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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They will likely find a closed circulation, IMO.
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lowest pressure seen by HH is 1009.1 so far
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New Orleans
NEXRAD Radar

Type
Velocity Azimuth Display Wind Profile ° Elevation
Range
124 NMI

Member Since: July 3, 2005 Posts: 419 Comments: 127371
13 of the 20 CMC 00Z ensemble members had 94L as a TS or weak cat 1 in 48 hours. 12 of the 20 did the same for 93L, although 4 of the 12 ensemble members were below 972 mb by 00Z Saturday. As people have been saying...there may not be much official warning for this unless Ray goes out on a limb like Bloomberg did.
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Do we have a closed low?
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Quoting Jax82:
Remaining names on this years list.

Lee
Maria
Nate
Ophelia
Philippe
Rina
Sean
Tammy
Vince
Whitney



On monday we will use at least 2 of them ..... with only 8 names remaining the Greek Letter is more possible than ever !
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no closed low reported yet = no Lee
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Good afternoon

Katia is attempting a comeback on the convection front but the low level center continues to push to the West. The combination of shear and a fast forward speed is preventing the new blow up convection from overtopping the low level center. I just looked at the ADT center fix and it has it right underneath the big blow up which clearly does not square away with the visible loop.

There is about 20 knots of Westerly shear ripping across the top half of Katia and stripping away the CDO to the Eastern semi-circle of the circulation. With 18 mph forward speed and 20 knots from the West over the top the convection will continue to lag behind.

The system is near 49W which is only about 660 miles to the East of the Leeward Islands and closing quickly. Several of the models will probably respond by taking Katia very near if not just over those Islands on the NE of the chain.
Member Since: August 19, 2006 Posts: 0 Comments: 15687
Quoting cat5hurricane:

Yep


Every once in a blue moon, the NHC screws the pooch on track. And I mean every once in a while. For the most part, they're pretty much scary accurate within 50-100 miles.

But when you have a steering pattern that would give even the best meteorologist a severe nosebleed, you do the best you can with the technology and inner gut that you can do.

Afterall, like us....They are only human.
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Member Since: July 3, 2005 Posts: 419 Comments: 127371
Quoting Jax82:
I feel sorry for the NHC, they just got ridiculed about Irene and the hype regarding intensity, then now they have to deal with 93L in the Gulf, not knowing where its going or how strong its going to get, and every model doing 360's and 720's. Wherever it goes, hopefully there is enough warning.
Only the uneducated or truly ignorant--or those who blindly hate anything having to do with the government--would find fault with the overall job the NHC does. And since those people are fools whose opinion doesn't really matter much, I doubt anyone at the NHC will lose much sleep over what they think. But, yes, I too feel sympathy, or at least empathy, for the NHC folks; when things get this crazy, they definitely get put through the wringer.
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Quoting cat5hurricane:
Data coming in indicates TS Lee is out there...

No W winds,no Lee
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Quoting P451:
While the Gulf is loaded with convection the system itself is quite small located just south of LA moving parallel to the shoreline in a general westward heading.



What are the chances of the large amounts of convection east of the system becoming organized?
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Quoting interstatelover7165:
We Have Lee!
Not quite, the HH's aren't at the Center just yet, & they have yet to confirm west winds. We need a close low first. As of right now it's just a strong tropical wave.
Member Since: August 31, 2009 Posts: 0 Comments: 5628
425. jpsb
Quoting interstatelover7165:
We Have Lee!
Don't we need a closed low to have Lee? (or any kind of TC)
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424. IKE
48 hour 12Z ECMWF....


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Quoting SeaMule:
actually, there are two competing LLC's.

the one south of the one "racing" off to the west will win out. It is meandering, but pulling energy to it. It's about a few hundred miles south of the one that will NOT develop.

we will have a cat 3 hurricane in the GOM inside of 60 hours.

you heard it here first.

a cat 5 in 4 days

DOOMcaster!
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Quoting Patrap:


The Pumps, "pump" the Rainfall over the Gates Guy,, thats how they keep the pressure off the walls.




What keeps the pressure off the walls is reducing the flow capacity of the outfall pumps to match that of those ricky-ticky things the corps installed. They can't do a half inch an hour with the gates down, especially out the London Avenue Canal. I just hope that is the COC and it's off to visit TX and drags all that convection with it.

Fortunately New Orleans has extensive ponding storage areas. Unfortunately its where we park our cars.
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17th St. Canal 3-D overview

Member Since: July 3, 2005 Posts: 419 Comments: 127371
Quoting Jax82:
I feel sorry for the NHC, they just got ridiculed about Irene and the hype regarding intensity, then now they have to deal with 93L in the Gulf, not knowing where its going or how strong its going to get, and every model doing 360's and 720's. Wherever it goes, hopefully there is enough warning.


Part of the job. They're used to it.
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Quoting GTcooliebai:
17:25:00Z 27.633N 87.883W 648.5 mb
(~ 19.15 inHg) 3,824 meters
(~ 12,546 feet) 1009.9 mb
(~ 29.82 inHg) - From 115° at 23 knots
(From the ESE at ~ 26.4 mph) 8.2°C
(~ 46.8°F) 4.6°C
(~ 40.3°F) 23 knots
(~ 26.4 mph) 40 knots
(~ 46.0 mph) 3 mm/hr
(~ 0.12 in/hr) 40.0 knots (~ 46.0 mph)
Tropical Storm
We Have Lee!
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Quoting Patrap:
New Frame shows the expansion and organization continuing.






I just have a question, why do people post old graphics? This is from July. I see this quite often and am just curious.
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We have a few vortice's embedded around 93L's large center.




Member Since: July 3, 2005 Posts: 419 Comments: 127371
How high are the winds expected to be over the next few days in Southeast Louisiana? I live near a levee that is still broken and anytime anything comes this way it scares me. I already have all my important things put up high in case we flood again. Guess my hurricane go away and nothing else form dance didn't work huh? LOL
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Quoting Jax82:
I feel sorry for the NHC, they just got ridiculed about Irene and the hype regarding intensity, then now they have to deal with 93L in the Gulf, not knowing where its going or how strong its going to get, and every model doing 360's and 720's. Wherever it goes, hopefully there is enough warning.
I wonder what the extent of the tropical storm advisories will look like.
Member Since: August 31, 2009 Posts: 0 Comments: 5628
Quoting Jax82:
I feel sorry for the NHC, they just got ridiculed about Irene and the hype regarding intensity, then now they have to deal with 93L in the Gulf, not knowing where its going or how strong its going to get, and every model doing 360's and 720's. Wherever it goes, hopefully there is enough warning.


they will do fine with 93L..its the blog that will have issues with 93L and the NHC..
Member Since: August 19, 2006 Posts: 13 Comments: 14250
Quoting WetBankGuy:


Not if it parks somewhere that forces them to close the gates.


The Pumps, "pump" the Rainfall over the Gates Guy,, thats how they keep the pressure off the walls.

Member Since: July 3, 2005 Posts: 419 Comments: 127371
actually, there are two competing LLC's.

the one south of the one "racing" off to the west will win out. It is meandering, but pulling energy to it. It's about a few hundred miles south of the one that will NOT develop.

we will have a cat 3 hurricane in the GOM inside of 60 hours.

you heard it here first.

a cat 5 in 4 days
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406. Jax82
I feel sorry for the NHC, they just got ridiculed about Irene and the hype regarding intensity, then now they have to deal with 93L in the Gulf, not knowing where its going or how strong its going to get, and every model doing 360's and 720's. Wherever it goes, hopefully there is enough warning.
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Quoting P451:


93L if designated would be a weak TD.
94L if designated would likely jump to TS as 35kt winds is it's present intensity.



If they initialized advisors at the same time (at TS strength) then 93L being the first invest would get Lee and 94L Maria.
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404. IKE

Quoting ncstorm:
Takes it over this area....washout ahead....
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Quoting Patrap:
I guess were gonna see how well the new COE Outfall Canal Pumps are gonna work pumping excessive rainwater into Lake P.


Not if it parks somewhere that forces them to close the gates.
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Quoting carcar1967:


Was the spinning counter-clock wise?

actually yes
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Quoting P451:


93L if designated would be a weak TD.
94L if designated would likely jump to TS as 35kt winds is it's present intensity.

Yeah but do you see the winds they're finding on the ESE side.
Member Since: August 31, 2009 Posts: 0 Comments: 5628
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.
Member Since: July 3, 2005 Posts: 419 Comments: 127371
Quoting NoVaForecaster:
Poll Time!

Which AOI becomes Lee?

A. 93L
B. 94L
C. Something Else

Which AOI becomes Maria?
A. 93L
B. 94L
C. Something Else

Which is more of a threat to the US?

A. 93L
B. Katia
C. 94L
D. None

93L:


94L:


Katia:


I say B,A,A
ABA
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Quoting midgulfmom:
Perhaps showing us the track?...LOL


Was the spinning counter-clock wise?
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Member Since: August 19, 2006 Posts: 13 Comments: 14250
Quoting midgulfmom:
Perhaps showing us the track?...LOL


lol! well, he is a smart one ;)
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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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