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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Get gas today, tomorrow the prices will go up.
GOM rigs being evacuated.
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194. 7544
are those highs closing off the weakness or are the joining each other to block katia and have her going west tia ?Link
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Quoting ncstorm:
12Z NOGAPS

Link
I love the second storm that comes up at 144...LOL
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I CAN'T HEAR YOU CLOUDBURST!!!!!!!!
Member Since: September 2, 2006 Posts: 110 Comments: 6874
Quoting CaneHunter031472:
Katia looks more like a strong tropical storm to me on Visible. Tha should explain why the movement to the west now according to the NHC.

It's getting sharred!
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Quoting GTcooliebai:
Anyone know whether NOAA Hurricane Hunters are going to be dropping dropsondes in the GOM to get a better idea of the surrounding environment in terms of steering?


Yes
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Quoting GatorWX:
93 could have a lot to do with the trough that eventually effects Katia.
I guess it could pump the ridge for Katia. :P
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know I have been downcasting 93L as far as tracking into Texas and I still believe that to be the case. Of course I SWORE to my wife that Ike was no threat to us as it would curve out to sea or be an East coast hit.

So even though I believe 93L will be going east to Louisiana or even as far as the Florida Panhandle it would be foolish of me not to take stock and be prepared and I would suggest everyone along the Gulf Coast does as well. Stuff in the Gulf has to hit somewhere.

So I will make sure the cars are full of gas tonight but hold off on the generator gas, water and food we always have with day one of the season. And if this thing comes even close to me, I have a tree that I HATE that I have a feeling will go down in a safe direction in the storm. (No matter what wind direction that baby is falling) My wife likes the tree but it is a Tallow which is a weed here in TX and while the shade is nice it is starting to effect my Magnolia which I like much more.

I counted 3 dead Magnolia trees this morning within 3 blocks of my house and I do not want to be number 4.
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Quoting cloudburst2011:
satellite pics show that 93L is becoming better organized and a TROPICAL DEPRESSION may be forming just s of the la coast...pressures have continued to fall and the outflow is starting to show up to the south of the center...people in se la should pay attention TROPICAL STORM WARNINGS may be issued as soon as 5pm this evening....already GALE FORCE WINDS ARE OCCURING OFFSHORE WITH SOME HEAVY RAIN BANDS..WE COULD START TO SEE SOME RAPID INTENSIFICATION SINCE THE SHEAR HAS SLACKENED UP QUITE A BIT...this is a dangerous situation developing for the northern gulfcoast.NOT JUST THE 15-20 INCHES OF RAIN NOW WE MATY HAVE DAMAGING WINDS TO DEALK WITH ALSO..i would not be surprised to see a HURRICANE WATCH ISSUED FOR THE NORTHERN GULFCOAST LATE TONIGHT OR SATURDAY...
And then it explodes into a Cat 5 as it plows into Houston-Galveston or Brownsville by mid next week.

Really...easy on the doomcasting, please.

At best, we have a hybrid/subtropical depression by tonight, slowly evolving into a subtropical storm (Lee or Marie) by this time tomorrow morning as it approaches the south LA coast.

Then, it's all up to that trough coming down through the weekend. If it successfully picks it up, then it goes into LA/MS as a mid- to high-end TS, maybe a borderline Cat 1 hurricane, then rains itself out over MS/AL as a drought buster.

If the trough doesn't pick it up, then it meanders off the LA coast for the Labor Day weekend until the Rockies ridge builds in and pushes it WSW/SW along the Texas coast...probably building it into a Cat 1 or 2 hurricane due to toasty waters, less shear, and pumping of the ridge. Maybe even Cat 3, though that's a long shot due to the close proximity to land as it rakes the TX coast.

Either way it goes, it's going to be a serious rain maiker for TX/LA/MS coast, and a decent wind maker for the offshore waters and possibly the TX coast if it doesn't lift out. (And let's not forget the isolated tornado threat, either, from the feeders coming onshore.)

Personally, I'd rather it go into TX and rain itself out there. They need the rain a hell of a lot more than we do...though we're pretty dry, too.


Anthony
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Link

sorry theres a link to it
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69Viking -  you've got mail! 
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P451,

Can you post link to the rapid fire sats? please and thankyou
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Katia looks more like a strong tropical storm to me on Visible. Tha should explain why the movement to the west now according to the NHC.

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Quoting 69Viking:


Highly unlikely along the Gulf Coast, wouldn't be the first time a system spun up there and gave us only a day or two to prepare. I'd say Florida and anywhere along the Gulf Coast are better prepared than anyone when it comes to Hurricanes, no worries!


Ask the relatives of those who lost their lives in Allison over 10 years ago in Houston.
Any tropical system with that much rain can lead to a loss of life. Especially with little warning...even in Texas and the Gulf States.
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Quoting cloudburst2011:



NO I DONT THINK SO WE ARE NOT A WASHINGTON DC THREAT...WE ARE THE PEONS HERE...
LOL, Cloudburst well than I guess we should turn off the tv & shutdown our computers & wait for the storm to blindside us


{Sarcasm Flag:On}
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Quoting will40:



hopefully it shows now it did in preview



Nope. Still a black screen.
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Quoting Minnemike:
suppose this could be bad in the long run, regarding a CONUS hit... weak system more likely to travel due.. everybody now!


West of due west?
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Quoting ncstorm:
12Z NOGAPS

Link


interesting eh?
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hopefully it shows now it did in preview
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Quoting GatorWX:
ok, well lets try again:



Possible, but would have to be a much shallower trough than GFS and Euro!


i do not like that graph...
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93 could have a lot to do with the trough that eventually effects Katia.
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Quoting P451:


It's up now. Remember that the data lags about 30 minutes up to 60 minutes with Google Earth. It's not real-time.

thanks bro
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171. jpsb
Quoting P451:


Improve? Not in the near term consult some wide view WV imagery and you'll see what is coming for her. Katia is heading for increasingly hostile conditions.

She may even decouple at this rate.

I don't see her getting past those 2 ULL intack. She's eating dry air and getting ripped big time by shear and there is more to come.
Member Since: June 30, 2009 Posts: 0 Comments: 1174
ok, well lets try again:



Possible, but would have to be a much shallower trough than GFS and Euro!
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Anyone know whether NOAA Hurricane Hunters are going to be dropping dropsondes in the GOM to get a better idea of the surrounding environment in terms of steering?
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This is the only thing right now that would make me say hmmm! Obviously not the consensus, but when storms are a week out and east of the islands, nothing is set in stone.

Sorry guys, had to do it! lol, going west baby!

NOGAPS @ 144hrs

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164. 7544
Quoting will40:



12z GFS on crack


t your post always show black screen ?/????
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Most of us along the Gulf Coast/Panhandle have our emergency supplies ready ALL the time. 
We would have to secure the boat & move some plants inside - generator is ready to go... We are prepared.
Quoting 69Viking:


Highly unlikely along the Gulf Coast, wouldn't be the first time a system spun up there and gave us only a day or two to prepare. I'd say Florida and anywhere along the Gulf Coast are better prepared than anyone when it comes to Hurricanes, no worries!

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12Z NOGAPS

Link
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Thanks for the update....however, it looks like 93 will not do TX any favors.
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192 Hours

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158. IKE
Looks like the 12Z GFS has 93L picked up by the trough swinging into the SE USA....
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Quoting HurricaneHunterJoe:
Has NHC cancel Teal 70 HH flight into GOM? Didn't see it,but it's not on Google Earth yet and it's supposed to take off at 1630Z.


Hurricane Hunters just took off

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156. 7544
Quoting GatorWX:


no about track change, they'd only dg to 70, wouldn't amount to anything different in the grand scheme of things and conditions are only going to improve.



oh ok thanks for the answer
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12z GFS on crack
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Quoting DocBen:
Seems like 93 is in a perfect location to explode. Very warm waters under and around it.


Three words that will keep it from exploding now or any time soon - most likely....

Extreme Dry Air
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Steady breeze blowing in SW LA north of Lake Charles.
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152. IKE
12Z GFS @ 102 hours...


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Rita is Neil Frank still on the air in Houston?
He has to be at least 80 now. I remember when he ran the NHC.
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FEMA problems portend a major problem if anything hits ANY US coast from here forward. A Congress in gridlock is just going to make it worse. Living on the FL coast (I do) makes me wonder, though I just got back from CT yesterday and it is still bad there... Thanks everybody for the insightful information on this blog...
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Has NHC cancel Teal 70 HH flight into GOM? Didn't see it,but it's not on Google Earth yet and it's supposed to take off at 1630Z.
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Quoting tiggeriffic:
I have a silly question....in Dr Ms blog it said this

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,

so what about the states between FL and NC? what are the chances it would hit in that region


Webpage
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that is farther west with Katia

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Katia a cat 4
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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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