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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2745. DFWjc
Quoting tiggeriffic:
im done...in the last 24 hours this blog has been more about politics, arguing moot points about the NHC, and someone trying to start a race riot... i will return when the 3 billy goats eat the trolls under the bridges and weather is the main topic...


night tigger
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Quoting MississippiWx:
Katia has reached the important 50W longitude. It's really no surprise why her convection is ballooning right now.

Indeed. Impressive how just an increase in ocean heat content can help promote updrafts, and thus help the cyclone intensify...considerably.
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2742. Oct8
Quoting tiggeriffic:


does it matter? the color of one's skin has no bearing on the type of person...but i will put MONEY that my ancestors were here LONG before yours


We all have the same ancestors. Believe it or not. Now back to the weather...
Member Since: August 26, 2011 Posts: 0 Comments: 39
2740. liljade
Quoting katharsiss:
Houston here. I have never felt the call to become a wishcaster so strongly as I do now.
LOL me too, we really need the rain.
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2739. DFWjc
Quoting KEEPEROFTHEGATE:


not this time KOG, i'm putting my foot down, this has to stop and stop now...
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84 hour rainfall total from the NAM

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Quoting LAnovice:
Using wind speed and a COC to determine the effects of a storm has been debated in the past few years/maybe decades. The NOAA/NHC is charged with a larger picture - IMHO - the NHC purpose is to alert citizens about damaging weather and the effect such weather will have on the populace it is charge to protect.
So - within that line of thinking - perhaps it is the rule book that needs to be changed. A storm can have great damaging effects - without the wind or a defined COC that a named storm or depression would require. Rain and tidal flooding are aspects of a tropical storm that are not included in the "rule book" for naming storms.
Me - I am happy to be told that there is something out there that warrants my actions - to prepare to shelter in place or move to higher ground. Don't care if that is called an "invest" or a TD. Unfortunately without a name or other designation - many people would not take a storm seriously.
Perhaps we need to look at changing the yardstick by which tropical systems and their damage is measured...


All you need to do is look at the damage caused to VT and Upstate NY by Irene to appreciate this post. I would rather have the forecasters/experts be on the safe side than to err because they're afraid of what people might think. The only issue I'm worried about is that if another storm system threatens an area that was evac'd but had no real damage that the people will ignore the warnings and then find themselves in dire straights or dead.
Here in MN, some counties have started the sirens for severe thunderstorm warnings - not just tornadoes - which has caused many of us to look at the sky, check the news and say "wtf?" One of these days people will be caught off-guard from the too frequent crying of wolf.
I personally appreciate all the work of the experts and amateurs on this site since whatever is said factors into decisions that can affect my family in big ways. Thanks for the info/input you all give.
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2735. Patrap
Quoting TomTaylor:
ridiculous rainfall forecast

Stay safe in nola, pat




will do,, thanx
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The 0 Z NAM looks good for a Katia deflection.

Link
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2733. DFWjc
Quoting zerveftexas:
You're obviously a communists. Only commies say that softy politically correct crap. Did I hurt your feelings or something?


No, I just tired of the f'n division or distractions from what needs to be solve on this planet. If we can't see past color, creed, or any other human trait, then we will never solve the NECESSARY problems of the planet we live on...
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Houston reporting in.

This evening we've had a few passing clouds with winds out of the east, today I received a few raindrops during the noontime hours and it's been hot otherwise.

Confidence in getting rainfall the next few days: fair.
Confidence in getting 2+ inches of rain over the next few days: poor.

Confidence that Fresca might be tasty: mighty fine.
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2731. KEEPEROFTHEGATE (Mod)
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The Governor can go it alone and issue a "State of Emergency" declaration and the EOP is up and running regardless-

Don't worry, those governors/mayors tend to flee the state at a moment's notice.
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I got my money on more than 3 feet falling by Monday morning in the French Quarter.

Treat every storm as an "event" now , ... They are.

These water models suck , nature is making more rain than they are seeing.
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2727. Skyepony (Mod)
Wow 15+" on NOLA..you are doom... & curve the Katia cone toward FL..

I talked about this yesterday 94L formed too far north...this is why i argued it would stay too cold core. It's just not deep enough, attached to that front. Had it happened farther south as expected there would be a gaping hole in the ridge for Katia to follow. Now the front is our only hope or FL will be doom too.
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2714. zerveftexas 2:53 AM GMT on September 02, 2011

The fact that you are not banned yet is more pathetic than your racist comments

Last I checked its 2011 not the 1960s. You need a serious reality check.
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im done...in the last 24 hours this blog has been more about politics, arguing moot points about the NHC, and someone trying to start a race riot... i will return when the 3 billy goats eat the trolls under the bridges and weather is the main topic...
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Quoting P451:


A discussion over whether or not a system warranted an upgrade is a tropical weather discussion and is important to those who discussed it.

To label it an argument is short sighted on your part.

I don't see a single attack between the users involved nor do I see any drama.

It's a valid debate about a system that was questionably upgraded.


+100
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Quoting FLdewey:


Yeah, I was flirting with the idea that since she weakened she'd get shoved West more, but it's still pretty clear she's a right hook.


I was thinking the same thing this afternoon... thought she might keep walking west.

Don't look that way now.... and I'm lookin' for that big turn.
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Quoting firecane:
http://www.southerndecadence.net/

Talk about raining on someone's parade...




This Link is highly relevant on many levels...
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2721. KEEPEROFTHEGATE (Mod)
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Well, if on day five, she heads wnw, (per nhc 11pm) under the sub trop ridge, then the whole east coast from cental FL to NC will be in the cone. If the ridge really builds in strong, it could send Katia even more westerly. imo.
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2718. beell
Quoting P451:


I love how they mention "SATELLITE".

One look at any satellite image of this would make you laugh at the upgrade. But that's just a line they always use when typing up these reports.


So if this is a TD then what was 94L today? What was the previous invest in the same location while Gert was south of Bermuda? What was the system that moved across the BOC into Mexico?

The answer would be: Tropical Cyclones.


So, you see, it's not so much about TD13 being prematurely named, or the stretching of the rules to name it, it's about systems they decide to hold to strict rules that then go unnamed.

Seems to me it's become a make the rules on the fly situation.

That is not what I would expect from an official entity would you?




I wonder how many state and local emergency operating plans are tied to the NWS and NHC's watch and warning criteria. I wonder how long it takes to assess the threat for the possibility of 20" of rain and make sure transportation, communications, public works, firefighting/rescue, mass care (Red Cross), special needs, etc, etc, etc, are awake and working out the details and making guesses on where the greatest impact(s) will be for TD 13.
Quite a bit of work.

The Governor can go it alone and issue a "State of Emergency" declaration and the EOP is up and running regardless-but it probably helps if NOAA is on your side.

Does seem like there needs to be a happy medium between the criteria for emergency operations and storm classification. We failed to find this middle ground on TD 13 today.


"Happy Medium"

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Quoting extreme236:


Just on that last point, 94L is better organized than TD13 and isn't classified.


I think TD13 was a discretionary call made based on its proximity to land.
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is TD13 still expected to stall?
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Quoting Patrap:
ridiculous rainfall forecast

Stay safe in nola, pat
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2713. will40
2682. zerveftexas


welcome to ignore you nut head
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Quoting DFWjc:
People we are HUMAN, not black, white, we are men, we are female, we are gay, we are straight, get used to it and stop the bickering on f'n race, I'm so sick of this crap...


Well said....
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Katia has reached the important 50W longitude. It's really no surprise why her convection is ballooning right now.

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Quoting Halon056:


Get in line tigger...


You tell him Tigger !
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http://www.southerndecadence.net/

Talk about raining on someone's parade...

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2707. DFWjc
People we are HUMAN, black, white, we are men, we are female, we are gay, we are straight, get used to it and stop the bickering on f'n race, I'm so sick of this crap...
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2705. Drakoen
Quoting Skyepony:


94L is attached to a front & should not be organized..


No it is not attached to a front.
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anyone by chance check out the 11pm 5-day track for Katia, a bend back to the WNW happens between days 4 and 5
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Quoting MiamiHurricanes09:
Although the focus is mainly on 13L at the moment, I'd like to point out that Katia's convection is basically erupting as we speak. Looks like the cyclone has found it's sweet spot.



Was looking at it... she's about to get her mojo back... next day or so is big for her.

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Quoting tiggeriffic:


does it matter? the color of one's skin has no bearing on the type of person...but i will put MONEY that my ancestors were here LONG before yours


Last year in this blog there was a racist called KerryinNola... He was banned, due to calling Latinos and different people racist names...
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Quoting MiamiHurricanes09:
Although the focus is mainly on 13L at the moment, I'd like to point out that Katia's convection is basically erupting as we speak. Looks like the cyclone has found it's sweet spot.


She found 50W, which makes it no surprise...

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2698. DFWjc
Quoting zerveftexas:

Well I'm a white man and I believe it is perfectly fine. I mean they get what they deserve, basically. They're inferior in every way, save for a few wild animal characteristics.


*POOF*
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Quoting zerveftexas:

hmmmmmmmmmm.....what race are YOU?
The human race.... Which you are obviously not a part of.... Go back to your own planet....
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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.