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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1745. red0
Ars Technica published a short retrospective on Irene today.

http://arstechnica.com/science/news/2011/09/a-loo k-at-hurricane-forecasting-from-irenes-path.ars

Ars's science section has been doing quite a few weather related articles here in the last few months. Always good stuff.
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1.) Did recon find a closed circulation?
A. Yes
B. No

2.) Did recon find tropical depression winds?
A. Yes
B. No

3.) Is there convection associated with the system?
A. Yes
B. No

The answer to all those is yes...Which means 93L is a tropical depression, no matter your opinion. It meets criteria...even if the circulation is very weak and the convection isn't perfect.
Member Since: July 6, 2010 Posts: 113 Comments: 31860
1742. Patrap
Member Since: July 3, 2005 Posts: 423 Comments: 127803
Quoting MiamiHurricanes09:
Doesn't matter. WU must get there early and F5 until their pointer finger grows a bicep the size of Joe Bastardi's arm.

LOL
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1740. tj175
I think you are right on Clearwater. Everytime they have put us in the 5 day cone starting off we never get anything. I was just looking at the setup of how Hurricane Andrew and it seems similar to what might be trying to happen. That will be crazy if it heads this way but only time will tell and by the end of the weekend we should have a pretty good idea of where she is headed. Im calling it now she will head towards Florida and enter the gulf possibly affecting the panhandle
Quoting Clearwater1:
lol
Shields up. You said it before me. But remember, if we Fl is in the first US landfall cone, then the storm will def. miss us. . Historically speaking with tongue-in-cheek.
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Has there ever been a storm with so many loop-d-loops as to where it _might_ go?
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Plus one for the Florabamma..haven't been there in years but nice to hear its still around
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Quoting TropicalAnalystwx13:


Depends on if it takes advantage of DMAX tonight or night. If so, we will have Lee. Or would that be Maria?

Idk...Tropical cyclone races are confusing.
It might pull a "No way Jose" on us.
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Quoting KoritheMan:


Good evening, Kerry.

Lee reminds me a lot of our other notoriously wet systems in the past, like Frances in 1998 and Allison in 2001.
Good Evening Kori!
Don't forget Hurricane Juan 1985.
Link
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Quoting TropicalAnalystwx13:


Nah, they don't update before 23:30 UTC/7:30 p.m. EDT.
Doesn't matter. WU must get there early and F5 until their pointer finger grows a bicep the size of Joe Bastardi's arm.
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2 fish storms
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Quoting ecflweatherfan:
Been a few days, but have been eyeing Katia out there. I do not like how the models have been consistently pushing west with her path. I guess accounting for a more sheared system from an upper Low and a stronger A-B High? Those are my only thoughts on it, I guess.
looks to me that Katia is going to come closer to the US coastline than the models are predicting
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1731. Marou
hi everybody ! I know we are in an active phase of the hurricane season, and we already have lot of evidences of that (TD 13, katia, 94L) ... but do we know what the MJO looklike now and for the next several days ? noboby no longer talk about it ...
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1729. LBAR
Quoting Levi32:
I see we have TD 13...a bit sooner than I expected, but the NHC this year has been willing to put these systems into forced labor in order to birth them in time to put warnings up sufficiently in advance for nearby land areas.


Or to further an agenda.
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Quoting washingtonian115:
2005 all over again.Lol.but 2011 isn't no 2005 by a long shot.
So far, but only half way home.
Member Since: August 26, 2006 Posts: 0 Comments: 1547
They found crayons on TWC and it's not showing any rain for TX and maybe some for me next to TX. Katia is downgraded to a TS again.
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1725. o22sail
Quoting CybrTeddy:
Sigh, I go offline for 20 minutes to watch the news and yet another TD forms.

AL, 13, 2011090118, 01, CARQ, 0, 266N, 914W, 30, 1008,

TD 13's formation, which will likely be Lee soon, continues to mark at this time one of the most active hurricane seasons ever.

Not possible.
This season was pronounced dead at the beginning of last month. ;)
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Quoting CybrTeddy:
Sigh, I go offline for 20 minutes to watch the news and yet another TD forms.

AL, 13, 2011090118, 01, CARQ, 0, 266N, 914W, 30, 1008,

TD 13's formation, which will likely be Lee soon, continues to mark at this time one of the most active hurricane seasons ever.


If Lee forms anytime in the next week, it will mark the 4th earliest formation of the "L" storm...

- 2005
- 1995
- 1936
- 2011?
- 1933
Member Since: July 6, 2010 Posts: 113 Comments: 31860
Quoting aislinnpaps:


We'll have to start a cancelled plans club.
Sounds good to me. I have enough food in the freezer to feed 20 people....all I need is to lose power!!!
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Been a few days, but have been eyeing Katia out there. I do not like how the models have been consistently pushing west with her path. I guess accounting for a more sheared system from an upper Low and a stronger A-B High? Those are my only thoughts on it, I guess.
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Quoting MiamiHurricanes09:
If it has a good DMAX, no doubt that we'll wake up to Maria, or Lee, lol.
2005 all over again.Lol.but 2011 isn't no 2005 by a long shot.
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come on 94L am rooting for you
Member Since: May 21, 2006 Posts: 5091 Comments: 114914
Quoting MiamiHurricanes09:
*Deploy F5 team onto NHC website in T-minus 5 minutes*

23:25UTC/7:25p.m EDT

//


Nah, they don't update before 23:30 UTC/7:30 p.m. EDT.
Member Since: July 6, 2010 Posts: 113 Comments: 31860
1716. o22sail
Quoting twincomanche:
Go anyway and spend time in the Florabama.

Oh, the memories... :)
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expect tropical storm warnings for the northern Gulf Coast
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HELP!
Just in from Henry Margusity
"I really just hope the models are not correct. I don't think they are, but you never know. What they are showing is just insult to injury to folks in the Northeast and Mid-Atlantic. First Lee hits with heavy rains then Katia backs in to add more per the Euro and GFS."
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The NHC reports that the first advisory of TD #13 may be delayed slightly due to the large size of the cone of probabilities Forecaster Pasch had to make a quick trip to Walmart for more crayons!! LOL
Member Since: May 31, 2011 Posts: 57 Comments: 566
Sigh, I go offline for 20 minutes to watch the news and yet another TD forms.

AL, 13, 2011090118, 01, CARQ, 0, 266N, 914W, 30, 1008,

TD 13's formation, which will likely be Lee soon, continues to mark at this time one of the most active hurricane seasons ever.
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West Central Coast of Florida getting smacked by heavy rain and lightening right now. An inch and a half in the rain gauge since five o clock. Dark ominous clouds.
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Quoting will40:



thats cuzz i didnt send the shield back lol



Lol. Well thank you for that. Good to see you back. Hoping the shield sends Katia away from you. Sigh, is this what I get for wishin them away last year? Lol. Big oopsy?
Member Since: August 24, 2010 Posts: 0 Comments: 58
*Deploy F5 team onto NHC website in T-minus 5 minutes*

23:25UTC/7:25p.m EDT

//
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Quoting washingtonian115:
I think invest 94L might get declared maybe sometime in the near future.Maybe not now though.


Depends on if it takes advantage of DMAX tonight or night. If so, we will have Lee. Or would that be Maria?

Idk...Tropical cyclone races are confusing.
Member Since: July 6, 2010 Posts: 113 Comments: 31860
The HH guys are going to meet themselves coming and going between the three storms.
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Flora-Bama and I share the same zipcode.
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Quoting washingtonian115:
I think invest 94L might get declared maybe sometime in the near future.Maybe not now though.
If it has a good DMAX, no doubt that we'll wake up to Maria, or Lee, lol.
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Quoting FrankZapper:
Katia and Lee are the players now. Lee may not be. He is Lee,a big rainmaker. Now Katia (just like Katrina) could be the one to remember. Katia could be the one. Irene was an appetizer.
Yea and Lee is the before dinner drinks to WET the whistle....
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Quoting Kibkaos:
Sitting here in Pearland TX outside in 98 degree heat at 6:00. We need rain now. This is the biggest tease yet. So close but yet so far.


I hear that... I have lived in Houston my entire life and this is by far the worst I have ever seen here. I drove to Austin last weekend and that looked like a desert. I didn't see a single lawn that had anywhere near green grass. It is sad.

I am just afraid if we do not get any significant rainfall soon or through out the end of this year.. we may be in a worse drought next year. I can't even imagine what that would be like.
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Main article: Meteorological history of Hurricane, para phrased from Wikapedia


A tropical wave moved off the coast of Africa on August 14. Under the influence of a ridge of high pressure to its north, the wave tracked quickly westward, developing into a Tropical Depression late on August 16 about 1,630 mi (2,620 km) east-southeast of Barbados. By August 17, the depression intensified into a Tropical Storm , and by the following day had organized convection and estimated winds of 50 mph (80 km/h). Shortly thereafter the thunderstorms decreased markedly,[3] and as the storm turned to the northwest it encountered southwesterly wind shear from an upper-level low. On August 19, a Hurricane Hunters flight into the storm failed to locate a well-defined center, and the next day a flight found only a broad circulation with an unusually high pressure of 1,015 mb (30.0 inHg). Around that time, the upper-level low degenerated into a trough, which decreased the wind shear over the storm. In addition, a strong ridge developed over the southeastern United States, which built eastward and caused Andrew to turn to the west.


This of course is a report on Andrew, but change the dates a bit and it reads all to similar to some of the more recent reports about Katia, or what you may be reading at eleven pm and 5 am
Member Since: August 26, 2006 Posts: 0 Comments: 1547
Quoting saintsfan06:
There goes my weekend in Gulf Shores....just cancelled my reservations!!!!! Not a happy camper right now...


We'll have to start a cancelled plans club.
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Oh yea, definately know the drill. It's just two different game plans depending on strenght. It's the difference of getting everything up a couple of feet...or moving stuff to relatives houses to protect it. Obviously, putting things up a couple of feet is a heck of a lot easier than it is to move everything across town. Plus I have poultry that comes into play if it's stronger than a TS.
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There goes my weekend in Gulf Shores....just cancelled my reservations!!!!! Not a happy camper right now...
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I think invest 94L might get declared maybe sometime in the near future.Maybe not now though.
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Quoting FrankZapper:
Katia and Lee are the players now. Lee may not be. He is Lee,a big rainmaker. Now Katia (just like Katrina) could be the one to remember. Katia could be the one. Irene was an appetizer.


Good evening, Kerry.

Lee reminds me a lot of our other notoriously wet systems in the past, like Frances in 1998 and Allison in 2001.
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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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