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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2663. sporteguy03
3:42 AM GMT on September 22, 2007
West end
Member Since: July 7, 2005 Posts: 0 Comments: 5279
2662. thelmores
1:53 PM GMT on September 21, 2007
looks to me 93L is trying to close off its center, and build convection.....

Member Since: September 8, 2005 Posts: 0 Comments: 3805
2660. Cavin Rawlins
1:50 PM GMT on September 21, 2007
NEW BLOG IS UP
Member Since: July 24, 2005 Posts: 407 Comments: 19076
2659. fireflymom
1:50 PM GMT on September 21, 2007
Our Houston area weather folk seem more interested in the Pacific NW storm-how will this affect the GOM activity. Some one please give me an idea?
Member Since: June 5, 2007 Posts: 0 Comments: 588
2658. Cavin Rawlins
1:49 PM GMT on September 21, 2007
Posted By: Bonedog at 9:41 AM AST on September 21, 2007.

huh 456? I lost yea there


When i say shallow warm-core, I mean a system that is warm-cored in the low levels but becomes cold-core in the upper levels. TCs are warm-core thoughout the atmopshere and thus are termed deep warm-core systems.

There are two systems that present themselves as shallow warm-core systems - subtropical cyclones and warm-seclusions systems.

A warm seclusion is the mature phase of the extratropical cyclone lifecycle. This was conceptualized after the ERICA field experiment of the late 1980s, which produced observations of intense marine cyclones that indicated an anomalously warm low-level thermal structure, secluded (or surrounded) by a bent-back warm front.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
2657. msphar
1:48 PM GMT on September 21, 2007
Dust and shear. Dust and shear. Time ticking by. CV not producing much this month, 10 day til Oct starts. Its been eight days since the last storm was named. Maybe the downward adjusted Dr. Gray number will be reached or maybe not.
Member Since: August 20, 2006 Posts: 0 Comments: 289
2656. v7fan16
1:48 PM GMT on September 21, 2007
the steering is now running from south to north over florida, I can see why 93L is drifting NNE, plus its feeling a little tug from the front off the east coast, but I think it will stall before getting to the coast, the high to the north and east is expected to shift a bit further south, therefore we may see 93L drift southward this afternoon
Its not drifting NNE... its moving wnw at about 5mph.
2655. Thunderground
1:48 PM GMT on September 21, 2007
well LA, I'm very new at this, but IMO the WV seems to support what you're saying
Member Since: August 31, 2007 Posts: 0 Comments: 103
2654. thelmores
1:47 PM GMT on September 21, 2007


looks like recon is trying to get a vortex fix....
Member Since: September 8, 2005 Posts: 0 Comments: 3805
2649. seflagamma
1:45 PM GMT on September 21, 2007
new blog up.
Member Since: August 29, 2005 Posts: 298 Comments: 40892
2648. CocoaShutterman
1:45 PM GMT on September 21, 2007
Thanks, Dr. M
2646. thelmores
1:43 PM GMT on September 21, 2007
Mandatory Data...

Observation Time: Friday, 13:27Z
Radar Capability: Yes
Aircraft Altitude: Below 10,000 meters
Coordinates: 29.5N 85.3W (View map)
Location: 52 miles (83 km) to the SSE (155) from Panama City, FL, USA.
Turbulence: None
Conditions Along Flight Route: In the clear
Pressure Altitude: 460 meters
Flight Level Wind: From 120 at 23 knots (From the ESE at ~ 26.4 mph)
- The above is a spot wind.
- Winds were obtained using doppler radar or inertial systems.
Flight Level Temperature: 22C
Flight Level Dew Point: 21C
Weather (within 30 nautical miles): Thunderstorm(s)
Mean Sea Level Pressure (MSLP): 1007 mb (extrapolated)

Optional Data...

Estimated Surface Wind: From 90 at 20 knots (From the E at ~ 23.0 mph)
Member Since: September 8, 2005 Posts: 0 Comments: 3805
2644. Bonedog
1:41 PM GMT on September 21, 2007
huh 456? I lost yea there
Member Since: July 14, 2005 Posts: 14 Comments: 7418
2643. StormJunkie
1:40 PM GMT on September 21, 2007
456, click on the ascending pass right off the African coast. Shows the pass on the QS front page, but there is no data when you select it. Something is fishy with the QS, maybe it will get back on track with the descending pass.
Member Since: August 17, 2005 Posts: 26 Comments: 16348
2641. catastropheadjuster
1:38 PM GMT on September 21, 2007
Dixiegal: You welcome. Anytime.
Sheri
Member Since: August 24, 2006 Posts: 21 Comments: 3671
2640. Cavin Rawlins
1:37 PM GMT on September 21, 2007
The non tropical low is a shallow warm-core system. These are either warm seclusions or subtropical cyclones and the non tropical low is definately not a warm seclusion.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
2639. NEwxguy
1:37 PM GMT on September 21, 2007
bonedog,I've been watching that low the past couple of days,it's really been wrapping up.
Member Since: September 6, 2007 Posts: 877 Comments: 15710
2638. Bonedog
1:37 PM GMT on September 21, 2007
yea I read that JP. I have been watching that since it brough rains to my area earlier last week. Its got the potential, the time, the water and the environment to make the transition.

Don't forget that a system thats extratropical can use cooler waters (as low as 21*c) to make itself tropical. I found that information out the other day reading the psu met:241 online course material
Member Since: July 14, 2005 Posts: 14 Comments: 7418
2637. apocalyps
1:36 PM GMT on September 21, 2007
That convection in the carribian looks like something to watch.
If this developes we could have another hurricane landfall.
Member Since: May 10, 2007 Posts: 0 Comments: 960
2636. Cavin Rawlins
1:34 PM GMT on September 21, 2007
SJ, ohh well

Thats how i normally see it...lets see if anything changes.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
2633. Bonedog
1:32 PM GMT on September 21, 2007
I know this doesnt have to do with 93L but look at how far the extratropical Low in the central north atlatic is pulling convection! Almost has convection to the LA's

w
Member Since: July 14, 2005 Posts: 14 Comments: 7418
2631. StormJunkie
1:31 PM GMT on September 21, 2007
Posted By: Weather456 at 1:19 PM GMT on September 21, 2007.
Quikscat is processing those areas...look at quikscat about 1, 2 ,3 hours from now and u will see new passes added hour by hour.


Not sure about this 456, The Ascending pass is the morning pass and it seems that all of those are from yesterday. The descending is the evening pass and it seems to have not hit any of it's passes either as much of the descending are still blank.

QuickSCAT


Find that page as well as forecast models, imagery, marine data, preparedness info, and much more from the
Quick Links page.
Member Since: August 17, 2005 Posts: 26 Comments: 16348
2629. thelmores
1:30 PM GMT on September 21, 2007
Observation Time: Friday, 13:07Z
Radar Capability: Yes
Aircraft Altitude: Below 10,000 meters
Coordinates: 29.3N 85.3W (View map)
Location: 64 miles (104 km) to the SSE (160) from Panama City, FL, USA.
Turbulence: None
Conditions Along Flight Route: In the clear
Pressure Altitude: 450 meters
Flight Level Wind: From 240 at 15 knots (From the WSW at ~ 17.2 mph)
- The above is a spot wind.
- Winds were obtained using doppler radar or inertial systems.
Flight Level Temperature: 24C
Flight Level Dew Point: 21C
Weather (within 30 nautical miles): Shower(s) (continuous or intermittent precipitation - from cumuliform clouds)
Mean Sea Level Pressure (MSLP): 1005 mb (extrapolated)

Optional Data...

Estimated Surface Wind: From 360 at 30 knots (From the N at ~ 34.5 mph)
Member Since: September 8, 2005 Posts: 0 Comments: 3805
2627. houstonstormguy
1:30 PM GMT on September 21, 2007
Good Morning All.

Can someone tell me what the currect thinking is on the blob/disturbance in the caribean. What is this forecast to do @ what intensity?

Thanks
Member Since: September 18, 2007 Posts: 0 Comments: 180
2626. Tazmanian
1:29 PM GMT on September 21, 2007
SUBJ/TROPICAL CYCLONE FORMATION ALERT 211200Z SEP 07//
WTNT 01 KNGU 211200Z
RMKS/
1. FORMATION OF A SIGNIFICANT TROPICAL CYCLONE IS POSSIBLE WITHIN
100 NM EITHER SIDE OF A LINE FROM 28.8N 85.5W TO 30.0N 88.5W
WITHIN THE NEXT 00 TO 24 HOURS. AVAILABLE DATA DOES NOT JUSTIFY
ISSUANCE OF NUMBERED TROPICAL CYCLONE WARNINGS AT THIS TIME.
WINDS IN THE AREA ARE ESTIMATED TO BE 25 TO 30 KNOTS. METSAT IM-
AGERY AT 211200Z INDICATES THAT A CIRCULATION CENTER IS LOCATED
NEAR 28.8N 85.5W. THE SYSTEM IS MOVING WEST-NORTHWEST AT 05 KNOTS.2. REMARKS:
3. THIS ALERT WILL BE REISSUED, UPGRADED TO WARNING OR CANCELLED BY 221200Z
Member Since: May 21, 2006 Posts: 5091 Comments: 114956
2624. LeeInNaplesFl
1:28 PM GMT on September 21, 2007
Is there any interest in the "blob" south of Cuba in NW Carib? I think the UKMT had this developing earlier in the week, but now none of the models show anything for it.
Member Since: August 8, 2007 Posts: 0 Comments: 23
2623. Bonedog
1:27 PM GMT on September 21, 2007
I think once the blog surpasses 50 pages it goes into post eating mode :)
Member Since: July 14, 2005 Posts: 14 Comments: 7418
2622. Tazmanian
1:26 PM GMT on September 21, 2007
what is with the Modify Comment evere time you try to Modify Comment your commet it takes you too the Complete Archive or one of dr m old blogs Archive
Member Since: May 21, 2006 Posts: 5091 Comments: 114956
2621. catastropheadjuster
1:26 PM GMT on September 21, 2007
dixiegal: Last night he e-mailed asking me to try to find out and PascagoulaGal said it was some word he said. And PascagoulaGal said she e-mailed him and told him.
Sheri
So where do you all think 93 is going?
Member Since: August 24, 2006 Posts: 21 Comments: 3671
2620. PensacolaDoug
1:26 PM GMT on September 21, 2007
A lot further north this morning than has been progged.
Member Since: July 25, 2006 Posts: 0 Comments: 556
2619. Cavin Rawlins
1:24 PM GMT on September 21, 2007
.....
Member Since: July 24, 2005 Posts: 407 Comments: 19076
2618. thelmores
1:25 PM GMT on September 21, 2007
man, the blog is hosed this morning!


Member Since: September 8, 2005 Posts: 0 Comments: 3805
2617. dixiegal1
1:24 PM GMT on September 21, 2007
i walked outside this morning and can hardly believe there is a storm of anytype coming this way... its cool, a little breezy, no clouds, and smells like fall!!! i LOVE this time of year
Member Since: August 26, 2006 Posts: 0 Comments: 77
2616. Cavin Rawlins
1:22 PM GMT on September 21, 2007
....
Member Since: July 24, 2005 Posts: 407 Comments: 19076
2615. thelmores
1:20 PM GMT on September 21, 2007
deleted
Member Since: September 8, 2005 Posts: 0 Comments: 3805
2614. Cavin Rawlins
1:19 PM GMT on September 21, 2007
Quikscat is processing those areas...look at quikscat about 1, 2 ,3 hours from now and u will see new passes added hour by hour.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
2613. louisianaweatherguy
1:20 PM GMT on September 21, 2007
Thunder:

I was saying if upperlevel outflow begins to develop over this thing (aka Anticyclonic turing in the upper levels) we could see a rapidly intensifying system - - - that's IF we see one develop...

I believe it's not out of the question... I'm already seeing signs of outflow already happening, but at the same time - DRY AIR is preventing this thing from completely wrapping into itself
Member Since: July 9, 2007 Posts: 0 Comments: 692

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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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