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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UKMET model 12z run is a reason why we can't let our guard down on Katia.

Also it points the picture in which the wave near 29w/8n will move into the Caribbean Sea with it so far south and the high strong enough.
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Quoting MississippiWx:


The NHC likes to go with the TVCN which is way away from Houston on the 18z models.


Well we will probably see at 5PM, looks like a renumber coming up.
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93L Floater - Infrared Channel 4 Loop
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792. IKE

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Quoting MississippiWx:


I hope it is Houston. Got too many things going on this weekend for there to a flood here. :-D


We wouldn't mind it however I don't want it sitting for a while turn into a major and then bam.....

If it stayed a TS or even a cat 1. I'm good.
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Quoting xtremeweathertracker:

Levi your thoughts on the models moving 93L north when steering currents at least temporarily should take it northwest!


lets just wait for a definite center of circulation to form with a HH measured MSLP before nit picking NNW vs NW vs N
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As Brock pointed out a little earlier, the UKMET has shifted quite a bit to the south with Katia.

Member Since: September 2, 2009 Posts: 130 Comments: 21091
Quoting nrtiwlnvragn:



Look at the 93L 18Z SHIPS which has track:
FORECAST TRACK FROM OFPI

On the SHIPS text, lat and lon are not shown (xx.x)
So find a plot with SHIPS or LGEM and you have OFPI track.


The NHC likes to go with the TVCN which is way away from Houston on the 18z models.
Member Since: July 15, 2006 Posts: 17 Comments: 10159
Oh geez, someone get the kids out of here, there coloring all over the place with these models for 93L. So 93L can actually affect Katia by making it go more west?
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Quoting wunderweatherman123:
hey are we neutral now or a weak la nina again because the recent nino 3.4 reigon sst was -0.6C i know we had a strong la nina last season and we are neutral (cool) to a weak la nina now but would an el nino have to form to end the texas drought or would neutral enso conditions have to persist for like 2 years?


The "neutral" this summer was a ruse... the PDO is negative and the atmosphere never stopped behaving like a strong La Nina was in play. Essentially we're heading for a 3rd-year La Nina. It won't officially be La Nina again until we have a 3-month period where Nino3.4 SST anomalies average -0.5C or lower. It will probably take another year or so and a transition into a weak El Nino to really cure the Texas drought.
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From the Houston/Galveston discussion...

IMPACTS FOR SE TX...GIVEN A QUASI STATIONARY LOCATION OFF THE LA
COAST...COULD HAVE LARGE FIRE WEATHER IMPACTS WITH DRIER AIR
WRAPPING AROUND IT FOR THE NORTHERN HALF OF SE TX.
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Quoting TexasHurricane:


yeah, huh?


I hope it is Houston. Got too many things going on this weekend for there to a flood here. :-D
Member Since: July 15, 2006 Posts: 17 Comments: 10159
Quoting MississippiWx:


Huh?



Look at the 93L 18Z SHIPS which has track:
FORECAST TRACK FROM OFPI

On the SHIPS text, lat and lon are not shown (xx.x)
So find a plot with SHIPS or LGEM and you have OFPI track.
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Quoting P451:


When dealing with a system that meanders or is stationary it will only get so strong before upwelling causes it to weaken some and then level off. A storm that stays in one place long enough eventually cools off a region just by virtue of the torrential rain it drops into the sea as well.

How strong it gets and where it drops to and levels off in such a scenario I'm not sure.

You wouldn't see a storm grow to Cat 5 just sitting there though. Can't happen.

Maybe Cat 2 or 3 (if it has a decent forward motion at first) that drops back down to Cat 1 or 2 (if it then stalls for a long period of time).


If it only makes it to Cat 1 (because it is just stalled from the start) and sits and spins it'll drop down to strong TS.



Thanks. That was very informative.
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Quoting Bluestorm5:
Well, NHC's track for Katia is starting to make me nervous... I know it might curves away, but it just look like a sharp curve if it does that.


Making me a bit uncomfortable too.
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Quoting MiamiHurricanes09:
94L's convection has been displaced considerably to the east over the past few hours. However, just a minor increase in convective activity and yet another name will be wasted on a cyclone that lasts a few hours, lol. Don't think it'll make it though...upper-level conditions are pretty darn hostile.

does not matter high seas event anyway and it will be next to nothing
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Quoting Levi32:


Yeah unfortunately. It could happen, but the timing would have to be perfect and everything. We're in the pattern of the 1950s. You've heard me and others mention it regarding more than one kind of weather pattern. Here it's the dryness in Texas. The mid-1950s was a perpetual drought period for that area.
The fifties (I can't remember the exact years) remain the worst overall drought on record in Texas.
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Quoting MiamiHurricanes09:
94L's convection has been displaced considerably to the east over the past few hours. However, just a minor increase in convective activity and yet another name will be wasted on a cyclone that lasts a few hours, lol. Don't think it'll make it though...upper-level conditions are pretty darn hostile.

Yep, the surface circulation is definitely there. NHC almost could have named it this morning, although its probably best they waited for some persistence, because of how it looks now.

Anyway, yea if it just gets some thunderstorms over the top...could be looking at our 4th tropical thunderstorm (yes, tropical thunderstorm) to form off a frontal boundary so far this year.
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Quoting Levi32:


That's a little better lol.

Levi your thoughts on the models moving 93L north when steering currents at least temporarily should take it northwest!
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Quoting MiamiHurricanes09:
94L's convection has been displaced considerably to the east over the past few hours. However, just a minor increase in convective activity and yet another name will be wasted on a cyclone that lasts a few hours, lol. Don't think it'll make it though...upper-level conditions are pretty darn hostile.



Doesn't look any worse than Jose did.. just instead of the convection being displaced to the south, it's displaced to the east.
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Quoting MississippiWx:


Huh?


yeah, huh?
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Quoting Levi32:


Yeah unfortunately. It could happen, but the timing would have to be perfect and everything. We're in the pattern of the 1950s. You've heard me and others mention it regarding more than one kind of weather pattern. Here it's the dryness in Texas. The mid-1950s was a perpetual drought period for that area.
isn't 1950s the time when East Coast kept getting nailed by hurricanes, such as Hazel?
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Quoting Levi32:


Well the La Nina finally left...lol.

hey are we neutral now or a weak la nina again because the recent nino 3.4 reigon sst was -0.6C i know we had a strong la nina last season and we are neutral (cool) to a weak la nina now but would an el nino have to form to end the texas drought or would neutral enso conditions have to persist for like 2 years?
Member Since: August 23, 2011 Posts: 0 Comments: 1291
770. IKE

Quoting nrtiwlnvragn:


NHC is thinking Houston
I think they need to move it east a tad.
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12z UKMET: Cat 1 hurricane moving into Louisiana on Monday, pretty close to my forecast. These models are starting to make me feel better lol.

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Quoting nrtiwlnvragn:


NHC is thinking Houston


Huh?
Member Since: July 15, 2006 Posts: 17 Comments: 10159
94L's convection has been displaced considerably to the east over the past few hours. However, just a minor increase in convective activity and yet another name will be wasted on a cyclone that lasts a few hours, lol. Don't think it'll make it though...upper-level conditions are pretty darn hostile.

Member Since: September 2, 2009 Posts: 130 Comments: 21091
Quoting IKE:
Zeroing in on 93L?




That's a little better lol.
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Quoting ackee:
what will the NHC track for Katia be like at 5PM

A LEFT
B RIGHT
C THE SAME

WHAT WILL become of 93L

A TS
B TD
C CANE
D DISSCIPATE


E.high impacting flooding event
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Quoting IKE:
Zeroing in on 93L?




NHC is thinking Houston

Add: NE from Houston
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Well, NHC's track for Katia is starting to make me nervous... I know it might curves away, but it just look like a sharp curve if it does that.
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Can someone explain why the blog is so narrow on my screen? It cuts off the text on the right side of the longer posts. I have opened the blog in IE, Mozilla and Chrome. Same format in all. Anyone have a remedy? TIA
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93L is starting to look more like a tropical cyclone. I'm starting to notice some banding features on visible. The wall of shear is still present, but appears to be slowly letting go.

Member Since: July 15, 2006 Posts: 17 Comments: 10159
Quoting xtremeweathertracker:



ok, is this new? this has yellow over my area and that is more than 1-2 inches....
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new models runs all show Lee moving into lousiana now except the canadian which shows texas/lousiana border. intensity could be from a weak ts to a cat 3 im leaning more towards a 1 now but that could change if Lee gets a day or 2 more in the Gulf from a cat 1 to 3 in the boiling GOMEX is quite possible.
Member Since: August 23, 2011 Posts: 0 Comments: 1291
Quoting ackee:
what will the NHC track for Katia be like at 5PM

A LEFT
B RIGHT
C THE SAME

WHAT WILL become of 93L

A TS
B TD
C CANE
D DISSCIPATE
C-B
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Quoting TexasHurricane:


so, I wonder how that drought ended...


Well the La Nina finally left...lol.

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Quoting Levi32:


Yeah unfortunately. It could happen, but the timing would have to be perfect and everything. We're in the pattern of the 1950s. You've heard me and others mention it regarding more than one kind of weather pattern. Here it's the dryness in Texas. The mid-1950s was a perpetual drought period for that area.


so, I wonder how that drought ended...
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753. ackee
what will the NHC track for Katia be like at 5PM

A LEFT
B RIGHT
C THE SAME

WHAT WILL become of 93L

A TS
B TD
C CANE
D DISSCIPATE
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Quoting cycleranger:


If we're lucky the border of TX/LA gets 1-2 inches from 93L.

Nothing different than some of the brief disturbances we've gotten over the Summer.

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Quoting Levi32:
Wall of shear:

Upper divergence on one side, upper convergence on the other
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Quoting Levi32:


Sorry my quote messed up and my post didn't show. I edited it in.


thanks Levi
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Quoting scott39:
Is it showing any signs of weakening? Because when that wall collapses, 93L owns the GOM!


Not much yet, but tomorrow it should be starting to break down, and we may have a TD or TS by that point.
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Time: 19:06:30Z
Coordinates: 26.0167N 89.0333W
Acft. Static Air Press: 959.3 mb (~ 28.33 inHg)
Acft. Geopotential Hgt: 463 meters (~ 1,519 feet)
Extrap. Sfc. Press: 1010.8 mb (~ 29.85 inHg)
D-value: -
Flt. Lvl. Wind (30s): From 177° at 28 knots (From the S at ~ 32.2 mph)
Air Temp: 23.8°C (~ 74.8°F)
Dew Pt: 22.8°C (~ 73.0°F)
Peak (10s) Flt. Lvl. Wind: 29 knots (~ 33.3 mph)
SFMR Peak (10s) Sfc. Wind: 38 knots (~ 43.7 mph)
SFMR Rain Rate: 1 mm/hr (~ 0.04 in/hr)
(*) Denotes suspect data
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Quoting Levi32:
Wall of shear:

and to the right wall of water
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This morning I said: What is that ball of convection near Burmuda?
Now NHC says: 50% of TS formation. Only a slight increase in convection will result in TS formation.
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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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