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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Katia a cat 4
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Quoting wxobsvps:
6Z GFS +120: Off shore Brownsville, TX

12Z GFS +114: Over NOLA
And 0z GFS had it going into NE Mexico.
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Quoting Minnemike:
suppose this could be bad in the long run, regarding a CONUS hit... weak system more likely to travel due.. everybody now!


Here we go.... Wait and see, too far out!
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FWTIW I am in Tallahassee and conditions are starting to get a little breezy and some of the low level clouds are starting to move towards the developing low to our West in the Gulf..........I think Drak can confirm my observations.....More to Follow.
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Quoting tiggeriffic:
I have a silly question....in Dr Ms blog it said this

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,

so what about the states between FL and NC? what are the chances it would hit in that region

Chances should be 12 - 16% then.
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Quoting Patrap:
Just Videoed and took pics of the Biggest Green Grasshopper or my Furst Locust on my Porch.

That cant be good at all.


I have seen a lot of them lately.. quite a few try to take a drink out of the swimming pool .. some fly away and some don't
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Quoting 7544:
katia is loosing its punch maybe dg to a ts on the next update will this have go further west now now toward the iswlands can we see a big cone change at 5pm ?


no about track change, they'd only dg to 70, wouldn't amount to anything different in the grand scheme of things and conditions are only going to improve.
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137. jpsb
Quoting ScottLincoln:
Already getting some much-needed rainfall here in northshore metro New Orleans.
Good for you, take what you need and then send the rest over here to Texas!
Member Since: June 30, 2009 Posts: 0 Comments: 1193
Quoting TerraNova:


Agreed. If I'm understanding this correctly, wouldn't a shallower system be more likely to stick to a more southerly track?


Well....there's a massive difference between a storm that has stayed weak and never strengthened, and a system that has strengthened and now weakened. She's not going to lose that much depth if she has already made it to hurricane strength and then fallen off again. She's still going to have a presence in higher levels of the atmosphere, more so than if she had remained a tropical storm this entire time and ended up at the same intensity.
Member Since: November 24, 2005 Posts: 635 Comments: 26652
this looks farther west to me..

Member Since: August 19, 2006 Posts: 13 Comments: 15662
Quoting TerraNova:


Agreed. If I'm understanding this correctly, wouldn't a shallower system be more likely to stick to a more southerly track?


That can't be good...
Member Since: September 2, 2006 Posts: 110 Comments: 6878
Quoting Levi32:
Katia is no longer a hurricane if her center is becoming this exposed. I fully expect a downgrade next advisory:

suppose this could be bad in the long run, regarding a CONUS hit... weak system more likely to travel due.. everybody now!
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Quoting Levi32:
If 93L is to become a hurricane, it will have to happen after the weekend, which means it will have to stay over the water until that time. If it moves inland before the weekend is up, it will likely be just a tropical storm. The upper pattern is very unfavorable for the moment, but will be improving as the upper-level trough gets bullied around and somewhat out of the way by the upper high associated with 93L. A lot of heat is getting released in the gulf, and this should allow wind shear to decrease a bit during the next two days.

oh ye, bearer of such happy news... just pickin' Levi. I just don't like home-grown systems that sit and visit too long in our backyard.
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Quoting P451:
We're in RSO for Goes now. Until the last frame where normal operations continued. It will go back RSO I would think. You can see some sort of rotation south of LA out ahead of the thunderstorms. You can also see the intense shear out there - note the storms in the western part of the image being sheared off.





how do you get to that rapid scan? LSU? RAMSDIS???
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Quoting RitaEvac:
93L is Neil Frank's nightmare. Opportunity to explode with no lead time to evacuate, equates to devastation and large loss of life


I was wondering this morning if he's going to come out of hibernation for this one. Would love to get his opinion.
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Quoting RitaEvac:
93L is Neil Frank's nightmare. Opportunity to explode with no lead time to evacuate, equates to devastation and large loss of life


Highly unlikely along the Gulf Coast, wouldn't be the first time a system spun up there and gave us only a day or two to prepare. I'd say Florida and anywhere along the Gulf Coast are better prepared than anyone when it comes to Hurricanes, no worries!
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If 93L is to become a hurricane, it will have to happen after the weekend, which means it will have to stay over the water until that time. If it moves inland before the weekend is up, it will likely be just a tropical storm. The upper pattern is very unfavorable for the moment, but will be improving as the upper-level trough gets bullied around and somewhat out of the way by the upper high associated with 93L. A lot of heat is getting released in the gulf, and this should allow wind shear to decrease a bit during the next two days.
Member Since: November 24, 2005 Posts: 635 Comments: 26652
127. 7544
katia is loosing its punch maybe dg to a ts on the next update will this have go further west now now toward the iswlands can we see a big cone change at 5pm ?
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Member Since: September 2, 2006 Posts: 110 Comments: 6878
125. jpsb
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.

Thanks, I heard the water levels in a lot of our lakes are way down, some are even dried up. Just curious what another 6 months of this would do, since I've read we can expect another six months at least.

I'm lucky in that the water table here is high, I've got water 20 feet down so the larger trees are not dying yet, but everything else is. Local MUD has us on no watering the yard but it is voluntary since they can't legally enforce it. Sure hope we get rain out of Lee.
Member Since: June 30, 2009 Posts: 0 Comments: 1193
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Quoting Levi32:
Katia is no longer a hurricane if her center is becoming this exposed. I full expect a downgrade next advisory:



Agreed. If I'm understanding this correctly, wouldn't a shallower system be more likely to stick to a more southerly track?
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Quoting P451:
We're in RSO for Goes now. Until the last frame where normal operations continued. It will go back RSO I would think. You can see some sort of rotation south of LA out ahead of the thunderstorms. You can also see the intense shear out there - note the storms in the western part of the image being sheared off.






Member Since: September 2, 2006 Posts: 110 Comments: 6878
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115. Patrap 12:22 PM EDT on September 01, 2011

Hey Pat; have not been on much and missed your posts below.......Nice to see you back and keep the data coming for this one........ :)
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@135HR:



Pretty much nothing left... unless it decides to go back over water.

Overall... GFS keeps it a at moderate TS to low end.
Member Since: August 14, 2008 Posts: 4 Comments: 4976
Quoting Patrap:
Just Videoed and took pics of the Biggest Green Grasshopper or my Furst Locust on my Porch.

That cant be good at all.

oh no.....just saw the radar....rains already rollin' in.
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Katia is no longer a hurricane if her center is becoming this exposed. I fully expect a downgrade next advisory:

Member Since: November 24, 2005 Posts: 635 Comments: 26652
New Orleans
NEXRAD Radar

Type
Velocity Azimuth Display Wind Profile ° Elevation
Range
124 NMI

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I have a silly question....in Dr Ms blog it said this

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,

so what about the states between FL and NC? what are the chances it would hit in that region
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I hope that Patrap comes out of hibernation for this one.......
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i see some nice spin going on now in 93l. this may get interesting. what do you think?
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For those that wonder what becomes of tropical systems once they exit stage...

Former Irene's circulation has been absorbed into a storm system near Iceland.

You can see a really neat loop of Irene's degeneration across Canada and Greenland here.

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that is scary
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Just Videoed and took pics of the Biggest Green Grasshopper or my Furst Locust on my Porch.

That cant be good at all.
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Quoting SPLbeater:
93L looks pathetic...not expecting a TD this week


It does indeed look pathetic right now, but I have a feeling if it stays over water, it'll spin up fast in to a tc, not sure about strength since it could be somewhat hybrid, although could also end up being completely tropical. It looks to me as of now it'll develop in a more sub-tropical manner, perhaps transitioning down the road. My point is it's going to look frontal and develop a spin somewhere and go from there.
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Quoting SPLbeater:
93L looks pathetic...not expecting a TD this week
Quoting DocBen:
Seems like 93 is in a perfect location to explode. Very warm waters under and around it.
all i gotta say is there be a LOT of precipitable moisture available... thinkin DocBen has a better handle on this one ;)
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Already getting some much-needed rainfall here in northshore metro New Orleans. Hoping that we keep in the "much-needed" category and don't jump up to extreme amounts, but if it just sits there right off the coast, it is almost certain that we will get several inches of rainfall. We are preparing for significant river rises if this are to happen, although the on-going drought has soil moisture very low, helping to mitigate runoff. Now it all comes down to intensity - if we get most of the rain in heavy thunderstorm bands, the soil could be bone dry and heavy runoff would still occur.
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93L is Neil Frank's nightmare. Opportunity to explode with no lead time to evacuate, equates to devastation and large loss of life
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Quoting wxobsvps:
Huge flip from 6Z to 12Z on GFS... can't make up its mind.

108 COC over NOLA


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.
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Quoting daw222:
What is an invest?

Glossary of NHC Terms
A weather system for which a tropical cyclone forecast center (NHC, CPHC, or JTWC) is interested in collecting specialized data sets (e.g., microwave imagery) and/or running model guidance. Once a system has been designated as an invest, data collection and processing is initiated on a number of government and academic web sites, including the Naval Research Laboratory (NRL) and the University of Wisconsin Cooperative Institute for Meteorological Satellite Studies (UW-CIMSS). The designation of a system as an invest does not correspond to any particular likelihood of development of the system into a tropical cyclone; operational products such as the Tropical Weather Outlook or the JTWC/TCFA should be consulted for this purpose.
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100. HCW
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Quoting wxobsvps:


actually that image shows that the trough has it...



It has some influence, but not to drag it to the NE and out.
Member Since: August 14, 2008 Posts: 4 Comments: 4976
Thanks Dr. M. A storm brewing in the Gulf with weak steering currents, and an uncertain intensity issue, is a potential nightmare for lots of folks along a large swath of the N Gulf coast going into next week.
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Seems like 93 is in a perfect location to explode. Very warm waters under and around it.
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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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