOODING CONCERNS. EMERGENCY
MANAGEMENT OFFICIALS SHOULD CLOSELY MONITOR THE WEATHER SITUATION
AND BE PREPARED TO ACTIVATE FOR INCLEMENT...POSSIBLE TROPICAL
WEATHER IMPACTS.


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Wall of shear:

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Anyone know how long Camille sat in the gulf before coming onshore in Gulfport? I had heard it sat there a while. Just thinking...
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Quoting Patrap:
New Orleans
NEXRAD Radar

Type
Storm Total Surface Rainfall Accumulation Elevation
Range
124 NMI


Given that radar clutter can be taken a snapshot of under clear conditions and then subtracted out of realtime data updates, one would think they had figured out that the Causeway souldn't be showing in those.
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New Jersey Hurricane Irene
08/31/2011 06:07 PM EDT

New Jersey Hurricane Irene

Major Disaster Declared August 31, 2011 (DR-4021) [ En Espaol ]
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If we're lucky the border of TX/LA gets 1-2 inches from 93L.

Nothing different than some of the brief disturbances we've gotten over the Summer.
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Katia TVCN shifted quite a bit west for one model cycle

12Z
AL 12 2011090112 03 TVCN 168 319N 641W



18Z
AL 12 2011090118 03 TVCN 168 291N 710W
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T.C.F.W.
012/H/K/C1
MARK
16.23N/50.67W



Member Since: July 15, 2006 Posts: 175 Comments: 54864
Quoting Levi32:


I fully expect a downgrade at 5pm. Never have I seen a hurricane where you can see its center exposed through the cirrus canopy, and I don't expect that I ever will.
Yeah, I'm not sure why they haven't downgraded it already since the satellite estimates no longer support the idea of a hurricane either.

SSD site has it at 3.5/4.0 which is indicative of a storm just below hurricane status since 4.0 is the cutoff. CIMSS ADT estimates also haven't had it at hurricane status for several hours now

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Quoting Levi32:
Quoting TexasHurricane:


ok, this just don't sound good for TX at all.

Let me ask you this. Do you see anything down the road that may could help us out?



Well if not 93L, then there is still some hope this month. The ensembles still favor ridging over southern Canada, which will bring storms close to the U.S., and the weakest point in the ridge will be over the central-eastern GOM by mid-month according to the GFS ensembles. This could bring some storms close to Texas if they come in from far enough south like from the Caribbean, or home-brew. However, all season long it may be difficult to drive a tropical cyclone straight into the heart of Texas, unfortunately.

does that mean until the death ridge breaks down completly texas wont get a system to go across most of the state like and ike where it moved through all of eastern texas.. man that death high wont just break apart..
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POSS Tropical.Cyclone.Formation.Alert
XX/INV/93L
MARK
27.95n/87.91w
Member Since: July 15, 2006 Posts: 175 Comments: 54864
Quoting hahaguy:


There's that F word again
I'm guessing it's been mentioned several times today? LOL.

I'm interested in knowing if 93L were to get caught up in the trough and head northeastward, would that allow for Katia to move more westward, or vice versa? Almost inevitable that 93L's track will affect Katia's steering in some way.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
Is Katia going to putter out and keep moving W?
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Quoting ncstorm:


a hard left and then a hard right?


Is possible but have doubts about the sharpness.
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Quoting P451:


When dealing with a system that meanders or is stationary it will only get so strong before upwelling causes it to weaken some and then level off. A storm that stays in one place long enough eventually cools off a region just by virtue of the torrential rain it drops into the sea as well.

How strong it gets and where it drops to and levels off in such a scenario I'm not sure.

You wouldn't see a storm grow to Cat 5 just sitting there though. Can't happen.

Maybe Cat 2 or 3 (if it has a decent forward motion at first) that drops back down to Cat 1 or 2 (if it then stalls for a long period of time).


If it only makes it to Cat 1 (because it is just stalled from the start) and sits and spins it'll drop down to strong TS.

thanks
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Quoting MiamiHurricanes09:
Lol, I meant Frances. Corrected it.


There's that F word again
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New Orleans
NEXRAD Radar

Type
Storm Total Surface Rainfall Accumulation ° Elevation
Range
124 NMI


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Quoting bluebonnetgirl:
It's cool to see some from SE TX on here. I'm in Nederland and
I sure hope 93L gives us some rain in SE TX this weekend.
Ah, I used to live in Nerdland. Off of Spurlock near NHS. (The former tiny road that got 4-laned, but no new speed limit signs at the request of DPS...)
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1 suspect that the high to the north of Katia is showing a little sign of building to the west. This will allow Katia to continue west for sometime.
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Quoting Patrap:
New Orleans
NEXRAD Radar

Type
Velocity Azimuth Display Wind Profile ° Elevation
Range
124 NMI


Thanks for the description. Now I have some things to look so I can learn. Thanks!
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Quoting MiamiHurricanes09:
Lol, I meant Frances. Corrected it.


I'd like to see that too. lol

With the interaction with the GOM system anything's possible.
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It's cool to see some from SE TX on here. I'm in Nederland and
I sure hope 93L gives us some rain in SE TX this weekend.
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Quoting SeaMule:
katia
katrina

hmmmm

it will slice through Miami as a cat 5,
and enter the GOM...and curve north and wipe out Mobile, Al, as the worst natural disaster in the history of the CONUS
no Lee will do that duh, lol
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Quoting tropicfreak:
Well folks, what do y'all think? We have TD 13?
I *think* so, but it is marginal, IMO.
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Quoting Sfloridacat5:


I'd like to see that. Charley came out of the Carribean crossed Cuba and turned right towards S.W. Florida.
Lol, I meant Frances. Corrected it.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
Quoting TexasHurricane:


hmmm, I take that as a no...


Sorry my quote messed up and my post didn't show. I edited it in.
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Quoting TomTaylor:
Katia is also a struggling storm, just trying to hang on to hurricane status at the moment




Dry air to the north and west are the main issues for Katia as they've prevented any deep convection from getting established along the western side. The main core of convection is getting better positioned over the surface center now, but it may still be slightly exposed as indicated earlier by microwave and visible imagery. Cloud tops are also beginning to cool again as new convection begins to pierce the cirrus canopy as seen in the satellite image above.

Looking ahead, the dry air already mentioned, and an upper level low to the northwest hampering anticyclonic flow and divergence will be the main issues for Katia. NHC mentions this in their discussion as well. It will be interesting to see how significantly this ULL affects Katia's upper level environment. The ECMWF doesn't allow Katia to establish good anticyclonic flow aloft until around days 3/4. Meanwhile, the GFS just kind shoves off the ULL allowing the ULAC to remain over Katia for the next several days. So the differences between the two are pretty large, and its also reflected in the MSLP forecast for each model. The GFS shows steady strengthening throughout the forecast period, meanwhile the ECMWF shows a little strengthening over the next two days, then a little weakening, until strengthening again by days 4/5.


I fully expect a downgrade at 5pm. Never have I seen a hurricane where you can see its center exposed through the cirrus canopy, and I don't expect that I ever will.
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Quoting MiamiHurricanes09:
12z ECMWF has Katia doing something very similar to a Charlie, should 93L get caught in the trough. (Correct me if I'm wrong, just got home and am pretty much lost with everything that's happened today lol).


I'd like to see that. Charley came out of the Caribbean crossed Cuba and turned right towards S.W. Florida.
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Quoting Levi32:
Quoting TexasHurricane:


ok, this just don't sound good for TX at all.

Let me ask you this. Do you see anything down the road that may could help us out?


hmmm, I take that as a no...
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Quoting wxobsvps:
I hope NHC classifies it if for nothing else than to get to see what will probably be one of the funniest looking cones in history.

Here is the reigning Champion, from the past five years:



looks like an ice cream cone in a strong east-blowing hurricane
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Quoting carcar1967:


The best I have ever known.
Thats good. My dad is great too. Hopefully Your daughter and I wont keep having these unexpected B-lated birthday "gifts".
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Quoting GetReal:


93L is making every effort to pull the convection around to the west side of the system. Thankfully the westwerly wind shear has prevent that from occurring. IMO once 93L can wrap the convection around to the western semi-circle it will be game on...


Shear is beginning to slacken some.
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93L is making every effort to pull the convection around to the west side of the system. Thankfully the westwerly wind shear has prevent that from occurring. IMO once 93L can wrap the convection around to the western semi-circle it will be game on...
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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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