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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3095. WxLogic
@168HR Katia getting closer to CONUS on every run:

Member Since: August 14, 2008 Posts: 4 Comments: 4881
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Quoting louisianaboy444:
Wait wait some people are saying the 00Z GFS trended East some people are saying its coming in for a landfall in Western La too many people observing the same model way different i'm confused lol link please
I'm trying.  ugh! paste in address bar i can't link

http://mag.ncep.noaa.gov/NCOMAGWEB/appcontroller? prevPage=Model&MainPage=index&image=&p age=Param&cycle=09%2F02%2F2011+00UTC&rname =SFC-LAYER+PARMS&pname=10m_wnd_precip&pdes c=&model=GFS&area=NAMER&cat=MODEL+GUID ANCE&fcast=Loop+All&areaDesc=North+America +-+US+Canada+and+northern+Mexico&prevArea=NAME R&currKey=model&returnToModel=&imageSi ze=M
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Quoting louisianaboy444:
Wait wait some people are saying the 00Z GFS trended East some people are saying its coming in for a landfall in Western La too many people observing the same model way different i'm confused lol link please


She was trending a bit east- until 120 hours into the run when she takes a complete left-hand turn and goes due west for 36 hours before resuming a NW motion.
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3091. Dennis8
Quoting want2lrn:


You would be correct was all of 13 days old when Celia hit and not yet living in Corpus. Moved here in 1980 a month after Allen. Really have not been through a significant storm. To old to change careers now, but storms are fascinating to me. Learn a lot from amateurs and pros alike on this site.


1980 graduated from King HS...Hurricane Allen I remember that one too.
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Quoting Dennis8:


Hurricane Celia 1970 - Corpus Christi

on YOUTUBE just downloaded this year will show your neighborhood devastated by Celia..you look to young to have been around but I was 8 and at CC airport the winds clocked at 161 mph....this storm was what started my wx interest and sent me on to a meteorology degree.


You would be correct was all of 13 days old when Celia hit and not yet living in Corpus. Moved here in 1980 a month after Allen. Really have not been through a significant storm. To old to change careers now, but storms are fascinating to me. Learn a lot from amateurs and pros alike on this site.
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3088. ncstorm
Quoting Huracaneer:
I can't stop watching those GFS updates and I want to got to sleep! It's like a serial thriller, will Katia get the East Coast? Stay tuned to the next GFS frame!


lol...
Member Since: August 19, 2006 Posts: 13 Comments: 13423
3087. JGreco
Quoting Levi32:
TD 13's center is moving southwest now. It may reform somewhere else tomorrow closer to where it has been all day, or else stall and start coming back north. It's not all that well-defined so it can do whatever it wants at this point.



So what do you think about the model trends trying to pull it into Texas now. Is the Death Ridge now forecast to suddenly move?
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Quoting Levi32:
TD 13's center is moving southwest now. It may reform somewhere else tomorrow closer to where it has been all day, or else stall and start coming back north. It's not all that well-defined so it can do whatever it wants at this point.


Sort of like a teenager. Messes up the house and may not have direction in life yet.
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Quoting KoritheMan:
3051.

I don't see it. Though to be fair, it is rather difficult to pinpoint circulations using infrared.


I'd say right now Katia's center is right in the middle of the 0000Z and 1200Z forecast points in this animation (click on the Trop Pts. check box at this link)

In other words...she remains dead on track with the NHC track right now if you ask me....

And HOLY SMOKES (as Jim Cantore kept saying in the Chicago thunderblizzard)...that is a heck of a convective burst!!!
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Wait wait some people are saying the 00Z GFS trended East some people are saying its coming in for a landfall in Western La too many people observing the same model way different i'm confused lol link please
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I can't stop watching those GFS updates and I want to go to sleep! It's like a serial thriller, will Katia get the East Coast? Stay tuned to the next GFS frame!
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Quoting nofailsafe:


10N at 30W on the scatterometry.



oh ok
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3081. Dennis8
Quoting JLPR2:


Really surprised me too, wasn't expecting a closed LLC.

Posted by: LRandyB, 6:24 PM GMT on September 01, 2011
And while no one is talking about it yet, there is a fairly vigorous wave just off Africa a little south of the point where Katia got going.
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3080. Seastep
Quoting GTcooliebai:
I've seen Patrap mention that, I'll have to buy a case of that sometime.


It's gross, imo.
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Quoting Tazmanian:



there nothing there lol


10N at 30W on the scatterometry.

KNMI Scatterometry Data

EUMET IR
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3078. MTWX
Quoting MississippiWx:
GFS Rainfall through 99 hours:


ove rthe course of 12 hours estimated rain fall for my area went from .5" to 5+"... this is going to be interesting!!!
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3077. Levi32
TD 13's center is moving southwest now. It may reform somewhere else tomorrow closer to where it has been all day, or else stall and start coming back north. It's not all that well-defined so it can do whatever it wants at this point.
Member Since: November 24, 2005 Posts: 628 Comments: 26454
3076. JLPR2
Quoting TomTaylor:
its worth watching, but it will have shear and upper divergence issues as Katia's outflow expands aloft around the storm, especially to the SE.


Yeah and it's lacking model support, for the moment it's just another feature to follow.
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Can someone give me the link to the 00Z GFS
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3074. jpsb
Quoting redwagon:


The ensembles are calling for a tourcane or prairiecane, like Erin, if you remember:



Except 13 goes ashore in LA. Erin went all the way across the USA as a remnant, causing extreme flooding.
That track would be perfect, rain for most of Texas and Oklahoma too, sure hope we see something like that.
Member Since: June 30, 2009 Posts: 0 Comments: 1009
Quoting SavannahStorm:



TPW showing a lot of broad spin with the African wave- also showing the axis of TD13 moving faster west than may be anticipated...



93L's track via TPW does still appear to have a westerly component to it. Winds around here are all out of the east, even Galveston. Also, compared to this time yesterday, pressure at Scholes is lower by ~2mb.
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Quoting ncstorm:


it just turn west like the euro.


Yea, I see that- nearly due west between 120 and 144 hours...
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Well, looking at the stuff coming off Africa, we are not going to have a dull moment this season (2005 flashbacks).
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Quoting Drakoen:


Yes ramp up to actual TD status lol


Well at least the local impact has been noticeable, unlike with Bonnie, where I barely experienced a wind shift as the center passed over me.
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3069. Dennis8
Quoting want2lrn:


That particular meteorologist's forecast are typically "dead wrong" but a good guy none the less.


Who do u like down there?????? The wx in Corpus is easy forecast..WINDY! I was there Christmas Eve 2004 for the 5" snowfall.
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when dos the atcf site update
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That 00z GFS is purdy scary. Gonna make another close encounter with the eastern seaboard. 6 days out:



Moving due west under that flat troughing and zonal flow courtesy of the subtropical ridge.
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Quoting JLPR2:


Might claim the 95L label later today. Not bad.
Seems to have gone under the radar, Katia and TD13 need too much attention. XD


its worth watching, but it will have shear and upper divergence issues as Katia's outflow expands aloft around the storm, especially to the SE.
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3065. Dennis8
Quoting want2lrn:


That particular meteorologist's forecast are typically "dead wrong" but a good guy none the less.


Hurricane Celia 1970 - Corpus Christi

on YOUTUBE just downloaded this year will show your neighborhood devastated by Celia..you look to young to have been around but I was 8 and at CC airport the winds clocked at 161 mph....this storm was what started my wx interest and sent me on to a meteorology degree.
Member Since: Posts: Comments:
3051.

I don't see it. Though to be fair, it is rather difficult to pinpoint circulations using infrared.
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3063. ncstorm
Quoting SavannahStorm:


Actually, seems a little east of the 18Z run, but it slows down a lot after 110 hours, so it'll be hard to tell until we get farther in the run.


it just turn west like the euro.
Member Since: August 19, 2006 Posts: 13 Comments: 13423
3062. WxLogic
@135HR Katia starting to move W for the time being:



As remnants of TD#13 develop into a cut off low and back out some with a little ridging to the N of Katia.
Member Since: August 14, 2008 Posts: 4 Comments: 4881
Quoting nofailsafe:


KNMI:



METEOSAT:




there nothing there lol
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3059. Drakoen
Quoting KoritheMan:


Drak, if TD13 ramps up in the morning, I am holding you fully responsible. ;)


Yes ramp up to actual TD status lol
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Quoting tropicfreak:
Is the 00z gfs trending west of other runs so far?


Actually, seems a little east of the 18Z run, but it slows down a lot after 110 hours, so it'll be hard to tell until we get farther in the run.
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Evening all. And we aren't gonna get much rain? Now the gfs has it more or less stalling ON  TX/LA.  HMMM.


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Quoting JNCali:

ahhhhhhh..a little sacrifice... i like it! any volunteers??

Virgins Only! oops, oh well thats the end of that! Wait we are all on the computer in the middle of the night... Maybe there's hope:)
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Quoting Tazmanian:



you most tell me more on why you are saying WOW about


KNMI:



METEOSAT:

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Quoting MiamiHurricanes09:
Indeed. Convection is finally covering the circulation as we head into DMAX. Might beat 13L to Lee.



Closed circulation on something that the NHC hasn't even mentioned in their TWO's. Not something you see everyday lol.

That system is almost better organized than 13L lol.



oh ok
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Quoting JLPR2:
Well now...
That deserves a Jason style WOW.
WOW!!

XD


Can we say “hello 95L”?
Member Since: September 2, 2006 Posts: 110 Comments: 6814
Quoting nofailsafe:


We've all had our eyes on 93L and Katia, this new spinny thing caught us (thought perhaps not all) by surprise.



TPW showing a lot of broad spin with the African wave- also showing the axis of TD13 moving faster west than may be anticipated...

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3051. 3211976
Does any body sees this too?

Katia way of track or I am just seen visions.


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Quoting washingaway:
No significant development as long as that ULL is there.



Most of the models forecast the ULL to move away to the WNW tonight and tomorrow as an upper level anticyclone develops over the GOM. Should see a better environment for gradual development by this time tomorrow.
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Quoting Dennis8:


I grew up there..many moons ago...left in 1988. Coming next weekend for my parents anniversary. I came to Houston in 1980's to study meteorology. How is Dale Nelson? :>)


That particular meteorologist's forecast are typically "dead wrong" but a good guy none the less.
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Quoting extreme236:
94L looking more impressive on NASA IR...looks to develop into possibly TS Lee by 5am.
Indeed. Convection is finally covering the circulation as we head into DMAX. Might beat 13L to Lee.



Quoting Tazmanian:



you most tell me more on why you are saying WOW about
Closed circulation on something that the NHC hasn't even mentioned in their TWO's. Not something you see everyday lol.

That system is almost better organized than 13L lol.
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3047. JLPR2
Quoting MiamiHurricanes09:
Western part of the system coming into view in the satellite image below. Near 10˚N 30˚W.



Might claim the 95L label later today. Not bad.
Seems to have gone under the radar, Katia and TD13 need too much attention. XD


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Quoting Drakoen:


Confirming 13L's poorly organized...barely closed LLC.


Drak, if TD13 ramps up in the morning, I am holding you fully responsible. ;)
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3045. MTWX
Quoting TampaSpin:
Channel 2 Loop seems to show a nice LLC developing with TD13 much further South than NHC has it currently!

I noticed that too. looks like the center is well SE of the forcast point.
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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.