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 TropicalAnalystwx13:
For those who don't know, even though it is relatively old news...

* Louisiana has declared a state of emergency.


Huh? The fires? Leaking BP oil rig? The large cluster of thunderstorms in the gulf? Nagin's back?

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Quoting Drakoen:


Sorry but this cloud signature at the lower levels and convective presentation is not unique. I have seen this for storms in the beginning stages when they want to form a well defined circulation. Dvorak T numbers clearly reflect the lack of organization. I think they could have waited till tomorrow. The only reason this is a depression is because it is in the GOM near land.


I've seen blizzard watches before there was a blizzard. I've seen tornado watches before there was a tornado (by definition actually)... Why can't they issue tropical watches before there is an actual storm?

If that is indeed true... Seems like the classic definition of beuracracy to me... Procedures and policies getting in the way of common sense...
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Quoting wxguesser:

I've heard there are some areas that flood with moderate rainfall (3-5")..my guess is you would be safe to leave in the morning.


Thanks to you both. There will most certainly be at least minor flooding here, and I think my little cottage might take some water. Live about 75' off of Gause Blvd. We had a couple inches of sporadic downpours and drizzle today up to Pearl River, and the streets were hazardous even then. Cannot imagine what peak 3-5 inches an hour will do on top of a weekend-long storm.
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2292. Drakoen
If they declared 93L a duhpression. I don't see why they could have with 94L.
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NAO Forecast


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Now they're saying possibly Lee by morning, which goes along with what Levi said. I guess we'll see come the am.
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lee could be a hurricane at landfall if he gets 1 just 1 day more over water and that is very possible
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Quoting mrpuertorico:

A couple of girls some dave mathews and bucket of fried chicken :D
What could be better?
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Quoting P451:


It was flat out ridiculous to declare it IMO.

01/2345 UTC 26.4N 91.3W T1.0/1.0 13L

Really? 1.0? Does that even qualify as a tropical cyclone? A thundershower?

Has anyone taken the time to put to coordinates of the center on a satellite image? I mean I see everyone gawking at the convection 100s of miles AWAY from the center. But what about the center itself? Take into account a complete lack of vertical organization in the system? Is there even a mid level circulation?

This is a joke of a declaration. If this is what it takes to get a tropical upgrade then we would be at TD31 not TD13 right now.





This is a sprawled out area of disorganized showers and thunderstorms focused along a trof.

A couple of odd swirls decayed into a broad area of low pressure well away from any convection at all.

There was never any persistent convection over the center.

Under high shear all day.


While this may be a tropical cyclone in the coming days it is _NOT_ one right now.

If it is, as I said, we should have TD31 not TD13, and they should go back post-season and upgrade a whole slew of blobs.


I'm not trying to be rude, 451 or Drak, or anybody for that matter, but the NATIONAL HURRICANE CENTER declared it as a tropical depression. That means it IS a tropical depression, no matter what you think (Again, not being rude).
Member Since: July 6, 2010 Posts: 113 Comments: 31862
Keep gaining that latitude Katia !!
New 0 Z

Link
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Quoting mrpuertorico:

A couple of girls some dave mathews and bucket of fried chicken :D

can't afford all that...i'll stick with the southern comfort and ice...
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2282. Drakoen
LOL P451, i'm glad you see it the way I do.
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Quoting TXCaneCrasher:


Thanks Cane, I live on the Middle Texas Coast and this is the driest I have ever seen it. Not wishcasting for anything serious. Just would like a little rain every now and then


Trust me, we are still recovering here in Mississippi, not fully recovered yet, but in much better shape. I wish I had better news for the folks in TX, but this is the way I see it. The problem Texas is having is fully related to that very stron ridge on top of the state, and having another La nina winter will only mean that the dry weather will persist perhaps until 2012 Spring or even the Summer. Still it is worth to watch what will happen with potential Lee, but my fear is that even if for some reason Lee moved towards Texas it would evaporate just as Don did in the beginning of the season. I love Texas and you are all in my prayers. BTW our next president will be from there lol.
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Evening folks...

Looking at rainbow loop for TD13... anyone hazard a guess where the center is...

Maybe I missed that part of the discussion... just trying to see what everything will try to spin around.

Is that it maybe around 25.5N 88.5W?

Looking at the NHC lat/long I'm wondering if it's relocating.
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guys if we get over 21 named storms our season will be the 2nd most active on RECORD beating 1933 which had 21. i already see maria off africa so early september and already on maria. kinda reminds me of a season.. oh wait 2005 0__0
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Mike Seidel on his way to New Orleans. At least you didn't get Cantore. The mayor of NO just made some declaration, but I didn't get to hear what it was.
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For those who don't know, even though it is relatively old news...

* Louisiana has declared a state of emergency.
Member Since: July 6, 2010 Posts: 113 Comments: 31862
Quoting Jamiekins:
had to share this from Facebook



Now that is hilarious!!!! LOL!!
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2274. Drakoen
Quoting MississippiWx:


Like I said, I don't believe it's a TD yet either, but it's certainly closer than you're stating.


I guess we will agree to disagree and leave it at that.
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Quoting muddertracker:

What mixes with Fresca?

A couple of girls some dave mathews and bucket of fried chicken :D
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Sitting on the balcony of the condo we rented in Destin for this week listening to what already sounds like a major hurricane out there!

Beautiful beach weather Tuesday but the surf started getting bad yesterday and today is really bad!
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2271. Patrap
Quoting muddertracker:

What mixes with Fresca?


Southern Comfort, ice..
Member Since: July 3, 2005 Posts: 423 Comments: 127804
Quoting Jamiekins:
had to share this from Facebook



hahaha
Member Since: July 6, 2010 Posts: 113 Comments: 31862
Quoting Patrap:
Me tinks some Fla and Tex folks are a tad tropically depressed.



Try a cold Fresca.

What mixes with Fresca?
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2268. Patrap
FunkTop

Member Since: July 3, 2005 Posts: 423 Comments: 127804
Quoting TropicalAnalystwx13:
If I had to guess:

September: 6 named storms

October: 4 named storms

November: 2 named storms

December: 1 named storm??

Total: 24 named storms.



You what I kinda agree with ya, basically what I was thinking!
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Quoting HurricaneSwirl:
So many storms have had their names stolen this year.. Remember Don? We were calling him pre-Cindy. Remember Harvey? We were calling him pre-Franklin.. then pre-Gert. Remember Katia? We were calling her pre-Jose. Wouldn't be surprised if "pre-Lee" ends up being Maria and 94L steals Lee. XD
Darn storm name stealers...
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Quoting Drakoen:


Sorry but this cloud signature at the lower levels and convective presentation is not unique. I have seen this for storms in the beginning stages when they want to form a well defined circulation. Dvorak T numbers clearly reflect the lack of organization. I think they could have waited till tomorrow. The only reason this is a depression is because it is in the GOM near land.


Like I said, I don't believe it's a TD yet either, but it's certainly closer than you're stating.
Member Since: July 15, 2006 Posts: 17 Comments: 10196
2264. Walshy
Guys, I think I failed my chemistry test please pray for me tomorrow. : /

Anyway, the southern Apps could also use rain from future Lee.
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2263. Patrap
Quoting Drakoen:


Brown must have slipped Avila one.


..ooofh
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Quoting Jamiekins:
had to share this from Facebook



lol!!!
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Quoting Jamiekins:
had to share this from Facebook



lol
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Quoting Jamiekins:
had to share this from Facebook



Tea just came out of my nose hilarious
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Quoting CaneHunter031472:


I think that the trough will still pull it. The only effect would be more time over water which would translate into more strenghtening, and the landfall spot being moved to the east perhaps as far east as NOLA which is not the best case scenario. The other option which is not as likely is that it does not get pulled by the Trhough and it lingers in the GOMEX even longer, and perhaps eventually move towards Mexico in a wsw motion. Texas has a very persistent ridge anchored in place. This stubborn Ridge will deflect storms sp as far as the ridge is there TX will remain dry unfortunately, and winter is fast approaching, which by the way will be a La Niña winter similar to last winter.


Thanks Cane, I live on the Middle Texas Coast and this is the driest I have ever seen it. Not wishcasting for anything serious. Just would like a little rain every now and then
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Quoting atmoaggie:
You'd have to be near Bayou Liberty for rain to be much of an issue in Slidell.

Unless there is somewhere that street-flooding gets in houses that I don't know about...

I've heard there are some areas that flood with moderate rainfall (3-5")..my guess is you would be safe to leave in the morning.
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2257. Drakoen
Quoting Patrap:
Me tinks some Fla and Tex folks are a tad tropically depressed.



Try a cold Fresca.


Brown must have slipped Avila one.
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2256. Levi32
Quoting wunderweatherman123:

levi now that the nhc came out with their track are you going to change your single loop track or keep it for now?


Will keep it for now....loop could be very small and it would kind of look like one sweeping track, but who knows lol. We shall see.

I'm off to dinner and class for the evening. Later all.
Member Since: November 24, 2005 Posts: 635 Comments: 26585
If I was living in the Leewards , I would keep a close eye on Katia
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Quoting Jamiekins:
had to share this from Facebook



LOL LOL LOL!!! +100000000
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Quoting Patrap:
Me tinks some Fla and Tex folks are a tad tropically depressed.



Try a cold Fresca.


I don't have one, but want one!!!! :(
Member Since: July 6, 2010 Posts: 113 Comments: 31862
If I had to guess:

September: 6 named storms

October: 4 named storms

November: 2 named storms

December: 1 named storm??

Total: 24 named storms.

Member Since: July 6, 2010 Posts: 113 Comments: 31862
Quoting Patrap:


Sw La and Central La are in Drought beaucoup.

You are most certainly correct...would anyone else like a drought?
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Well i can tell you all one thing that is for certain the next 4 weeks are going to very interesting for all of us here on the doc's blog
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2247. Patrap
Me tinks some Fla and Tex folks are a tad tropically depressed.



Try a cold Fresca.
Member Since: July 3, 2005 Posts: 423 Comments: 127804
2246. Drakoen
Quoting MississippiWx:


"Isn't even close" is a bit dramatic. While it may not be a tropical depression by the book, it's certainly close. We have a closed low with organized convection on one side. Yeah, it's still sort of broad, but it's close.


Sorry but this cloud signature at the lower levels and convective presentation is not unique. I have seen this for storms in the beginning stages when they want to form a well defined circulation. Dvorak T numbers clearly reflect the lack of organization. I think they could have waited till tomorrow. The only reason this is a depression is because it is in the GOM near land.
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Quoting twincomanche:
I think tomorrow mid day would be the earliest that I would even be thinking about making a decision. This thing has little direction or strength information to know much yet.


Thank you. I am concerned because this isn't a July or even August storm. Gulf is at 88 degrees and the potential center of circulation is uncomfortably far out with weak steering winds and strong high pressure from the west. I am all too reminded of Allison's effects on Houston. The last thing we need here is a meandering 3-day tropical storm.
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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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