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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Do you think New Orleans will get massive flooding? Less than Katrina but pretty close?
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Looks as if 93L may want to form a little closer to the coast than what the models are toying with. I would think that would be good news for people down there being that would be one more factor working agianst to organize, would also bring the rain without the wind. It boggles my mind how stubborn this storm is given the wind shear out of the west. Be thankful that shear is there, hopefully it stays there.
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Quoting summerland:

This is especially true given the temperatures of the Gulf -- near 90F! 93L has a vast amount of moisture available to turn into rain. I only wish the steering was less of a mystery. As unlikely as it is that a TS Lee could veer SW all the way to South Texas, we sure could use the rain.


There is no Lee
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Quoting TerraNova:
Current sea surface temperatures in the Gulf (full res):

Thank you for the description. I am trying to learn as much as I can, while I watch where my kids are.
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Quoting JGreco:


Ivan yes that was it. All I remember was that we ended up staying because our local news was suggesting only up to strong Cat 1 winds. It did that mess and we ended up in Cat 3 winds. It was terrible.:o


I was two miles from the coast for IVAN - we knew it was coming 3 days out. Weather bouys caught waves 35'+ 3 days out - and no mention of that on the news beforehand...that would have really changed a lot of people's minds about staying/taking their valuables with them. I think ground zero was Palmetto Bay or something like that - I was east of that.
I think Danny was the one that sat in Mobile Bay for what seemed like days and sucked all the water out of the bay. Totally freaky.
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850 mb vorticity

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More bands coming thru Uptown now.

Low scud with the surface flow.
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Quoting GTcooliebai:
From Golden Triangle Weather Page:



Or it may become "Maria" too. And, what the heck are they talking about? LOL. That is a GREAT consensus!
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Quoting cloudburst2011:



YOU ARE CLUELESS YOU NEED TO LOOK AT THE RGB YOU CAN CLEARLY SEE A COC SPINNING AT 25N AND 89W....THIS WILL BE LEE BY THIS EVENING...SHEAR HAS SLACKENED AND THE SSTs ARE APPROCAHING THE 90 DEGREE MARK...NOT GOOD LOOKING VERY BLEAK FOR THE NORTHERN GOM...15/20 INCHES OF RAIN WHICH ALREADY STARTED..NUMEROUS HEAVY SQUALLS ALL STARTING TO ORGANIZE...MY FRIEND YOU HAVE MORE THEN A TROPICAL DEPRESSION HERE...


Will you please quit with the all caps? Do you not know that typing in caps means you are screaming in emails and blogs? If not, consider yourself educated. If you can read others' words in lower case and then answer back in all caps......hmmmmm something wrong with that scenario.
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Quoting WhoDat42:


I'm in Mandeville too, off 1088. Looks to be a nerve racking weekend!
i agree! stay safe neighbor
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93L/Lee or Maria track may be one of the whackiest ones we have ever seen.
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From Golden Triangle Weather Page:

Member Since: August 31, 2009 Posts: 0 Comments: 5628
Quoting Levi32:


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.


I hear you, just realized how broad the low is that's trying to form. Kind of a mess with the ULL, shear and the low trying to form. It's pretty obvious we won't see any rapid development at this time but some areas sure could see a lot of heavy rain.....
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Quoting sarahjola:
mandeville less than a mile off the lake


I'm in Mandeville too, off 1088. Looks to be a nerve racking weekend!
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279. HCW
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Im thinking the threat of 93L being a big rainmaker TS is > it being a destructive hurricane. Shear should remain moderate through its life span, and it is on the big side already.
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NCEP NAM/WRF simulated cloud brightness out 45 hours (an interesting tool to use since it uses a similar IR color scheme to CIMSS's satellite imagery):

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katia is trying to fight back the dry air...convection just blew over/around center

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CIMSS 93L Real Time Tracker
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I didn't realize that one of the local papers was doing a profile on me...

Hurricane Preparedness - the Man Behind the Mission
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Quoting WhoDat42:
Sarahjola - what part of northshore are you?
mandeville less than a mile off the lake
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I am wondering how big the potential for tornadoes from 93L is?
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damn lightening always catches me off guard. good light show out on the northshore right now
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Quoting CloudGatherer:

Really? We're going to see a tropical cyclone named Ophelia this year? They're going to name a storm after the most famous death-by-drowning in all of literature?

That ranks right up there with the combo of Katia and Rina. Doesn't anyone vet this stuff?
This years names were terrible all around.
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Quoting AllStar17:
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.

This is especially true given the temperatures of the Gulf -- near 90F! 93L has a vast amount of moisture available to turn into rain. I only wish the steering was less of a mystery. As unlikely as it is that a TS Lee could veer SW all the way to South Texas, we sure could use the rain.
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Quoting WhereIsTheStorm:
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


Check the verbiage the 'scientist' uses in this article... community collage REPRESENT!
Member Since: September 9, 2010 Posts: 5 Comments: 1034
Quoting LAlurker:

Ivan 2004


Ivan yes that was it. All I remember was that we ended up staying because our local news was suggesting only up to strong Cat 1 winds. It did that mess and we ended up in Cat 3 winds. It was terrible.:o
Member Since: September 22, 2005 Posts: 0 Comments: 322
Sarahjola - what part of northshore are you?
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Quoting Jax82:
Remaining names on this years list.

Lee
Maria
Nate
Ophelia
Philippe
Rina
Sean
Tammy
Vince
Whitney


Really? We're going to see a tropical cyclone named Ophelia this year? They're going to name a storm after the most famous death-by-drowning in all of literature?

That ranks right up there with the combo of Katia and Rina. Doesn't anyone vet this stuff?
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thanks patrap! correct me if i'm wrong but hasn't shear dropped some near 93l? if not isn't it expected to drop a lot by friday? thanks!
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Would the West coast of FL have any higher tides or any other issues related to this storm?
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Quoting Levi32:
We're going to have a long time to watch 93L sit there, and it will take it a while to wind up into a storm due to the wind shear and its broadness. If it becomes a TD late tonight or tomorrow morning it would likely remain one for some time before beginning to strengthen.

Back after breakfast.
that means rain,rain and more rain.
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Current sea surface temperatures in the Gulf (full res):

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get ready for a ton of water orleans man the pumps
Member Since: July 15, 2006 Posts: 171 Comments: 53809
Quoting HCW:

Hurricane Danny 1997 ?


I was hoping someone with more knowledge of storm history would know. All I know was it was a surprise when it happened. I've been through sooo many of these over the past decades the experiences are blurring together:0
Member Since: September 22, 2005 Posts: 0 Comments: 322
Quoting JGreco:


I just wrote about the easternmost possibilities with 93L. My concern is the possibility of this getting as far east as the tip of the Mississippi Delta region of Louisiana. I can't remember which storm it was that barely missed the Mississippi Delta and plowed into Alabama which put the Western Panhandle on the bad side. I just hope that the worst case scenario does not develop in terms of 93L or it develops as far South as you suggest:0

Ivan 2004
Member Since: July 24, 2008 Posts: 0 Comments: 156
We're going to have a long time to watch 93L sit there, and it will take it a while to wind up into a storm due to the wind shear and its broadness. If it becomes a TD late tonight or tomorrow morning it would likely remain one for some time before beginning to strengthen.

Back after breakfast.
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So, maybe a swell from 93L on Florida's west coast?....nah, off to east coast for some long period Katia for days & days......
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Quoting Jax82:
Remaining names on this years list.

Lee
Maria
Nate
Ophelia
Philippe
Rina
Sean
Tammy
Vince
Whitney



There's really not that many remaining, especially considering the current pace of cyclone development.
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251. HCW
Quoting JGreco:


I just wrote about the easternmost possibilities with 93L. My concern is the possibility of this getting as far east as the tip of the Mississippi Delta region of Louisiana. I can't remember which storm it was that barely missed the Mississippi Delta and plowed into Alabama which put the Western Panhandle on the bad side. I just hope that the worst case scenario does not develop in terms of 93L or it develops as far South as you suggest:0

Hurricane Danny 1997 ?
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Quoting sarahjola:
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!



Stay up on the latest with it,,but its gonna take some time to get a true center ,but the fetch into Se La is well established so flooding is possible in the watch areas as we go forward today and the next 48-72.

Unfortunately.
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249. Jax82
Remaining names on this years list.

Lee
Maria
Nate
Ophelia
Philippe
Rina
Sean
Tammy
Vince
Whitney

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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.


I just wrote about the easternmost possibilities with 93L. My concern is the possibility of this getting as far east as the tip of the Mississippi Delta region of Louisiana. I can't remember which storm it was that barely missed the Mississippi Delta and plowed into Alabama which put the Western Panhandle on the bad side. I just hope that the worst case scenario does not develop in terms of 93L or it develops as far South as you suggest:0
Member Since: September 22, 2005 Posts: 0 Comments: 322
Quoting StormHype:


All that the models are saying at this point is "uncertainty". It could sit in the GOM for days and go in anywhere from Brownsville to Tampa.
,seriously doubt tampa,northern gulf coast somewhere or tx,defnot flimo
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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.
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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.