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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It is still imperative to remember that even if 93L only manages Tropical Storm status...it could still be a significant threat with flooding rains. We just witnessed Irene and that was only a Tropical Storm when it devastated Vermont with flooding rains. Being a hurricane isn't necessary to cause big interruptions and damage.
Member Since: June 29, 2009 Posts: 13 Comments: 5313
Quoting Patrap:
Be Prepared! Guides, Brochures and More
pat- what is your opinion on 93l? could this be a tropical storm by friday evening? do you think it will stall out over water for a few days before deciding to move along? its already raining on the northshore. are you still suggesting we prepare for a cat. 1? thanks!
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Quoting 69Viking:


Levi I trust your input but have to ask, couldn't that also be caused by the ULL over South LA? I'm thinking the tropical low is going to develop further South closer to where the core of all the convection is but I'm not weather expert.


The center could choose to tighten up anywhere between 26N and 29N, given how broad the low pressure envelope is right now. The ULL is fully separated from the surface circulation and thus it is not causing any illusions on visible satellite imagery.
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The WV Loop shows the ULL slowly lifting N ,,ahead of 93L

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Quoting dfwWxDude:


Those who rely on their own water wells, many of them are having to get them drilled deeper, or do without.

Most of the big cities have aquifers or lakes to pump from, but have implemented yard watering restrictions to twice a week. The next step is once a week watering and then no watering.

Another side affect, ERCOT is asking Utility companies to restart mothballed generating plants, as existing plants may have to be shutdown do to a lack of cooling water.



Water is not the only reason these plants might be firing up. The new CSAPR (Cross-State Air Pollution Rule)ruling is a potential disaster for electric reliability in Texas. A lot of jobs a stake with this one.
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Quoting ackee:
can I get link to this


http://moe.met.fsu.edu/tcgengifs/
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ESL by LSU 93L page


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Convection is rebuilding over the centre of Katia. 94L looks pretty sheared but tropical...CMC had this one 5 days out.
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Looks like a bad hair day:

Member Since: August 31, 2009 Posts: 0 Comments: 5628
Quoting Patrap:

Just finished cutting the grass - and the rains from 93L begin!
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Quoting Patrap:
93L FunkTop



Weather is getting really Nasty here in Gautier Mississippi. I'm schedule to go on Navy sea trials out to see in the middle of the GOMEX, but for what I can see it will be canceled.
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Be Prepared! Guides, Brochures and More
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Quoting Levi32:
High-resolution visible imagery already suggests that there are weak westerly winds due south of central Louisiana on the south side of 93L's low pressure envelope. If the circulation tightens up a bit more, we could have a tropical depression as soon as late tonight.


Levi I trust your input but have to ask, couldn't that also be caused by the ULL over South LA? I'm thinking the tropical low is going to develop further South closer to where the core of all the convection is but I'm not weather expert.
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231. jpsb
Quoting mynameispaul:
Reading on my home barometer has really dropped off today.
Thanks you just reminded me to pull out my old ships barometer, 1014 (or 29.9+) here on west Galveston bay.
Member Since: June 30, 2009 Posts: 0 Comments: 1193
Orleans
Flash Flood Watch, Coastal Flood Watch
Statement as of 11:54 AM CDT on September 01, 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.





1151 am CDT Thu Sep 1 2011

... Coastal Flood Watch in effect through Saturday evening...

The National Weather Service in New Orleans has issued a coastal
Flood Watch... which is 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.
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93L FunkTop

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228. ackee
Quoting GatorWX:
ok, well lets try again:



Possible, but would have to be a much shallower trough than GFS and Euro!
can I get link to this
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Quoting tropicfreak:


Heck I'm not ruling out getting to the Greek Alphabet.

Don't forget about pre 95L, we may see it develop tomorrow, 4 tropical systems in the Atlantic.

Unreal


Well if 93L and 94L develop...we'd be up to 14 cyclones and 13 named storms. Still with two peak months to go (September and October can have quite a bit of activity, too....i.e. Wilma)...I'd certainly think 20 named storms is in reach.
Member Since: June 29, 2009 Posts: 13 Comments: 5313
06z GFS Katia..


12z GFS Katia


12Z much farther west
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I've been reading this blog for several years. Usually people seem to be knowledgable about hurricanes. This year though I've seen a lot of doom and gloom. It's almost like the several years without a hurricane has been getting people here punch drunk. Tone it down, not every invest is going to become a hurricane. I hope the people that know what they're talking about keep challenging these people. Thank goodness Dr. Masters continues to provide a meaningful blog. It's like watching Channel 7 in Miami at 11 PM. TRACKING THE TROPICS
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Quoting angiest:

I also have seen the evidence on store shelves.
People will buy groceries just before a storm so it does not sit around and spoil. We all stock up on certain items just before the storm when we are fully convinced it is coming our way. TV is HYPE.
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Quoting Levi32:


I'll weep if it does, but maybe. The NHC seems to like it.


LOL the beloved frontal boundaries.
Member Since: September 2, 2006 Posts: 110 Comments: 6878
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Quoting angiest:

The oft-televised rush on supplies and plywood just before a storm would (sadly) seem to contradict that statement.


That's the northerners (north of the Florida state line) that just moved to the coast. ;)
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Quoting AllStar17:
Possibly three tropical cyclone active by tonight...and it is only September 1???


Heck I'm not ruling out getting to the Greek Alphabet.

Don't forget about pre 95L, we may see it develop tomorrow, 4 tropical systems in the Atlantic.

Unreal
Member Since: September 2, 2006 Posts: 110 Comments: 6878
Second giant ice island set to break off Greenland glacier

Link
http://www.msnbc.msn.com/id/44353322/ns/us_news-e nvironment/#.Tl-3S2o-axA

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Quoting tropicfreak:


Levi do you believe 94L may beat 93L to becoming Lee?

Kinda reminds me of Franklin a few weeks back...


I'll weep if it does, but maybe. The NHC seems to like it.
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Quoting AllStar17:
Possibly three tropical cyclone active by tonight...and it is only September 1???
not good
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Reading on my home barometer has really dropped off today. Much lower than normal. Going to get my Mom's blood pressure medicine re-filled later. Have 3 days gas stored and generators ready to go. Breeze is picking up here north of Lake Charles, LA.
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Quoting 69Viking:


I'm not saying there's no risk but overall we are better prepared than the rest of the country. Some people naturally prepare better than others and know what to do to stay out of harms way.


I'd agree with that. I also think that since Allison, humberto, et al, the news folks have done a better job of alerting the public of these sneaky gulf storms.
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Quoting gugi182:
sorry about that



That's fine.
Member Since: September 2, 2006 Posts: 110 Comments: 6878

Quoting divdog:
Thats because its TV. Most of us are prepared. The mad rush is the small percentage that r unprepared and the group that the TV shows for ratings.
I also have seen the evidence on store shelves.
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sorry about that

Quoting tropicfreak:


Putting it in caps doesn't put a lot of emphasis on what you are saying.
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Possibly three tropical cyclones active by tonight...and it is only September 1???
Member Since: June 29, 2009 Posts: 13 Comments: 5313
Quoting 7544:
are those highs closing off the weakness or are the joining each other to block katia and have her going west tia ?Link


both
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Quoting gugi182:
TO ALL THE BLOGGERS ON WUNDERGROUND I WANT TO WISH YOU ALL A GREAT DAY AND STAY SAFE WHERE EVER YOU ARE


Putting it in caps doesn't put a lot of emphasis on what you are saying.
Member Since: September 2, 2006 Posts: 110 Comments: 6878
Quoting angiest:

The oft-televised rush on supplies and plywood just before a storm would (sadly) seem to contradict that statement.
Thats because its TV. Most of us are prepared. The mad rush is the small percentage that r unprepared and the group that the TV shows for ratings.
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TO ALL THE BLOGGERS ON WUNDERGROUND I WANT TO WISH YOU ALL A GREAT DAY AND STAY SAFE WHERE EVER YOU ARE
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Quoting houstonstormguy:


Ask the relatives of those who lost their lives in Allison over 10 years ago in Houston.
Any tropical system with that much rain can lead to a loss of life. Especially with little warning...even in Texas and the Gulf States.


I'm not saying there's no risk but overall we are better prepared than the rest of the country. Some people naturally prepare better than others and know what to do to stay out of harms way.
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Quoting Levi32:
High-resolution visible imagery already suggests that there are weak westerly winds due south of central Louisiana on the south side of 93L's low pressure envelope. If the circulation tightens up a bit more, we could have a tropical depression as soon as late tonight.


Levi do you believe 94L may beat 93L to becoming Lee?

Kinda reminds me of Franklin a few weeks back...
Member Since: September 2, 2006 Posts: 110 Comments: 6878

Quoting Beachfoxx:
Most of us along the Gulf Coast/Panhandle have our emergency supplies ready ALL the time. 
We would have to secure the boat & move some plants inside - generator is ready to go... We are prepared.

The oft-televised rush on supplies and plywood just before a storm would (sadly) seem to contradict that statement.
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Some rain for Texas would be nice but won't want to see too much as the grounds are extremely dry. As of 94L will it become LEE before 93L has the chance of becoming a tropical depression in the near future. And as for Katia can you become a huge hurricane but out to see please we would love to see her beauty only on the ocean not affecting no land mass. We have enough to clean up thanks to IRENE.
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Quoting will40:
Link

sorry theres a link to it


No, Will, that doesn't work either. You can no longer link to images on that site, they have it disabled. You can see it because the image is cached on your computer, but everyone else gets the black box.
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Quoting GatorWX:
P451,

Can you post link to the rapid fire sats? please and thankyou


One webpage which has instructions to build your own loop
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Still does not work
Quoting will40:
Link

sorry theres a link to it

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Quoting nrtiwlnvragn:


Yes
Thank you, I was getting a bunch of 5 digit # when I typed in Dropsounde Observations.
Member Since: August 31, 2009 Posts: 0 Comments: 5628
Quoting Patrap:


Pat, can you post long range and long duration NOLA radar? I'm one of those phoney too cheap to pay college kids with no credit card! lol TIA Definitely starting to notice more and more curvature to the rain bands. I have the NWS long range up and going, but doesn't compare to the long duration WU radar!
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High-resolution visible imagery already suggests that there are weak westerly winds due south of central Louisiana on the south side of 93L's low pressure envelope. If the circulation tightens up a bit more, we could have a tropical depression as soon as late tonight.
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Link

Get gas today, tomorrow the prices will go up.
GOM rigs being evacuated.
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About

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.