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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1445. DFWjc
Quoting StormSurgeon:
¿Alguno de ustedes piensa 963L alcanzará fuerza de tormenta tropical?


let's wait until tomorrow to make that answer...
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¿Alguno de ustedes piensa 963L alcanzará fuerza de tormenta tropical?
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GFS shows East Texas receiving 35 to 45 Knot Winds!!!

Member Since: May 31, 2011 Posts: 57 Comments: 572
Quoting Patrap:

..Our Invest, in da middle of da Gulf..


Madness!
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I think I hear rain......yes, it is rain... :)
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Quoting WeatherNerdPR:

Wasn't Franklin frontal as well?
ummmmm.....yes.
.
.
.
.
.
*bites tongue*
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1439. WxLogic
@114HR Katia getting closer:

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Interesting...
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Quoting AtHomeInTX:

Lol. K. That's better. Everything back to normal now. :D Thanks you do it soo much better than I.  Lol.


Glad I could help!
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Quoting MiamiHurricanes09:
Around 78 hours out on the 18z GFS, Katia goes from a 320 heading to about 285 (roughly).

Around 96 hours, it resumes a 320 course.

LOL, turns 280 again at 102 hours. Blehhhh.
model is showing the ridge rebuilding strong. honestly if the trough is weak and the ridge keeps on buidling west katia could recurve directly into north carolina if trends continue. i didnt see this coming..
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I almost hate to ask but is Katia starting to remind anyone of Andrew?
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Quoting BrockBerlin:


Seems to be more on board with the west bending models now, as the ridge strengthens overhead


No, it's just does a short west jog and then back to the big curve near Bermuda, not a big change at all from previous gfs runs. unless you mean 93 and that heads directly up into LA
Member Since: August 26, 2006 Posts: 0 Comments: 1548




lol guys look like its a 3v3 well see which team wins
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Quoting Patrap:


Looks like outflow channels developing from 340 degrees all the way around to 190. If so...this is going to be big.
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1430. Patrap
Quoting TexasHurricane:


haha... :)



ACK !

: )
Member Since: July 3, 2005 Posts: 426 Comments: 128874
Quoting Patrap:

..Our Invest, in da middle of da Gulf..


haha... :)
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1427. DFWjc
Quoting twincomanche:
Most of the people I know from Texas speak little or no Spanish. What is your point?


In Texas, English is conventionally used in government; the state has no official language. The continual influx of Spanish-speaking immigrants increased the import of Spanish in Texas. Even in the 21st century, Texas's counties bordering Mexico are mostly Hispanic, hence, Spanish is the common language of the region's multi-generational Mexican Americans, yet, they are more English-proficient than their southern counterparts.
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1424. Patrap

..Our Invest, in da middle of da Gulf..
Member Since: July 3, 2005 Posts: 426 Comments: 128874
Quoting BrockBerlin:


Actually it appears you have made another goof they did not say that about Hurricane Lenny in 1999.
lolol and Omar 2008
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1422. WxLogic
@93HR 18Z GFS:

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1420. breald
I hope that westward trend of Katia is just the computer models screwing with us.
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The mouse is useless when the blog goes this fast :-)
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Quoting notanothergoof:
could the sw periphery fall apart maybe?


The only reason a portion of a ridge can be eroded is if there is a trough that moves into the area. This is not the case because if you look at the steering I posted, the flow in the mid latitudes is very zonal with no major troughs on the way to weaken the ridge. The reason she will turn to the NW soon is because there is a break in between the ridge over the southeast U.S. and the subtropical ridge in the Atlantic.
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Quoting Sfloridacat5:
We're having a major downpour in South Fort Myers. The rain filled up a bucket in a matter of minutes.


Send that bucket to Texas. ;)
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Quoting TropicalAnalystwx13:
2011 Atlantic Hurricane Season Progress So Far:

- Arlene (TS)
- Bret (TS - Frontal)
- Cindy (TS - Frontal)
- Don (TS)
- Emily (TS)
- Franklin (TS)
- Gert (TS)
- Harvey (TS)
- Irene (C3)
- Jose (TS)
- Katia (C1)


Funny thing is....the only one I really remember is Irene.....sad isn't it...
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Quoting MiamiHurricanes09:
Around 78 hours out on the 18z GFS, Katia goes from a 320%u02DA heading to about 285%u02DA (roughly).


Huh?
Member Since: July 6, 2010 Posts: 113 Comments: 32347
Quoting WeatherNerdPR:

Wasn't Franklin frontal as well?


mhm...
Member Since: July 6, 2010 Posts: 113 Comments: 32347
1410. Patrap
Member Since: July 3, 2005 Posts: 426 Comments: 128874
In Central/South Texas floods are a way of life. Seriously...
It's very hilly, so water drains quickly, recharging aquifers etc.
Just don't build in a flood plain & avoid driving through creeks etc.
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Quoting JamesSA:


I don't know where you live, but obviously not around here. Central TX could handle 20" right now with just flash flooding in the usual areas. The ground is porous and parched to great depth, it would absorb more than you might imagine.


It would definitely not hold 20"...Maybe somebody else can explain in detail?
Member Since: July 6, 2010 Posts: 113 Comments: 32347
Around 78 hours out on the 18z GFS, Katia goes from a 320 heading to about 285 (roughly).

Around 96 hours, it resumes a 320 course.

LOL, turns 280 again at 102 hours. Blehhhh.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
Quoting TropicalAnalystwx13:
2011 Atlantic Hurricane Season Progress So Far:

- Arlene (TS)
- Bret (TS - Frontal)
- Cindy (TS - Frontal)
- Don (TS)
- Emily (TS)
- Franklin (TS)
- Gert (TS)
- Harvey (TS)
- Irene (C3)
- Jose (TS)
- Katia (C1)

Wasn't Franklin frontal as well?
Member Since: July 7, 2010 Posts: 0 Comments: 5694
1404. Patrap
Member Since: July 3, 2005 Posts: 426 Comments: 128874
2011 Atlantic Hurricane Season Progress So Far:

- Arlene (TS)
- Bret (TS - Frontal)
- Cindy (TS - Frontal)
- Don (TS)
- Emily (TS)
- Franklin (TS - Frontal)
- Gert (TS)
- Harvey (TS)
- Irene (C3)
- Jose (TS)
- Katia (C1)
Member Since: July 6, 2010 Posts: 113 Comments: 32347

Quoting TexasHurricane:


LOL!!! It's ok, calm down.... The Hurricane season isn't over yet. If not this one hopefully another.

Did I do good with my pep talk? :)
Lol. K. That's better. Everything back to normal now. :D Thanks you do it soo much better than I.  Lol.
Member Since: August 24, 2010 Posts: 0 Comments: 250
Quoting xtremeweathertracker:

This means rain for the Golden Triangle...Channel 6 forecasters are nuts!!!




I don't know. The models keep switching. Hopefully late tonight or early tomorrow it will be more accurate. :)
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1399. JamesSA
Quoting TropicalAnalystwx13:


No, because a lot of it would be run-off if it is heavy rain.


I don't know where you live, but obviously not around here. Central TX could handle 20" right now with just flash flooding in the usual areas. The ground is porous and parched to great depth, it would absorb more than you might imagine.
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1398. IKE
81 hour 18Z GFS...




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SW Louisiana, North of Lake Charles. Breezy conditions all day. Winds increasing with small gusts now. Barometric pressure dropping throughout the day. Starting to look and feel a lot more tropical now.
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Quoting tulsahurrcane:


If BP is sponsoring, don't eat the shrimp


Won't even have to cook the shrimp if you go get them out of that marsh fire.
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1395. Patrap
Member Since: July 3, 2005 Posts: 426 Comments: 128874

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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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