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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Just got this alert from the University of Houston...

The University of Houston DPS is monitoring the Tropical Disturbance in the Gulf of Mexico. Forecasters believe this disturbance will develop into a tropical storm during the next two days. The storm is expected to stall in the Gulf of Mexico off the coast of Louisiana well into next week. Although a precise forecast remains uncertain, UH is preparing for potential heavy rain and street flooding.
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1344. DFWjc
Quoting JamesSA:


We'll take the damage. I keep seeing comments about the hard baked soil... Many do not understand the expansive clays in large areas of Central Texas... they are not hard but are light and airy like a sponge with deep cracks 2 or 3 feet deep and several inches wide in places. These soils could take 12" of rain now before there would be runoff. Areas with limestone rock are another matter, but we would be better off with flooding than what this drought is doing to us. It is death dealing drought.


I agree, rather have too much water than none at all..
Member Since: July 19, 2011 Posts: 1 Comments: 1006
1341. JamesSA
Quoting TropicalAnalystwx13:
The last thing Texas needs right now is 93L/TD #12/Lee, or whatever you want to call it. 93L promises to be a HUGE rain-maker, and torrential rains up to 20" is not good for Texas. It would cause significant flooding, and would probably be as damaging as Tropical Storm Allison (2001).

What Texas needs is several days of LIGHT rain, nothing heavy.


We'll take the damage. I keep seeing comments about the hard baked soil... Many do not understand the expansive clays in large areas of Central Texas... they are not hard but are light and airy like a sponge with deep cracks 2 or 3 feet deep and several inches wide in places. These soils could take 12" of rain now before there would be runoff. Areas with limestone rock are another matter, but we would be better off with flooding than what this drought is doing to us. It is death dealing drought.
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93L is very close to becoming a tropical or subtropical cyclone. Once shear lets off tomorrow I'm growing concerned for the development potential over those 31C+ waters. Also, TPW imagery shows a large moisture surge in the Gulf, pushing the dry air back over the continent so I don't think dry air will be too big of a problem.

I'm figuring there may be a lot of new people on the blog due to 93L or Katia, or just the fact this is a busy hurricane season. For those new or old, looking to keep up with all the images posted here and looking for the sites they come from, here is a great website that has a ton of links to computer model runs, satellite imagery, recon data, radars, wind analysis, and much more.

Link

I hope it helps!
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I have hay fields with no hay, and soybeans drying up in the fields. What exactly do I have to do to get some rain?! I have 5 dry ponds, have lost 4 calves this summer, and we finally have a storm with major precipitation show up in the Gulf and we get NOTHING?! COME ON!! Oh, and it's been over 100 degrees for fracking EVERRRRRR.
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Quoting WeatherNerdPR:
Site is currently overloaded. Please try again in a few minutes...
LOL Did anyone else get this message?


yes i did but it loaded next time i tried
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Quoting MrstormX:


If that is the case, why is it not a tropical cyclone already?


Because it still lacks a bit of organization, shear is preventing convection on the west side of the storm. However, I expect classification by 5PM tomorrow afternoon, with the most likely at 11PM or 5AM.

@Miami: They declared Irene with a VERY weak low-level circulation, probably weaker than 93L's.
Member Since: July 6, 2010 Posts: 113 Comments: 31451
Quoting notanothergoof:
what about 94 could that be a big problem? gonna track it closely the next few days to see


Should begin to move out to sea either ENE or NE later tonight or tomorrow. No threat to land and will be another colossal waste of a name just like Jose if the NHC decides to designate it lol.
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Quoting WeatherNerdPR:
Site is currently overloaded. Please try again in a few minutes...
LOL Did anyone else get this message?

lol ya
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1334. hahaguy
First time getting the "site is overloaded" message.
Member Since: August 12, 2007 Posts: 2 Comments: 2838
Hey Pat have you gotten any rain today????
We sure have 3 rounds of Thunderstorms....

Taco :o)
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Quoting TropicalAnalystwx13:
The last thing Texas needs right now is 93L/TD #12/Lee, or whatever you want to call it. 93L promises to be a HUGE rain-maker, and torrential rains up to 20" is not good for Texas. It would cause significant flooding, and would probably be as damaging as Tropical Storm Allison (2001).

What Texas needs is several days of LIGHT rain, nothing heavy.


Yeah, I live in Galv and as much as I hate to say it you are right. Steady downpours would be bad. I was in NOLA when we flooded twice in the late 80s and early 90s from just steady downpours and it was a freaking nightmare. Nobody needs this. I want just good 'ol frontal systems bringing regular rain. Is that too much to ask weather gods???
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Quoting WeatherNerdPR:
Site is currently overloaded. Please try again in a few minutes...
LOL Did anyone else get this message?


yep..
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Quoting WaterWitch11:


thanks
You're welcome. :) The HPC seems to agree with a stall.

Keeps it stalled on TX/LA for days. But it may be off shore rather than on.


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Quoting TropicalAnalystwx13:


Ummm...93L has a closed, low-level center that is steadily organizing. Latest pass from recon just found 1007 mb.


If that is the case, why is it not a tropical cyclone already?
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1327. DFWjc
Quoting TropicalAnalystwx13:
The last thing Texas needs right now is 93L/TD #12/Lee, or whatever you want to call it. 93L promises to be a HUGE rain-maker, and torrential rains up to 20" is not good for Texas. It would cause significant flooding, and would probably be as damaging as Tropical Storm Allison (2001).

What Texas needs is several days of LIGHT rain, nothing heavy.


I thought the models show 15+" for LA/MS and and 6-8" for the upper coastal Texas shores..
Member Since: July 19, 2011 Posts: 1 Comments: 1006
Quoting PennGator:
Just checking the latest models for Katia & it seems that they are trending a little to the west. With a recent ''demotion'' to a tropical storm status, I would not be terribly surprised if the trend continues w/ the upcoming model runs, as the poleward movement might not be as vigorous w/ weaker system as initially anticipated. Curious @ interaction of 93L w/ a potentially further west & south Katia? Please share any thoughts ...


93L will be out of the way long before Katia arrives anywhere near its circulation envelope. There won't be any interaction.
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channel 6 lowered our rain chances. :(
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You know it's September when you get this banner every few minutes when you upload the page lol.



Quoting TropicalAnalystwx13:


Ummm...93L has a closed, low-level center that is steadily organizing. Latest pass from recon just found 1007 mb.
Still very broad...probably why it isn't a tropical depression. No doubt that it'll be one by tomorrow afternoon, the latest.
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1323. Levi32
"Site is currently overloaded. Please try again in a few minutes...
Copyright The Weather Underground, Inc.
Employment | Contact Us | Help | Terms of Service | Advertise Here"

Wow - big day on the blogs I guess.

Recon finding pressures 2mb lower at 1008mb over a very large area. A pressure fall over an area this large is likely due to diurnal variation, which just recently reached a trough in its cycle for the day.
Member Since: November 24, 2005 Posts: 635 Comments: 26547
Nope, didn't get that message...
Member Since: July 6, 2010 Posts: 113 Comments: 31451
Quoting Chucktown:


Nothing weak about a Cat 3.
Stop with the unnessary comments, a few seconds ago wunder showed me a site overload page for a while, PLEASE WAIT SITE IS AT FULL LOAD.
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Site is currently overloaded. Please try again in a few minutes...
LOL Did anyone else get this message?
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1319. DFWjc
Quoting Chucktown:


Nothing weak about a Cat 3.


I realize but i guess i should have said not even close to a Cat 4...
Member Since: July 19, 2011 Posts: 1 Comments: 1006
Complete Update

I wonder if Katia saw a picture of someone really ugly wearing her dress... and she is going to go and get it back??

TS BUSTED FORECAST ALIBI





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Quoting FookyMonster:


O Noes!!! love it ;)
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Quoting cat6band:
Ok.....anyone familiar please feel free to answer....My band is supposed to be closing out the Shrimp and Petroleum Fest tomorrow night in Morgan City, La. Is it pretty safe to say that it's gonna be a wash out? Morgan City is about 30 miles west of Houma...TIA..
Shrimp AND Petroleum fest. It sounds like you might be better off having that rained out.
.
.

.
.
j/k....I understand the importance of both to your area.
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Quoting DFWjc:


Strong Cat 2 or a weak Cat 3


Nothing weak about a Cat 3.
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Quoting Drakoen:


I'm going to disagree and assert the notion that the system will remain fairly large.


Agree. It'd not be surprising to see a rather extensive in size tropical storm, based on the circumstances
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Quoting MrstormX:
93L barely even has a circulation and is dealing with 30kts of shear, no need to go into freak out mode yet.


Ummm...93L has a closed, low-level center that is steadily organizing. Latest pass from recon just found 1007 mb.
Member Since: July 6, 2010 Posts: 113 Comments: 31451
1311. Drakoen
Quoting kmanislander:


Hi Drak. The opportunity was too good to pass up LOL


Indeed, I thought I was the only one that would notice/get that.
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Back later
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Quoting MrstormX:
93L barely even has a circulation and is dealing with 30kts of shear, no need to go into freak out mode yet.
Not the main probleme, there well likly be major flooding even if it only stays a strong invest.
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The last thing Texas needs right now is 93L/TD #12/Lee, or whatever you want to call it. 93L promises to be a HUGE rain-maker, and torrential rains up to 20" is not good for Texas. It would cause significant flooding, and would probably be as damaging as Tropical Storm Allison (2001).

What Texas needs is several days of LIGHT rain, nothing heavy.
Member Since: July 6, 2010 Posts: 113 Comments: 31451
Was Joe writing on 150 characters or less?
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1306. DFWjc
Quoting notanothergoof:
what will katria be on monday? ts? or cat 4?


Strong Cat 2 or a weak Cat 3
Member Since: July 19, 2011 Posts: 1 Comments: 1006
93L barely even has a circulation and is dealing with 30kts of shear, no need to go into freak out mode yet.
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Quoting Drakoen:


lmao


Hi Drak. The opportunity was too good to pass up LOL
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1303. WxLogic
@24HR 18Z GFS:

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I think 93l is going to be with us for a few days if not longer. We p/u .47 of rain from a strom that came off the Gulf around 5:00 am. I sure we will see a lot more. I can give my lawn pump a break.
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1300. Drakoen
Quoting kmanislander:


No, the word is "write" not "right"


lmao
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1299. DFWjc
Quoting notanothergoof:
nope


outter bands yes, the "eye" no
Member Since: July 19, 2011 Posts: 1 Comments: 1006
Quoting notanothergoof:
get the generators ready 93l could be huge


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Quoting galvestonhurricane:
Does anyone think there is any way that 93L could hit Texas?


Certainly, but Texas as of now is on the drier side and East Texas needs rain.
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Just checking the latest models for Katia & it seems that they are trending a little to the west. With a recent ''demotion'' to a tropical storm status, I would not be terribly surprised if the trend continues w/ the upcoming model runs, as the poleward movement might not be as vigorous w/ weaker system as initially anticipated. Curious @ interaction of 93L w/ a potentially further west & south Katia? Please share any thoughts ...
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18z GFS might have initialized with some incorrect data looks to be a garbage run.
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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.