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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93L looks pathetic...not expecting a TD this week
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Quoting P451:
We're in RSO for Goes now. Until the last frame where normal operations continued. It will go back RSO I would think. You can see some sort of rotation south of LA out ahead of the thunderstorms. You can also see the intense shear out there - note the storms in the western part of the image being sheared off.





Yes it will go back, housekeeping period every day during the 15Z hour.
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Interesting nogaps pertaining to Katia (yes, obviously it's an outlier and a long way out):



And the CMC seems to think TX will get its needed rain from 93, and perhaps some wind as well:



Interesting to say the least.
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Quoting JamesSA:


Absolutely! Yet uncontrolled development continues in the San Antonio area and nobody wants to breach the subject of that maybe not being such a good idea in a drought prone area with limited water resources.

If the pattern goes La Nina and we have a dry winter, next year could be a VERY desperate situation.


2012
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Quoting sunlinepr:
New guest from Africa...


Those are some low latitude blobs. Just saying...

Heard on news today FEMA is broke from Irene. They only had $800M in reserves pre-storm, while we planned $800M gift to Pakistan and continue to help out Wall Street thug banksters with 10s of billions of bailout and interest-free loans. Outrageous. Blows my lid.



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downtown mobile Alabama is looking rough out to the gulf for sure
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New system will hardly miss the islands...

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Quoting jpsb:
Any chance Texas could run out of drinking water if this drought keeps going?


Absolutely! Yet uncontrolled development continues in the San Antonio area and nobody wants to breach the subject of that maybe not being such a good idea in a drought prone area with limited water resources.

If the pattern goes La Nina and we have a dry winter, next year could be a VERY desperate situation.
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@93hr:

TROF about to miss it again

Member Since: August 14, 2008 Posts: 4 Comments: 4972
Quoting ackee:
I THINK 94l COULD VERY well end up being LEE first that would be quite a suprise


That kinda reminds me of Franklin...lol.
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Quoting jpsb:
Any chance Texas could run out of drinking water if this drought keeps going?


Those who rely on their own water wells, many of them are having to get them drilled deeper, or do without.

Most of the big cities have aquifers or lakes to pump from, but have implemented yard watering restrictions to twice a week. The next step is once a week watering and then no watering.

Another side affect, ERCOT is asking Utility companies to restart mothballed generating plants, as existing plants may have to be shutdown do to a lack of cooling water.

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Just did a line projection on Google earth, it's now 950 miles east of the Lessler Antillies.
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I THINK 94l COULD VERY well end up being LEE first that would be quite a suprise
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77. HCW
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@93HR 12Z GFS:

Member Since: August 14, 2008 Posts: 4 Comments: 4972
Seems we should have a new Invest...

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Quoting sunlinepr:


Is that 95L??
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11:00am Advisory
*Click graphics to magnify (Graphics can also be magnified more by clicking on them in the Link window)

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Quoting P451:
We're in RSO for Goes now. Until the last frame where normal operations continued. It will go back RSO I would think. You can see some sort of rotation south of LA out ahead of the thunderstorms. You can also see the intense shear out there - note the storms in the western part of the image being sheared off.





Sorry still learning but RSO for GOES now means what?
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New guest from Africa...
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the sky is growling in mandeville. i hope the parish will come dig my ditch out today. wst just did maintance on the electric lines so hopefully no more power outages today.
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I was looking at the HWRF and GFDL both seem to build the high pressure back in after the exit of 94.
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Quoting HCW:


WTH? all over the place
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I put a graphic of their projected path on my photo page.  Very strange track....skimming the coast from TX/La border (as a TS) to landfall in Brownsville (as Hurricane).
http://www.wunderground.com/wximage/ Allyson00/


Current Location: 26.9N/90.2W
Geographic Reference: 165 miles southwest of the Mississippi Delta
Movement: West-northwest less than 5 mph
Max Winds: 35 mph
Organizational Trend: Slowly becoming better organized
Chance of Development to a Tropical Storm within 48 hours: 90%
Chance of Development to a Tropical Storm beyond 48 hours: 95%
Forecast Track Confidence: Below average due to poor model agreement.
Changes From Our Previous Forecast
We have increased the development chances from 80% to 90% during the first 48 hours.



Our Forecast
Disturbance 35 is expected to move very slowly toward southwestern Louisiana today and tomorrow. Once near the Louisiana coast it will become virtually stationary, and could remain in that general area through the weekend. By early next week we think it will begin a track to the southwest. We think landfall will be in South Texas or northeastern Mexico around the middle of next week. Alternate scenarios include a track into southern Louisiana or inland near Sabine Pass on the Texas/Louisiana line. We think those scenarios are unlikely due to high pressure expected to build to the north.



Widespread showers and thunderstorms extend across much of the central and eastern Gulf of Mexico. Some outer squalls are already moving into southeastern Louisiana and coastal Mississippi, and extend southward into the northwestern Caribbean Sea. Upper-level wind shear across the area is a prohibiting factor in development. The shear appears to be decreasing and is expected to completely diminish over the next 24 hours. The result will be conditions that are favorable for strengthening. This disturbance could be declared a depression or even a tropical storm later today or tomorrow. It could become a hurricane over the weekend if it does not interact with land before moving away to the southwest. Confidence in the intensity forecast remains average.



Expected Impacts on Land
Mississippi/Louisiana Coasts: Squalls are already moving into the area with locally heavy rain and gusty winds likely for several days.
Texas/Southwest Louisiana Coasts: The disturbance may spread heavy rain into the area by late tomorrow or Saturday. Due to the very slow motion expected near the coast, the squalls may last for several days.



Expected Impacts Offshore
Northwest Gulf of Mexico: Thunderstorms are increasing over much of the Gulf east of 90W. Scattered showers and thunderstorms prevail west of 90W. Increasing squalls are expected over most of the central and western Gulf through the weekend. Tomorrow will be the last good day of flying weather for areas west of 92W.



The next update will be issued by 3PM CDT.
Meteorologists: Jim Palmer/Kevin Smith
© ImpactWeather, Inc. All rights reserved
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Quoting jpsb:
Any chance Texas could run out of drinking water if this drought keeps going?


In progress
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62. jpsb
Any chance Texas could run out of drinking water if this drought keeps going?
Member Since: June 30, 2009 Posts: 0 Comments: 1192
Correct me if I'm wrong, didnt the bad "K" storm form, then weaken and continue west? Then..well the rest is history...

Wondering about the effects on Miami airport in about a week's time.

Only because I need to get my Mother in Law the heck OUTTA my hair .. :-(
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Quoting HCW:


Funny, the track models my 3 year old son formulated last night are eerily similar.
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Will the real Lee please stand up?



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Looks like if Katia doesn't make that WNW turn soon, Lessler Antillies may be in trouble.
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Quoting hahaguy:
I'm not liking how some of the models have Katia bending back to the west at the end.


I was noticing that too....
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I'm out for a bit be back later.
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HurricaneKatia's path has shifted evermore westward over the past 24hours,
from 287degrees(WNW) between 6amGMT and 12pmGMT on 31August...

...to 277.1degrees(W) between 6amGMT and 12pmGMT on 1September.

Both of the 4 eastern line-segments represent HurricaneKatia's path
and both of the westernmost line-segments are the straightline projections.

Click on the links above the maps for more details.
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Quoting Moussifer:


I'm past laughing and moving into hysteria. Up in the Humble area we are seeing most of our hardwoods dying. Whole oak trees are just turning brown and giving up. Our pine trees are not doing much better. All the smaller plants are pretty much giving up the ghost too, unless they're watered. Farmers are going under. Things are bad.


I am in Humble too, and am going to cry big alligator tears if this system doesn't bring us any rain. Worse even if we get high winds. The whole place is a cinder, will go up quickly with the least provocation.
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Quoting P451:
Katia being affected by the ULL to her NW. Katia headed for an even more hostile environment. Entity off of NC heading SE had been modeled to head NE. That would of course now be a big wrench in the model runs. How far south that feature gets will be something that needs to be watched. Could Katia now weaken substantially and slip under both entities and find herself to be a player for the Mid-Atlantic coastline? Or could Katia be disrupted and then swept out to sea by that feature and the trof both of which were modeled to be weak and pull NE but have instead strengthened and moved SE?

I think Dr. M puts out good advice in regards to the models and Katia: give it a couple of days.





Nicely analyzed, SO MUCH uncertainty with Katia and so MANY 'what if's' that I think the NHC and meteorolgists (not to mention some on this board) will look like your avatar by Labor Day....
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Poor Katia...

Close shave.

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48 hour GFS..

Member Since: July 15, 2006 Posts: 17 Comments: 10250
I'm not liking how some of the models have Katia bending back to the west at the end.
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NHC is thinking 94L could be a tropical storm already. Maybe a warm core in the lowest 12km is enough given the ASCAT data signature is more closely related to a tropical than a subtropical cyclone.
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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.