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 washingtonian115:
No offense....but T.D 13 has got to be one of the ugliest T.D's I have seen.


TD 13 looks like a moderate Category 2 hurricane compared to No way Jose.
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Two feet of rain anyone?

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1843. Pallis
Texas has a disaster fund.When hurricane Ike hit Galveston in 2008 Texas told FEMA they did not require their assistance.FEMA barged in on their cleanup and angered a lot of Texans.The reason they came in was so they could use the national guard to keep local contractors from entering the most exclusive neighborhoods.We pay for our own robbery.FEMA families are all millionaires.Most States now have no disaster plan and some are trying to point fingers at someone who is trying to get his State more emergency funds without a useless bureaucracy stealing from it first.FEMA's got some splainin' to do.
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1842. Patrap
FunkTop

Member Since: July 3, 2005 Posts: 428 Comments: 129903
it might take a while for the track lol
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Quoting Levi32:


It's reasonable based on only 48 hours over water. That intensity will shift significantly if the track slows down at all.


Significantly?
Member Since: July 6, 2010 Posts: 113 Comments: 32861
Quoting Levi32:


It's reasonable based on only 48 hours over water. That intensity will shift significantly if the track slows down at all.


Or relocates south, which is certainty possible.
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No offense....but T.D 13 has got to be one of the ugliest T.D's I have seen.
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You notice after a NW turn the track on Katia seems to be coming back almost due West around 65-70 West?
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Quoting MiamiHurricanes09:
Doesn't exceed 50kts. Seems reasonable.

FORECAST VALID 03/1800Z 29.3N 92.6W
MAX WIND 50 KT...GUSTS 60 KT.
50 KT... 30NE 60SE 0SW 30NW.
34 KT...150NE 90SE 30SW 100NW.
hey miami i am starting to believe that Katia is not going to head North west as the models indicate, and i have noticed with every run a further west trend , does it looks like the northern islands are in danger
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1832. WxLogic
:)
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1831. Dakster
Special Advisory Products for 13 just issued!
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1830. Levi32
Quoting MiamiHurricanes09:
Doesn't exceed 50kts. Seems reasonable.

FORECAST VALID 03/1800Z 29.3N 92.6W
MAX WIND 50 KT...GUSTS 60 KT.
50 KT... 30NE 60SE 0SW 30NW.
34 KT...150NE 90SE 30SW 100NW.


It's reasonable based on only 48 hours over water. That intensity will shift significantly if the track slows down at all.
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000
WTNT43 KNHC 012342
TCDAT3

TROPICAL DEPRESSION THIRTEEN SPECIAL DISCUSSION NUMBER 1
NWS NATIONAL HURRICANE CENTER MIAMI FL AL132011
700 PM CDT THU SEP 01 2011

SATELLITE...SURFACE...AND NOAA RECONNAISSANCE AIRCRAFT DATA INDICATE
THAT THE LOW PRESSURE AREA OVER THE CENTRAL GULF OF MEXICO HAS
ACQUIRED A CLOSED CIRCULATION THAT IS DEFINED ENOUGH TO BE
CONSIDERED A TROPICAL DEPRESSION. HOWEVER...THE CENTRAL REGION
STILL CONSISTS OF A LARGE AREA OF LIGHT WINDS. THE AIRCRAFT DATA
AND BUOY OBSERVATIONS SUPPORT AN INITIAL INTENSITY OF 30 KT.
ALTHOUGH THERE IS WIND SHEAR OVER THE CYCLONE...AN UPPER-LEVEL
ANTICYCLONE IS FORECAST TO BUILD OVER THE GULF OF MEXICO DURING THE
NEXT DAY OR SO. THIS SHOULD PROVIDE A MORE FAVORABLE UPPER-LEVEL
ENVIRONMENT FOR STRENGTHENING. HOWEVER...SINCE THE CIRCULATION IS
LARGE ONLY GRADUAL STRENGTHENING IS ANTICIPATED. THE OFFICIAL
INTENSITY FORECAST FOLLOWS THIS REASONING AND IS CLOSE TO THE
SHIPS/LGEM GUIDANCE.

SINCE THE DEPRESSION IS IN ITS FORMATIVE STAGE THE INITIAL MOTION
IS HIGHLY UNCERTAIN. IN FACT...THE CENTER COULD REFORM WITHIN THE
LARGE CIRCULATION DURING THE NEXT 12-24 HOURS. THE DEPRESSION IS
CURRENTLY LOCATED TO THE SOUTH OF A MID/UPPER LEVEL RIDGE OVER THE
CENTRAL UNITED STATES. THE RIDGE IS FORECAST TO SLIDE EASTWARD AND
WEAKEN DURING THE NEXT 2-3 DAYS...LEAVING THE CYCLONE IN WEAK
STEERING FLOW. THE OFFICIAL FORECAST SHOWS A SLOW NORTHWESTWARD
MOTION DURING THE NEXT 24 HOURS...FOLLOWED BY A TURN TOWARD THE
NORTH AND NORTHEAST. THE NHC TRACK IS IN BEST AGREEMENT WITH THE
GFS AND ECMWF MODELS.

THE DEPRESSION IS EXPECTED TO MOVE VERY SLOWLY DURING THE NEXT 5
DAYS PROLONGING THE PERIOD OF TROPICAL STORM CONDITIONS AND HEAVY
RAINFALL OVER PORTIONS OF THE NORTHERN GULF COAST.

FORECAST POSITIONS AND MAX WINDS

INIT 02/0000Z 26.6N 91.4W 30 KT 35 MPH
12H 02/0600Z 27.5N 92.3W 35 KT 40 MPH
24H 02/1800Z 28.2N 92.6W 40 KT 45 MPH
36H 03/0600Z 28.7N 92.7W 45 KT 50 MPH
48H 03/1800Z 29.3N 92.6W 50 KT 60 MPH
72H 04/1800Z 30.1N 92.3W 40 KT 45 MPH...INLAND
96H 05/1800Z 31.1N 91.5W 30 KT 35 MPH...INLAND
120H 06/1800Z 32.0N 90.5W 25 KT 30 MPH...INLAND

$$
FORECASTER BROWN/AVILA
Member Since: September 2, 2009 Posts: 130 Comments: 21194
Quoting CybrTeddy:
Meanwhile.. back in the CATL.. Katia's jealousy for TD13 suddenly stealing her spotlight is becoming increasingly obvious. Making its run back for hurricane status.


The low level center is near the western edge of all that strong convection though. She is still a pretty sheared cyclone right now. Wait until this time tomorrow and things will have improved markedly for her.
Member Since: September 24, 2005 Posts: 33 Comments: 9265
2010 had 12 named storms after September 1.

2009 has 5 named storms after September 1.

2008 had 8 named storms after September 1.

2007 had 9 named storms after September 1.

2006 4 named storms after September 1.

2005 15 named storms after September 1.

2004 8 named storms after September 1.

2003 10 named storms after September 1.

2002 7 named storms after September 1.

2001 10 named storms after September 1.

2000 11 named storms after September 1.

2000, 2001, 2003, 2004, 2005, 2007, 2008, 2010 are good indications of what I think we will see for the rest of the season.
Member Since: July 6, 2010 Posts: 113 Comments: 32861
60mph at peak. 11% chance of a hurricane.

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1824. JGreco
Quoting MiamiHurricanes09:
Moving nearly due west. Me no likey...but then again, it's the NOGAPS.


Are these two storms having or going to have a influence on each other. I've been shocked by the models so far...I really don't know what to expect from either:o
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Doesn't exceed 50kts. Seems reasonable.

FORECAST VALID 03/1800Z 29.3N 92.6W
MAX WIND 50 KT...GUSTS 60 KT.
50 KT... 30NE 60SE 0SW 30NW.
34 KT...150NE 90SE 30SW 100NW.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
1822. wpb
22:28:30Z 26.767N 90.233W 615.9 mb
(~ 18.19 inHg) 4,225 meters
(~ 13,862 feet) 999.7 mb
(~ 29.52 inHg
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Patrap, your images make it look so much bigger.

They just announced her TD 13 officially.
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1819. aquak9
Quoting notanothergoof:
omg thats a frightening site


someone sedate him, please...his nonchalant hysteria is pushing me to the edge.
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TROPICAL DEPRESSION THIRTEEN SPECIAL ADVISORY NUMBER 1
NWS NATIONAL HURRICANE CENTER MIAMI FL AL132011
700 PM CDT THU SEP 01 2011

...TROPICAL DEPRESSION FORMS OVER THE CENTRAL GULF OF MEXICO...
...TROPICAL STORM WARNINGS ISSUED FOR PORTIONS OF THE NORTHERN GULF
COAST...


SUMMARY OF 700 PM CDT...0000 UTC...INFORMATION
----------------------------------------------
LOCATION...26.6N 91.4W
ABOUT 225 MI...360 KM SW OF THE MOUTH OF THE MISSISSIPPI RIVER
MAXIMUM SUSTAINED WINDS...35 MPH...55 KM/H
PRESENT MOVEMENT...NW OR 315 DEGREES AT 6 MPH...9 KM/H
MINIMUM CENTRAL PRESSURE...1007 MB...29.74 INCHES


WATCHES AND WARNINGS
--------------------
CHANGES WITH THIS ADVISORY...

A TROPICAL STORM WARNING HAS BEEN ISSUED FOR THE COAST OF THE
NORTHERN GULF OF MEXICO FROM PASCAGOULA MISSISSIPPI WESTWARD TO
SABINE PASS TEXAS.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT...

A TROPICAL STORM WARNING IS IN EFFECT FOR...
* PASCAGOULA MISSISSIPPI WESTWARD TO SABINE PASS TEXAS

A TROPICAL STORM WARNING MEANS THAT TROPICAL STORM CONDITIONS ARE
EXPECTED SOMEWHERE WITHIN THE WARNING AREA...IN THIS CASE WITHIN
24 HOURS.
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Quoting P451:


If this was out in the middle of the Atlantic it would just continue on as an Invest for the night.

Since it's close to land it's upgraded?

I just have issues with that line of reasoning is all.

They're going to do what they want to do with a system regardless of my reservations about it.


All necessary conditions have been met for tropical cyclone formation. Warm core, a closed LLC (weak I know), persistent convection over or near the LLC for 12 hours or more (not a great deal but just enough), sustained winds of at least 30 mph measured by RECON instruments or observations from the ground.
Member Since: September 24, 2005 Posts: 33 Comments: 9265
..TROPICAL DEPRESSION FORMS OVER THE CENTRAL GULF OF MEXICO... ...TROPICAL STORM WARNINGS ISSUED FOR PORTIONS OF THE NORTHERN GULF COAST...
7:00 PM CDT Thu Sep 1
Location: 26.6°N 91.4°W
Max sustained: 35 mph
Moving: NW at 6 mph
Min pressure: 1007 mb
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The Entire Western Pacific. Monster near Japan.
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1813. Patrap
Member Since: July 3, 2005 Posts: 428 Comments: 129903
Three of six spaghetti models I just looked at have Katia heading west...
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Shear is beginning to drop over/near the center...



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P451.. you forgot to flag the sarcasm flag!!
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1807. ncstorm
P451:

You are cracking me up!
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Quoting aislinnpaps:


LOL, thanks! Looks like we'll be getting some this weekend for sure. Even if it loop-d-loops east of us, she/he looks big enough to deliver to you and I both.
Yeah. That's what I'm thinking. I went to the Dr. and had my fingers permanently crossed so I 'm hoping it wasn't all for nothing. Lol.
Member Since: August 24, 2010 Posts: 0 Comments: 254
Hwrf/Gfdl runs should be comming out soon for the 18/s intrested to see what they have to say.
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Quoting HurricaneDean07:
THIS SEASON HAS BEEN PSYCHOTIC!!!
(BOLD: Check! ; ITALIC: Possible in the next 2 weeks)
Arlene
Bret
Cindy
Don
Emily
Franklin
Gert
Harvey
Irene
Jose
Katia
Lee

Maria(Maybe 94L)
Nate(Possible from Tropical Wave train shown by models)
Ophelia(Possible form TW train shown by models)
Phillipe(Probably Sept)
Rina(Probably Sept)
Sean(Possible Sept/Oct)
Tammy(Possible Sept/Oct)
Vince(Possible Oct/Nov)
Whitney(Possible Oct/Nov)
THE GREEK ALPHABET WE GO! Rut Roh...

This is crazy, almost 13 NS(TD13/94L), and were just beginning SEPTEMBER, Thats right. not October, SEPTEMBER
AND THEY WON'T STOP COMING!!!!
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Historically... more than 3/4 of all hurricanes in 'that' area have veered off and recurved out into the Atl. due to consistency of the coriolis force.
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Meanwhile.. back in the CATL.. Katia's jealousy for TD13 suddenly stealing her spotlight is becoming increasingly obvious. Making its run back for hurricane status.
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We'll just have to hope that TD 13 can move ashore faster than originally thought, because having it looping around the NW Gulf for 4 to 5 days is not the best thing in the world...
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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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