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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Member Since: July 3, 2005 Posts: 423 Comments: 127874
Ok, confused..so is it no going up to LA then turning and coming down the TX Coast?
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Quoting Levi32:


Thanks...didn't know that. Sometimes I wonder how you get so much information Nrt. You're darn good at it lol. Is there a readme file for the ACTF file format anywhere?
Here's one: http://www.nrlmry.navy.mil/atcf_web/docs/database /new/abrdeck.html

(But, I don't think it covers the details nrt pointed out.)
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Quoting atmoaggie:
I still think they should post TS watches for most of the LA coast, regardless. 93L or TD 13 is debatable, but not the possibility of TS conditions in the near future for the LA coast.


That's why I wonder why they don't change the rules so that they can issue watches if development near the coast is expected with TS conditions.
Member Since: November 24, 2005 Posts: 635 Comments: 26611
Quoting cmahan:


Only on the SyFy Channel.

+1
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Quoting TropicalAnalystwx13:


Remote-Linking-Is-Disabled-!-!-!

lol...seriously though, you can see the image, but other people cannot.
Quoting TomTaylor:
Remote Linking Disabled!



SOAB. I keep forgetting!!!
Member Since: July 15, 2006 Posts: 17 Comments: 10220
Quoting Levi32:


Thanks...didn't know that. Sometimes I wonder how you get so much information Nrt. You're darn good at it lol. Is there a readme file for the ACTF format anywhere?


ATCF Data Formats
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In advance of the weather, BP and ExxonMobil ordered their Gulf rigs evacuated and have shut down their wells, spokesmen for those companies told CNN. Chevron, meanwhile, has ordered nonessential workers off the platforms, and Shell said it had begun taking some of its workers back to shore Thursday afternoon.

Read more: http://www.wxii12.com/news/29050469/detail.html#ix zz1WjaMz9EN
Member Since: May 17, 2009 Posts: 2 Comments: 904
Quoting MississippiWx:
12z GFDL had a 973mb hurricane in Louisiana moving NE at 102 hours:



Remote Linking Disabled!

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Quoting MississippiWx:
12z GFDL had a 973mb hurricane in Louisiana moving NE at 102 hours:





Remote-Linking-Is-Disabled-!-!-!

lol...seriously though, you can see the image, but other people cannot.
Member Since: July 6, 2010 Posts: 113 Comments: 31917
Quoting Levi32:
I don't really think we'll see an upgrade of 93L yet. Maybe later tonight.
I still think they should post TS watches for most of the LA coast, regardless. 93L or TD 13 is debatable, but not the possibility of TS conditions in the near future for the LA coast.
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Quoting atl134:




The cat of nine tails (or maybe cat o' nine tails) is the name given to a 9 pronged whip used by pirates if I remember correctly.
Also used by b'os'uns in the Royal Navy as a form of punishment, in addition to a rattan.
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"
Member Since: July 15, 2006 Posts: 17 Comments: 10220
Quoting nrtiwlnvragn:
For what its worth, storm motion is classified in the ATCF system as follows:

I = S, R, O; straight mover, recurver, odd mover.



Thanks...didn't know that. Sometimes I wonder how you get so much information Nrt. You're darn good at it lol. Is there a readme file for the ACTF file format anywhere?
Member Since: November 24, 2005 Posts: 635 Comments: 26611
Quoting washingaway:


I never understood the term "recurve". Something would have to have curved once before, before for someone can conclude it has recurved. Somthing must occur before it can reoccure. We may want to rethink our use of the word. If I was to return to the top of the page, that means I've been there before.
There's the first curve (curve poleward/northward) which is a result of the storm making it around the subtropical ridge, and then the second curve (eastward) which is a result of upper level westerlies or troughs in the mid-latitudes.
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Quoting Pipejazz:


Lee has been named????


Not yet.
Member Since: July 6, 2010 Posts: 113 Comments: 31917
Quoting LargoFl:
I had heard they were or Are considering raising the max limit of categories to cat-7


Quoting oldgranddad:
Cat of nine? I'm sure that the hurricane scale only goes up to 5.


The cat of nine tails (or maybe cat o' nine tails) is the name given to a 9 pronged whip used by pirates if I remember correctly.
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Quoting BrockBerlin:


A recurve bow





The bow has two curves, so it curved before.
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Quoting stoormfury:
I am in total disagreement with LEVI'S explanation of recurve. i have said it oh this blog ,that something can only recurve after it has curved. it should be said that the system has moved away or curved away from land
He is giving you the met community usage of that word. Whether you like it or not, and/or if it fits the many ambiguous rules of the English language, is irrelevant.
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Quoting cloudburst2011:
i dont like the way things are setting up with lee...we could have a cat 3 in our back yard by late saturday....feeder bands are beginning to become morthis is turninge concentrated...with the ssts near 90 degrees this spells disaster for the northern gulf coast..this is turning into a dangerous situation....


Lee has been named????
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Quoting washingaway:


I never understood the term "recurve". Something would have to have curved once before, before for someone can conclude it has recurved. Somthing must occur before it can reoccure. We may want to rethink our use of the word. If I was to return to the top of the page, that means I've been there before.


Doesn't really matter to me, since there is no other word in meteorology that conflicts with it.
Member Since: November 24, 2005 Posts: 635 Comments: 26611

Quoting BrockBerlin:


A recurve bow



Which curves back, or recurves. ;)

I think the recurve would actually be the curve from Northward to Eastward, with the curve having been Westward to Northward (limiting myself to the Atlantic basin).
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Quoting tristanh72:


you forgot "though it is hard to know with certainty."
and "But Dr. Brown put the odds of experiencing the same degree of extreme dryness again as “very small.”"


I think that part is wishful thinking and spin. It looks very probable from my perspective, and there is plenty of historical precedence.
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Quoting stoormfury:
I am in total disagreement with LEVI'S explanation of recurve. i have said it oh this blog ,that something can only recurve after it has curved. it should be said that the system has moved away or curved away from land
A storm can recurve and still hit land, so Levi is correct. Here are some hypothetical tracks involving a recurve before landfall (don't mean to scare anybody, just trying illustrate a point):

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920. DFWjc
Quoting LargoFl:
I had heard they were or Are considering raising the max limit of categories to cat-7


Link

"If I could do it, I would do away with categories," says Bill Read​, director of NOAA's National Hurricane Center (NHC). "The whole indexing [of hurricanes] was done back in the '60s and '70s when we had no way to convey the variables of damage that the storm did. We didn't measure it that carefully; we didn't have the tools."

Even nowadays, instruments to measure actual wind speed are often destroyed during extreme storms, so estimates have to be extrapolated from satellite images and other data. Actual observations can also be suspect. It took 14 years for the World Meteorological Organization to acknowledge that an anemometer in Australia recorded a world record wind speed of 407 kph (253 mph) during Tropical Cyclone Olivia in 1996. Wind speed science has improved over the years. Since the 1990s direct wind measurements from hurricane-hunter aircraft have replaced central pressure measurements, which were often a proxy for wind speeds.
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If 93L would get it's act together then I could plan my weekend!
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For what its worth, storm motion is classified in the ATCF system as follows:

I = S, R, O; straight mover, recurver, odd mover.

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Quoting baytwntx11:


That is odd.... Lake Chares hasn't put out an update either.
They must still be coordinating forecasts.
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Quoting washingaway:


I never understood the term "recurve". Something would have to have curved once before, before for someone can conclude it has recurved. Somthing must occur before it can reoccure. We may want to rethink our use of the word. If I was to return to the top of the page, that means I've been there before.


agreed!
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Quoting LargoFl:
I had heard they were or Are considering raising the max limit of categories to cat-7


hahaha, no.
Member Since: July 6, 2010 Posts: 113 Comments: 31917
Quoting washingaway:


I never understood the term "recurve". Something would have to have curved once before, before for someone can conclude it has recurved. Somthing must occur before it can reoccure. We may want to rethink our use of the word. If I was to return to the top of the page, that means I've been there before.
Good...now you're in charge of explaining to TAZ that someone has to be ported before they can be RE-PORTED.
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Thunderstorms starting to fire up around the center at 27N91W. However, they are still being sheared as they form. That will change in 12-18 hrs as ULL over central La coast clears out to NW. COC will likely follow in this direction.
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Quoting LargoFl:
I had heard they were or Are considering raising the max limit of categories to cat-7


Only on the SyFy Channel.
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Quoting oldgranddad:
Cat of nine? I'm sure that the hurricane scale only goes up to 5.
I had heard they were or Are considering raising the max limit of categories to cat-7
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Orleans
Coastal Flood Watch, Flash Flood Watch
Statement as of 3:12 PM CDT on September 01, 2011

... Coastal Flood Watch now in effect through Sunday evening...

The coastal Flood Watch is now in effect through Sunday 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.






310 PM 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 will continue to impact
coastal Mississippi and southeast Louisiana 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: 423 Comments: 127874
Quoting Levi32:
I should also really point out a big slip in terminology that is working its way into the blog. I am guilty of it as well sometimes in my videos. We can't say that a "recurving storm" means one that is missing land. That is entirely incorrect. In fact, the majority of storms that hit North America ARE recurving. The question should be whether the storm will hit land as it recurves, not whether it will recurve. Most storms do recurve into the mid-latitudes, and that can occur over the ocean or over land.


I never understood the term "recurve". Something would have to have curved once before, before for someone can conclude it has recurved. Somthing must occur before it can reoccure. We may want to rethink our use of the word. If I was to return to the top of the page, that means I've been there before.
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Quoting Neapolitan:

The 2011 drought is by far the worst single-year one in Texas--far worse, that is, than any that occurred during the 1950s (or any other period). The current drought is affecting a wider area, and it's been more profound, with much hotter temperatures, less precipitation, and drier soil. Of course, the 1950s multi-year drought lasted longer; it remains to be seen whether the current will continue long enough to surpass the old one(s). FWIW, Texas State Climatologist Dr. Nielsen-Gammon says that that Texas is "likely to be" at the start of a multiyear drought.


you forgot "though it is hard to know with certainty."
and "But Dr. Brown put the odds of experiencing the same degree of extreme dryness again as “very small.”"
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906. 996tt
Quoting BrockBerlin:


Pretty much it actually had an extremely unusual track in that ridge was so strong it shoved it southwest into Cuba.


I was thinking it was Gustav, but could have been Ike, that was supposed to recurve, then hit east coast, then hit Tampa and then forecast kept moving west every hour it seemed. NHC and models kept saying it was going to turn, but never did.
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Quoting TropicalAnalystwx13:
Well, they declared Irene with a very weak and broad center of circulation, so why not 93L?
you got a point, plus it's close to land.
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18z SHIPS forecasts that upper-level winds to be marginally favorable for Katia around this time tomorrow, and exceptionally favorable for the remainder of the long weekend.

SHEAR (KT) 12 20 19 12 7 11 2 7 6 10 7 11 8
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Quoting TerraNova:


I dunno, that's what I've been hearing...albeit very weak west winds, probably not worthy of an upgrade.



Love how that was my 4000th comment and I didn't even notice until I had already posted it lol.
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I am in total disagreement with LEVI'S explanation of recurve. i have said it oh this blog ,that something can only recurve after it has curved. it should be said that the system has moved away or curved away from land
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Quoting atmoaggie:
I *think* that is going to be expected with this system for a while, yet. This is an odd one where the mid-level circulation isn't as developed as the surface circulation. Even the 5 knot flight level west wind had a 22 knot surface wind.

So far, all of the stronger areas of surface winds have been under a slower flight level wind.

This system is vorticity inverted...
Or the extrapolation is just off...
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Member Since: July 3, 2005 Posts: 423 Comments: 127874
Quoting GTcooliebai:
And one must question why they call Florida the sunshine state in times like this...


Yeah, sunshine state (at least the bottom 1/2) is all about the dry season (Nov - May). During those months its pretty much sunny and dry everyday.

Summer (rainy season) from June -Sept we have T-Storms almost everyday.
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Quoting angiest:
Seems odd that there is no afternoon update to the Houston forecast discussion yet.


That is odd.... Lake Chares hasn't put out an update either.
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896. IKE
18Z NAM @ 33 hours....


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Quoting Neapolitan:

The 2011 drought is by far the worst single-year one in Texas--far worse, that is, than any that occurred during the 1950s (or any other period). The current drought is affecting a wider area, and it's been more profound, with much hotter temperatures, less precipitation, and drier soil. Of course, the 1950s multi-year drought lasted longer; it remains to be seen whether the current will continue long enough to surpass the old one(s). FWIW, Texas State Climatologist Dr. Nielsen-Gammon says that that Texas is "likely to be" at the start of a multiyear drought.


If this is the case parts of it could become uninhabitable at this rate... No water to drink. No water to put out fires. Widespread deforestation/defoliation. Massive number of houses and buildings destroyed by the subsidence of expansive clay soils under their foundations.

At some point many of us would have to just abandon everything and leave.
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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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