Complicated Gulf of Mexico disturbance 93L primarily a rain threat

By: Dr. Jeff Masters , 1:42 PM GMT on September 20, 2007

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A very complicated weather situation over the Gulf of Mexico and Atlantic waters off the Southeast U.S. coast associated with a non-tropical low pressure system (93L), has brought heavy rains to Florida, Georgia, and South Carolina over the past 12 hours. A cold-cored upper level low pressure system a few hundred miles southwest of Tampa, Florida is primarily responsible for the the action. Late yesterday afternoon, a separate area of surface low pressure formed near Daytona Beach, bringing high surf and heavy rains of up to five inches along the Florida coast from Daytona to Jacksonville. This low moved inland over Florida, but the associated surge of moisture rotated northwards all the way to South Carolina. High surf warnings and coastal flood watches have been posted for Charleston, South Carolina today. This morning's QuikSCAT pass showed winds up to 50 mph well offshore of South Carolina. These winds have created a storm surge of up to two feet along the South Carolina coast. This second low pressure system was identified as "93L" by NHC beginning at 2 pm EDT yesterday. However, now that the low has weakened crossing the Florida Peninsula, the "93L" designation has been taken away from it, and attached to the upper level low pressure system in the Gulf of Mexico.

Recent Satellite loops and the Tampa Bay long range radar show that this non-tropical low pressure system is beginning to get more organized and is acquiring tropical characteristics. Substantial pressure falls are occurring at the surface underneath the upper level low, and this system is on its way to becoming a subtropical depression. A surface low pressure system vertically aligned with a cold-cored upper level low will usually take two or more days to make the transition to a warm-cored tropical storm. Rapid intensification cannot occur until the system is fully warm-core. Since landfall is expected Saturday between the Florida Panhandle and Southeast Louisiana, 93L probably does not have time to become fully tropical. If 93L makes landfall Saturday, it should not have winds stronger than about 55 mph. The GFDL, HWRF, and SHIPS intensity models all keep 93L's winds below 55 mph. If the storm spends an extra day over water and makes it to Texas, as the ECMWF model predicts, 93L could become fully tropical and make landfall as a strong tropical storm with 60-70 mph winds. However, there is plenty of dry air in the environment, and I don't think the storm will be able to intensify to a strong tropical storm. The primary threat from 93L will be heavy rain, and the northern Gulf Coast from the Florida Panhandle to Texas border can expect a soaking from this system.

The Air Force Hurricane Hunters are scheduled to investigate 93L this afternoon at 2pm EDT.


Figure 1. Current long range radar out of Tampa Bay, Florida.


Remains of Ingrid
The remains of Tropical Storm Ingrid are still active, triggering some heavy thunderstorm activity a few hundred miles north of the northernmost Lesser Antilles Islands. Puerto Rico long range radar and satellite loops show that this activity remains disorganized. Wind shear has dropped to about 10 knots today, and we will need to watch this area for development. However, the upper level winds are not in a particularly favorable configuration, and Ingrid's remains are so disorganized, that any development will be slow to occur. The remains of Ingrid are in a region of weak steering currents, and little movement is expected over the next 3-5 days.

I'll have an update Friday morning.

Jeff Masters

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463. MisipiGrl
4:30 PM GMT on September 20, 2007
Thelmores....I always enjoy your maps. They really help me to "see" what is being discussed. Thanks for this one as I have been struggling to locate the "true" center since last night.
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462. aubiesgirl
4:30 PM GMT on September 20, 2007
Posted By: thelmores at 4:29 PM GMT on September 20, 2007.

as best I can tell, GS is right..... the LLC is to the NE of the heaviest convection....

when/if this LLC gets under the heavy convection, we all may have to "re-think" things.....


rethink for the better or worse?..not tryin to be a smartypants..just wonderin..
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461. 0741
4:29 PM GMT on September 20, 2007
3. REMARKS: AN AEROSONDE WILL DEPART KEY WEST AT 21/1900Z,
OPERATE IN THE STORM AT 3,OOO FT OR BELOW AND DEPART
THE STORM BY 22/0500Z.

is that remote control plane? i think their testing that
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459. flzepher
4:27 PM GMT on September 20, 2007
Posted By: BrDennisH at 4:26 PM GMT on September 20, 2007.

Is it just me are will some people not admit what they see with their own eyes unless Dr. Masters or the NHC tells the to see it. Look at the satellite view. Everything is starting to spin around the old discounted 93L not the new and improved 93L under the old ULL.

93L, that transversed across Florida definately is spinning without question. IMO this will be the developing low

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458. louisianaboy444
4:29 PM GMT on September 20, 2007
Link

If the southern surface low near Tampa forms this is the tracks
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457. thelmores
4:29 PM GMT on September 20, 2007
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456. Michfan
4:28 PM GMT on September 20, 2007
Ingrid is sitting in the TUTT. Thats whats unfavorable about her upper level winds.
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455. thelmores
4:28 PM GMT on September 20, 2007
as best I can tell, GS is right..... the LLC is to the NE of the heaviest convection....

when/if this LLC gets under the heavy convection, we all may have to "re-think" things.....
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454. franck
4:27 PM GMT on September 20, 2007
Think Gulfscotsman is right. The Maypole dance has begun!
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453. NWWNCAVL
4:25 PM GMT on September 20, 2007
Posted By: mostormspotter at 4:22 PM GMT on September 20, 2007.

Oil is at $82.14, Though no mention of this storm on the national news that I can find.


They evaced more than 700 off rigs yesterday. You better get use to it.
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452. KarenRei
4:26 PM GMT on September 20, 2007
Everything is starting to spin around the old discounted 93L not the new and improved 93L under the old ULL.

What are you people calling "the old discounted 93L"? The old 93L is gone. If you're talking 27.5N, 83.7W, I'm pretty sure that's the ULL (see my previous post)
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450. MisipiGrl
4:25 PM GMT on September 20, 2007
"busy day in EMA though...."

Went to a breakfast this morning...all the talk was on this system. MS Power is meeting,probably precautionary and strategic, at the same time. Lots of people have gotten the automated message from the Governor. Local Mets are encouraging people to stay alert. Seems as though we have ourselves in a good mode right now...calm and prepared.
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449. Littleninjagrl
4:27 PM GMT on September 20, 2007
hey all, At work and can't stay on long. Can someone give me a quick run down on the tropics. I know threre is a mess in the gulf and a blob in the carribean? I'm in Tampa. Anything I should watch for? TIA
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448. lilbitofhonesty
4:25 PM GMT on September 20, 2007
I'll second that Chucktown..I live in Mobile and we had horrible flooding and my power was out for two whole weeks after Katrina...though I don't believe this one will be as strong as she was.
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447. Eyewall911
4:26 PM GMT on September 20, 2007
Guys/Gals this 93L looks to be ramping up rather quickly now and a hurricane is not out of the question.
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445. StormJunkie
4:25 PM GMT on September 20, 2007
This is tropical cyclogenesis 101 folks..... along with some very complex upper and mid level Fujiwhara stuff going on.

lol GS, that is pretty good; 101 with a dash of 501 thrown in?

Afternoon all :~)
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444. BrDennisH
4:22 PM GMT on September 20, 2007
Is it just me are will some people not admit what they see with their own eyes unless Dr. Masters or the NHC tells the to see it. Look at the satellite view. Everything is starting to spin around the old discounted 93L not the new and improved 93L under the old ULL.

Link
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443. Chucktown
4:22 PM GMT on September 20, 2007
Everyone needs to remember that the center of whatever 93L becomes will not be the dangerous part. It will most likely be the NE quadrant, so a NOLA landfall would mean FL panhandle gets the worst of it with strong onshore flow and heavy rain.
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442. KarenRei
4:21 PM GMT on September 20, 2007
Ingrid still has a floater and convection. Not sure about winds; last Quikscat missed her. Deserves watching.

Does anybody have a clue what the NHC means when it says upper level winds are unfavorable for Ingrid? What's so unfavorable about a low-shear environment?
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440. Sophmom
4:20 PM GMT on September 20, 2007
What I remember is that she came out of FL heading NE to SW when all the models were run on a storm going SE to NW and that Friday morning the new model runs were moving landfall hundreds of miles west to LA, so I came here and Dr. M called it Friday early (noonish?) while the NHC moved the cone westward little by little with each release. I don't think the NHC likes sudden changes. JMHO.
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439. flzepher
4:20 PM GMT on September 20, 2007
Posted By: Eyewall911 at 4:13 PM GMT on September 20, 2007.

little spin action in the SW carib blob. Could we be seeing our next invest?

Yes, I beleive this will be something to watch. Got a bit of shear now. This is the same area as models a few days ago showed some development and moving N in the GOM as a strong Hurricane. I mentioned it this morning. Does anyone forsee this BLOB has any potental to develope down the road
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438. emagirl
4:22 PM GMT on September 20, 2007
we may go to bed tonight and wake up to something totally different in the morning....maybe i worry too much...busy day in EMA though....
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437. KrazyKaneLove
4:11 PM GMT on September 20, 2007
my local met in wpb says la. or texas still
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436. mostormspotter
4:21 PM GMT on September 20, 2007
Oil is at $82.14, Though no mention of this storm on the national news that I can find.
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435. chklingon
4:20 PM GMT on September 20, 2007
12Z run from NAM shows a strike on NOLA. (Not a highly reliable tropical model, but still an possible early look at the GFS soon to follow.)
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433. KarenRei
4:16 PM GMT on September 20, 2007
Watch the WV loop. Without any further doubt the ULL is drifting and fading SW just a bit WNW of the Keys and its weak surface reflection is near the keys.

I think you have it backwards. Here's the 0h 950 mb vorticity, showing vorticity in the south. We also have these coordinates claiming that the surface low is in the south.

Clearly this issue needs to be resolved, because while both threaten LA, a northern low likely provides threats to MS, AL, and FL, while a southern low likely threatens TX. Northern would be preferable (reduced time and reduced warm water before impact), so I hope you're right, but it doesn't appear that way to me.
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432. JUSTCOASTING
4:15 PM GMT on September 20, 2007
So is Ingrid completly gone now or where is she at ?
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431. iahishome
4:10 PM GMT on September 20, 2007
OK, speaking of physics... any mets wanna comment on how the angular momentum of that circulation that came across Florida will affect that of the 'main' circulation to its Southwest?

I think Dr. M's forecast is probably reasonable if this thing keeps a northward component. Where's a good picture of this high pressure I've been reading about?

Woops, too many questions.
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429. saltydog1111
4:16 PM GMT on September 20, 2007
PascMS: Well hello neighbor... I have a feeling it'll be a whole helluva lot different in a couple of days!!!
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428. aubiesgirl
4:17 PM GMT on September 20, 2007
hey TWC 10 day forecast..calls for wind andrain...this weekend..pretty ambiguous if you ask me...lol
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427. PensacolaDoug
4:15 PM GMT on September 20, 2007
Karenrei, when was that Katrina model run? 8/26/05? What time?

That was from the morning of the 26th, yes. Everything shifted on the afternoon of the 26th, and then it made impact on the morning of the 29th. I.e., in three days, it went from a forecasted impact on the Florida panhandle with reasonably good model agreement to an impact on MS. And this was a storm that was already well-formed, with winds of 100MPH, unlike our current low

I remember the 11:30am five day outlook had it going to PC Florida. Then the 5:30 pm switched 300 miles west. What a jump.
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426. aubiesgirl
4:16 PM GMT on September 20, 2007
Posted By: PensacolaDoug at 4:15 PM GMT on September 20, 2007.

"Head On", "Active ON" "Prefer ON"
and now the latest addition to the product line-up. Treats "ED". Guess the name anyone?


lol
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424. FloridaScuba
12:16 PM EDT on September 20, 2007
so how many LPM's does it take to make 1 knot?

dunno, i have not seen a knot
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423. nash28
4:15 PM GMT on September 20, 2007
I will not be a happy camper if the "heavy rain" forecast goes belly up AGAIN in the Tampa area.
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422. PascMississippi
4:14 PM GMT on September 20, 2007
saltydog1111, yes it is!
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421. Sophmom
4:14 PM GMT on September 20, 2007
Yeah, Karen. I remember that day like it was yesterday. Thanks for that model map.
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420. aubiesgirl
4:14 PM GMT on September 20, 2007
I turned off the AC and opened all the windows...hey no humidity..sounds like that might be ruined this weekend..argh!
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419. snowboy
4:09 PM GMT on September 20, 2007
yes KarenRei, there are 3 systems to watch:
- 93L;
- former Ingrid;
- Caribbean blob.

Of the 3, convection is LEAST impressive over 93L just now..
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418. PensacolaDoug
4:06 PM GMT on September 20, 2007
"Head On", "Active ON" "Prefer ON"
and now the latest addition to the product line-up. Treats "ED". Guess the name anyone?
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417. FloridaScuba
12:14 PM EDT on September 20, 2007
the model's and experts have been fooled in the past.

how do you fool a model? you say something
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416. TampaSpin
12:12 PM EDT on September 20, 2007
JPHurri--witch one would pull the other more toward each other LL or Ul if they were the exact same intensity.
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414. dixiegal1
4:14 PM GMT on September 20, 2007
LOL floridascuba.. thats pretty funny
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413. KarenRei
4:08 PM GMT on September 20, 2007
Karenrei, when was that Katrina model run? 8/26/05? What time?

That was from the morning of the 26th, yes. Everything shifted on the afternoon of the 26th, and then it made impact on the morning of the 29th. I.e., in three days, it went from a forecasted impact on the Florida panhandle with reasonably good model agreement to an impact on MS. And this was a storm that was already well-formed, with winds of 100MPH, unlike our current low.

You just can't get complacent with these things.
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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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