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Complicated Gulf of Mexico disturbance 93L primarily a rain threat

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

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

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

Reader Comments

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2110. stayawaycantore
4:45 AM GMT on September 21, 2007
Looking at NOAA's west atlantic infrared loop, it seems like either a wobble to the southwest that will correct itself as the storm continues NW, or maybe the Southwest quad is just firing up more.

Any thoughts from the more experienced folks?
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2109. stormybil
4:44 AM GMT on September 21, 2007
looks like ex ingrid trying to refire tonight during dmax too
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2101. SouthernLady
11:45 PM CDT on September 20, 2007
2 more Thunderstorm warnings:


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2099. tampabayfish
4:43 AM GMT on September 21, 2007
General, really doesn't appear like we'll see all that much down here, unless things change rapidly. Development seems to be taking place north of us, just a spritz or two here and there for me in St. Pete and probably less out east in Brandon...
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2096. tampabayfish
4:39 AM GMT on September 21, 2007
General, don't let your guard down, these storms will probably fire up all night if this thing is trying to get its act together... The Dmax comes into effect here...
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2093. SouthernLady
11:38 PM CDT on September 20, 2007
My daughter was in Iraq, she's in the military so that WE have the freedom of speech ect...even if we don't like what the other is saying, now enough!

Back to the weather...I can't find a center either, it's a mess, but a BIG mess!
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2091. runningfromthestorms
4:31 AM GMT on September 21, 2007
Tincup - since her name is designed to incite trouble and discord, admin may see it differently - I feel sick at heart for her pain, but everytime she posts there is going to be trouble
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2085. tampabayfish
4:33 AM GMT on September 21, 2007
People, no more military talk, there's a time and a place, but this ain't it... Please refrain, its weather blog
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2083. Tincup
4:31 AM GMT on September 21, 2007
Gen...I am truly sorry to hear that. God Bless you and your family. Unfortunately, disrespect will not bring him back. I will not say anymore because I certainly can not feel your pain. Again, God Bless.
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2082. duprk452
4:33 AM GMT on September 21, 2007
I'm with stayawaycantore im new at all this too but have been through many hurricanes... it almost looks like two seperate storms out there.. but i could be imagining things too
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2080. SouthernLady
11:32 PM CDT on September 20, 2007
From the looks of the WV, the dry air seems to be vamoosing. LOL Link
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2079. tampabayfish
4:28 AM GMT on September 21, 2007
Still not a TD, 29 knot winds blowing in a circle does not constitute a tropical cyclone. This thing has a lot of work to do... I thought we would see a more COC centralized burst of convection by now and we havent... still heading towards Dmax but runnin out of time...
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2078. rareaire
4:30 AM GMT on September 21, 2007
general betrayus why choose that handle? Knowing its disrespectful to our family members who are in irag and Afganistan..
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2077. stayawaycantore
4:32 AM GMT on September 21, 2007
Hi, I'm new to this blog, obviously. I'm not a pro or anything, but I've weathered enough hurricanes to start noticing some patterns.

I've been watching the center of circulation on 93L all day and it seems to have turned SSw or maybe straight SW since about 10:30CST. Like I said, I'm no pro, but that's what it looks like to me.

If it remains on that path, wouldn't it wind up in warmer waters, have a greater chance to develop, etc.?

This thing has done a lot of wobbling around since reaching the east coast of florida, so I could just be imagining the turn to the SW.
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2076. cattlebaroness
4:31 AM GMT on September 21, 2007
Where is the current loop in relation to this system. I figure if I keep asking the question, someone will eventually answer me. :)
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2073. Michfan
4:26 AM GMT on September 21, 2007
Its starting to band really nicely but it still needs to get its act together on its southern side. Too much dry air.
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2071. Tincup
4:26 AM GMT on September 21, 2007
frank...I agree that his handle is disrespectful to our military (my son-in-law is an active Marine), unfortunately, you aren't going to be able to do anything about it on this blog. Probably should get back to the weather.
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2070. GetReal
4:24 AM GMT on September 21, 2007
Conditions at SGOF1 as of
(12:00 am EDT)
0400 GMT on 09/21/2007:

Wind Direction (WDIR): ENE ( 70 deg true )
Wind Speed (WSPD): 30 kts
Wind Gust (GST): 32 kts
Atmospheric Pressure (PRES): 29.79 in
Pressure Tendency (PTDY): +0.00 in ( Steady )
Air Temperature (ATMP): 76.8 F
Water Temperature (WTMP): 84.6 F
Dew Point (DEWP): 71.6 F

This reporting station just south of Apalachicola, Fl., has been reporting sustained winds above 29 knots for the last three hours now... I believe that a TD has finally formed just south of this location.
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2064. SouthernLady
11:23 PM CDT on September 20, 2007
This thing is blowing my mind, I can't keep up with all the changes or even where the dang thing actually is! LOL
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Cat 6 lead authors: WU cofounder Dr. Jeff Masters (right), who flew w/NOAA Hurricane Hunters 1986-1990, & WU meteorologist Bob Henson, @bhensonweather

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