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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I'm surprised I have not heard "Katia is going to Florida" yet!
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Quoting Levi32:


Well the monsoon trough portion of the ITCZ is still there from Africa to 40W...not sure why it's not analyzed this morning. From that point, the trade winds from 40W into the Caribbean are actually all southeasterly, and there is little sign of northeast trades meeting them, which is the definition of the ITCZ boundary. Part of this is likely due to Katia messing up the northeast trade wind flow in the central Atlantic. Also, pressure have been much higher than normal near and just north of the equator recently, with below-normal pressures in the SW Atlantic. This would tend to shift the ITCZ farther north than normal in a very active position, but due Katia and so much low pressure in the SW Atlantic, the trade wind flow is getting distorted and thus there is no real solid convergence zone. In reality though, this pattern is a very active one.

img
Levi do we need to be prepare here in Puerto Rico src="http://www.esrl.noaa.gov/psd/map/images/fnl/s lptrop_07b.fnl.gif" style="max-width: 501px; width: 500px; ">

Levi do we need to be prepare here in Puerto Rico for the visit of Katia???
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Quoting IKE:
This should clear it up...




One of them is bound to be right.
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Quoting IKE:
This should clear it up...




Unfortunately, most of the models have shifted away from Texas this afternoon.
Member Since: July 15, 2006 Posts: 17 Comments: 10253
Quoting hurricanehanna:

Lee-on is getting larger


LMAO!
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Levi, could 93 get big and we may could get more rain than they may be thinking right now? I am in SE TX about 10-15 min from the LA border.

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Recon found a broad center with westerlies, but the area of lowest pressures (~1010mb) is very large. We saw this with Irene. It will take a while to consolidate that into a tight low worthy of classification.

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clouds rolling in & winds picking up over here. (Lafayette)
My inlaws live in Cameron Parish, which is SW Louisiana. Rita & Ike wiped them out. Looks like I'll be heading over there tomorrow to help them pack up. I realize this one won't be nearly as bad, but they don't take ANY chances anymore.
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Quoting MississippiWx:


We don't need to use satellite estimates when we have an actual plane in the system. If the NHC feels that the convection is sufficient enough, it will be TD13 at 5pm. It's a sheared system for sure, but we'll see. I think it will warrant an upgrade, especially considering the proximity to land.
If the model guidance solidifies a little more, I'd expect a TS watch for coastal LA, too.

(Doesn't require a landfall, only possible TS conditions in 48-? hours).
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@240HR ECMWF 12Z:



Shoots NE... I'm not quite buying that sharp turn.
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New Orleans
NEXRAD Radar

Type
Velocity Azimuth Display Wind Profile ° Elevation
Range
124 NMI

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633. IKE
This should clear it up...


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Plenty of west winds...

Member Since: July 15, 2006 Posts: 17 Comments: 10253
Quoting MississippiWx:


No, probably won't be for another month.
hard to find a cv storm that affected the conus after sept 15
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Quoting Levi32:


Well no...just because we know where it is now doesn't mean we know where it's going to make landfall.

I'd describe conditions this weekend and early next week to be "good," but not excellent. Restricted upper-level outflow and possible dry air entrainment may both be negative issues, but it is sitting atop sizzling water.
I hope I dont end up on the E side of whatever 93L is going to be. Hopefully Mother Nature will give Texas a break.
Member Since: June 13, 2009 Posts: 0 Comments: 6784
Quoting pottery:
Hi, Levi, if you are on...

I find it very strange that the ITCZ is almost non-existent right now....
Apart from a wave in the East Atl, nothing for a couple of days.

Any idea on this?
Why it should be so?
Dont recall seeing this in Aug/Sept before.

Thanks!


Well the monsoon trough portion of the ITCZ is still there from Africa to 40W...not sure why it's not analyzed this morning. From that point, the trade winds from 40W into the Caribbean are actually all southeasterly, and there is little sign of northeast trades meeting them, which is the definition of the ITCZ boundary. Part of this is likely due to Katia messing up the northeast trade wind flow in the central Atlantic. Also, pressures have been much higher than normal near and just north of the equator recently, with below-normal pressures in the SW Atlantic. This would tend to shift the ITCZ farther north than normal in a very active position, but due to Katia and so much low pressure in the SW Atlantic, the trade wind flow is getting distorted and thus there is no real solid convergence zone. In reality though, this pattern is a very active one.

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Quoting Levi32:
Some of the 12z GFS ensembles get Katia to 75W before curving out. The threat to the U.S. is not yet over, so it should be watched closely. The pattern is a dangerous one, but I still feel that Katia will be too far north by the time she gets to the west and will end up escaping between Cape Hatteras and Bermuda. Lee (or Maria?) should help with that.



thats not good at all..
Member Since: August 19, 2006 Posts: 13 Comments: 15311
Quoting bohonkweatherman:
Watch out for major flooding if that area gets as much rain as they are predicting. Predictions of over 15 inches.
Quoting txag91met:


It won't be too bad...but expect power outages.
Umm, this person said "south Louisiana, lower than NOLA" and might live in a place where storm surge from whatever NAM and ECMWF is spinning up could be a real problem.

NolaJoniW, take note of anything your emergency manager in your parish puts out. Visit your parish website.
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Hi everyone...

Just filled up my car. Not really sure why, but I did.

Any model updates on 93L?
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Wishcasting for all of you in Texas, at least enough water for a reservoir refill.
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Quoting DocBen:
Two inter-related things seem to be happening out in the Atlantic that could push Katia into the US. The mid-Atlantic high seems to be holding up well and extending towards the CONUS. And, the trof that had seemed to be off the coast has closed off into a low - and an invest if its own. I have a feeling Katia may keep going due west for a while.


Given the model trends west I would say this is not a set in stone fish storm just yet. The LLC is racing westward, which is a good thing in terms of it intensifying rapidly. However, a rapidly intensifying Katia would tend to move more poleward, so it is a catch-22.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
Quoting Levi32:
Some of the 12z GFS ensembles get Katia to 75W before curving out. The threat to the U.S. is not yet over, so it should be watched closely. The pattern is a dangerous one, but I still feel that Katia will be too far north by the time she gets to the west and will end up escaping between Cape Hatteras and Bermuda. Lee (or Maria?) should help with that.



I have a suspicious feeling that Katia won't be as far north as predicted.
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Quoting MississippiWx:


We don't need to use satellite estimates when we have an actual plane in the system. If the NHC feels that the convection is sufficient enough, it will be TD13 at 5pm. It's a sheared system for sure, but we'll see. I think it will warrant an upgrade, especially considering the proximity to land.


Possibly, the estimates still matter to some extent as part of the definition of a TC is organized deep convection...however, perhaps the T-numbers would be higher when initialized with the center location that we see now.
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583. ncstorm 6:48 PM GMT on September 01, 2011

lol..good one
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Quoting hahaguy:


That proves women can't drive LOL.

lol
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Quoting Patrap:
Look at the Growth rate in the Channel 4 IR..

Floater - Infrared Channel 4 Loop

Lee-on is getting larger
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Wet from Mobile to Morgan City and further..


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Quoting carcar1967:
Looking like the 3 year curse my daughter has on Louisiana is happening again.
When she was born on 8/29/02, hurricane Lili hit LA about a month later.
Three years later on her birthday, Katrina hit LA on her birthday.
Three years after that, Gustav hit LA on Sept 1st.
Now it has been three years and LA has yet another Potential hurricane at its door step.
When will the curse end??????
It is your fault, like my parents. You planned us to be born at a time when hurricane season is starting to peak. You also moved us on the Gulf Coast. Lol Im just giving you a hard time. My B-day is 8/26
Member Since: June 13, 2009 Posts: 0 Comments: 6784
Will this hurricane hunter data make it into the 18z model runs or the 0z runs?
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Morning everyone

While everyone is eyeballing 93L, 94L has pretty much lost all hopes of becoming named




Shear has pushed the small thunderstorm activity well off from the LLC. We'll see if some more convection tries to fire up, but it is looking unlikely at the moment given the hefty shear values, which are only forecasted to increase. SSTs will also become too cool in about 36 hrs.
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Lee may be north of Bermuda - and Maria preparing to visit Cajun land.
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getting some weak W winds....could be closing off
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Quoting TheNewGuy:
Seem's like a very weak circulation

Might not even get a VDM



Quoting extreme236:
I just don't see how they could classify this even with a closed circulation. It has no organization at all according to satellite estimates. It should be at least T1.5.

01/1745 UTC 26.6N 90.8W TOO WEAK 93L -- Atlantic


Danny (09) looked more pathetic than this and it was classified
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Quoting scott39:
1) Whenever the NHC determines the true center and how far W 93L tracks, will that determine where on the Gulf Coast 93L makes landfall? 2) What are the conditions going to be in the GOM starting on Friday until Wednesday? Fair, moderate, or rocket fuel for a TC?


Well no...just because we know where it is now doesn't mean we know where it's going to make landfall.

I'd describe conditions this weekend and early next week to be "good," but not excellent. Restricted upper-level outflow and possible dry air entrainment may both be negative issues, but it is sitting atop sizzling water.
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Quoting extreme236:
I just don't see how they could classify this even with a closed circulation. It has no organization at all according to satellite estimates. It should be at least T1.5.

01/1745 UTC 26.6N 90.8W TOO WEAK 93L -- Atlantic


We don't need to use satellite estimates when we have an actual plane in the system. If the NHC feels that the convection is sufficient enough, it will be TD13 at 5pm. It's a sheared system for sure, but we'll see. I think it will warrant an upgrade, especially considering the proximity to land.
Member Since: July 15, 2006 Posts: 17 Comments: 10253
Orleans
Coastal Flood Watch, Flash Flood Watch
Statement as of 12:00 PM CDT on September 01, 2011

... Coastal Flood Watch remains in effect through Saturday
evening...

A coastal Flood Watch remains in effect through Saturday evening.

* Coastal flooding: tides are currently running 1 to 2 feet
above normal this morning. Tides are expected to continue to
rise to 2 to 3 feet above normal. Tides are expected to be
highest in areas bordering Lake Borgne and along the Hancock
County Mississippi coast. Tides could be significanly higher
if the surface low becomes stronger than currently expected or
is much closer to the region.

* Timing: the highest tides are expected to begin Friday and
last through the weekend.

* Impacts: the high tide levels may produce flooding in low
lying areas outside of hurricane protection levees in
southeast Louisiana and in low lying areas along the
Mississippi coast and Lake Pontchartrain. This will cause
inundation of mostly secondary roadways. These higher tide
levels will also inhibit drainage of area rivers.

Precautionary/preparedness actions...

A coastal Flood Watch means that conditions favorable for
flooding are expected to develop. Coastal residents should be
alert for later statements or warnings... and take action to
protect property.



32


1154 am CDT Thu Sep 1 2011

... Flash Flood Watch remains in effect through Sunday evening...

The Flash Flood Watch continues for

* portions of southeast Louisiana and southern Mississippi...
including the following areas... in southeast Louisiana...
Assumption... lower Jefferson... lower Lafourche... lower
Plaquemines... lower St. Bernard... lower Terrebonne...
Orleans... St. Charles... St. James... St. John The Baptist...
upper Jefferson... upper Lafourche... upper Plaquemines... upper
St. Bernard and upper Terrebonne. In southern Mississippi...
Hancock... Harrison and Jackson.

* Through Sunday evening

* efficient and torrential tropical rains are beginning to develop
this morning and will continue to impact the mid-Gulf region
through the Labor Day weekend. Rain rates of 1 to 3 inches per
hour can result in flash flooding and general ponding of water
in streets. Model estimates and the NOAA Hydrometeorological
Prediction Center indicates an average of 10 inches may occur
this weekend across the watch area. Localized higher amounts 15
to 20 inches are possible... depending on future developments of
the Gulf system into early next week.


Precautionary/preparedness actions...

Residents and businesses in the watch area should ensure that
drainage ditches... catch basins... and culverts are cleared of
debris before rains onset to allow for adequate drainage.

A Flash Flood Watch means that conditions may develop that lead
to flash flooding. Flash flooding is a very dangerous situation.

You should monitor later forecasts and be prepared to take action
should flash flood warnings be issued throughout the weekend.
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Quoting Patrap:
Look at the Growth rate in the Channel 4 IR..

Floater - Infrared Channel 4 Loop


It's exploding!
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Quoting NolaJoniW:
Levi,
I just recently moved out if my parents house. I live in south Louisiana...lower than new Orleans. Should I start preparing with food and candles and things...is it even going to get that bad?
Watch out for major flooding if that area gets as much rain as they are predicting. Predictions of over 15 inches.
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Two inter-related things seem to be happening out in the Atlantic that could push Katia into the US. The mid-Atlantic high seems to be holding up well and extending towards the CONUS. And, the trof that had seemed to be off the coast has closed off into a low - and an invest if its own. I have a feeling Katia may keep going due west for a while.
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Observation Time: Thursday, 18:34Z
Radar Capability: Yes
Aircraft Altitude: Below 10,000 meters
Coordinates: 25.6N 90.9W
Location: 307 miles (494 km) to the S (190°) from New Orleans, LA, USA.
Turbulence: None
Conditions Along Flight Route: In the clear
Pressure Altitude: 460 meters
Flight Level Wind: From 280° at 8 knots (From the W at ~ 9.2 mph)
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Quoting tatoprweather:
Sorry for the question but...it's the CV season over?



nop not even c close
Member Since: May 21, 2006 Posts: 5091 Comments: 115131
600. JLPR2
Quoting tatoprweather:
Sorry for the question but...it's the CV season over?


Cv season runs till late September.
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Quoting ncstorm:


now come on, Lee is in the GOM with a busted GPS and wont ask for directions...


True.
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Some of the 12z GFS ensembles get Katia to 75W before curving out. The threat to the U.S. is not yet over, so it should be watched closely. The pattern is a dangerous one, but I still feel that Katia will be too far north by the time she gets to the west and will end up escaping between Cape Hatteras and Bermuda. Lee (or Maria?) should help with that.

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Looking like the 3 year curse my daughter has on Louisiana is happening again.
When she was born on 8/29/02, hurricane Lili hit LA about a month later.
Three years later on her birthday, Katrina hit LA on her birthday.
Three years after that, Gustav hit LA on Sept 1st.
Now it has been three years and LA has yet another Potential hurricane at its door step.
When will the curse end??????
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Quoting tatoprweather:
Sorry for the question but...it's the CV season over?


CV season usually ends near the end of September.
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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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