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Gulf of Mexico disturbance 93L a Lousiana flood threat; Katia a hurricane

By: Dr. Jeff Masters, 3:28 PM GMT on September 01, 2011

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

Hurricane

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

Reader Comments

Quoting MississippiWx:


Gross...


No way! Lol people either say they love it or hate it.
Quoting Klolly23:


U need to make a rain turtle in the sand/dirt...aka your lawn(unfortunately). Trust the rain turtle. Joking aside you all need rain bad. Hope it's not much longer.

Last 2 times I did a rain dance with the drum, we got tornados, but I swear I didnt do Joplin! :) I am stopping the dance, but leaving windows down on the trucks & feed sitting in the back. That usually does the trick. A little something for the storm gods Maybe:)
ASCAT caught a partial of TD13 just over an hour ago. Scene type is definitely still Shear here...

Quoting hurricane23:


Horrid model. Way of with katia.


LOL...if I were in Texas...why root for a storm like Katia WAY OUT THERE when there is TD 13 at your doorstep?

I hope TD13 can bring some rain to Texas....though Levi's latest Tidbit explains it will and that death upper ridge could block its chances somewhat...

The drought has gone on for so long that it will take a lot to beat down the death ridge....
3005. GetReal
Quoting jpsb:
Is that an ULL spining on the Tx/La border?


It is a weak ULL, that is forecast to move NW tonight, or tomorrow morning. IMO that is what has been shearing this system.
Quoting MiamiHurricanes09:
LOL, I'm gonna PM you the best one...hold on.


I thought this was.
3007. JNCali
Quoting totalamature:

Last 2 times I did a rain dance with the drum, we got tornados, but I swear I didnt do Joplin! :) I am stopping the dance, but leaving windows down on the trucks & feed sitting in the back. That usually does the trick. A little something for the storm gods Maybe:)

ahhhhhhh..a little sacrifice... i like it! any volunteers??
Windsat completely missed the gulf of Mexico.
Quoting caneswatch:


I thought this was.


Tripod makes their own drinks? Huh.
Quoting KoritheMan:


Even if that were to happen, the steering pattern still favors the LA/MS area, not Florida, primarily because the first trough is forecast to bypass TD13, which should allow it to keep moving northwest until the second trough picks it up.

Yes, I can see that it should move N or NW not NE, but still, that is never a totally comfortable location for a tropical system for the Tampa Bay Area
3011. Dennis8
It appears center MAY be reforming to the southeast based on my analysis of satellite...NHC indicated system in formative stages next 12-24 hours. I will be watching EVERY frame to see if it reforming within the broad circulation center and then when the NHC experts will either confirm or deny this based on their many tools. I advise everyone to stay alert. I am a retired form the field of meteorology and got my degree from Dr. Meisner at the University of St. Thomas in Houston in the mid 1980's before the program ended there. I was with Universal Wx at Hobby and Fox 26 Houston.
Quoting atmoaggie:
Howdy, backatcha.

G'Nite, all.


Howdy. Both my parents are aggies. I on the other hand, chose Rice.
3013. Dennis8
Quoting GetReal:


It is a weak ULL, that is forecast to move NW tonight, or tomorrow morning. IMO that is what has been shearing this system.


Yes and drawing in dry air
Quoting JGreco:


But didn't Irene re-develop its center pretty far North also under her convected burst?


It did...but Irene's reformation was not a jump by 200 miles...with TD 13 there will very likely be some center consolidation toward the SE with that convective bursting...but it will not suddenly get far SE into the center of the convective burst when the burst is that far away...
Quoting TomTaylor:

Yeah..really.

I didn't know you were a met until today when you sorta threw it into my face when we were discussing recon's findings.





When it comes to that sort of thing, I respect that you're a met and have put in the time, but please don't try and use your schooling as a reason for why you're right, or why I shouldn't question your reasoning. I'm sure your classes have given you a much better understanding behind everything weather related, but it doesn't mean casual enthusiasts can't also know what they're talking about, and it certainly doesn't mean you are always right.

Maybe you didn't intend your wording to come off that way, but fats how I interpreted it when I read your post: "I'm a met, don't question me".
No, no, no, you misunderstand and I didn't make it clear. (throw-in-face and me-always-right and don't-question-me is not my style, period.)

I was talking to a PhD tropical met. A guy way, way more qualified than myself, published in cyclogenesis, etc. I barely understand him some of the time.

Sorry if you got the impression I was talking down to you or anyone else. In addition, some of the amateurs in here are better skilled at recognizing conditions, at times, in satellite loops, etc. than I am. I've acknowledged before that some of the amateurs are as knowledgeable, or more so, than most graduates in meteorology. Especially in the realm of applied meteorology and real-world situations. (Makes sense if the university was teaching all theory and the like.)
3016. JLPR2
Well now...
That deserves a Jason style WOW.
WOW!!

XD
Quoting Huracaneer:

Yes, I can see that it should move N or NW not NE, but still, that is never a totally comfortable location for a tropical system for the Tampa Bay Area


Understandable. Logically though, there is no possible way for TD13, even with a center relocation, to strike Tampa.
3019. Dennis8
Quoting want2lrn:


Since i really only read (lurk) as it is called. I had you pegged by what i perceived as a lot of knowledge. If i may a stab at your screen name. atmo=atmosphere=met, aggie=gig'em? aka HOWDY! Just my 2 cents.
.
Where are you at in Corpus? My hometown?
Quoting NCHurricane2009:


LOL...if I were in Texas...why root for a storm like Katia WAY OUT THERE when there is TD 13 at your doorstep?

I hope TD13 can bring some rain to Texas....though Levi's latest Tidbit explains it will and that death upper ridge could block its chances somewhat...

The drought has gone on for so long that it will take a lot to beat down the death ridge....


Rainfall i believe with rival that of allison when its all said and done.
3021. jpsb
Quoting Zeec94:


Here we go with the Fresca again. LOL
Lol, I think I will have a "Fresca" too.
Quoting JLPR2:
Well now...
That deserves a Jason style WOW.
WOW!!
WOW!! Did not expect that whatsoever. Might go straight to orange/red on the next TWO.
3023. WxLogic
GFS/NAM Comparison

@84HR 00Z GFS:


@84HR 00Z NAM:



Not too bad.
No significant development as long as that ULL is there.

3025. 3211976
I think the center of Katia is at 16.5N  52W and if what i am seen is true,  that is way of track.


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


WOW!! is right. It's a little low though.
3027. CCkid00
Quoting MiamiHurricanes09:
WOW!! Did not expect that whatsoever. Might go straight to orange/red on the next TWO.


which storm is that for?
3028. JLPR2
Quoting MiamiHurricanes09:
WOW!! Did not expect that whatsoever. Might go straight to orange/red on the next TWO.


Really surprised me too, wasn't expecting a closed LLC.
Quoting atmoaggie:
No, no, no, you misunderstand and I didn't make it clear. (throw-in-face and me-always-right and don't-question-me is not my style, period.)

I was talking to a PhD tropical met. A guy way, way more qualified than myself, published in cyclogenesis, etc. I barely understand him some of the time.

Sorry if you got the impression I was talking down to you or anyone else. In addition, some of the amateurs in here are better skilled at recognizing conditions, at times, in satellite loops, etc. than I am. I've acknowledged before that some of the amateurs are as knowledgeable, or more so, than most graduates in meteorology. Especially in the realm of applied meteorology and real-world situations. (Makes sense if the university was teaching all theory and the like.)
ok gotcha, you were speaking of him still. Didn't catch that part.

It's all good then, sorry for the confusion. I saw you were trying to get to bed...night, catch ya later


edit: yea, it is interesting to note that some amateur enthusiasts are better at real world application than mets who've been at school for several years now.
3030. JLPR2
Quoting nofailsafe:


WOW!! is right. It's a little low though.


Seems to be very close to the spot where Katia formed.
GFS Rainfall through 99 hours:

3032. JLPR2
Quoting CCkid00:


which storm is that for?


TW around 30W
Quoting CCkid00:


which storm is that for?
Western part of the system coming into view in the satellite image below. Near 10˚N 30˚W.

Quoting Dennis8:
.
Where are you at in Corpus? My hometown?


It is hot and humid here in Pharaoh Valley.
Quoting washingaway:
No significant development as long as that ULL is there.



The ECMWF 200 mb winds show a rather significant change in the next 24 hours with upper level winds becoming lighter and much more SW, which would reduce the shear quite a bit.
94L looking more impressive on NASA IR...looks to develop into possibly TS Lee by 5am.
3037. WxLogic
@111HR 00Z GFS:



Not a good steering for Katia to be on that close to CONUS/Bahamas.
Microwave Rain Rate would be nice right about now, don't you think?

Quoting MiamiHurricanes09:
WOW!! Did not expect that whatsoever. Might go straight to orange/red on the next TWO.



you most tell me more on why you are saying WOW about
3040. Drakoen
Quoting Skyepony:
ASCAT caught a partial of TD13 just over an hour ago. Scene type is definitely still Shear here...



Confirming 13L's poorly organized...barely closed LLC.
3041. Dennis8
Quoting want2lrn:


It is hot and humid here in Pharaoh Valley.


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? :>)
Quoting JLPR2:


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


We've all had our eyes on 93L and Katia, this new spinny thing caught us (thought perhaps not all) by surprise.
Is the 00z gfs trending west of other runs so far?
3044. jpsb
Quoting GTcooliebai:
I'll have to buy a case of that sometime.
My fresca is made in Scotland, very tasty stuff.
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.
Quoting Drakoen:


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


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


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.
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.
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.
3051. 3211976
Does any body sees this too?

Katia way of track or I am just seen visions.