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 Gearsts:
Doesnt look close yet.
HH found some west winds.
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1144. Gearsts
Quoting NICycloneChaser:
Am I the only person who thinks 93L looks like it has a completely closed LLC?
Doesnt look close yet.
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1143. JGreco
Quoting Bretts9112:
Im in the fl panhandle near destin fl guess we are just going to see a lot of rain from 93l?


It depends. Impacts might be greater if the storm takes a track towards Alabama putting us on the east side of however strong the storms become.
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OceanSat, shows broad circulation, don't think it has the resolution to show a tigher circulation though one may exist.


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1141. DFWjc
Quoting AtHomeInTX:

Hey Tex. Hang in there there's still some hope. :)


TWC said is could be a TD or TS at 5pm EST
Member Since: July 19, 2011 Posts: 1 Comments: 1006
Quoting atmoaggie:
What we've been figuring, with the fast model development, is a potential vorticity inversion.

Interesting, but weird, shtuff.
You realize the inversion you are looking at exists between the surface level and the 1,500ft/960mb flight level, right? Recon is not flying at the standard 700-850mb flight level. This entire mission has been at the 960mb level.
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Quoting bohonkweatherman:
The problem is this state needs something major to happen. I was hoping for a wave to come thru but since the gulf is almost 90 degrees something has to develop. The fact that the system is east of Texas and is pulling in very dry air, the front coming thru early next week will most likely come thru dry due to lack of moisture in the air. You were hoping and praying just like every Texan. I just hope some of Texas gets some rain even though it wont be me.


I understand....
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1138. IKE
SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE MOBILE AL
238 PM CDT THU SEP 1 2011

ALZ051>064-FLZ001>006-MSZ067-075-076-078-07 9-021045-
CHOCTAW-WASHINGTON-CLARKE-WILCOX-MONROE-CONECUH-B UTLER-CRENSHAW-
ESCAMBIA-COVINGTON-UPPER MOBILE-UPPER BALDWIN-LOWER MOBILE-
LOWER BALDWIN-INLAND ESCAMBIA-COASTAL ESCAMBIA-INLAND SANTA ROSA-
COASTAL SANTA ROSA-INLAND OKALOOSA-COASTAL OKALOOSA-WAYNE-PERRY-
GREENE-STONE-GEORGE-
INCLUDING THE CITIES OF...BUTLER...LISMAN...SILAS...CHATOM...
MILLRY...JACKSON...THOMASVILLE...GROVE HILL...CAMDEN...
PINE HILL...HOMEWOOD...MONROEVILLE...EVERGREEN...GREENV ILLE...
LUVERNE...BRANTLEY...ATMORE...BREWTON...EAST BREWTON...
ANDALUSIA...OPP...MOBILE...PRICHARD...SARALAND... BAY MINETTE...
TILLMANS CORNER...THEODORE...DAPHNE...FAIRHOPE...FOLEY...
SPANISH FORT...CENTURY...FLOMATON...MOLINO...PENSACOLA...
FERRY PASS...BRENT...WEST PENSACOLA...BELLVIEW...ENSLEY...
MYRTLE GROVE...JAY...PACE...MILTON...GULF BREEZE...CRESTVIEW...
WRIGHT...FORT WALTON BEACH...NICEVILLE...DESTIN...SEMINOLE...
EGLIN AFB...VALPARAISO...WAYNESBORO...RICHTON...BEAUMONT ...
NEW AUGUSTA...LEAKESVILLE...MCLAIN...WIGGINS...LUCEDAL E
238 PM CDT THU SEP 1 2011

...POTENTIAL EXTREME HEAVY RAINFALL TO MATERIALIZE FOR THIS LABOR DAY WEEKEND
ALONG THE NORTH CENTRAL GULF COAST...

AS A LOW PRESSURE SYSTEM GRADUALLY EVOLVES IN THE GULF OF MEXICO OVER
THE NEXT FEW DAYS...THE NORTH CENTRAL GULF COAST REGION IS UNDER A
THREAT FOR EXTREMELY VERY HEAVY RAINFALL...WITH THE MOST INTENSE PERIOD
EXPECTED TO BE FROM SATURDAY EVENING THROUGH MIDDAY MONDAY. IT IS NOT OUT
THE QUESTION FOR SOME AREAS OVER COASTAL ALABAMA AND NORTHWEST
FLORIDA TO RECEIVE AS MUCH AS 10 TO 15 INCHES OF RAIN...WITH LOCALLY
HIGHER ISOLATED AMOUNTS WERE RAINBANDS BECOME ESTABLISHED. A BREAK
DOWN IS GIVEN BELOW.

ALONG THE COASTAL COUNTIES OF ALABAMA AND NORTHWESTERN FLORIDA...SHOWERS
AND THUNDERSTORMS WILL BEGIN TOMORROW MORNING AND GRADUALLY INCREASE
IN COVERAGE AND INTENSITY DURING THE DAY. BY SUNSET TOMORROW... TWO TO FOUR
INCHES OF RAIN COULD FALL LOCALLY....MAINLY WEST OF PENSACOLA AND
VERY CLOSE TO THE COAST.

LOOKING INTO THE FRIDAY NIGHT THROUGH SATURDAY EVENING TIME
FRAME...RAIN WILL CONTINUE. AN ADDITIONAL ONE TO THREE INCHES OF
RAIN COULD FALL...BRING TOTALS UP TO A FORECAST OF FOUR TO SIX INCHES
FROM PENSACOLA WEST TO MOBILE...AND MAINLY SOUTH OF I-10.

FINALLY...THE SITUATION COULD BE FURTHER EXACERBATED SATURDAY NIGHT THROUGH
EARLY MONDAY AS RELATIVE HEAVIER RAINFALL BECOMES ESTABLISHED ON THE
EAST SIDE OF A GULF SURFACE LOW THAT IS EXPECTED TO DEVELOP. GIVEN
THE CURRENT UNCERTAINTY ASSOCIATED WITH THE DEVELOPING SURFACE
LOW...EXACTLY WHERE THE HEAVIEST RAINFALL SETS UP WILL REQUIRE
CONSTANT MONITORING. DESPITE THIS...IT IS REALIZED THAT OUR REGION
WILL MOST LIKELY BE ON THE EAST SIDE OF THE STORM SYSTEM. WITH
THIS...WE COULD EITHER BECOME SITUATED UNDER A DETACHED HEAVY
RAINBAND IF THE SURFACE LOW MOVES FURTHER WEST...OR WITHIN HEAVY
RAINBANDS IF THE SYSTEM MOVES CLOSER. EITHER WAY...OUR REGION IS IN
FOR POTENTIALLY EXTREMELY HEAVY RAINFALL. IT MUST BE EMPHASIZED THAT
5 TO 10 INCHES OF RAIN COULD FALL JUST IN THE SATURDAY EVENING TO
EARLY MONDAY TIME FRAME ALONE.

THIS TYPE OF RAINFALL WILL LIKELY BRING ABOUT ISOLATED FLASH
FLOODING BY SATURDAY NIGHT...IF NOT EARLIER. THIS COULD EXPAND INTO
AREAL FLOODING EVENTUALLY EVOLVING UPSCALE TO LOCAL COASTAL RIVER
FLOODING BY LATE WEEKEND THROUGH EARLY NEXT WEEK...MAINLY AFFECTED
THE RIVERS OF SOUTHEAST MISSISSIPPI...COASTAL ALABAMA AND THE WESTERN
FLORIDA PANHANDLE. A FLASH FLOOD WATCH WILL LIKELY BE ISSUED BY EARLY
FRIDAY FOR THE PERIOD FROM MID-WEEKEND THROUGH MONDAY.

PLEASE STAY TUNED TO LOCAL MEDIA OUTLETS...NOAA WEATHER RADIO...AND
YOUR LOCAL NWS WEB PAGE (SEE HTTP://WWW.SRH.NOAA.GOV/MOB) FOR LATER
UPDATES...GRAPHICAL FORECASTS AND FAST BREAKING WATCH OR WARNING
INFORMATION. THIS IS A POTENTIAL VERY SERIOUS SITUATION AND NOW IS
THE TIME TO BEGIN PREPARATIONS.

JMM 23 / DS 12
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Quoting AtHomeInTX:



Granted. All of Texas needs rains. Never said any different. But I wouldn't begrudge anyone who needs the rain getting some. Was hoping some of the models taking it into south TX would come true. But our grass is just as dry. Our lakes and ponds are just as empty. Making it harder to put out forest fires. Hell I hope everyone gets drenched. And I wouldn't complain about that even if I wasn't getting a drop.


Houston averages 47" of rain a year...we have had 10.5", I have had 9.5" in Tomball. And I only had 33" last year!

The driest year on record is 1917 ( I think ) at 17-18"!
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93L will most likely be just a tropical storm and go to Mexico, katia will most likely go out to sea, lol. I'm running with those predictions because that seems to fit the pattern we have had over 2 years now. Sarcastic flag on
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Quoting NICycloneChaser:


Glad to hear that I'm not going crazy :P

Also, I believe a round of applause is in order for calling 94L a few days ago, and also saying it had a good chance this morning when it was given 10%.


Thanks, at least somebody was listening to me!

lol.
Member Since: July 6, 2010 Posts: 112 Comments: 31342
1133. Levi32
Quoting atmoaggie:
What we've been figuring, with the fast model development, is a potential vorticity inversion.

Interesting, but weird, shtuff.


I dunno about you but I've seen many, many times that the recon will find faster SFMR readings than flight-level in a system that has not yet been classified or strengthened above a weak tropical storm. Slower surface winds are nearly a pure result of friction in the PBL. A tropical cyclone's circulation generally weakens with height. In a particularly weak system, it may not be too surprising to see slightly faster winds at the surface right where the inflow into the thunderstorms is coming from. It's also unclear to me how much of an error the SFMR instrument has in weak wind situations (minimal TS force or less).
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Quoting bohonkweatherman:
Parts of Southeast Texas have had a little bit more rain than Central Texas but they average about twice as much. The Houston area has had about as much rain as I have had and that is unbelievable because I use to go to Houston often and it seemed like it rained every time i went there but not this past year.


Granted. All of Texas needs rains. Never said any different. But I wouldn't begrudge anyone who needs the rain getting some. Was hoping some of the models taking it into south TX would come true. But our grass is just as dry. Our lakes and ponds are just as empty. Making it harder to put out forest fires. Hell I hope everyone gets drenched. And I wouldn't complain about that even if I wasn't getting a drop.
Member Since: August 24, 2010 Posts: 0 Comments: 671
Quoting TropicalAnalystwx13:


It does.


Glad to hear that I'm not going crazy :P

Also, I believe a round of applause is in order for calling 94L a few days ago, and also saying it had a good chance this morning when it was given 10%.
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Quoting TropicalAnalystwx13:


There isn't a lot of mid-level shear right now, and it should continue to decrease. I could see how dry air may be a problem, but not wind shear.


Deep layered shear is still 25-30 kts and even if we see the ULL exit the northern Gulf Coast to the NW sometime soon the location of the upper ridging to its SW will still impart around 15 kts. There isn't a lot of mid-level shear, but once the system becomes a moderate tropical storm this doesn't have as much of an effect as the deep layered shear when the system is trying to grow into the upper levels. I think this is what will prevent 93L from becoming anymore than a 50-60 mph tropical storm at best.
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Quoting NICycloneChaser:
Am I the only person who thinks 93L looks like it has a completely closed LLC?
Nope. Me too.
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1128. Patrap
93L Floater - RGB Color Infrared Loop

Member Since: July 3, 2005 Posts: 419 Comments: 127377
Quoting TexasHurricane:


I am not really complaining in the sense for just us but for "all" of us. Was really hoping LEE could make landfall and go through the state. (nothing major however) :)
The problem is this state needs something major to happen. I was hoping for a wave to come thru but since the gulf is almost 90 degrees something has to develop. The fact that the system is east of Texas and is pulling in very dry air, the front coming thru early next week will most likely come thru dry due to lack of moisture in the air. You were hoping and praying just like every Texan. I just hope some of Texas gets some rain even though it wont be me.
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Quoting NICycloneChaser:
Am I the only person who thinks 93L looks like it has a completely closed LLC?


It does.
Member Since: July 6, 2010 Posts: 112 Comments: 31342
Quoting Bretts9112:
Im in the fl panhandle near destin fl guess we are just going to see a lot of rain from 93l?


Guess again, just check your forecast, shows Heavy Rain and Wind for Sunday and Monday, Happy Labor Day! I'd like to see it go West so I can chill out on the boat at Crab Island!
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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


That is absolutely false. All 3 storms hit Florida directly. Go back and look at storm tracks. In fact, I'll post them here...




and a brush with Rita in the Keys:
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Quoting AtHomeInTX:

Hey Tex. Hang in there there's still some hope. :)


I agree with you, I think we have a good chance of feeling something off of 93L at least here on the Tx/La border in southeast Texas Hopefully further west.
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Am I the only person who thinks 93L looks like it has a completely closed LLC?
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1121. Patrap



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1120. Levi32
12z GFS 48-hour 200mb map shows dramatic improvement in the actual shear values over the northern gulf, but there is still a small upper trough to the northwest impinging upon the high, making it asymmetrical. This will be 93L's difficulty, as that could open up the NW quad to dry air entrainment, and outflow would also be scarce there. However, I would describe conditions there overall to be "good," just not excellent. They would support a strengthening tropical storm.

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Quoting Progster:


Like a cold low (polar)? Shouldn't there be a pronounced vortmax at or about H 500? There is a vorticity maximum over the N central Gulf but it may have been too weakly analyzed. If the mechanism for development is indeed baroclinic instability, development will be slow. And yet may of the hi-res models show rapid intensification. Confusing!
What we've been figuring, with the fast model development, is a potential vorticity inversion.

Interesting, but weird, shtuff.

Back L8R (phone's ringing).
Member Since: August 16, 2007 Posts: 6 Comments: 12461
1097: Also keep in mind that a very large area of intense convection can moisten the mid levels as well as decrese shear that is associated with a small pocket of lower heights as the entire upper atmosphere warms and begins to turn into a well defined anticyclone. So long as 93L is producing daily intense convection, conditions for strengthening should steadily improve.
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Member Since: July 6, 2010 Posts: 112 Comments: 31342
1115. Patrap
Member Since: July 3, 2005 Posts: 419 Comments: 127377

Dennis.
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1113. IKE
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
412 PM EDT THU SEP 1 2011

.SHORT TERM (TONIGHT THROUGH SATURDAY NIGHT)...ALL EYES ARE ON
THE GULF OF MEXICO THIS AFTERNOON WHERE A POTENT TROPICAL WAVE IS
GRADUALLY BECOMING BETTER ORGANIZED. 12Z GUIDANCE HAS COME INTO
SOMEWHAT BETTER AGREEMENT WITH SLOW MOVING LOW PRESSURE DEEPENING
OVER THE NORTHWESTERN GULF TONIGHT INTO THE WEEKEND...BEFORE
LIFTING NORTH OF NORTHEAST INTO THE DEEP SOUTH BY LATE IN THE
WEEKEND OR EARLY NEXT WEEK. STEERING CURRENTS ARE FORECAST TO BE
VERY WEAK INTO EARLY NEXT WEEK SO THERE IS STILL QUITE A BIT OF
UNCERTAINTY AS TO HOW LONG THE SYSTEM REMAINS OVER WATER...HOW
MUCH IT DEEPENS...AND HOW FAR EAST THE EVENTUAL TRACK MIGHT BE.

REGARDLESS OF THE EXACT TRACK...CONFIDENCE IN THE GUIDANCE IS
INCREASING ENOUGH TO SPECULATE THAT THE SYSTEM WILL HAVE SOME
IMPACT ON THE WEATHER ACROSS THE TRI-STATE REGION...ESPECIALLY FOR
AREAS IN THE FLORIDA PANHANDLE AND THE COASTAL WATERS. WOULD
EXPECT TO SEE AN INCREASE IN SHOWERS AND THUNDERSTORMS ALONG THE
PANHANDLE BEACHES BEGINNING FRIDAY AFTERNOON AND CONTINUING INTO
SATURDAY NIGHT AND BEYOND. HEAVY RAIN WILL BE POSSIBLE FOR THIS
AREA...ESPECIALLY TOWARDS LATE SATURDAY INTO SUNDAY.

THE POPS WILL DROP OFF SHARPLY TO THE NORTHEAST OVER THE NEXT
SEVERAL DAYS AS THE INCOMING MOISTURE FROM THE TROPICAL SYSTEM
MEETS A VERY DRY AIRMASS CURRENTLY FILTERING IN FROM THE
CAROLINAS. DEWPOINTS IN SOUTHEAST GEORGIA HAVE DROPPED INTO THE
UPPER 50S THIS AFTERNOON AND THIS AIRMASS WILL SPREAD INTO THE
NORTHERN TWO-THIRDS OF THE FORECAST AREA FOR FRIDAY. FOR
FRIDAY...POPS WILL RANGE FROM AROUND 50 PERCENT ALONG THE COAST
TO LESS THAN 10 PERCENT ACROSS SOUTH GEORGIA. HIGHER POPS WILL
SLIDE SLOWLY NORTHEAST ON SATURDAY. HOWEVER...APPRECIABLE RAIN IS
NOT EXPECTED ACROSS SOUTH GEORGIA UNTIL SUNDAY.

WILL NEED TO CONTINUE TO MONITOR THE DEVELOPMENT OF THE SYSTEM TO
DETERMINE IN OTHER IMPACTS ON COASTAL AREAS...SUCH AS HIGH SURF
AND COASTAL FLOODING. THE CURRENT FORECAST HAS THE HIGHEST SURF AND
STRONGEST ONSHORE FLOW NOT SETTING IN UNTIL LATER SATURDAY INTO
SUNDAY. THEREFORE...WILL HOLD OFF ON ANY COASTAL FLOOD PRODUCTS
UNTIL THE FORECAST BECOMES A BIT MORE CERTAIN.L
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Quoting atmoaggie:
? The surface winds are stronger at the surface than at flight level all around 93L.

Really, talking to a tropical met PhD here, now, about it. Baroclinic instability-driven system...


Like a cold low (polar)? Shouldn't there be a pronounced vortmax at or about H 500? There is a vorticity maximum over the N central Gulf but it may have been too weakly analyzed. If the mechanism for development is indeed baroclinic instability, development will be slow. And yet may of the hi-res models show rapid intensification. Confusing!
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Quoting gbreezegirl:
I live in the Pensacola Florida area and Dennis was terrible. Somebody needs to do their research! We were without power for days and had significant damage.


I lived just to the East of Navarre and watched from a friends house in Fort Walton Beach as the eastern eyewall went over my house! I waded through 3 feet of water to check on my house after Dennis went through and I'm just thankful my house was elevated and built after Ivan hit in 2004 so it was built to a better code, others weren't so lucky!
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Quoting atmosweather:


Size of the circulation will be huge. But remember the conditions in the upper atmosphere won't be perfect...there will still be moderate shear and mid level dry air. We know what 31-32 degree water has done with systems in the GOM, but those storms also had almost perfect upper level environments to go along with it.


There isn't a lot of mid-level shear right now, and it should continue to decrease. I could see how dry air may be a problem, but not wind shear.
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1108. Patrap
Member Since: July 3, 2005 Posts: 419 Comments: 127377
Im in the fl panhandle near destin fl guess we are just going to see a lot of rain from 93l?
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Quoting TexasHurricane:


Hi AtHome :)
Hey Tex. Hang in there there's still some hope. :)
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1105. Patrap


Click on fronts here,

93L Floater - RGB Color Infrared Loop
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1104. Becca36
Quoting rmbjoe1954:


Wilma in 2005?

Yes! Wilma's eye went right over my house in Boca Raton,FL and broke our back slider(we now have shutters). That was a scary day.
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Quoting atmoaggie:
? The surface winds are stronger than at flight level all around 93L.

Really, talking to a tropical met PhD here, now, about it. Baroclinic instability-driven system...
Ok you're right the area of stronger surface winds is pretty much across the entire gulf region, not just a few random observations as I thought.

Anyway, how does baroclinic instability explain this?
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1072:
I'd wager that has alot to do with that ULL. as it weakens and retrogrades, I'd assume flight level winds would pick up. I do agree that it is receiving some forcing from baroclinic processes currently. Alot of heat is building at the upper levels and I expect that will shunt/weaken the ULL and cause the system to take on more purely tropical characteristics.
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1100. Patrap
Member Since: July 3, 2005 Posts: 419 Comments: 127377
Quoting Drakoen:


Let's wait till it becomes an actual system first.


Okay.

Quoting Levi32:


Euro last night I think was overdone, but illustrated how the environment will support strengthening. I think if 93L is over the water Monday, it will likely be a hurricane. If it comes ashore before the weekend is over, it may just be a tropical storm.


Okay, thanks.
Member Since: July 6, 2010 Posts: 112 Comments: 31342
Quoting Samantha550:


Thanks, sometimes we are not considered Texas by most folks. Sure wish my hill country family could get some rain, they really need it.


Man, I'm glad I didn't post my "That's not east Texas, it's west Louisiana comment."

Oh wait, crap.
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Quoting Drakoen:
I don't like the way 93L looks like satellite imagery. It looks like it could become a large system and powerful. The upper level low inhibiting the system is gradually moving out and the upper level outflow is already being established over the eastern portion of the system. RGB imagery clearly indicates broad rotation at the lower levels occurring.



Size of the circulation will be huge. But remember the conditions in the upper atmosphere won't be perfect...there will still be moderate shear and mid level dry air. We know what 31-32 degree water has done with systems in the GOM, but those storms also had almost perfect upper level environments to go along with it.
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Quoting JeffMasters:


Recurvature is a term from physics describing the motion of a spinning storm system on the surface of the Earth. Low pressure systems in the NH will always recurve towards the pole, and high pressure systems will recurve towards the Equator.

From:
http://www.applet-magic.com/recurvature.htm

"The explanation for recurvature lies in the fact that cyclones (and anticyclones) possess angular momenta with respect to their spin axes. This will be referred to as their spin angular momenta. They also possess angular momenta with respect to the axis of rotation of the Earth, which will be called their terrestrial angular momenta. The turning of the spin angular momentum vector with the rotation of the Earth is a forced precession which creates a torque on the cyclone that accelerates it toward the nearest pole. As the cyclone moves toward its pole it gets closer to the axis of rotation of the Earth. The preservation of the terrestrian angular momentum then requires it to increase its velocity toward the east."

Jeff Masters
Thanks Jeff
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Quoting LAlurker:

????????


Oh really. Don't remember this part of Florida being annex to Alabama!
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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.