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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1945. Patrap
Member Since: July 3, 2005 Posts: 420 Comments: 127543
Quoting atmoaggie:
I am not sold that a strong cat 1 cannot come from this in ~36 hours, a la Humberto.

Just seems ripe enough, to me.


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.
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1943. JLPR2
Katia, 13, 94L and these two...

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1942. Levi32
Quoting atmoaggie:
? Monday? Who said anything about Monday?


I did? I'm confused. I said it would be a hurricane if it was still over water Monday, but not before. It appeared that you misunderstood and thought that I thought this would pull a Humberto.
Member Since: Posts: Comments:
lived in deltona florida for charley . Deltona was nothing but pine trees. eye moved through us. 90 sustained gusting 100 plus with many tornados.... not a pine tree left..... almost month without power
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1940. hahaguy
Quoting DFWjc:


I've got an unused grenade on my desk AtHome..


Sold!
Member Since: August 12, 2007 Posts: 2 Comments: 2838
Quoting atmoaggie:
Foundation crackers...after they fall through the house.
Quoting Patrap:
Bucktown,,post K 6years ago.

Big uns.



Sure that aint cypress trees or lolly leaf pines Pat? kinda blurry, I have never seen a Pine uproot. They always break about 5 foot up. Looks like a bounch of splinters!
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Ugh!  Got your rubber boots ready?
Quoting Patrap:
Gov. Declares State Of Emergency For Tropical Disturbance

POSTED: 6:26 pm CDT September 1, 2011
UPDATED: 6:40 pm CDT September 1, 2011

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(0)


NEW ORLEANS -- Louisiana's governor has declared a state of emergency as a slow-moving area of storms lumbers toward the state from the Gulf of Mexico, bringing the possibility of flash floods and stormy seas.
Gov. Bobby Jindal says the National Weather Service is not predicting a hurricane but says a tropical storm is likely and could dump 12 to 15 inches of rain onto coastal and inland areas over the next 48 hours.
Charlotte Randolph, president of low-lying Lafourche Parish, also declared a state of emergency Thursday, saying coastal parts of the parish might get up to 18 inches of rain through Monday.
Jindal says the emergency he declared will last through Friday.


Read more: http://www.wdsu.com/weather/29054910/detail.html#i xzz1WkTnA9FW

Member Since: Posts: Comments:
1936. Levi32
Quoting galvestonhurricane:


Any chance this could track further west towards SE/E Texas?


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.
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1935. mig123
I hope your right!!


Quoting atmosweather:


Impossible to tell because all storms are unique and come with different set of circumstances in different atmospheric patterns. Those who are trying to make it seem like Katia is the second coming of Hurricane Andrew are clutching at straws. There are SOME similarities with the first 2 DAYS of the overall synoptic history...that's all. There is not, however, going to be an unusually strong and deep area of high pressure stretching from MS to the western Atlantic to steer Katia towards Florida after reaching the western Atlantic, like there was with Andrew. There was an amazing amount of large scale changes that affected Andrew that were extremely lucky for the storm and were also unusual for the time of year.
Member Since: Posts: Comments:
1934. vince1
Quoting DFWjc:


I've started watering my Apartment roof and my neighbors said i was crazy, the next day they started doing it too...

Only to have it evaporate within the hour?
Member Since: Posts: Comments:
1933. aquak9
(grabs Jug'o'Haldol and rocket launcher)
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1932. DFWjc
Quoting AtHomeInTX:

Ummm? Could you...um....can I get in on that?  :D


I've got an unused grenade on my desk AtHome..
Member Since: July 19, 2011 Posts: 1 Comments: 1006
Quoting Levi32:


Hmm? Monday is 96 hours from now.
? Monday? Who said anything about Monday?
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1930. Patrap
Gov. Declares State Of Emergency For Tropical Disturbance

POSTED: 6:26 pm CDT September 1, 2011
UPDATED: 6:40 pm CDT September 1, 2011

Email Print
Comments
(0)


NEW ORLEANS -- Louisiana's governor has declared a state of emergency as a slow-moving area of storms lumbers toward the state from the Gulf of Mexico, bringing the possibility of flash floods and stormy seas.
Gov. Bobby Jindal says the National Weather Service is not predicting a hurricane but says a tropical storm is likely and could dump 12 to 15 inches of rain onto coastal and inland areas over the next 48 hours.
Charlotte Randolph, president of low-lying Lafourche Parish, also declared a state of emergency Thursday, saying coastal parts of the parish might get up to 18 inches of rain through Monday.
Jindal says the emergency he declared will last through Friday.


Read more: http://www.wdsu.com/weather/29054910/detail.html#i xzz1WkTnA9FW
Member Since: July 3, 2005 Posts: 420 Comments: 127543
1929. ackee
Quoting MississippiWx:
The center is probably going to feel a nice tug by this convection north of the Yucatan. Shear is a good deal lower the farther south you go in the Gulf, so if the center tries to reform a little farther southeast it might could keep the convection closer.

agree
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1926. mig123
im scared....Katia reminds me of Andrew.... Us here in florida need to get ready...
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1925. Levi32
Quoting atmoaggie:
I am not sold that a strong cat 1 cannot come from this in ~36 hours, a la Humberto.

Just seems ripe enough, to me.


Hmm? Monday is 96 hours from now.
Member Since: Posts: Comments:
Quoting mig123:
is Katia taking andrews path ??


Impossible to tell because all storms are unique and come with different set of circumstances in different atmospheric patterns. Those who are trying to make it seem like Katia is the second coming of Hurricane Andrew are clutching at straws. There are SOME similarities with the first 2 DAYS of the overall synoptic history...that's all. There is not, however, going to be an unusually strong and deep area of high pressure stretching from MS to the western Atlantic to steer Katia towards Florida after reaching the western Atlantic, like there was with Andrew. There was an amazing amount of large scale changes that affected Andrew that were extremely lucky for the storm and were also unusual for the time of year.
Member Since: Posts: Comments:
Holy cow, it's gonna rain in Louisiana for the next 4-5 days?

Good luck w/ that.
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Quoting aquak9:

(aims, misses horribly. Dumps out Valium. Reloads with Thorazine.)
Ummm? Could you...um....can I get in on that?  :D
Member Since: August 24, 2010 Posts: 0 Comments: 676
1920. Dakster
Quoting aquak9:

(aims, misses horribly. Dumps out Valium. Reloads with Thorazine.)


Dakster passes water dog a .45.. Fully loaded...

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Quoting Levi32:
NHC track follows the model consensus into western Louisiana in 48 hours. This short of a time over water means a moderate tropical storm is all TD 13 would get to, making it a big water storm, dumping over a foot of rain in LA. Any slowing of this track or meandering in the NW gulf could result in a stronger storm. As I said this morning, if it's over water on Monday, it should be a hurricane. If it goes ashore before that, it's just a tropical storm.



Any chance this could track further west towards SE/E Texas?
Member Since: June 18, 2010 Posts: 0 Comments: 528
Quoting doorman79:


Yea, ya'll got some big pines in your neck of the woods!

Foundation crackers...after they fall through the house.
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The center is probably going to feel a nice tug by this convection north of the Yucatan. Shear is a good deal lower the farther south you go in the Gulf, so if the center tries to reform a little farther southeast it might could keep the convection closer.

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Pretty handy for watching storms roll in all over the world Link
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1914. Patrap
Bucktown,,post K 6years ago.

Big uns.

Member Since: July 3, 2005 Posts: 420 Comments: 127543
1913. doubtit
Quoting notanothergoof:
gonna stayed glued to the weather channels here in florida and heed the warnings


I smell a TROLL, do you have a brother named Jason?
Member Since: Posts: Comments:
Quoting Levi32:
NHC track follows the model consensus into western Louisiana in 48 hours. This short of a time over water means a moderate tropical storm is all TD 13 would get to, making it a big water storm, dumping over a foot of rain in LA. Any slowing of this track or meandering in the NW gulf could result in a stronger storm. As I said this morning, if it's over water on Monday, it should be a hurricane. If it goes ashore before that, it's just a tropical storm.

I am not sold that a strong cat 1 cannot come from this in ~36 hours, a la Humberto.

Just seems ripe enough, to me.
Member Since: Posts: Comments:
1911. aquak9
Quoting notanothergoof:
gonna stayed glued to the weather channels here in florida and heed the warnings

(aims, misses horribly. Dumps out Valium. Reloads with Thorazine.)
Member Since: Posts: Comments:
Quoting Patrap:



What most never understand,itsa da water, not the Wind.

That DOES say two feet of rain on NOLA in 5 days, doesn't it. Good lord.
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1907. Patrap
Quoting emcf30:


Yep, just ask the folks up in the NE



V hull..good for the Burbs, keep the lower unit High though
Member Since: July 3, 2005 Posts: 420 Comments: 127543
1906. Walshy
Member Since: Posts: Comments:
Quoting atmoaggie:
For most...

Up here in the piney woods, a.k.a. the hills, wind more of a problem.


Yea, ya'll got some big pines in your neck of the woods!

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Member Since: June 18, 2010 Posts: 0 Comments: 528
1903. Levi32
NHC track follows the model consensus into western Louisiana in 48 hours. This short of a time over water means a moderate tropical storm is all TD 13 would get to, making it a big water storm, dumping over a foot of rain in LA. Any slowing of this track or meandering in the NW gulf could result in a stronger storm. As I said this morning, if it's over water on Monday, it should be a hurricane. If it goes ashore before that, it's just a tropical storm.

Member Since: Posts: Comments:
SHOWER ACTIVITY ASSOCIATED WITH A LOW PRESSURE SYSTEM LOCATED ABOUT
500 MILES SOUTH OF HALIFAX NOVA SCOTIA HAS NOT BECOME ANY BETTER
ORGANIZED DURING THE PAST SEVERAL HOURS. HOWEVER...THIS SYSTEM IS
PRODUCING WINDS OF TROPICAL STORM FORCE...AND ONLY A SLIGHT
INCREASE IN ORGANIZATION COULD RESULT IN THE FORMATION OF A
TROPICAL STORM. THE LOW IS MOVING LITTLE AT THIS TIME...BUT SHOULD
BEGIN TO MOVE NORTHEASTWARD AT 10 TO 15 MPH TONIGHT. THIS SYSTEM
HAS A MEDIUM CHANCE...40 PERCENT...OF BECOMING A TROPICAL CYCLONE
DURING THE NEXT 48 HOURS.
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1900. emcf30
Quoting Patrap:



What most never understand,itsa da water, not the Wind.


Yep, just ask the folks up in the NE

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1899. Patrap
Superdome Budweiser, 38F last report
Member Since: July 3, 2005 Posts: 420 Comments: 127543
000
ABNT20 KNHC 012354
TWOAT

TROPICAL WEATHER OUTLOOK
NWS NATIONAL HURRICANE CENTER MIAMI FL
800 PM EDT THU SEP 1 2011

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

THE NATIONAL HURRICANE CENTER IS ISSUING ADVISORIES ON TROPICAL
STORM KATIA...LOCATED ABOUT 930 MILES EAST OF THE NORTHERN LEEWARD
ISLANDS AND ON NEWLY FORMED TROPICAL DEPRESSION THIRTEEN LOCATED
ABOUT 225 SOUTHWEST OF THE MOUTH OF THE MISSISSIPPI RIVER.

SHOWER ACTIVITY ASSOCIATED WITH A LOW PRESSURE SYSTEM LOCATED ABOUT
500 MILES SOUTH OF HALIFAX NOVA SCOTIA HAS NOT BECOME ANY BETTER
ORGANIZED DURING THE PAST SEVERAL HOURS. HOWEVER...THIS SYSTEM IS
PRODUCING WINDS OF TROPICAL STORM FORCE...AND ONLY A SLIGHT
INCREASE IN ORGANIZATION COULD RESULT IN THE FORMATION OF A
TROPICAL STORM.
THE LOW IS MOVING LITTLE AT THIS TIME...BUT SHOULD
BEGIN TO MOVE NORTHEASTWARD AT 10 TO 15 MPH TONIGHT. THIS SYSTEM
HAS A MEDIUM CHANCE...40 PERCENT...OF BECOMING A TROPICAL CYCLONE
DURING THE NEXT 48 HOURS.

ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.

PUBLIC ADVISORIES ON TROPICAL DEPRESSION THIRTEEN ARE ISSUED UNDER
WMO HEADER WTNT33 KNHC AND UNDER AWIPS HEADER MIATCPAT3.
FORECAST/ADVISORIES ARE ISSUED UNDER WMO HEADER WTNT23 KNHC AND
UNDER AWIPS HEADER MIATCMAT3.

$$
FORECASTER BROWN/AVILA
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1897. doubtit
Quoting kuppenskup:

For what 2012?


Are you questioning Miss Cleo or the psychic friends Network???
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Quoting Patrap:



What most never understand,itsa da water, not the Wind.



Goodnight, Irene.
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1895. Patrap
Member Since: July 3, 2005 Posts: 420 Comments: 127543

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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.