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 notanothergoof:
those 3 storms just gave some of the edge to florida but not a direct hit or to close to a hit the last were jeanne francis and charley in 2004


Incorrect again..... Hurricane Wilma was a direct hit coming in from the west coast accross S.E. Florida
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1044. angiest

Quoting xtremeweathertracker:

FWIW NAM Still has rain for SE Texas!!

Hah, the corner of SE Texas than needs it the least (due to heavy July rainfall.)
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Quoting notanothergoof:
florida hasnt had a hurricane since 2004


Wilma in 2005?
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1042. cmagag
Quoting xtremeweathertracker:

FWIW NAM Still has rain for SE Texas!!



Awesome, that might get us up to 15 inches down for the year. ;-)
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The shape of the coastline where 93L is likely to stall should also help it wind up more quickly. 93L could end up being more than just a rain threat for South Central Louisiana. The constant rains will make the soil very soft and large trees will be much more susceptible to being uprooted in strong tropical storm/hurricane force winds.

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Quoting Progster:



Like a baroclinic system...or a tornado :)
Or its just an extrapolation error. Or its the result of a downdraft. I've seen this happen many times this year (higher extrapolated surface winds than flight level winds), seems especially common with weak storms (ie weak TSs or yet to be TSs like 93L), although this may just be because most of our storms so far have been weak.
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Quoting Levi32:


Well...

New Orleans, Louisiana (Airport)
Updated: 2:53 PM CDT on September 01, 2011

81 °F / 27 °C
Light Rain
Humidity: 82%
Dew Point: 75 °F / 24 °C
Wind: 4 mph / 6 km/h / 1.5 m/s from the SE

Pressure: 29.98 in / 1015 hPa (Steady)


29.96 at the Fairgrounds Racetrack. (No, their not open yet. I live across the street).

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I thought 93 l was supposed to loop around for several days? People are talking as if Tx won't get any rain now. What will the effect of SE Tx/ SW La be? Thanks
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Quoting xtremeweathertracker:

FWIW NAM Still has rain for SE Texas!!



well, we will see.
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no Lee or TD 13 and no Maria (94l) at 5pm ?
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1033. skfnek
This was released by UTMB Hospital in Galveston.
From: UTMB Broadcast Account
Sent: Thursday, September 01, 2011 9:56 AM
Subject: Tropical Weather Update - Thursday, Sept. 1, 10 a.m.



We are tracking the tropical weather disturbance moving into the Gulf of Mexico that forecasters believe will develop into a strong tropical storm over the next two days. The storm is expected to stall in the Gulf of Mexico off the coast of Louisiana and bring a considerable amount of rain to the Louisiana and upper Texas coasts (including the Galveston and greater Houston area) over the next several days. Although a precise forecast remains uncertain, there is a considerable likelihood that the storm will develop into a low intensity hurricane and track toward the Texas coast when it resumes movement early next week. Even though the current forecast is for landfall in South Texas, given the uncertainty, UTMB is preparing for the possibility of an impact to the Galveston area.

UTMB is closely monitoring the storm. Using an abundance of caution and acknowledging the coming holiday weekend, we will likely move to the first level of preparedness with our Emergency Operations Plan later today. The first level of preparedness requires that departments begin to review and be ready to implement their emergency plans, and that employees review their emergency responsibilities and contact information. As part of the first level of preparedness, we also advise employees to review their personal emergency preparedness plans.

At this time, we expect heavy rains with possible street flooding and road closures over the holiday weekend. We will continue to monitor the storm, moving to the appropriate level of preparedness and/or emergency operations in advance of the forecast. All employees are encouraged to please stay tuned to institutional announcements and are asked to remain aware of weather changes and advisories. We will continue to provide updates as we receive them.

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Quoting stormhank:
would we have any affects from 93L / TD / LEE,,,here in the Fla. panhandle over the holiday weekend??


RAIN, high surf, rip currents, flash flooding, and very breezy, are all likely.
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Quoting notanothergoof:
florida hasnt had a hurricane since 2004


Incorrect.... We had 2 hurricanes in 2005...
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Quoting notanothergoof:
florida hasnt had a hurricane since 2004


Aw man, not-another-goof.

Florida was hit by Hurricane Wilma in 2005.
Member Since: July 8, 2005 Posts: 259 Comments: 24484
1027. Levi32
Quoting luigi18:

Levi they did issue


Maybe the island governments did, but I recall nothing from the NHC until the first advisory.
Member Since: November 24, 2005 Posts: 635 Comments: 26684
Quoting hurricanehanna:
ESE winds here in Lafayette...rain heading our way...just the beginning of a loooooong weekend


Yea we getting some nice winds near downtown! Even a few nicer gusts.
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Quoting Progster:


Luck 'o' the Irish.


lol - must be since I have no issues seeing it either. :)
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1024. cmagag
Quoting TexasHurricane:
I won't be surprised if they start decreasing our rain chances over the weekend.


Son of a b&#*@ :(
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Quoting TexasHurricane:
I won't be surprised if they start decreasing our rain chances over the weekend.

FWIW NAM Still has rain for SE Texas!!

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with the weakening of Katia. the system will track west with the 700-850 mb steering current. the trough which was supposed to pull Katia northwards , has weakend allowing the ridge to the north to rebuild and to get stronger
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Sooooo...nothing for 93L?
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Quoting wxobsvps:




Luck 'o' the Irish.
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1019. vince1
Quoting MississippiWx:


SOAB. I keep forgetting!!!

No idea why, but I can see the image you remotely linked.
Member Since: August 6, 2006 Posts: 0 Comments: 210
WV imagery indicating the LA ULL is retrograding NW, if it moves faster than forecast intenstity could be underdone for 93L in the short term.
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ESE winds here in Lafayette...rain heading our way...just the beginning of a loooooong weekend
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Quoting Patrap:


Looks to me like it is starting to wrap up in the Gulf. Not liking the proximity of this one to NOLA.
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I won't be surprised if they start decreasing our rain chances over the weekend.
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Models for both looking interesting...
Katia, East Coast creeping back into the picture?:


Soon To Be Lee,now clustered on LA,MS and FL:
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TROPICAL STORM KATIA DISCUSSION NUMBER 15
NWS NATIONAL HURRICANE CENTER MIAMI FL AL122011
500 PM AST THU SEP 01 2011

KATIA HAS TAKEN THE APPEARANCE OF A SHEARED TROPICAL CYCLONE.
VISIBLE AND MICROWAVE SATELLITE IMAGERY CONTINUE TO INDICATE THAT
THE LOW-LEVEL CENTER IS DISPLACED TO THE WEST OF THE CONVECTION.
THE CURVED BAND THAT WAS LOCATED SOUTH OF THE CENTER HAS
DISSIPATED...AND CONVECTION IS NOW LIMITED TO THE NORTHEAST
QUADRANT OF THE SYSTEM. BASED ON A BLEND OF DVORAK CI AND T NUMBERS
FROM SAB AND TAFB...THE INTENSITY HAS BEEN LOWERED TO 60 KT FOR
THIS ADVISORY.


UW-CIMMS SHEAR ANALYSIS CONTINUES TO INDICATE THAT SOUTHWESTERLY
SHEAR OF ABOUT 15 KT IS CURRENTLY IMPACTING KATIA. AN UPPER-LEVEL
LOW LOCATED TO THE NORTHWEST OF THE CYCLONE APPEARS TO BE THE
PRIMARY SOURCE OF THIS SHEAR. KATIA IS EXPECTED TO CONTINUE TO
INTERACT WITH THIS LOW FOR THE NEXT 24 TO 36 HOURS. AFTER
THAT...THE UPPER-LEVEL LOW IS EXPECTED TO LIFT TO THE
NORTH...RESULTING IN A MORE CONDUCIVE ENVIRONMENT FOR
INTENSIFICATION. THE OFFICIAL FORECAST HAS BEEN LOWERED SLIGHTLY
DUE TO THE MARGINAL ENVIRONMENTAL CONDITIONS IN THE SHORT
TERM...HOWEVER IT STILL BRINGS KATIA TO A MAJOR HURRICANE IN A FEW
DAYS.


KATIA CONTINUES TO MOVE TO THE WEST AT 16 KT. IT IS EXPECTED TO SLOW
DOWN AND BEGIN A GRADUAL TURN TO THE NORTHWEST AS IT APPROACHES A
WEAKNESS IN THE SUBTROPICAL RIDGE. THE GFS...ECMWF...AND HFIP
CONSENSUS MODELS ARE IN GOOD AGREEMENT FOR THE FIRST 3 DAYS. AFTER
THAT THERE IS MORE UNCERTAINTY IN THE FORECAST AS THE MODEL SPREAD
INCREASES. SOME MODELS SUGGEST A TURN TOWARD THE WEST AS THE
SUBTROPICAL RIDGE REBUILDS TO THE NORTH OF KATIA...WHILE OTHERS
SUGGEST THAT THE WEAKNESS WILL PERSIST
...BRINGING THE CYCLONE
FARTHER NORTH. THE OFFICIAL FORECAST LIES BETWEEN THESE SCENARIOS
AND IS VERY CLOSE TO THE HFIP CONSENSUS.

FORECAST POSITIONS AND MAX WINDS

INIT 01/2100Z 16.1N 49.2W 60 KT 70 MPH
12H 02/0600Z 16.8N 51.0W 65 KT 75 MPH
24H 02/1800Z 17.7N 52.9W 70 KT 80 MPH
36H 03/0600Z 18.7N 54.6W 75 KT 85 MPH
48H 03/1800Z 19.7N 56.1W 85 KT 100 MPH
72H 04/1800Z 21.6N 59.0W 95 KT 110 MPH
96H 05/1800Z 23.5N 62.0W 100 KT 115 MPH
120H 06/1800Z 25.5N 65.0W 105 KT 120 MPH

$$
FORECASTER ZELINSKY/CANGIALOSI
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1009. BA
Quoting angiest:

Which curves back, or recurves. ;)

I think the recurve would actually be the curve from Northward to Eastward, with the curve having been Westward to Northward (limiting myself to the Atlantic basin).


ding ding

think of a bow and you nail the definition perfectly
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Quoting CharlestonTigress:
I like how one (only one!) of the ensemble models has it going straight through Charleston. (not *like* like, know what I mean)
this recurve is looking less likely, huh
And this is exactly why the debate began in the first place.

As Levi said, people are not using the word properly. A recurve simply means the storm will curve a second time.

In this case with Katia, a recurve will still happen, the question is whether or not it will occur over the ocean or over land. In other words, no the recurve is not looking less likely, the recurve before land is looking less likely...there is a difference lol
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1007. GetReal
Quoting Levi32:


Well...

New Orleans, Louisiana (Airport)
Updated: 2:53 PM CDT on September 01, 2011

81 °F / 27 °C
Light Rain
Humidity: 82%
Dew Point: 75 °F / 24 °C
Wind: 4 mph / 6 km/h / 1.5 m/s from the SE

Pressure: 29.98 in / 1015 hPa (Steady)


Hopefully it is my equipment deciding to go wacky just now!!! LOL
Member Since: July 4, 2005 Posts: 204 Comments: 8898
Ughhh I finally have some time to post again lol. Been working 50 out of the last 72 hours. I haven't followed Katia all that much since she is way out in the open ocean but looking at long term loops she looks pretty disorganized for a strong tropical storm, compared to yesterday at least. Appears as if SW-erly shear is doing a number on her but I haven't really checked the CIMSS maps. Now we have 93L and with very little steering currents at all, even if we do not get a significant tropical system there will be some unbelievable rainfall over the next 5 days around the northern Gulf Coast.
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interesting discussion from the SJU NWS office this afternoon especially after katia passes the carib here read it pretty nice discussion of future tropical development in atl.....



LABOR DAY-TUE...KATIA WILL BE MAKING ITS CLOSEST APPROACH TO THE
ISLANDS SOME 400 MILES NE OF THE ISLANDS. WHILE KATIA HAS BEEN
MOVING MORE WWD OVR THE PAST 12 HOURS AND IS LIKELY TO DO IT FOR
ANOTHER DAY OR TWO WATER VAPOR IMAGERY SHOWS AN AMPLIFYING TROUGH
ACROSS THE NORTHEASTERN US WHICH IS FCST TO CUT OFF ACROSS THE WRN
ATLC. THIS IS LIKELY TO IMPART A MORE POLEWARD MOTION ONCE IT
REACHES 20N AND 60W ALONG WITH A SIG REDUCTION IN FORWARD SPEED.
ACCORDING TO THE GLOBAL MODELS...AREA WILL BE UNDER STRONG
SUBSIDENCE ON THE PERIPHERY OF KATIA AND VERY LITTLE PRECIP IS
EXPECTED EARLY NEXT WEEK. ONLY IMPACTS FROM KATIA ARE SWELLS THAT
WILL INCREASE THE RISK OF RIP CURRENTS SUN AND MON.

AFTER KATIA CLEARS THE AREA EARLY NEXT WEEK...MODELS SHOW A
SIGNIFICANT CHANGE TO THE UPPER LEVEL PATTERN WITH TUTTS/TROUGH
THAT ARE CURRENTLY PRESENT ACROSS THE ATLC TO BE REPLACED BY A
STRONG RIDGE ALOFT. THIS WILL BLOCK ANY POTENTIAL TROPICAL
CYCLONES ORIGINATING IN THE TROPICAL ATLC FROM TAKING THE NORTHERN
ROUTE. WHILE WE ARE MORE THAN LIKELY TO DODGE THE BULLET WITH
KATIA THIS MAY NOT BE THE CASE FOR FUTURE STORMS IN THE NEXT 7-14
DAYS.
Member Since: July 10, 2006 Posts: 1 Comments: 833
1003. Levi32
Quoting JNCali:
recurve..schmeecurve I'm still wondering why they call the study of weather meteorology.. isn't that the study of meteors???


Meteoron is the Greek root for "high in the sky" and generally means any atmospheric phenomenon. The English word "Meteor" comes from the same root for obvious reasons. "Meteorology" is the study of atmospheric phenomenon, and thus the study of the atmosphere.
Member Since: November 24, 2005 Posts: 635 Comments: 26684
Quoting Progster:



Like a baroclinic system...or a tornado :)
Exactly.
Member Since: August 16, 2007 Posts: 6 Comments: 12463
I see the 12z models have shifted west, most notably the GFS and ECMWF, with Katia in response to the building ridge to the north. Will be interesting over the next coming days to see how the models depict the interaction between the subtropical ridge to the north of Katia and the trough over the eastern U.S.
Member Since: October 28, 2006 Posts: 57 Comments: 30615
Is Texas going to get screwed out of rain?
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Quoting Levi32:


I could be wrong, but I can't remember the NHC issuing watches when there was no classified storm at the time when the watch was issued. They issued nothing for the Antilles islands when Irene was 50 miles away with 45kt winds, because she wasn't yet classified.

Levi they did issue
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Quoting quasigeostropic:
Re-curve connotes that it has at least curved prior. A storm turning out to sea the FIRST time, I would use "curving". If a storm is going West and then starts turning northward but misses the trough, goes West again, then catches the second trough and turns north again, that SECOND turn would technically be considered a re-curve.

Not going to make a big deal about it though.:)
yes, that would also be a recurve, but the most common second curve is one out to the east, so when people say "recurve" its usually safe to assume that is the type of curve they mean.


btw, I've seen your tropical tutorial blog, some pretty good stuff, thanks for that
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I like how one (only one!) of the ensemble models has it going straight through Charleston. (not *like* like, know what I mean)
this recurve is looking less likely, huh
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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.