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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1794. Patrap
Member Since: July 3, 2005 Posts: 424 Comments: 128259

Quoting xtremeweathertracker:


This looks ok to me!!!

Sweet. Ya know those Weather Channel mets know their stuff! :)
Member Since: August 24, 2010 Posts: 0 Comments: 120
Quoting AtHomeInTX:

Hope you get some rain. I tried to push that storm up to ya. But it was just moving too fast. Sigh. ;-)


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.
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1791. Skyepony (Mod)
Fresh windsat of Katia
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Quoting Clearwater1:


Oh no. You may be referring to the psychic twins, who appeared on the View several months back. They said that a storm of a cat 4, would hit FL, then move up the eastern seaboard. They were close, but no cigar, with Irene. But keep in mind, they didn't say which storm or give exact dates. So, who knows, they may be able to claim Katia as their vision. . . or the next one . . . or the next one.
Well if anything i got a good chuckle out of what they wrote.
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1789. Thrawst
Quoting SPLbeater:
some1 tell Katia to strengthen again, i want a hurricane with no land threat to track for a few days, lol. Cone seems to keep shifting more south, not the direction i like


means more good swell for me :D yusss!!
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93L (Now TD#13) earlier today

Link
Member Since: July 7, 2010 Posts: 0 Comments: 5682
1786. Patrap
Member Since: July 3, 2005 Posts: 424 Comments: 128259
Quoting DavidHOUTX:


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.
Alot of peoples fears and that is what is being predicted due to La Nina.
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some1 tell Katia to strengthen again, i want a hurricane with no land threat to track for a few days, lol. Cone seems to keep shifting more south, not the direction i like
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Quoting SPLbeater:


oh,when did that come out? was keeping the puppy occupied lol


Just a little while ago on the NAVY/ATCF pages...Awaiting the National Hurricane Center advisory.
Member Since: July 6, 2010 Posts: 113 Comments: 32022
Quoting CybrTeddy:


At least it has one vortex center!! *cough* Emily off Florida *cough*
That circulation is larger/broader than Gabrielle Sidibe though lol.

I wouldn't call 93L a tropical depression just yet, but as P451 mentioned, since it's close to land, the NHC is a lil' more loose with classifying a system...a lot more loose as a matter of fact.
Member Since: September 2, 2009 Posts: 130 Comments: 21193
Quoting HurricaneNewb:
At some point this morning on here someone posted about some breaking news that a physic had forcasted Katia to coninue west over florida. Think i might see if i can find that story cause if that happened im sure that person might know this weeks Powerball numbers.


Oh no. You may be referring to the psychic twins, who appeared on the View several months back. They said that a storm of a cat 4, would hit FL, then move up the eastern seaboard. They were close, but no cigar, with Irene. But keep in mind, they didn't say which storm or give exact dates. So, who knows, they may be able to claim Katia as their vision. . . or the next one . . . or the next one.


Edit: Can't be the same psycics, because they said they never use their powers for the Power Ball, "that would be wrong". They only use it for good. . . and of course to be on the View.
Member Since: August 26, 2006 Posts: 0 Comments: 1548
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
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1778. hotrods
Quote me if i am wrong, but can someone take a look at the shortwave loop on katia, it looks like she missed her next stepping stone!
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Quoting Flawestcoast:
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.


Yeah here in Sarasota we just started getting in on the action. Slow start to rainy season but it sure has picked up lately, minus the few days of dry weather Irene brought us.
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Quoting TropicalAnalystwx13:


Other than TROPICAL DEPRESSION THIRTEEN, no.


oh,when did that come out? was keeping the puppy occupied lol
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so anyone thinking katia will train west for a few days????
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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.


At least it has one vortex center!! *cough* Emily off Florida *cough*
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Quoting P451:


It's not an East Coast storm. Reed would be out of his element.

Katia on the other hand. :)

I can see Reed now talking about his east coast models and that NYC may be at danger.Lol.I just had to get a laugh.
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1769. Patrap
Member Since: July 3, 2005 Posts: 424 Comments: 128259
Quoting SPLbeater:
any new news?


Other than TROPICAL DEPRESSION THIRTEEN, no.
Member Since: July 6, 2010 Posts: 113 Comments: 32022
Quoting P451:


Pulling for you guys to get rain.

Just not flooding...


This looks ok to me!!!

Member Since: May 31, 2011 Posts: 57 Comments: 571
any new news?
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Quoting aislinnpaps:
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.
Hope you get some rain. I tried to push that storm up to ya. But it was just moving too fast. Sigh. ;-)
Member Since: August 24, 2010 Posts: 0 Comments: 120
At some point this morning on here someone posted about some breaking news that a physic had forcasted Katia to coninue west over florida. Think i might see if i can find that story cause if that happened im sure that person might know this weeks Powerball numbers.
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Quoting HurricaneDean07:
TAWX,
If we already have TD 13(IN GOM), then that would be Lee, even if Maria is named first


It doesn't matter which storm reaches TD strength first. It just matters which storm reaches tropical storm strength first.
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Katia isn't liking that T.D 13 or pre Lee is trying to steal the show from her.
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1760. Patrap
Member Since: July 3, 2005 Posts: 424 Comments: 128259
nic way too start SEP LOL
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Looks like you're getting a bit of rain, Patrap.
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1756. aquak9
Quoting saintsfan06:
Sounds good to me. I have enough food in the freezer to feed 20 people....all I need is to lose power!!!

Got any ribs?

LouisianaWoman- it's just too early to tell right now. Hate to say that, but it's a huge disorganized mess of a TD.
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Quoting HurricaneDean07:
TAWX,
If we already have TD 13(IN GOM), then that would be Lee, even if Maria is named first


No, it wouldn't.
Member Since: July 6, 2010 Posts: 113 Comments: 32022
1754. Dakster
Quoting Clearwater1:
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


That is what I was afraid of...
Member Since: March 10, 2006 Posts: 0 Comments: 10279
H.Katia's_6pmGMT_ATCF : Starting 31August_6pmGMT and ending 1Sept_6pmGMT

The 4 eastern line-segments represent HurricaneKatia's path
and the westernmost line-segment is the straightline projection.

Using straightline projection of the travel-speed&heading derived from the
ATCF coordinates spanning the 6hours between 12pmGMT then 6pmGMT :
H.Katia's travel-speed was 19.7mph(31.7k/h) on a heading of 287.1degrees(WNW)
H.Katia was headed toward passage over Inagua,Bahamas ~3days6hours from now

Copy&paste 14.4n41.7w-14.8n43.6w, 14.8n43.6w-15.1n45.2w, 15.1n45.2w-15.3n46.9w, 15.3n46.9w-15.8n48.6w, iga, 15.3n46.9w-21.131n73.055w into the GreatCircleMapper for more info

The previous mapping (for 1Sept_12pmGMT)
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TAWX,
If we already have TD 13(IN GOM), then that would be Lee, even if Maria is named first
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Quoting Clearwater1:
So far, but only half way home.
September and October might prove to tell the story.
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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.
Member Since: July 6, 2010 Posts: 113 Comments: 32022
1747. Patrap
Member Since: July 3, 2005 Posts: 424 Comments: 128259

Quoting Vero1:
Maria behind Katia?

That looks pretty close to us.  If it does become better organized I would think we would get some rain.  Wonder if our local mets know about this  strange NHC place?
Member Since: August 24, 2010 Posts: 0 Comments: 120
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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About

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.