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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Quoting mojofearless:


I don't think I've ever seen that ad, actually. Sure you don't have some sort of malware?
Just ran all my scans earlier today clean system, i beleive it might be region or ip related adds for specific areas, like facebook does, but if upgrading memebership makes all adds go away i will do that.
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Quoting MiamiHurricanes09:
01/2345 UTC 26.4N 91.3W T1.0/1.0 13L


Well, I feel threatened. ;)
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Levi!! Where are you??
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Quoting atmoaggie:
Eh, I think you are correct about that.

Something just nagging at me about the potential...


It's not impossible because there remains the possibility that the upper level high extends a little further NE-ward and provides at least 2 outflow channels and only 5-10 kts of shear. Then we would have to consider a minimal hurricane being possible if she has at least 36-48 hours. But the big factor for me is its broad circulation and very weak core. We see this all the time with tropical cyclones, those that have very well defined banding features and a well organized core are much more likely to rapidly strengthen. Those that don't - even in near ideal conditions - tend to strengthen more gradually.
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2041. xcool
Weather Station
Eastridge Drive The Roy's, SlidellElevation
53 ft
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Quoting Levi32:


Its NW motion should get halted before it can move into the middle of Texas. I would say that getting it to even Galveston would be pushing it. But hey, there's always hope in weak steering currents.


"Go West Young Man (insert TD), GO West" Texas PLeeeeze
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Quoting Patrap:


No Im 20 ft elevation near Audubon bend by Magazine and Jefferson.

r at a Glance
Weather Station
Uptown, New Orleans
Elevation
20 ft


Glad to know that.
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2038. bappit
Quoting aquak9:

(loads BB gun with Valium)

Send me some. They had predicted high 90's and it got to 101. Started out looking hopeful. Some nice cumulus at 11 am. By noon looked like most of the moisture had mixed out. By 5 pm the cloud base was up where the cloud tops were at noon.

Still, there were a few weenie clouds ... weenie cumulus.
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2037. Patrap
Vermont showed during Irene and many other areas..being above or below sea level means diddly under the right situ.
Member Since: July 3, 2005 Posts: 421 Comments: 127631
Quoting xtremeweathertracker:
18Z GFDL HMMMM I dunno i dont think SE Texas would get a drop of rain from this!!! Sarcasm Flag: ON



I think the GFDL has a bug in the code, and keeps showing a western bias...but we will see.
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I see we have TD#13, if its anything like when it was in its beginning stages here in the NW Caribbean, could be a potent system if even just a strong TS, they all have their own personality just saying... and Lee sounds kinda of tough :)
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The tropical wave behind Katia is in a very dangerous position, around 30w and 8-9n.
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Quoting HurricaneNewb:
Oh no Columbian cupid.com is getting me in trouble with the wife tryin to tell her its an advertisement on this blog. Might be time to upgrade my membership. anyone know if the adds go away if you upgrade? Tia


I don't think I've ever seen that ad, actually. Sure you don't have some sort of malware?
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Quoting TerraNova:


I do believe the correct term is "U MAD?".


That's the pic it originated from.
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Quoting DFWjc:


AtHome would beg to differ, Taz....


as well as I taz.. regardless of the models and NHC forecast track.. this is far from being a certain hit on anywhere in LA. I wouldn't be surprised if TD13 followed the far left side of the track.
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2030. Patrap
Quoting aislinnpaps:
Patrap, you don't live in a flood zone, do you?


No Im 20 ft elevation near Audubon bend by Magazine and Jefferson.

r at a Glance
Weather Station
Uptown, New Orleans
Elevation
20 ft
Member Since: July 3, 2005 Posts: 421 Comments: 127631

Quoting aquak9:

I'm aiming for the goofball. Not the storm.
I know. The guy who posted that lives one town north of me. He just seemed a bit stressed. Lol. Aggravation with our local mets. I understand completely! :)
Member Since: August 24, 2010 Posts: 0 Comments: 680
Quoting MiamiHurricanes09:
01/2345 UTC 26.4N 91.3W T1.0/1.0 13L


lol...
Member Since: July 6, 2010 Posts: 113 Comments: 31519
Quoting HurricaneNewb:
Anyone know what the fastest a storm went from TD to hurricane is in hours?

Humberto i think. 18 hours
Paula in 2010 tied it until it was said in the post season she went from td to H in 24 hours.
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Humberto was 2007.
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Quoting hahaguy:


You mad bro?


He mad bro LOL
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01/2345 UTC 26.4N 91.3W T1.0/1.0 13L
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2023. KEEPEROFTHEGATE (Mod)
Quoting Patrap:



Down from Spring as we have been below normal in Rainfall.
don't worry thats about to get fixed
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Quoting caneswatch:


You mad.


I do believe the correct term is "U MAD?".
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2021. JLPR2
Quoting bappit:

Bermuda is land the last time I checked.


And Jose was a warm core storm. So all that stament was simply wrong. :)
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2020. laguna2
Quoting Col15thTex:


Not sure where you live, but Texas could use inches of rain NOW. With the extent of the drought a slow soaking rain will not make a dent. We need inches falling on the aquifer recharge zones. I don't think folks realize how serious Texas' plight is. This is far worse than the 1953-56 drought. Springs and creeks have dried up that were still flowing in the '50's.



I totally agree. This is NOT your usual, run-of-the-mill drought...even for Texas. This one + the hottest summer EVER (by a long shot) is almost beyond description for those who haven't endured it. Texas and the contiguous drought areas around it need a drought buster. The most likely candidate (aka SAVIOR) is a tropical cyclone. I've lived through several hurricanes and tropical storms in my 50+ years, and I can honestly say that this drought is as devastating as ANY of them including Beulah and Allen, both major storms. In fact, it may be worse because it's a slow death that rates very little attention and no relief. Whereas, with a tropical cyclone re-building can start after it's over. (And yes, there have, sadly, been plenty of deaths from this drought and heat wave also.)
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Quoting KoritheMan:


Something like this:



LOOP!
Member Since: July 6, 2010 Posts: 113 Comments: 31519
2018. scott39
Quoting fldude99:
Hopefully 13 barrels into TX. They can use the precipitation...maybe Perry can say it was a blessing...a message from Glenn Beck maybe
Blessings come in disguise all around us :)
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Patrap, you don't live in a flood zone, do you?
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2016. hahaguy
Quoting caneswatch:


You mad.


You mad bro?
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Oh no Columbian cupid.com is getting me in trouble with the wife tryin to tell her its an advertisement on this blog. Might be time to upgrade my membership. anyone know if the adds go away if you upgrade? Tia
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2014. Patrap
Member Since: July 3, 2005 Posts: 421 Comments: 127631
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Loop
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Quoting TropicalAnalystwx13:


Well what did you expect?


Something like this:

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Quoting atmosweather:


Upper air conditions are not ideal and won't be ideal even when the forecasted upper anticyclone develops in the GOM. TD 13 is also an extremely broad and ill defined system and considering the 20-30 kts of shear over her for at least the next 18-24 hours she will not be very organized once the upper pattern becomes more conducive. Therefore I think she finds it very very difficult to strengthen until at least Saturday, by which time she may only have a day to work with with land interaction also potentially impacting its development.
Eh, I think you are correct about that.

Something just nagging at me about the potential...
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Quoting KoritheMan:


Something like this:

Loop-de-loop?
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Tropical storm warning issued from LA TX border to MS AL border.
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Not so beautiful.
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2006. Patrap
Quoting emcf30:

Hey Pat, how are the river levels in your area?



Down from Spring as we have been below normal in Rainfall.
Member Since: July 3, 2005 Posts: 421 Comments: 127631
.
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Quoting twincomanche:
Give it a rest.


You mad.
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2003. Ossqss
Does anyone have the link to the barometer bob show?
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2000. Patrap
Beach Rd, Waveland,Miss October 05..

Bout 200 ft from the Bay.



Member Since: July 3, 2005 Posts: 421 Comments: 127631
1999. DFWjc
Quoting PcolaDan:


Your icon is how i feel right now...confused
Member Since: July 19, 2011 Posts: 1 Comments: 1006
1998. bappit
Quoting kilgores97:


I don't get why the TPC is so hellbent on naming storms that aren't warm core storms, like Jose (and no threat to land). Is it to pump up their numbers for some political agenda (man made global warming)?

Bermuda is land the last time I checked.
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Quoting atmoaggie:
Umm, no, I just think it could.

Not analyzing what you might have said about it.


I been doing this for awhile now since the 90s and if i was you Levi i would not say something cant happen with these Gulf coast storms more than most you will get burned
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Quoting aquak9:

I'm aiming for the goofball. Not the storm.


Hands Aqua a glass of Amaretto on the rocks. May get myself one.
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18z HWRF doesn't seem too realistic on Katia. Notice how it turns the cyclone almost towards the NNW in a matter of 6 hours. That intensity at the end of the run is bizarre.

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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.