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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Oh, for anybody who doesn't know...

TROPICAL DEPRESSION 13 HAS FORMED
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1543. ncstorm
Quoting BrockBerlin:
Although the east coast trough pattern is still the same the 18z GFS has Katia getting considerably more west than the 00z, decently close to the Carolinas. That being said I hate the 18z GFS.


hopefully this is not a westward trend..if so the next run will show it hitting NC..

06Z GFS


12Z GFS


18Z GFS
Member Since: August 19, 2006 Posts: 13 Comments: 15666




Round and Round they go
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1539. Patrap
Quoting ironbanks:
Seeing some heavy squall come through NOLA today. They are tropical in nature for sure. Having lived here all my life I have seen this before. I think this one will be remembered for the amount of rain it dumps.


It does has that September Flavor to it dosent it?
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Quoting Skyepony:
Recon is finding an interesting area. 1006.6mb at 26.633N 91.033W with some interesting wind shifts..


Just read that too Skye...they also did a little loop as if they are trying to confirm that there is a closed LLC down there. Looks like it's been close all afternoon but now they may have just enough to declare the system a tropical depression.
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Quoting TexasHurricane:
I think I hear rain......yes, it is rain... :)
Lol. Yeah. I wasn't sure but yep. Whoa. Suns still firing through it lol.
Member Since: August 24, 2010 Posts: 0 Comments: 245
Getting some rain and easterly winds here in Vidor, Texas. First we've had in a while! At least we are getting something from Invest 93l!
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1534. Dennis8
Quoting Sfloridacat5:


I had some good times in Corpus. I have a lot of friends there.
The Island is now very built up (North Padre Island - neighborhoods). A major hurricane could cause some serious damage out on the island. They haven't had a bad storm in a long time.

Celia ...when I was 8 161mph at the airport....on youtube there is a video of the aftermath just posted this year..AMAZING...90% of the homes damaged....Lookup Celia-Corpus Christi. Goes through the whole city afterward and a little bit during the storm. Homes demolished in Pharoah Valley by I lived. My parents on the island now and retired.
Member Since: August 15, 2008 Posts: 0 Comments: 446
Seeing some heavy squall come through NOLA today. They are tropical in nature for sure. Having lived here all my life I have seen this before. I think this one will be remembered for the amount of rain it dumps.
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I was really pulling for yall in Texas-lord knows, we don't need any of this in Southeastern La. And I think you all could handle the 20". When they opened the Morganza spillway, the prdicted flooding really didn't happen because the ground mostly just sucked the water right up.
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AHEM.
invest_RENUMBER_al932011_al132011.ren
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1530. KEEPEROFTHEGATE (Mod)
T.C.F.W.
012/H/K/C1
MARK
16.45N/50.15W



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13L at 7:30-8:00p.m.
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WoW, I changed my mind. The GFS has katia really more to the west, when you watch the whole run. In fact, the east coast does not appear out of the woods at all. What the hell happened?
Member Since: August 26, 2006 Posts: 0 Comments: 1548
re post


we now have TD 13


BEGIN
NHC_ATCF
invest_RENUMBER_al932011_al132011.ren
FSTDA
R
U
040
010
0000
201109012228
NONE
NOTIFY=ATRP
END
INVEST, AL, L, , , , , 13, 2011, DB, O, 2011083118, 9999999999, , , , , , METWATCH, , AL132011
AL, 13, 2011083100, , BEST, 0, 214N, 845W, 25, 1012, DB, 0, , 0, 0, 0, 0,
AL, 13, 2011083106, , BEST, 0, 225N, 855W, 25, 1012, DB, 0, , 0, 0, 0, 0,
AL, 13, 2011083112, , BEST, 0, 236N, 865W, 30, 1012, DB, 0, , 0, 0, 0, 0,
AL, 13, 2011083118, , BEST, 0, 241N, 870W, 30, 1012, DB, 0, , 0, 0, 0, 0, 1014, 100, 75, 0, 0, L, 0, , 0, 0, INVEST, S,
AL, 13, 2011090100, , BEST, 0, 245N, 875W, 30, 1010, DB, 0, , 0, 0, 0, 0, 1014, 100, 75, 40, 0, L, 0, , 0, 0, INVEST, M,
AL, 13, 2011090106, , BEST, 0, 256N, 887W, 30, 1010, DB, 0, , 0, 0, 0, 0, 1013, 100, 75, 40, 0, L, 0, , 0, 0, INVEST, M,
AL, 13, 2011090112, , BEST, 0, 261N, 900W, 30, 1008, DB, 0, , 0, 0, 0, 0, 1013, 140, 90, 40, 0, L, 0, , 0, 0, INVEST, M,
AL, 13, 2011090118, , BEST, 0, 266N, 914W, 30, 1010, DB, 34, NEQ, 0, 0, 0, 0, 1013, 180, 75, 40, 0, L, 0, , 0, 0, INVEST, M,
Member Since: Posts: Comments:
Quoting MiamiHurricanes09:
Katia gets dangerously close to OBX on the 18z GFS. What's interesting is how both the GFS and ECMWF show Katia getting kicked out towards the northeast very rapidly. Don't really see such a sharp turn occurring...
agreed this is not an emily recurve where from north west it turn north east and east north east a recurve for katia would be from nw to nnw to north to nne kinda like irene...
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Quoting violet312s:


Same with the mets here. They would point it out but say what they should say. Too early to tell.

Question - has there ever been a year where the NC outer banks were hit by more than one hurricane?
1996 when it got hit 3 times.
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Quoting Patrap:
Interesting..

93L


Multiplatform Satellite Surface Wind Analysis

Link
hey pat! sorry to bother you but can you tell me if there is any change with 93l. i know earlier that it was looking as if it could become a depression tonight. is that still the case? are we still looking at a potential hurricane before its over with? thanks!
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Quoting MiamiHurricanes09:
Katia gets dangerously close to OBX on the 18z GFS. What's interesting is how both the GFS and ECMWF show Katia getting kicked out towards the northeast very rapidly. Don't really see such a sharp turn occurring...


This run shows Katia interacting with the remnants of 93L over the US SE. Southeasterly flow around the periphery of 93L is "capturing" Katia and pulling her farther west, while the trough lifts farther north.
Member Since: September 22, 2005 Posts: 18 Comments: 2343
Member Since: Posts: Comments:
hello TD 13


BEGIN
NHC_ATCF
invest_RENUMBER_al932011_al132011.ren
FSTDA
R
U
040
010
0000
201109012228
NONE
NOTIFY=ATRP
END
INVEST, AL, L, , , , , 13, 2011, DB, O, 2011083118, 9999999999, , , , , , METWATCH, , AL132011
AL, 13, 2011083100, , BEST, 0, 214N, 845W, 25, 1012, DB, 0, , 0, 0, 0, 0,
AL, 13, 2011083106, , BEST, 0, 225N, 855W, 25, 1012, DB, 0, , 0, 0, 0, 0,
AL, 13, 2011083112, , BEST, 0, 236N, 865W, 30, 1012, DB, 0, , 0, 0, 0, 0,
AL, 13, 2011083118, , BEST, 0, 241N, 870W, 30, 1012, DB, 0, , 0, 0, 0, 0, 1014, 100, 75, 0, 0, L, 0, , 0, 0, INVEST, S,
AL, 13, 2011090100, , BEST, 0, 245N, 875W, 30, 1010, DB, 0, , 0, 0, 0, 0, 1014, 100, 75, 40, 0, L, 0, , 0, 0, INVEST, M,
AL, 13, 2011090106, , BEST, 0, 256N, 887W, 30, 1010, DB, 0, , 0, 0, 0, 0, 1013, 100, 75, 40, 0, L, 0, , 0, 0, INVEST, M,
AL, 13, 2011090112, , BEST, 0, 261N, 900W, 30, 1008, DB, 0, , 0, 0, 0, 0, 1013, 140, 90, 40, 0, L, 0, , 0, 0, INVEST, M,
AL, 13, 2011090118, , BEST, 0, 266N, 914W, 30, 1010, DB, 34, NEQ, 0, 0, 0, 0, 1013, 180, 75, 40, 0, L, 0, , 0, 0, INVEST, M,
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1518. ncstorm
180 Hours 18Z GFS
Member Since: August 19, 2006 Posts: 13 Comments: 15666
1517. will40
180 hrs out the left bands are just off shore of obx
Member Since: September 19, 2005 Posts: 2 Comments: 4251
1515. Skyepony (Mod)
Recon is finding an interesting area. 1006.6mb at 26.633N 91.033W with some interesting wind shifts..
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1514. Patrap
catchy,, tune
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Quoting Levi32:
The models are starting to show a stronger weakness in the ridge over Louisiana before the Pacific Northwest shortwave even gets there. They keep the Texas/4-corners ridge in place, with a second high center over the southeast United States. The weakness in between is causing the models to start showing a landfall for 93L in 48-72 hours instead of 96-120 hours. This would be good news since 93L would have less time to strengthen over water, but this is also a swing within one or two models cycles, and they haven't really honed in on the situation just yet.


I'd really rather send it to Texas, since they really need it, but if we're gonna have it here, hope it gets on with it, rather than lolling around in the gulf forever. I know we're gonna get hammered with rain, but hoping to avoid high winds. I'm worried more about power outages, due to a sick elderly dad.
Member Since: Posts: Comments:
Quoting Hou77083:


I don't think Texas is getting the much needed rain.
:(


no, don't think so. It is a shame to have something this close and yet nothing.

Hopefully we will have another chance for a rain soaker storm.
Member Since: July 2, 2009 Posts: 0 Comments: 2811
Katia gets dangerously close to OBX on the 18z GFS. What's interesting is how both the GFS and ECMWF show Katia getting kicked out towards the northeast very rapidly. Don't really see such a sharp turn occurring...
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1510. ncstorm
171 hours 18z GFS
Member Since: August 19, 2006 Posts: 13 Comments: 15666
Quoting Patrap:


Hot towers...in the middle of our 'cane...
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Quoting Levi32:
The models are starting to show a stronger weakness in the ridge over Louisiana before the Pacific Northwest shortwave even gets there. They keep the Texas/4-corners ridge in place, with a second high center over the southeast United States. The weakness in between is causing the models to start showing a landfall for 93L in 48-72 hours instead of 96-120 hours. This would be good news since 93L would have less time to strengthen over water, but this is also a swing within one or two models cycles, and they haven't really honed in on the situation just yet.
hey levi i know your track for Lee is for him to take a single loop and then move north east into lousiana but what is your forecasted intensity for Lee? my track is literally the same as yours only i have lee sitting in the gulf 1 more day. my intensity if lee sits in the gulf for a while is a high end cat 1 weak cat 2 90-100mph hurricane and thoughts on katias westward shift as models forecast the bermuda high to build in strong causing katia to keep heading westerly...
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18Z GFS @ 168 hours.... He doesn't care what you think.

Member Since: September 22, 2005 Posts: 18 Comments: 2343
1506. Patrap
Interesting..

93L


Multiplatform Satellite Surface Wind Analysis

Link
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Quoting Dennis8:


I was born in Corpus Christi in 1962 and in Houston now. Family still there.


I had some good times in Corpus. I have a lot of friends there.
The Island is now very built up (North Padre Island - neighborhoods). A major hurricane could cause some serious damage out on the island. They haven't had a bad storm in a long time.
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Quoting CosmicEvents:
More like Tropics Gone Wild.


I would settle for a 93L reach around.
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Quoting HoustonWeather:


Sure

Member Since: August 26, 2006 Posts: 0 Comments: 1548
1501. DirtDan
Quoting Clearwater1:
Sure looks likes and they are pointed to FL, but that big trough is suppose to curve it nw then north. Like the GFS indicates. . . I hope.



Sorry, but I just don't see what you are. most of the models still take this thing clearly to the NW and that ULL still has a firm grip between the bermuda and atlantic highs. I'll be quite shocked if this thing gets anywhere near NC much less Florida.
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1500. Patrap
Quoting CosmicEvents:
More like Tropics Gone Wild.


I like dat un.
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1499. Dennis8
Quoting atmosweather:


The overall atmospheric pattern was different with Andrew. He was turned to the north by an extremely strong area high pressure that moved into the southeast U.S. and built pretty far eastward into the western Atlantic, with zonal flow to the north ensuring that no major troughs eroded any portion of the ridge. It's difficult to compare any historical storms with current storms because every single one is unique and comes with their own unique atmospheric conditions to work with.

Kinda like life..One day at a time huh? Each one is different.
Member Since: August 15, 2008 Posts: 0 Comments: 446
Quoting Sfloridacat5:
I think you must have crossed the border gringo!
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Quoting Patrap:
Full Frontal tropics?
More like Tropics Gone Wild.
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Quoting TexasHurricane:
channel 6 lowered our rain chances. :(


I don't think Texas is getting the much needed rain.
:(
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About

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.