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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18z GFS might have initialized with some incorrect data looks to be a garbage run.
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Quoting WeatherInterest:
Is Joe correct?
Latest from Joe Bastardi:
"East coast should not right off Katia... GFS ensembles have shifted west to 35 and 72.5 . Pattern favors east cst threat late nxt wk"


No, the word is "write" not "right"
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Quoting AtHomeInTX:


Levi's video explains it well.


thanks
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Quoting TropicalAnalystwx13:


I hope not...


i certainly hope so. Just not as a Cat 2 or higher
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1291. ncstorm
full 144 hours for CMC-12z run



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1290. Bonz
Quoting notanothergoof:
those 3 storms just gave some of the edge to florida but not a direct hit or to close to a hit the last were jeanne francis and charley in 2004


LOL. Wilma's eye came right over us and I live in Florida. Trust me, Wilma was a direct hit.
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We'll wake up 2 cat 4 Katia in the morning. Random guess cause P451 sat loop looks like a hurricane that i cant quite put my finger on...
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Quoting IKE:
Zeroing in on 93L?



Looking more and more like a SE LA/NOLA hit as a mid- to hi-level TS or weak Cat 1. hurricane  Nothing we here in Acadiana can't handle.

And...I'm sure that MS and AL would welcome the rain. NOLA and SE LA??  Not so much.

Sorry, Texas..we really did try. Maybe next storm.


Anthony
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Quoting StormSurgeon:


This whole weekend will be a bust.....BBQ off for sure. :(


I just hope power and cable stays on here so I can watch the LSU/Oregan college football opener.
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1285. hahaguy
Quoting Jebekarue:
In regards to Katia not feeling the poleward pull, if she is weak and not going to feel the pull, how come Dean and Felix were huge and cat 5 and didn't feel the pull, what is pulling the storms north this year but not those 2 in particular? tia


In 2007 The ridge was VERY strong which blocked them from moving north.
Member Since: August 12, 2007 Posts: 2 Comments: 2838
Quoting shred3590:


Here is my guess. In a disorganized system we are really looking at a series of thunderstorms. Inside the storm is primarily vertical movement. The surface winds are being drawn in to fill the void but without vertical movement. Therefore, the horizontal component of the surface winds will be greater than the horizontal component of the flight level winds. Again, this is just a guess based on my one semester of meteorology in 1990.
yes that makes sense. Combined with the fact that the sfmr estimates are usually too high with small systems in the first place.


I really have no idea what atmoaggie was trying to get at but he said he's a met so apparently I can't argue with him.
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In regards to Katia not feeling the poleward pull, if she is weak and not going to feel the pull, how come Dean and Felix were huge and cat 5 and didn't feel the pull, what is pulling the storms north this year but not those 2 in particular? tia
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Quoting galvestonhurricane:
Does anyone think there is any way that 93L could hit Texas?

Hmmmmm!!!
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2mb drop
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Quoting notanothergoof:
the last 3 days our mets said katia goes out to sea now what new models?


Throw out all the models they are worthless they change every run.
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So, September 9-11, I'm supposed to be at Topsail Beach with a bunch of teenagers. DO you guys think Coastal NC is going to be under Katia at that point?
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Quoting galvestonhurricane:
Does anyone think there is any way that 93L could hit Texas?


I hope not...
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Quoting AllyBama:


heck, I am going to have hubby drag the grill into the carport!..lol..


Think I'm going to go with a nice spread of fried shrimp, oysters and fish. Always works around here. Oops, sorry, off topic...

Any Coastal flood warnings issued yet? I haven't seen any.
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Quoting TropicalAnalystwx13:


Right when they downgrade, it decides to start organizing.


"hell hath no wrath like a woman scorned"

lol
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Quoting Gearsts:
Doesnt look close yet.
It IS Closed.
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Does anyone think there is any way that 93L could hit Texas?
Member Since: June 18, 2010 Posts: 0 Comments: 528
1270. Patrap
Member Since: July 3, 2005 Posts: 421 Comments: 127702
1269. IKE
Cloudy here...inland Florida panhandle. Humid as heck outside. East winds 10-15 mph.
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Quoting WaterWitch11:
exactly what would cause the stall of 93? anyone?

Levi's video explains it well.
Member Since: August 24, 2010 Posts: 0 Comments: 682
1266. DocBen
Gut feeling - with the weakening of Katia reudcing the poleward pull and the strengthening of the high ... look out Florida.

BTW - in regards of cyclones 'naturally' going poleward. Why to mid-latitude cyclones typically go toward the southeast?
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1264. ncstorm
Quoting tiggeriffic:
oh yay...TWC just used the term "disconcerting" as far as the models with Katia...and they just answered my question about 93L and Katia...i need a tums


I think all east coasters will need a tums after this season is over..LOL
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93L

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NEW YORK
Some historical evidence shows that a hurricane on the East Coast has also been preceded by another storm or hurricane shortly thereafter. Some of these are just storms that have affected the areas. An example of this are the years of 1815, 1850, 1954, 1964, 1972, 1985 and 1991, 1992, 1994, 1999, 2002, 2004 and 2005

NEW ENGLAND
However, an even greater history reveals that New England as a whole has seen multiple hurricane/Tropical Storm strikes. These years include 1782, 1804, 1815, 1830, 1861, 1954, 1991, 1992, 1996, 2002, 2003, 2004, 2005, 2006, 2007, 2008 and 2009
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Quoting BrockBerlin:


Thank you very much.


You're welcome. Atmoaggie will (I hope) have a more rigorous answer. I'm just an old met.
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Quoting WeatherInterest:
Is Joe correct?
Latest from Joe Bastardi:
"East coast should not right off Katia... GFS ensembles have shifted west to 35 and 72.5 . Pattern favors east cst threat late nxt wk"


No. right should be write.
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Quoting divdog:
lower pressure southeast of that location
I think it will form a center further south.
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1258. WxLogic
@12HR 18Z GFS:

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1257. Patrap
Member Since: July 3, 2005 Posts: 421 Comments: 127702
Quoting WhoDat42:


I live on this site during Hurricane season. we suppose to play sunday nite but it's looking too good, suppose to have heavy rain all weekend.
ck out levi update, scary stuff!
Maybe yall should've taken the Dallas gig!! lol


Yeah no doubt...That will be a bummer....Could have played for the Tigers Tail gate party...instead I'll be having a hurricane party...Cat 6 style!!
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1253. IKE
18Z GFS @ 12 hours....


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Quoting galvestonhurricane:
Latest computer model tracks = bad news for drought-stricken Texas.


In that case, reprogram those computers. -CTRL- -SHIFT- -WEST- .... That should do it. OK, run the models again!
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Quoting P451:
TS Katia



Right when they downgrade, it decides to start organizing.
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Notanothergoof is another goof to go poof.
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exactly what would cause the stall of 93? anyone?
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Quoting StormSurgeon:


This whole weekend will be a bust.....BBQ off for sure. :(


heck, I am going to have hubby drag the grill into the carport!..lol..
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Is Joe correct?
Latest from Joe Bastardi:
"East coast should not right off Katia... GFS ensembles have shifted west to 35 and 72.5 . Pattern favors east cst threat late nxt wk"
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Quoting galvestonhurricane:
Latest computer model tracks = bad news for drought-stricken Texas.


No, that is good news.
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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.