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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1395. Patrap
Member Since: July 3, 2005 Posts: 426 Comments: 128645
Quoting tropicfreak:


Watch your language sir.. lol.

Yes that is Irene.


Who? ;)
Member Since: July 6, 2010 Posts: 113 Comments: 32267
Recon data is showing that 93L's center is still fairly broad and there is a large area with pressures running 1008-1009mb. We need to see that tighten up for her to begin intensification. 30 knots of wind shear isn't helping.
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Quoting tropicfreak:
My question is, when will that WNW turn on Katia occur? If it doesn't happen soon enough, TS Watches may have to go up for portions of the Lessler Antillies.


She is going to approach the SW periphery of the Atlantic ridge in about 24 hours and should curve gradually to the NW through day 3. She will not affect the northern islands. After that we could see this ridge either build back westward to the N of the storm, or see a succession of mid latitude troughs continue to break it down and cause recurvature before Katia becomes a threat to any land areas.
Member Since: September 24, 2005 Posts: 33 Comments: 9265
It could go either way I guess... :)
Member Since: July 6, 2010 Posts: 113 Comments: 32267
Quoting taco2me61:
Hey Pat have you gotten any rain today????
We sure have 3 rounds of Thunderstorms....

Taco :o)


Hey Taco! Plenty of rain here today huh?
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TWC's Cantore mentioned that a potential "Lee" could influence what Katia does?? I hope Lee will put out the marsh fire......in New Orleans East(2300++) acres burned and busts the drought. I think the ground can handle it!! Cantore mentioned the dreaded double landfall.....Lee and Katia in different areas of the A-basin. Even the monkey grass has died from the drought**** Lee/93L looks like Juan from the mid-80's.
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Quoting TropicalAnalystwx13:


Holy New Avatar...


Watch your language sir.. lol.

Yes that is Irene.
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Quoting DFWjc:


Maybe I'm stupid, but if your in an area that has no water, and you get a 10+ inches of rain, wouldn't that cancel the negative amount of water we don't have now?


No, because a lot of it would be run-off if it is heavy rain.
Member Since: July 6, 2010 Posts: 113 Comments: 32267

Quoting xtremeweathertracker:

This means rain for the Golden Triangle...Channel 6 forecasters are nuts!!!


Hey neighbor! ;) Hope you're right. Lol.
Member Since: August 24, 2010 Posts: 0 Comments: 245
Quoting mynameispaul:


I just hope power and cable stays on here so I can watch the LSU/Oregan college football opener.


You just got on my good side!!! GEAUX Tigers!! No more talk about outages...
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Quoting tulsahurrcane:


If BP is sponsoring, don't eat the shrimp
LOL!
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Quoting AtHomeInTX:

Yep. It is what it is. I'm not sure everyone is clear on this. The only thing that has ever broken our droughts is tropical systems. Our rainy seasons have names like Rita, Carla, Allison, etc etc etc. Sigh. C'mon ridge! Back the F off!


LOL!!! It's ok, calm down.... The Hurricane season isn't over yet. If not this one hopefully another.

Did I do good with my pep talk? :)
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Quoting AtHomeInTX:

Yep. It is what it is. I'm not sure everyone is clear on this. The only thing that has ever broken our droughts is tropical systems. Our rainy seasons have names like Rita, Carla, Allison, etc etc etc. Sigh. C'mon ridge! Back the F off!


LOL... exactly!!
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Quoting TropicalAnalystwx13:
For those who are wanting floods rather than drought, just remember this...You can still go to the store for food, you still have a house to live in, and things like that. If your house is floating down the street, with no way to go to the store, how are you supposed to live?

Drought - Bad, but at least you have access to everything.

Flood - Bad, no access.



I guess if getting to the store is more important than your livelihood, then sure, take drought. Flash floods only last a few days. This drought has affected ALL facets of agriculture for MONTHS. Get stocked, sit on your couch, click on your computer. I'll roll the dice with rain. If you are one of those plan-challenged that your house floods every time we get two inches, then you deserve it. The rest of us, our crops, our livestock, wildlife, and foundations need rain.
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1377. DFWjc
Quoting TropicalAnalystwx13:
For those who are wanting floods rather than drought, just remember this...You can still go to the store for food, you still have a house to live in, and things like that. If your house is floating down the street, with no way to go to the store, how are you supposed to live?

Drought - Bad, but at least you have access to everything.

Flood - Bad, no access.



Maybe I'm stupid, but if your in an area that has no water, and you get a 10+ inches of rain, wouldn't that cancel the negative amount of water we don't have now?
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The weatherman in South Florida said Florida still needs to watch Katia. So those in Florida keep watching her, especially next week!
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1375. Patrap
Member Since: July 3, 2005 Posts: 426 Comments: 128645
Quoting tropicfreak:
My question is, when will that WNW turn on Katia occur? If it doesn't happen soon enough, TS Watches may have to go up for portions of the Lessler Antillies.


Holy New Avatar...
Member Since: July 6, 2010 Posts: 113 Comments: 32267
Quoting TexasHurricane:


yeah, I remember 12 saying BIG changes ahead in the weather pattern. Hmmmmm, really?

This means rain for the Golden Triangle...Channel 6 forecasters are nuts!!!


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We're having a major downpour in South Fort Myers. The rain filled up a bucket in a matter of minutes.
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1371. Patrap
Member Since: July 3, 2005 Posts: 426 Comments: 128645
18Z GFS has Katia slow waaaaay down. She's still not past 56W after 54 hours...
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Quoting bohonkweatherman:
Texas never gets several days of light rain FYI, With everything burning up or drying up Texas needs a Flood
Yep. It is what it is. I'm not sure everyone is clear on this. The only thing that has ever broken our droughts is tropical systems. Our rainy seasons have names like Rita, Carla, Allison, etc etc etc. Sigh. C'mon ridge! Back the F off!
Member Since: August 24, 2010 Posts: 0 Comments: 245
1368. Patrap
Member Since: July 3, 2005 Posts: 426 Comments: 128645
Quoting TropicalAnalystwx13:


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.
Still was better defined than 93L's. Plus they found 60mph winds. And, 97L (pre-Irene) was under the influence of <5 knots of wind shear, so I'm sure the NHC had the hope that the circulation was going to consolidate a lot faster than 93L, since it is under 20 knots of wind shear and has weak convective activity over top the circulation.

Don't get me wrong though, 93L is probably on the verge of becoming 13L.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
1366. IKE
18Z GFS @ 57 hours.....


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1365. DFWjc
Quoting TexasHurricane:


I don't speak spanish and have lived here all my life. :)


Been in Texas for 34 years and learning Spanish right now
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Quoting CosmicEvents:
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.


If BP is sponsoring, don't eat the shrimp
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My question is, when will that WNW turn on Katia occur? If it doesn't happen soon enough, TS Watches may have to go up for portions of the Lessler Antillies.
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Quoting Patrap:


Bout Half inch here Uptown


Only a dozen or so inches to go before the holiday weekend is out lol.
Member Since: September 24, 2005 Posts: 33 Comments: 9265


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Quoting notanothergoof:
could never live in texas to dry plus i dont speak spanish


I don't speak spanish and have lived here all my life. :)
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Quoting Patrap:


Bout Half inch here Uptown
pat i can finally breathe now out here in new orleans east since this rain helped out
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Quoting AtHomeInTX:

Yeah. That's what we figured. :(


yeah, I remember 12 saying BIG changes ahead in the weather pattern. Hmmmmm, really?
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1354. Patrap
Quoting taco2me61:
Hey Pat have you gotten any rain today????
We sure have 3 rounds of Thunderstorms....

Taco :o)


Bout Half inch here Uptown
Member Since: July 3, 2005 Posts: 426 Comments: 128645
For those who are wanting floods rather than drought, just remember this...You can still go to the store for food, you still have a house to live in, and things like that. If your house is floating down the street, with no way to go to the store, how are you supposed to live?

Drought - Bad, but at least you have access to everything.

Flood - Bad, no access.

Member Since: July 6, 2010 Posts: 113 Comments: 32267
Quoting WeatherNerdPR:
Site is currently overloaded. Please try again in a few minutes...
LOL Did anyone else get this message?
Also me.
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Quoting SouthDadeFish:
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!


I love canefever, have used it for about a year now.
Member Since: July 6, 2010 Posts: 113 Comments: 32267
Quoting SouthDadeFish:
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!
BAHAHHAHA Subtroical?I dont think so....
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1349. WxLogic
@48HR 18Z GFS:

Member Since: August 14, 2008 Posts: 4 Comments: 4977

Quoting TexasHurricane:
channel 6 lowered our rain chances. :(
Yeah. That's what we figured. :(
Member Since: August 24, 2010 Posts: 0 Comments: 245
Quoting 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.


Yep I think that's something a lot of people forget about. The barometric pressure should fall at any given area around .10 or .15 in Hg every afternoon.
Member Since: September 24, 2005 Posts: 33 Comments: 9265
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.
Texas never gets several days of light rain FYI, With everything burning up or drying up Texas needs a Flood
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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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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.