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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Quoting naplesdreamer28:
I'm surprised I have not heard "Katia is going to Florida" yet!
I know what you mean. But give time. You'll hear plenty of that in due time. But, my bet is that it will not get that far west. Now I notice the gfs 18z runs drops the storm behind her. . . maybe next run or two will it have reappear.
Member Since: August 26, 2006 Posts: 0 Comments: 1548
Quoting redwagon:
p>Well, I won my bet, if nothing else: the BOC system put water on TX faster than Lee did. By about 10 minutes.

Is anybody looking at that Panama spin?


Link
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Quoting TexasHurricane:


ok, this just don't sound good for TX at all.

Let me ask you this. Do you see anything down the road that may could help us out?


Well if not 93L, then there is still some hope this month. The ensembles still favor ridging over southern Canada, which will bring storms close to the U.S., and the weakest point in the ridge will be over the central-eastern GOM by mid-month according to the GFS ensembles. This could bring some storms close to Texas if they come in from far enough south like from the Caribbean, or home-brew. However, all season long it may be difficult to drive a tropical cyclone straight into the heart of Texas, unfortunately.
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12z ECMWF has Katia doing something very similar to a Frances (except with a recurvature), should 93L get caught in the trough. (Correct me if I'm wrong, just got home and am pretty much lost with everything that's happened today lol).
Member Since: September 2, 2009 Posts: 130 Comments: 21194
Quoting scott39:
He must be a good man then. Lol


The best I have ever known.
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Quoting carcar1967:


Your B-day is the same as my Dad.
He must be a good man then. Lol
Member Since: June 13, 2009 Posts: 0 Comments: 6914
Katia is also a struggling storm, just trying to hang on to hurricane status at the moment




Dry air to the north and west are the main issues for Katia as they've prevented any deep convection from getting established along the western side. The main core of convection is getting better positioned over the surface center now, but it may still be slightly exposed as indicated earlier by microwave and visible imagery. Cloud tops are also beginning to cool again as new convection begins to pierce the cirrus canopy as seen in the satellite image above.

Looking ahead, the dry air already mentioned, and an upper level low to the northwest hampering anticyclonic flow and divergence will be the main issues for Katia. NHC mentions this in their discussion as well. It will be interesting to see how significantly this ULL affects Katia's upper level environment. The ECMWF doesn't allow Katia to establish good anticyclonic flow aloft until around days 3/4. Meanwhile, the GFS just kind shoves off the ULL allowing the ULAC to remain over Katia for the next several days. So the differences between the two are pretty large, and its also reflected in the MSLP forecast for each model. The GFS shows steady strengthening throughout the forecast period, meanwhile the ECMWF shows a little strengthening over the next two days, then a little weakening, until strengthening again by days 4/5.
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Well folks, what do y'all think? We have TD 13?
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Quoting NoVaForecaster:


Because its not going to Florida and never has been forecasted to in its lifetime so far.....



HUH?? NOT so fast...new models are out and turn the systems westward, even TWC is commenting on this
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ok, I know the ECMWF just did not say that? Did it really just say that? It shows a STRONG storm in the gulf with the pressure dropping rapidly from a 985 MB storm on Monday to a 930 MB storm next Friday.

Monday
Link

Next Friday
Link

If that happened it would be VERY Bad on the gulf coast. The storm wanders a bit dumping excessive rainfall on the Central Gulf Coast before making landfall int he same area that it has dumped 15+ inches of rain.
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Here is the my million dollar question.....Just how strong does 93L have the potential to get, if its over water until Tue or Wed?
Member Since: June 13, 2009 Posts: 0 Comments: 6914
Quoting pottery:

Thank you for that.

You are a Benefit to this Blog, Levi.
Never dodge a question and always give good concise answers to all questions, as far as I can see.

It's MUCH APPRECIATED!

P.S., I hope that Wunderground is paying you for the Service you provide here!


Like Like Like Like
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Quoting scott39:
It is your fault, like my parents. You planned us to be born at a time when hurricane season is starting to peak. You also moved us on the Gulf Coast. Lol Im just giving you a hard time. My B-day is 8/26


Your B-day is the same as my Dad.
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Quoting Patrap:
93L Loop O Doom, or Rainbow Floater
p>Well, I won my bet, if nothing else: the BOC system put water on TX faster than Lee did. By about 10 minutes.

Is anybody looking at that Panama spin?
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Lafourche Parish
Emergency Operations Center
Emergency Information for Lafourche Residents
Phone: (985) 537-7603
UPDATED 08/15/2011 at 12:00 P.M.
Page refreshes every 90 seconds.

NO CURRENT EMERGENCY AT THIS TIME


Nothing at all on the Jefferson Parish (Grand Isle, Barataria) or Plaquemines Parish emergency web sites at this time.

NOLA mayor holding a press conference at 2:30 CDT.


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Quoting naplesdreamer28:
I'm surprised I have not heard "Katia is going to Florida" yet!
Im surprised I haven't heard 93L is going to hit NYC!! LOL
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Quoting naplesdreamer28:
I'm surprised I have not heard "Katia is going to Florida" yet!

I thought that was a 'given', LOL!
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Quoting scott39:
It is your fault, like my parents. You planned us to be born at a time when hurricane season is starting to peak. You also moved us on the Gulf Coast. Lol Im just giving you a hard time. My B-day is 8/26


Actually she is my step-daughter. But I call her my own because I am the one who is raising her.
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Quoting Levi32:


Well the monsoon trough portion of the ITCZ is still there from Africa to 40W...not sure why it's not analyzed this morning. From that point, the trade winds from 40W into the Caribbean are actually all southeasterly, and there is little sign of northeast trades meeting them, which is the definition of the ITCZ boundary. Part of this is likely due to Katia messing up the northeast trade wind flow in the central Atlantic. Also, pressure have been much higher than normal near and just north of the equator recently, with below-normal pressures in the SW Atlantic. This would tend to shift the ITCZ farther north than normal in a very active position, but due Katia and so much low pressure in the SW Atlantic, the trade wind flow is getting distorted and thus there is no real solid convergence zone. In reality though, this pattern is a very active one.


Thank you for that.

You are a Benefit to this Blog, Levi.
Never dodge a question and always give good concise answers to all questions, as far as I can see.

It's MUCH APPRECIATED!

P.S., I hope that Wunderground is paying you for the Service you provide here!
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Link
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If you closely at 93L on the IR RGB loop I think you can pretty clearly see the center trying to form around 26.5N and 91W. Just in the last couple frames convection is even building on the West side of the center, could be a depression sometime tonight IMO.

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Looking better for Bermuda in recent runs
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Quoting Levi32:


Like Atmo said, if it remained broad, a larger area of heavier rain could result, but it should tighten up a bit in the coming days. In east Texas it's going to be iffy and dependent on the track, as well as how well the NW quadrant of the storm fills out. LA should get most of it, possibly a bad flooding situation, but coastal Texas to 50 miles inland could get a few inches if 93L hangs close enough.


ok, this just don't sound good for TX at all.

Let me ask you this. Do you see anything down the road that may could help us out?
Member Since: July 2, 2009 Posts: 0 Comments: 2811
Quoting wxobsvps:
I hope NHC classifies it if for nothing else than to get to see what will probably be one of the funniest looking cones in history.

Here is the reigning Champion, from the past five years:

We will probably have a new record soon.
Member Since: June 13, 2009 Posts: 0 Comments: 6914
Quoting TexasHurricane:
Levi, could 93 get big and we may could get more rain than they may be thinking right now? I am in SE TX about 10-15 min from the LA border.



Like Atmo said, if it remained broad, a larger area of heavier rain could result, but it should tighten up a bit in the coming days. In east Texas it's going to be iffy and dependent on the track, as well as how well the NW quadrant of the storm fills out. LA should get most of it, possibly a bad flooding situation, but coastal Texas to 50 miles inland could get a few inches if 93L hangs close enough.
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Quoting atmoaggie:
Too bad they misspelled it...
;-)
Boom Boom!
Member Since: June 13, 2009 Posts: 0 Comments: 6914
Quoting NoVaForecaster:


Because its not going to Florida and never has been forecasted to in its lifetime so far.....
but it could
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Quoting atmoaggie:
I'm not Levi, but your rainfall would be much higher if 93L stays broad and disorganized. But, that is not my personal expectation of this system.

Where y'at? PA, Groves, Bridge City, Orangefield, Vidor?


Mauriceville
Member Since: July 2, 2009 Posts: 0 Comments: 2811
Quoting luigi18:

Levi do we need to be prepare here in Puerto Rico for the visit of Katia???


I would say no. While it is very good practice to watch a storm until it is physically passing you, it looks like it should easily clear the northeast Caribbean.
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Quoting scott39:
A few downpours here in the first city that gave Madi Gras its name :)
Too bad they misspelled it...
;-)
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Quoting PrivateIdaho:


One of them is bound to be right.


you weren't suppose to say that.... :)

why am I not surprised...
Member Since: July 2, 2009 Posts: 0 Comments: 2811
Quoting WxLogic:
@240HR ECMWF 12Z:



Shoots NE... I'm not quite buying that sharp turn.


a hard left and then a hard right?
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Quoting P451:



They have investigated the region that you can see on RGB imagery.



posted at 1753Z


There are indications from the surface stations of something like circulation Wish there were more surface obs. We need more bouys or require ever damn rig to put put a public weather station.

Pat, row yr pirogue out to about 90.5 w, 28 N and tell us which way the wind is blowing.
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Quoting TexasHurricane:
Levi, could 93 get big and we may could get more rain than they may be thinking right now? I am in SE TX about 10-15 min from the LA border.

I'm not Levi, but your rainfall would be much higher if 93L stays broad and disorganized. But, that is not my personal expectation of this system.

Where y'at? PA, Groves, Bridge City, Orangefield, Vidor?
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648. ackee
katia contiue to move west now seem like model will have no chioce but to shift futher west
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Quoting Patrap:
Wet from Mobile to Morgan City and further..


A few downpours here in the first city that gave Madi Gras its name :)
Member Since: June 13, 2009 Posts: 0 Comments: 6914
I'm surprised I have not heard "Katia is going to Florida" yet!
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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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