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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Removed (double post of vortex for TD#13)

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1594. ncstorm
18Z NOGAPS is back predicting doom..heading for the Bahamas

Link

Member Since: August 19, 2006 Posts: 13 Comments: 14412
1593. hahaguy
The nogaps really wants to go to disney world.
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Quoting TropicalAnalystwx13:
Oh, for anybody who doesn't know...

TROPICAL DEPRESSION 13 HAS FORMED
.Wunderground presents...Teeeeeeeeeee-D 13!
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2 things i wanna mention. ALL the models show a SIGNIFICANT westward shift with katia. the GFS shows a significant western shift although does a sharp recurve away from NC. also GFS has katia TOO FAR NORTH. lets connect the dots here shall we. katia will be further west and south than the NHC cone is. bermuda high buidling in meaning more west plus whats left of lee will have somekind of westward influence on katia. also trough IS NOT AMPLIFIED meaning no emily recurve like earlier this season more of an irene recurve so if you connect the dots thats either a scrape or a direct landfall on northcarolina. its not looking too good right now
Member Since: August 23, 2011 Posts: 0 Comments: 1288

Quoting uptxcoast:


Next week, or the week after that, and if not then the week after that.....and on and on and on......Hang in there. It has to break sometime.
I know. Thank you. :)  I'm sorry didn't mean to offend anyone earlier.  I hope he is right about the cooler weather. That would be lovely too. Watching the fire in DFW  on tv. burned 36 homes or I should say more homes.  This dry west side winds are going to be bad for the fires.
Member Since: August 24, 2010 Posts: 0 Comments: 676
1589. Dakster
Looks like the Northern GOM should get prepared for alittle rain...

Member Since: March 10, 2006 Posts: 0 Comments: 10034
Quoting AtHomeInTX:

Yep. It is what it is. I'm not sure everyone is clear on this. The only thing that has ever broken our droughts is tropical systems. Our rainy seasons have names like Rita, Carla, Allison, etc etc etc. Sigh. C'mon ridge! Back the F off!
If I was the ridge I would leave now. LOL
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TD13 has the look of TS Tammy in 2005.
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1585. Patrap
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Quoting Patrap:
..sometimes late when things are real, and people share the gift of gab between themselves..


I never gave anything to the Tin Man that he didn't already have :)) One of my favs. Hey long time no see :))
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1581. Patrap
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Quoting ackee:
so we have TD#13 now ?



yes
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The GFS trend is very scary. Can't wait for the next euro and see what it thinks
Member Since: August 26, 2006 Posts: 0 Comments: 1547
1578. Patrap
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LOL.

I posted on Jim Cantore's wall about the ATCF update, and the weather channel just briefly put a banner on the bottom saying that a Tropical Depression has formed in the Gulf of Mexico.
Member Since: July 6, 2010 Posts: 113 Comments: 31420
1575. WxLogic
Quoting MiamiHurricanes09:
Considering both Emily and Irene have had similar tracks, I wouldn't be surprised to see Katia follow in their footsteps.


Indeed... but this time is a bit more different since we have a Cut off low (courtesy of TD#13) in C/E CONUS which could make it a bit more challenging.
Member Since: August 14, 2008 Posts: 4 Comments: 4927
1574. Skyepony (Mod)
Quoting atmosweather:


Just read that too Skye...they also did a little loop as if they are trying to confirm that there is a closed LLC down there. Looks like it's been close all afternoon but now they may have just enough to declare the system a tropical depression.


I saw that quick turn around on Google(which tends to lag a few mins) & went to raw data, they'd already checked it out the second time. You don't see many U turns like that.
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Quoting MiamiHurricanes09:
It's gon' be a circle cone...


I'm hoping for a waffle cone.
Member Since: August 29, 2010 Posts: 0 Comments: 5236
1572. ncstorm
Quoting BrockBerlin:


Certainly looks like a westward trend to me, still very far out, will it windshield wiper or continuing trending. At least the GFS seems to be more in line with the other models however, the GFS seems to induce its west bend farther north.


yeah, it dosent show the hard right back out to sea like the Euro..
Member Since: August 19, 2006 Posts: 13 Comments: 14412
yeah whats with this switch of katia's movement to from wnw to w all day today.......... guess that upper level low has very little afect on her...... psuhing her w?
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1570. Patrap
Enhanced Infrared (IR) Imagery (4 km Mercator)

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Quoting tropicfreak:


Like VA needs another one, golly can't we catch a break from the bad weather, like Irene, and the earthquake, btw had another aftershock this morning, 3rd strongest one since the quake last week.
I feel for you, we cannot get rain and you are on the other end of disaster. Drought areas not getting any relief and neither are flooded areas, we need to reverse these for awhile. Very wet front or 2 headed for the Northeast also.
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It's gon' be a circle cone...
Member Since: September 2, 2009 Posts: 130 Comments: 21091
Quoting xtremeweathertracker:
Ha Ha luv it...local MET reducing rain chances and NWS increasing rain chances for SE Texas.. This is for the Golden Triangle Area!!

Tonight: Scattered showers and thunderstorms. Mostly cloudy, with a low around 75. East wind around 10 mph. Chance of precipitation is 50%.

Friday: Showers and thunderstorms likely, mainly after 1pm. Partly sunny, with a high near 90. East wind between 10 and 20 mph, with gusts as high as 20 mph. Chance of precipitation is 60%.

Friday Night: Scattered showers and thunderstorms. Mostly cloudy, with a low around 76. Northeast wind around 15 mph. Chance of precipitation is 40%.

Saturday: Showers and thunderstorms likely. Cloudy, with a high near 84. Windy, with a north wind between 15 and 25 mph, with gusts as high as 30 mph. Chance of precipitation is 60%.

Saturday Night: Showers and thunderstorms. Low around 75. North wind between 15 and 20 mph, with gusts as high as 25 mph. Chance of precipitation is 80%.

Sunday: Showers and thunderstorms. High near 79. North wind between 15 and 20 mph, with gusts as high as 25 mph. Chance of precipitation is 80%.

Sunday Night: Scattered showers and thunderstorms. Cloudy, with a low around 75. Windy, with a north wind between 20 and 25 mph, with gusts as high as 30 mph. Chance of precipitation is 50%.

Labor Day: Scattered showers and thunderstorms. Cloudy, with a high near 83. Windy, with a northeast wind around 25 mph, with gusts as high as 30 mph. Chance of precipitation is 50%.

Monday Night: A 20 percent chance of showers and thunderstorms. Mostly cloudy, with a low around 67. Windy, with a northeast wind between 20 and 25 mph, with gusts as high as 30 mph.


Sounds good to me! :)
Member Since: July 2, 2009 Posts: 0 Comments: 2811
Product: NOAA Vortex Message (URNT12 KWBC)
Transmitted: 1st day of the month at 22:30Z
Aircraft: Lockheed WP-3D Orion (Reg. Num. N42RF)
Mission Purpose: Investigate seventh suspect area (flight in the North Atlantic basin)
Mission Number: 1
Observation Number: 12
A. Time of Center Fix: 1st day of the month at 22:01Z
B. Center Fix Coordinates: 26°25'N 91°33'W (26.4167N 91.55W) (View map)
B. Center Fix Location: 262 miles (422 km) to the SSW (200°) from New Orleans, LA, USA.
C. Minimum Height at Standard Level: Not Available
D & E. Estimated (by SFMR or visually) Maximum Surface Wind: Not Available
F. Maximum Flight Level Wind Inbound: From 324° at 7kts (From the NW at ~ 8.1mph)
G. Location of Maximum Flight Level Wind Inbound: 7 nautical miles (8 statute miles) to the WSW (246°) of center fix
H. Minimum Sea Level Pressure: 1008mb (29.77 inHg) - Extrapolated
I. Maximum Flight Level Temp & Pressure Altitude Outside Eye: 26°C (79°F) at a pressure alt. of 458m (1,503ft)
J. Maximum Flight Level Temp & Pressure Altitude Inside Eye: 26°C (79°F) at a pressure alt. of 460m (1,509ft)
K. Dewpoint Temp (collected at same location as temp inside eye): 25°C (77°F)
K. Sea Surface Temp (collected at same location as temp inside eye): 30°C (86°F)
L. Eye Character: Not Available
M. Eye Shape: Not Available
N. Fix Determined By: Penetration and Wind
N. Fix Level: Other - Not surface, 1500ft, 925mb (if vortex is newer than about mid 90's; see note for more), 850mb, 700mb, 500mb, 400mb, 300mb or 200mb
O. Navigation Fix Accuracy: 1 nautical mile
O. Meteorological Accuracy: 1 nautical mile
Remarks Section:
Maximum Flight Level Wind: 27kts (~ 31.1mph) in the northeast quadrant at 19:42Z
Sea Level Pressure Extrapolation From: 1,500 fee
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1565. ackee
so we have TD#13 now ?
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Quoting Bluestorm5:
1996 when it got hit 3 times.


Oh it would be the Fran year. :(
Member Since: June 1, 2007 Posts: 0 Comments: 886
Quoting TexasHurricane:


yeah, as soon as it starts it stops. sigh...


Still going here, but nothing too heavy. I'll take what I can get. The rain along with the wind cooled things down quite a bit.
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They're really gonna' make a TD on this one. More practical than scientific. Doesn't seem to have the parameters of a TD, but it certainly could have the effects of that and more. I think in the end it's best to alert the public....I just pity whoever at the NHC has to come up with a forecast discussion. It'll probably read more like a local NWS warning than anything else. Nothing close to a definite here.
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1560. Patrap
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Looking at the latest GFS,it seems as though 93 has to be right on time, inland, for Katia to do her to the west coast run. Her turn west is in concert with 93L. This model will change when 93 get more organized and the models have a better handle. or not.
Member Since: August 26, 2006 Posts: 0 Comments: 1547
Quoting TropicalAnalystwx13:
Oh, for anybody who doesn't know...

TROPICAL DEPRESSION 13 HAS FORMED
i just wanna see the projected path lol intensity i thik nhc will call strong ts im going with upper end cat 1 :)
Member Since: August 23, 2011 Posts: 0 Comments: 1288
Quoting WxLogic:
@192HR Katia was quite close to US... which is why I didn't quite buy a sharp turn. If trends continues then we'll have to worry about Katia too:

Considering both Emily and Irene have had similar tracks, I wouldn't be surprised to see Katia follow in their footsteps.
Member Since: September 2, 2009 Posts: 130 Comments: 21091
Ha Ha luv it...local MET reducing rain chances and NWS increasing rain chances for SE Texas.. This is for the Golden Triangle Area!!

Tonight: Scattered showers and thunderstorms. Mostly cloudy, with a low around 75. East wind around 10 mph. Chance of precipitation is 50%.

Friday: Showers and thunderstorms likely, mainly after 1pm. Partly sunny, with a high near 90. East wind between 10 and 20 mph, with gusts as high as 20 mph. Chance of precipitation is 60%.

Friday Night: Scattered showers and thunderstorms. Mostly cloudy, with a low around 76. Northeast wind around 15 mph. Chance of precipitation is 40%.

Saturday: Showers and thunderstorms likely. Cloudy, with a high near 84. Windy, with a north wind between 15 and 25 mph, with gusts as high as 30 mph. Chance of precipitation is 60%.

Saturday Night: Showers and thunderstorms. Low around 75. North wind between 15 and 20 mph, with gusts as high as 25 mph. Chance of precipitation is 80%.

Sunday: Showers and thunderstorms. High near 79. North wind between 15 and 20 mph, with gusts as high as 25 mph. Chance of precipitation is 80%.

Sunday Night: Scattered showers and thunderstorms. Cloudy, with a low around 75. Windy, with a north wind between 20 and 25 mph, with gusts as high as 30 mph. Chance of precipitation is 50%.

Labor Day: Scattered showers and thunderstorms. Cloudy, with a high near 83. Windy, with a northeast wind around 25 mph, with gusts as high as 30 mph. Chance of precipitation is 50%.

Monday Night: A 20 percent chance of showers and thunderstorms. Mostly cloudy, with a low around 67. Windy, with a northeast wind between 20 and 25 mph, with gusts as high as 30 mph.
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Okay well I see they did a renumber on the ATCF site lol. So they did indeed find a tropical depression. Now we await the NHC's interpretations of the global models with respect to the possible strength of the steering currents and the changes to the deep layer ridge in the southern plains.
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Joe Bastardi will be beside himself...
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1553. KEEPEROFTHEGATE (Mod)
Tropical.Cyclone.Formation.Alert
013/TD/L/CX
MARK
25.95N/89.91W
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1552. ncstorm
192 Hours 18Z GFS
Member Since: August 19, 2006 Posts: 13 Comments: 14412
Quoting AtHomeInTX:

Lol. Yeah. I wasn't sure but yep. Whoa. Suns still firing through it lol.


yeah, as soon as it starts it stops. sigh...
Member Since: July 2, 2009 Posts: 0 Comments: 2811
Do we have a TD?
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1548. WxLogic
@192HR Katia was quite close to US... which is why I didn't quite buy a sharp turn. If trends continues then we'll have to worry about Katia too:

Member Since: August 14, 2008 Posts: 4 Comments: 4927
1547. Skyepony (Mod)
Not at all surprised to see the renumber.. the way recon hit it, but maybe not right on, turned right around & hit it again, pressure drop, looked closed, winds very light in the center..
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1546. DFWjc
Quoting AtHomeInTX:

Lol. Yeah. I wasn't sure but yep. Whoa. Suns still firing through it lol.


Finally for y'all down there in Houston area!!!
Member Since: July 19, 2011 Posts: 1 Comments: 1006
Oh, for anybody who doesn't know...

TROPICAL DEPRESSION 13 HAS FORMED
Member Since: July 6, 2010 Posts: 113 Comments: 31420

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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.